JP2008052289A - Light emitting device and electronic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that there occurs a variation in the brightness of a light emitting element caused by a variation in the characteristics of driving transistors. <P>SOLUTION: The present invention specifies characteristics of a driving transistor provided in a pixel and corrects a video signal to be input to the pixel based on the result of the specification. As a result, an effect of the variation in the characteristics of the transistors is prevented, and there provided are a light emitting device capable of achieving sharp multi-gradation display and its driving method. The present invention can also provide sharp multi-gradation display by suppressing a variation in the amount of current flowing between the two electrodes of the light emitting element caused by temporal change. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a light emitting device provided with a light emitting element and a transistor for controlling the light emitting element on a semiconductor substrate or an insulating surface, and a driving method thereof. More specifically, the present invention relates to a light-emitting device that prevents the influence of variations in characteristics of transistors that control light-emitting elements and a driving method thereof. The present invention also belongs to a technical field related to a light emitting device using a semiconductor element such as a transistor.

  In recent years, a light emitting device (image display device) using a light emitting element has been developed. Light emitting devices are roughly classified into a passive type and an active type. In an active light-emitting device, a light-emitting element and a transistor that controls the light-emitting element are provided over an insulating surface.

  A transistor using a polysilicon film has higher field effect mobility (also referred to as mobility) than a conventional transistor using an amorphous silicon film, and can operate at high speed. Therefore, it is possible to perform control of a pixel, which has been conventionally performed by a drive circuit outside the substrate, by a drive circuit formed on the same insulating surface as the pixel. Such an active light-emitting device can provide various advantages such as reduction in manufacturing cost, size reduction, increase in yield, and reduction in throughput by forming various circuits and elements on the same insulating surface.

As a main driving method of an active light emitting device, an analog method and a digital method can be given. The former analog method is a method of obtaining gradation by controlling luminance by controlling a current flowing through a light emitting element. On the other hand, in the latter digital method, the light emitting element is driven only in two states, that is, an on state (a state where the luminance is approximately 100%) and an off state (a state where the luminance is approximately 0%). However, in the case of the digital method, only two gradations can be displayed as it is, so a technique for realizing multi-gradation in combination with a time gradation method, an area gradation method, or the like has been proposed (for example, see Patent Document 1). ).
JP 2001-159878 A (pages 6 and 7)

  Here, a driving method of the light-emitting device will be described in detail with reference to FIGS. First, the structure of the light-emitting device will be described with reference to FIG. FIG. 14 illustrates an example of a circuit diagram of a pixel portion 1800 included in the light-emitting device. A gate signal line (any one of G1 to Gy) that transmits a gate signal supplied from the gate signal line driver circuit to the pixel is connected to a gate electrode of a switching transistor 1801 included in each pixel. One of a source region and a drain region of the switching transistor 1801 included in each pixel is a source signal line (S1 to Sx) for inputting a video signal, and the other is a driving transistor 1804 included in each pixel. Are connected to the gate electrode and the capacitor 1808 included in each pixel.

  A source region of the driving transistor 1804 included in each pixel is connected to a power supply line (any one of V1 to Vx), and a drain region is connected to the light emitting element 1806. Note that the potential of the power supply line (any one of V1 to Vx) is referred to as a power supply potential. A power supply line (any one of V1 to Vx) is connected to a capacitor 1808 included in each pixel.

  The light-emitting element 1806 includes an anode and a cathode, and an organic compound layer provided between the anode and the cathode. In the case where the anode of the light-emitting element 1806 is connected to the drain region of the driving transistor 1804, the anode of the light-emitting element 1806 is a pixel electrode and the cathode is a counter electrode. On the other hand, when the cathode of the light-emitting element 1806 is connected to the drain region of the driving transistor 1804, the anode of the light-emitting element 1806 is a counter electrode and the cathode is a pixel electrode.

  Note that the potential of the counter electrode is referred to as a counter potential, and a power source that applies the counter potential to the counter electrode is referred to as a counter power source. A potential difference between the potential of the pixel electrode and the potential of the counter electrode is a driving voltage, and this driving voltage is applied to the organic compound layer.

  FIG. 15 shows a timing chart when the light-emitting device shown in FIG. 14 is driven by an analog method. In FIG. 15, a period from selection of one gate signal line to selection of the next gate signal line is referred to as one line period (L). A period from when one image is displayed until the next image is displayed is referred to as one frame period (F). In the case of the light emitting device in FIG. 14, since there are y gate signal lines, y line periods (L1 to Ly) are provided in one frame period.

  The power supply lines (V1 to Vx) are kept at a constant power supply potential. The counter potential, which is the potential of the counter electrode, is also kept constant. The counter potential has a potential difference from the power supply potential to such an extent that the light emitting element emits light.

  In the first line period (L1), the gate signal line (G1) is selected by the gate signal supplied from the gate signal line driver circuit. Note that selection of a gate signal line means that a transistor having a gate electrode connected to the gate signal line is turned on.

  Then, analog video signals are sequentially input to the source signal lines (S1 to Sx). Since all the switching transistors 1801 connected to the gate signal line (G1) are on, the video signals input to the source signal lines (S1 to Sx) are driven through the switching transistor 1801. Input to the gate electrode of the transistor 1804.

  The amount of current flowing through the channel formation region of the driving transistor 1804 is controlled by the potential level (voltage) of the signal input to the gate electrode of the driving transistor 1804. Therefore, the potential applied to the pixel electrode of the light-emitting element 1806 is determined by the height of the potential of the video signal input to the gate electrode of the driving transistor 1804. That is, the light-emitting element 1806 emits light according to the amount of current that flows through the light-emitting element 1806 in accordance with the potential of the video signal.

  When the operation described above is repeated and the input of the video signal to the source signal lines (S1 to Sx) is finished, the first line period (L1) is finished. Next, in the second line period (L2), the gate signal line (G2) is selected by the gate signal. Similarly to the first line period (L1), video signals are sequentially input to the source signal lines (S1 to Sx).

  When the above-described operation is repeated and gate signals are input to all the gate signal lines (G1 to Gy), one frame period ends. All pixels display in one frame period, and one image is formed.

  In this manner, a method in which the amount of current flowing through the light emitting element is controlled by a video signal and gradation display is performed according to the amount of current is a driving method called an analog method. That is, in the analog method, gradation display is performed according to the potential of the video signal input to the pixel.

  On the other hand, the digital method realizes multi-gradation in combination with the time gradation method as described above. Although a detailed timing chart is not shown, in the digital method combined with the time gradation method, gradation display is performed according to the length of time during which current flows between both electrodes of the light emitting element.

Next, voltage-current characteristics of the driving transistor 1804 and the light-emitting element 1806 will be described with reference to FIGS. FIG. 11A illustrates only components of the driving transistor 1804 and the light-emitting element 1806 in the pixel illustrated in FIG. FIG. 11B illustrates voltage-current characteristics of the driving transistor 1804 and the light-emitting element 1806 illustrated in FIG. Note that the graph of voltage-current characteristics of the driving transistor 1804 illustrated in FIG. 11B indicates the magnitude of current flowing in the drain region of the driving transistor 1804 with respect to V _DS that is the voltage between the source region and the drain region. . FIG. 12 shows a plurality of graphs having different values of V _GS , which is a voltage between the source region and the gate electrode of the driving transistor 1804.

As shown in FIG. 11A, the voltage applied between the pixel electrode of the light emitting element 1806 and the counter electrode is V _EL , and the voltage applied between the terminal 3601 connected to the power supply line and the counter electrode of the light emitting element 1806 Is V _T. Note V _T is the value is fixed by the potential of the power supply line (V1 to Vx). The voltage between the source region and the drain region of the driving transistor 1804 is V _DS , and the voltage between the wiring 3602 connected to the gate electrode of the driving transistor 1804 and the source region, that is, the gate electrode and the source of the driving transistor 1804 Let V _GS be the voltage between the regions.

The driving transistor 1804 and the light emitting element 1806 are connected in series.
Therefore, the amount of current flowing through both elements (the driving transistor 1804 and the light emitting element 1806) is the same. Therefore, the driving transistor 1804 and the light-emitting element 1806 shown in FIG. 11A are at the intersection (operating point) of the graph showing the voltage-current characteristics of both elements.
Drive in. In FIG. 11B, V _EL corresponds to a voltage between the potential of the counter electrode 1809 and the potential at the operating point. V _DS corresponds to a voltage between the potential at the terminal 3601 of the driving transistor 1804 and the potential at the operating point. That is, V _T is equal to the sum of V _EL and V _DS .

Here, a case where V _GS is changed will be considered. As can be seen from FIG. 11B, the amount of current flowing through the driving transistor 1804 increases as | V _GS −V _TH | of the driving transistor 1804 increases, in other words, as | V _GS | increases. Note that V _TH is a threshold voltage of the driving transistor 1804. Therefore, as can be seen from FIG. 11B, as | V _GS | increases, the amount of current flowing through the light-emitting element 1806 at the operating point naturally increases. The luminance of the light emitting element 1806 increases in proportion to the amount of current flowing through the light emitting element 1806.

When | V _GS | increases and the amount of current flowing through the light emitting element 1806 increases, the value of V _EL also increases in accordance with the amount of current. Since the magnitude of V _T is determined by the potential of the power supply lines (V1 to Vx), when V _EL increases, V _DS decreases accordingly.

As shown in FIG. 11B, the voltage-current characteristics of the driving transistor 1804 are divided into two regions depending on the values of V _GS and V _DS . A region where | V _GS −V _TH | <| V _DS | is a saturation region, and a region where | V _GS −V _TH |> | V _DS | is a linear region.

The following formula (1) is established in the saturation region. Note that I _DS is the amount of current flowing through the channel formation region of the driving transistor 1804. Β = μC ₀ W / L, μ is the mobility of the driving transistor 1804, C ₀ is the gate capacitance per unit area, and W / L is the ratio of the channel width W to the channel length L in the channel formation region. .

  In the linear region, the following formula (2) is established.

As can be seen from Equation (1), the amount of current hardly changes depending on V _DS in the saturation region, and the amount of current is determined only by V _GS .

Further, as can be seen from Equation (2), in the linear region, the amount of current is determined by V _DS and V _GS . As | V _GS | increases, the driving transistor 1804 operates in the linear region. And V _EL gradually increases. Therefore, V _DS decreases as V _EL increases. In the linear region, the current amount decreases as V _DS decreases. Therefore, even if | V _GS | is increased, the amount of current hardly increases. When | V _GS | = ∞, the current amount = I _MAX . In other words, no matter how large | V _GS |, no current exceeding I _MAX flows. Here, I _MAX is the amount of current flowing through the light emitting element 1806 when V _EL = V _T.

By controlling the magnitude of | V _GS | in this way, the operating point can be set to a saturation region or a linear region.

By the way, it is desirable that all the characteristics of all the driving transistors 1804 are ideally the same, but in reality, the threshold V _TH and the mobility μ are different in each driving transistor 1804. Many. When the threshold value V _TH and the mobility μ of each driving transistor 1804 are different from each other, the equations (1) and (2)
As can be seen, even if the value of V _GS is the same, the amount of current flowing through the channel formation region of the driving transistor 1804 is different.

FIG. 12 shows current-voltage characteristics of the driving transistor 1804 in which the threshold value V _TH and the mobility μ are shifted. A solid line 3701 is a graph of ideal current-voltage characteristics, and 3702 and 3703 are current-voltage characteristics of the driving transistor 1804 when the threshold value V _TH and the mobility μ are different from the ideal values, respectively. .

The current-voltage characteristic graphs 3702 and 3703 are shifted from the current-voltage characteristic graph 3701 having the ideal characteristics by the same current amount ΔI ₁ in the saturation region, and the operating point 3705 of the current-voltage characteristic graph 3702 is in the saturation region. It is assumed that the operating point 3706 of the current-voltage characteristic graph 3703 is in the linear region. In that case, assuming that the deviation of the current amount at the operating point 3704 of the current-voltage characteristic graph 3701 having ideal characteristics and the current amount at the operating point 3705 and the operating point 3706 are ΔI ₂ and ΔI ₃ , respectively, the operating point in the saturation region The deviation ΔI _{3 at} the operating point 3706 in the linear region is smaller than the deviation ΔI _{2 at} 3705.

As a summary of the above operation analysis, FIG. 13 shows a graph of the current amount with respect to the gate voltage | V _GS | of the driving transistor 1804. When | V _GS | is increased and becomes larger than the absolute value | V _TH | of the threshold voltage of the driving transistor 1804, the driving transistor 1804 becomes conductive and current starts to flow. When | V _GS | is further increased, | V _GS | becomes a value satisfying | V _GS −V _TH | = | V _DS | Become an area.
As | V _GS | is further increased, the amount of current increases, and finally the amount of current saturates. At that time, | V _GS | = ∞.

As can be seen from FIG. 13, almost no current flows in the region of | V _GS | ≦ | V _TH |. The region of | V _TH | ≦ | V _GS | ≦ A is a region called a saturation region, and the amount of current changes depending on | V _GS |. This means that in the saturation region, when the voltage applied to the light emitting element 1806 changes even a little, the current flowing through the light emitting element 1806 significantly changes exponentially. The luminance of the light emitting element 1806 increases in direct proportion to the current flowing through the light emitting element 1806. That is, the analog method, which is a method of controlling the luminance and obtaining the gradation by controlling the current flowing through the light emitting element according to the value of | V _GS |, is mainly operated in the saturation region.

On the other hand, in FIG. 13, the region of A ≦ | V _GS | is a linear region, and the amount of current flowing through the light emitting element varies depending on | V _GS | and | V _DS |. In the linear region, even when the magnitude of the voltage applied to the light emitting element 1806 is changed, the amount of current flowing through the light emitting element 1806 does not change greatly. In the digital method, the light emitting element is driven only in two states, that is, an on state (the luminance is almost 100%) or an off state (the luminance is almost 0%). To obtain a state, when operating with A ≦ | V _GS |, since the current value is close to I _MAX at any time, the luminance is almost 100%. Further, in order to turn off the light emitting element, if it is operated at | V _TH | ≧ | V _GS |, the current value becomes almost zero and the luminance of the light emitting element becomes almost 0%. That is, a light emitting device driven in a digital manner is mainly operated in a region of | V _TH | ≧ | V _GS | and A ≦ | V _GS |.

  In a light emitting device driven in an analog manner, when a switching transistor is turned on, an analog video signal input to a pixel becomes a gate voltage of the driving transistor. At this time, the potential of the drain region is determined corresponding to the voltage of the analog video signal input to the gate electrode of the driving transistor, a predetermined drain current flows through the light emitting element, and the amount of light emission corresponding to the amount of current ( (Luminance), the light emitting element emits light. As described above, the light emission amount of the light emitting element is controlled by the video signal, and gradation display is performed by controlling the light emission amount.

  However, the analog method has a drawback that it is very weak in the characteristic variation of the driving transistor. Even if an equal gate voltage is applied to the driving transistor of each pixel, the same drain current cannot be supplied as long as the driving transistor has a characteristic variation. In other words, the amount of light emitted from the light-emitting element varies greatly even when video signals of the same voltage are input due to slight variations in characteristics of the driving transistors.

  As described above, the analog method is sensitive to the variation in characteristics of the driving transistor, which has been an obstacle in the gradation display of the conventional active light emitting device.

  Further, when the light emitting device is driven by a digital method in order to cope with the characteristic variation of the driving transistor, when the organic compound layer of the light emitting element deteriorates, the amount of current flowing through the organic compound layer changes.

  This is due to the fact that the light emitting element has the property of deteriorating with time. FIG. 18A shows a graph of voltage-current characteristics before and after deterioration of the light-emitting element. As described above, the digital method operates in the linear region. Accordingly, as shown in FIG. 18A, when the light emitting element is deteriorated, the graph of the voltage-current characteristic is changed, and the operating point is shifted. As a result, the amount of current flowing between both electrodes of the light emitting element changes.

  The present invention has been made in view of the above problems, and in a light-emitting device driven in an analog manner, the light-emitting device capable of preventing the influence of variations in transistor characteristics and displaying clear multi-gradation and driving the same It is an object to provide a method. Another object of the present invention is to provide an electronic device including the light emitting device as a display device.

  It is another object of the present invention to provide a light emitting device and a driving method thereof capable of suppressing a change in the amount of current flowing between both electrodes of the light emitting element due to a change with time and capable of clear multi-gradation display. Another object of the present invention is to provide an electronic device including the light emitting device as a display device.

  In view of the above situation, the present invention specifies the characteristics of a driving transistor provided in a pixel, and corrects a video signal input to the pixel based on the result, thereby affecting the influence of characteristic variation of the driving transistor. Provided are a light emitting device and a driving method thereof.

  Further, the present invention utilizes the fact that the light emission amount (luminance) of the light emitting element is controlled by the amount of current flowing through the light emitting element. That is, if a desired amount of current flows through the light emitting element, a desired amount of light emission can be obtained by the light emitting element. Therefore, a video signal corresponding to the characteristics of the driving transistor of each pixel is input to each pixel so that a desired amount of current flows through the light emitting element. Then, desired light emission can be obtained by the light emitting element without being influenced by the characteristic variation of the driving transistor.

  A method for specifying the characteristics of the driving transistor which is the basis of the present invention will be described below. First, an ammeter is connected to a wiring that supplies a current to the light emitting element, and a current value flowing through the light emitting element is measured. For example, an ammeter is connected to a wiring that supplies current to a light emitting element such as a power supply line or a counter power supply line, and a current value flowing through the light emitting element is measured. At this time, a video signal is input only to a specific pixel (preferably one pixel or a plurality of pixels) from the source signal line driver circuit, and no current flows through the light emitting elements of the other pixels. Like that. Then, it is possible to measure the value of current flowing only to a specific pixel by the ammeter. If video signals having different sizes (voltage values) are input, a plurality of current values corresponding to video signals having different sizes (voltage values) can be measured for each pixel.

  In the present invention, the video signal is P (P1, P2,..., Pn, n is a natural number of at least 2). A current value Q (Q1, Q2,..., Qn) corresponding to the video signal P (P1, P2,..., Pn) is displayed as a current value I0 when all the pixels of the display panel are not lit. It is obtained by calculating the difference between the current values I1, I2,..., In when only one pixel of the panel is lit. When P and Q are measured for each pixel, the characteristic of the pixel is obtained using an interpolation method. Interpolation is a method of calculating an approximate value of a point between function values using function values at two or more points in the function, or by giving (interpolating) a function value at a point in between. It is a way to expand. The equation that gives the approximate value is called an interpolation equation and is shown in equation (3).

  The video signal P (P1, P2,..., Pn) measured for each pixel and the current value Q (Q1, Q2,..., Qn) corresponding to the video signal are expressed in Equation (3). By substituting, the interpolation function F is obtained. The obtained interpolation function F is stored in a storage medium such as a semiconductor memory or a magnetic memory provided in the light emitting device.

  When an image is displayed on the light emitting device, the video signal (P) corresponding to the characteristics of the driving transistor of each pixel is calculated and obtained using the interpolation function F stored in the storage medium. When the obtained video signal (P) is input to each pixel, a desired amount of current can be supplied to the light emitting element, so that a desired luminance can be obtained.

  The light emitting device in the present invention means a display panel (light emitting panel) in which a pixel portion having a light emitting element and a driving circuit are enclosed between a substrate and a cover material, a light emitting module in which an IC or the like is mounted on the display panel, and a display device This category includes light-emitting displays used as a category. That is, the light emitting device corresponds to a generic term for a light emitting panel, a light emitting module, a light emitting display, and the like. Note that although the light-emitting element is not included in the essential constituent elements of the present invention, the light-emitting device is also referred to here even when the light-emitting element is not included.

  The present invention is a light emitting device having a display panel provided with a pixel including a light emitting element, current measuring means for measuring a current value of the pixel, and interpolation corresponding to the pixel using an output of the current measuring means Computation means for calculating a function, storage means for storing the interpolation function, and signal correction means for correcting a video signal using the interpolation function stored in the storage means.

  The current measuring means includes means for measuring a current value flowing between both electrodes of the light emitting element. For example, an ammeter, a circuit configured by a resistive element and a capacitive element, and performing measurement using resistance division, etc. It corresponds to. The calculating means and the signal correcting means have means for calculating, and correspond to, for example, a microcomputer or a CPU. The storage means corresponds to a known storage medium such as a semiconductor memory or a magnetic memory. The state in which the pixel is not lit corresponds to a state in which a light emitting element included in the pixel is in a non-light emitting state and a pixel in which a “black” image signal is input. The state in which the pixel is lit corresponds to a state in which a light emitting element included in the pixel emits light and a state in which a “white” image signal is input.

  The present invention is a driving method of a light emitting device having a display panel, wherein a current value I0 in a state where all pixels of the display panel are not lit is measured, and video signals P1, P2, .., Pn (n is a natural number), current values I1, I2,..., In are measured, and the difference between the current value I0 and the current value In is Q1, Q2,. And the video signals P1, P2,..., Pn and the interpolation formula Q = F (P), and an interpolation function F is calculated, and a video signal input to each pixel of the display panel using the interpolation function F. It is characterized by correcting.

  As a typical configuration of the pixel in the present invention, a first semiconductor element that controls a current flowing between both electrodes of the light emitting element, a second semiconductor element that controls input of a video signal to the pixel, and the video signal And a capacitor element that holds the capacitor. Note that the semiconductor element corresponds to an element having a switching function such as a transistor. The capacitor element has a function of holding electric charge, and the material of the capacitor element is not particularly limited.

  The present invention having the above-described structure can provide a light-emitting device capable of displaying a clear multi-gradation and a driving method thereof, in which the influence of variations in transistor characteristics is prevented in a light-emitting device driven in an analog manner. . Furthermore, the present invention can provide a light-emitting device and a driving method thereof that can suppress a change in the amount of current flowing between both electrodes of the light-emitting element due to a change with time and can display clear multi-gradation.

  The present invention calculates and obtains a video signal corresponding to the characteristics of the driving transistor of each pixel without changing the configuration of the pixel. When the obtained video signal is input to each pixel, a desired amount of current can be supplied to the light emitting element, so that desired light emission can be obtained. As a result, it is possible to provide a light-emitting device and a driving method thereof in which the influence of variation in characteristics of transistors that control the light-emitting elements is prevented.

  In addition, the present invention having the above-described structure provides a light-emitting device capable of displaying a clear multi-gradation and preventing the influence of variations in transistor characteristics in a light-emitting device driven in an analog manner and a driving method thereof. Can do. Furthermore, the present invention can provide a light-emitting device and a driving method thereof that can suppress a change in the amount of current flowing between both electrodes of the light-emitting element due to a change with time and can display clear multi-gradation.

(Embodiment)
An embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 shows an example of a circuit diagram of a light-emitting device. In FIG. 1, the light-emitting device includes a pixel portion 103 and a source signal line driver circuit 101 and a gate signal line driver circuit 102 which are arranged around the pixel portion 103. Note that in FIG. 1, the light-emitting device includes one source signal line driver circuit 101 and one gate signal line driver circuit 102; however, the present invention is not limited to this. The number of source signal line driver circuits 101 and gate signal line driver circuits 102 can be arbitrarily determined in accordance with the configuration of the pixel 100.

  The source signal line driver circuit 101 includes a shift register 101a, a buffer 101b, and a sampling circuit 101c. However, the present invention is not limited to this, and a holding circuit or the like may be provided.

The shift register 101a has a clock signal (CLK) and a start pulse (SP).
Is entered. The shift register 101a sequentially generates timing signals based on the clock signal (CLK) and the start pulse (SP) and sequentially inputs them to the sampling circuit 101c via the buffer 101b.

  The timing signal supplied from the shift register 101a is buffered and amplified by the buffer 101b. Since many circuits or elements are connected to the wiring to which the timing signal is input, the load capacity becomes large. For this reason, the buffer 101b is provided in order to prevent the rise or fall of the timing signal caused by the large load capacity.

  The sampling circuit 101c sequentially outputs video signals to the pixels 100 based on the timing signal input from the buffer 101b. The sampling circuit 101c has a video signal line 125 and sampling lines (SA1 to SAx). Note that the present invention is not limited to this structure, and may have a semiconductor element such as an analog switch.

  The pixel portion 103 is provided with source signal lines (S1 to Sx), gate signal lines (G1 to Gy), power supply lines (V1 to Vx), and counter power supply lines (E1 to Ey). The pixel portion 103 is provided with a plurality of pixels 100 in a matrix.

The power supply lines (V1 to Vx) are connected to the power supply 131 via the ammeter 130. Note that the ammeter 130 and the power source 131 may be formed on a different substrate from the substrate on which the pixel portion 103 is formed, and may be connected to the pixel portion 103 through a connector or the like, or if it can be manufactured. The pixel portion 103 may be formed over the same substrate.
The number of ammeters 130 and power supplies 131 is not particularly limited and can be arbitrarily determined. The ammeter 130 may be provided on a wiring for supplying current to the light emitting element 111. For example, the ammeter 130 may be connected to the opposed power supply lines (E1 to Ey). That is, the place where the ammeter 130 is provided is not particularly limited. The ammeter 130 corresponds to measurement means.

  The current value measured by the ammeter 130 is sent to the correction circuit 210 as data. The correction circuit 210 includes a storage medium (storage means) 211, a calculation circuit (calculation means) 202, and a signal correction circuit (signal correction means) 204. Note that the configuration of the correction circuit 210 is not limited to the configuration illustrated in FIG. 1, and an amplifier circuit, a conversion circuit, or the like may be provided. If necessary, only the storage medium 211 may be provided, and the configuration of the correction circuit 210 can be arbitrarily determined.

  The storage medium 211 includes a first memory 200, a second memory 201, and a third memory 203. However, the present invention is not limited to this, and the number of memories can be freely designed by a designer. As the storage medium 211, a known storage medium such as a ROM, a RAM, a flash memory, or a magnetic tape can be used. However, when the storage medium 211 is provided integrally on a substrate provided with a pixel portion or the like, a semiconductor memory is preferably used, and a ROM is particularly preferably used. In the case where the light-emitting device of the present invention is used as a computer display device, a storage medium 211 may be provided in the computer.

  The calculation circuit 202 has means for performing calculation. More specifically, from the current values I1, I2,..., In when the video signals P1, P2,. Subtracting means is provided for calculating current values Q1, Q2,..., Qn. In addition, it has means for calculating the interpolation function of the above-described equation (3). As the calculation circuit 202, a known calculation circuit, a microcomputer, or the like can be used. When the light-emitting device of the present invention is used as a computer display device, a calculation circuit 202 may be provided in the computer.

  The signal correction circuit 204 has means for correcting the video signal. More specifically, it has means for correcting the video signal input to the pixel 100 from the interpolation function F of the pixel 100 stored in the storage medium 211 and the above-described equation (3). As the signal correction circuit 204, a known signal correction circuit, a microcomputer, or the like can be used. When the light-emitting device of the present invention is used as a computer display device, a signal correction circuit 204 may be provided in the computer.

  The source signal lines (S1 to Sx) are connected to the video signal line 125 via the sampling transistor 126. One of the source region and the drain region of the sampling transistor 126 is connected to the source signal line S (any one of S1 to Sx), and the other is connected to the video signal line 125. The gate electrode of the sampling transistor 126 is connected to the sampling line SA (any one of SA1 to SAx).

  Next, an enlarged view of the pixel 100 provided in the i-th column and the j-th row is shown in FIG. In the pixel (i, j), 111 is a light emitting element, 112 is a switching transistor, 113 is a driving transistor, and 114 is a capacitor.

The gate electrode of the switching transistor 112 is connected to the gate signal line (Gi). One of the source region and the drain region of the switching transistor 112 is connected to the source signal line (Si), and the other is connected to the gate electrode of the driving transistor 113. The switching transistor 112 is a transistor that functions as a switching element when a signal is input to the pixel 100.
Note that the source signal line (Si) to which the switching transistor 112 is connected is connected to the video signal line 125 through the sampling transistor 126 as shown in FIG. 1, but is not shown in FIG. Yes.

  The capacitor 114 is provided to hold the gate voltage of the driving transistor 113 when the switching transistor 112 is in a non-selected state (off state). In this embodiment mode, the capacitor 114 is provided. However, the present invention is not limited to this, and the capacitor 114 may not be provided.

  The source region of the driving transistor 113 is connected to the power supply line (Vi), and the drain region is connected to the light emitting element 111. The power supply line (Vi) is connected to the power supply 131 via the ammeter 130, and is always given a constant power supply potential. The power supply line Vi is connected to the capacitor 114. The driving transistor 113 is a transistor that functions as an element (current control element) for controlling a current supplied to the light emitting element 111.

  The light emitting element 111 includes an anode and a cathode, and an organic compound layer provided between the anode and the cathode. When the anode is connected to the drain region of the driving transistor 113, the anode serves as a pixel electrode and the cathode serves as a counter electrode. Conversely, when the cathode is connected to the drain region of the driving transistor 113, the cathode is the pixel electrode and the anode is the counter electrode.

Note that a light-emitting element has a structure in which an organic compound layer is sandwiched between a pair of electrodes (an anode and a cathode). The organic compound layer can be manufactured using a known light-emitting material.
In addition, the organic compound layer has two structures, a single layer structure and a laminated structure, and either structure may be used. Luminescence in the organic compound layer includes light emission when returning from the singlet excited state to the ground state (fluorescence) and light emission when returning from the triplet excited state to the ground state (phosphorescence). It may be used.

  The counter electrode of the light emitting element is connected to the counter power source 121. Note that the potential of the counter power supply 121 is referred to as a counter potential. A difference between the potential of the pixel electrode and the potential of the counter electrode is a drive voltage, and the drive voltage is applied to the organic compound layer.

Next, in the light emitting device of the present invention shown in FIGS. 1 and 2, a method for specifying the characteristics of the driving transistor 113 provided in the pixel 100 and correcting the video signal input to the pixel 100 based on the result is shown. This will be described with reference to FIG.
Note that each step is referred to as step 1 to step 5 for easy understanding. FIG. 3B shows the correction circuit 210, and FIGS. 3A and 3B may be referred to.

  FIG. 4 is a timing chart of signals output from the driving circuits (the source signal line driving circuit 101 and the gate signal line driving circuit 102) provided in the light emitting device. Since y gate signal lines are provided in the pixel portion 103, y line periods (L1 to Ly) are provided in one frame period.

  4A, in one line period (L), one gate signal line G (any one of G1 to Gy) is selected, and y gate signal lines (G1 to Gy) are selected. In this case, one frame period elapses. FIG. 4B shows a state in which one line period elapses when x sampling lines SA (any one of SA1 to SAx) are sequentially selected and all sampling lines (SA1 to SAx) are selected. Show. FIG. 4C shows a state in which the video signal P0 is input to the source signal lines (S1 to Sx) in step 1. FIG. 4D shows how the video signals P1, P2, P3, and P0 are input to the source signal lines (S1 to Sx) in step 2.

  First, in step 1, the pixel portion 103 is brought into an all black state. The all black state means that all the light emitting elements 111 are not emitting light and all the pixels are not lighting. FIG. 4C illustrates a state in which the video signal P0 is input to the source signal lines (S1 to Sx) in Step 1. Note that FIG. 4C illustrates only the state in which the video signal P0 is input to the source signal lines (S1 to Sx) in one line period, but in reality, the video signal P0 is provided in one frame period (F). It is performed in all the line periods (L1 to Ly). When the same video signal P0 is input to all the pixels 100 in one frame period, all the light emitting elements 111 provided in the pixel portion 103 are in a non-light emitting state (all black state).

In such a state, a power supply line (V1 to Vx) using an ammeter 130
Is measured. The current value I0 measured at this time is that the part between the anode and the cathode of the light emitting element 111 is short-circuited, the part of the pixel 100 is short-circuited, or the FPC connected to the pixel unit 103 is accurate. This corresponds to the current value that has flown when not connected. Then, the measured current value I0 is stored in the first memory 200 provided in the correction circuit 210, and Step 1 ends.

  Next, in step 2, different video signals P1, P2, P3, and P0 are input to the pixels 100 provided in the pixel portion 103, respectively.

In the present embodiment, as shown in FIG. 4D, four video signals P1, P2, P3, and P0 that are changed stepwise are input to the source signal lines (S1 to Sx).
That is, four video signals P1, P2, P3, and P0 are input to one pixel 100 in one line period (L), and four pixels 100 are provided in all the pixels 100 provided in the pixel portion 103 in one frame period (F). Video signals P1, P2, P3, and P0 are input.

  Then, the current flowing through the driving transistor 113 corresponding to the three video signals P1, P2, and P3, that is, the current value flowing through the power supply lines (V1 to Vx) is measured by the ammeter 130.

  Here, in one line period (L), four video signals P1, P2, P3, and P0 that are changed stepwise are input to one pixel, but the present invention is not limited to this. For example, only the video signal P1 is input in one line period (L), the video signal P2 is input in the next one line period (L), and the video signal P3 is input in the next one line period (L). Also good. In the present embodiment, four video signals P1, P2, P3, and P0 that are changed stepwise are inputted. However, in the present invention, video signals having different magnitudes (voltage values) are inputted, and the magnitudes are inputted. What is necessary is just to measure the electric current value corresponding to the video signal from which (voltage value) differs. For example, a video signal changed into a ramp shape (sawtooth shape) may be input, and a plurality of current values may be measured using the ammeter 130 at certain intervals.

  Here, as an example, a case where the gate signal line (Gj) in the j-th row is selected by a gate signal supplied from the gate signal line driving circuit 102 will be described. In one line period (Lj), four video signals P1, P2, P3, and P0 are input to one pixel 100. Therefore, the video signal is input to the pixel 100 (here, (1, j)). Except for the pixel 100). Therefore, the current value measured by the ammeter 130 is a value obtained by adding the current value flowing through the driving transistor 113 of a specific pixel (the pixel of interest) 100 and the current value I0 measured in step 1. . Then, in the pixel 100 provided at (1, j), the current values I1, I2, and I3 corresponding to the video signals of P1, P2, and P3 are measured, and the current values IA, IB, and IC are calculated. 2 Save in the memory 201.

  Next, the video signal P0 is input to the pixel (1, j), and the light emitting element 111 of the pixel 100 is turned off and the pixel (1, j) is turned off. This is to prevent a current from flowing when measuring the next pixel (2, j).

  Then, four video signals P1, P2, P3, and P0 are input to the pixel 100 provided at (2, j). Current values I1, I2, and I3 corresponding to the video signals P1, P2, and P3 are acquired and stored in the second memory 201.

  In this way, the above-described operation is repeated, and the input of the video signal to the pixels 100 from the first column to the x-th column provided in the j-th row is completed. That is, when the input of video signals to all the source signal lines (S1 to Sx) is completed, one line period Lj ends.

Then, in the next line period L _{j + 1} , the gate signal line G _{j + 1} is selected by the gate signal supplied from the gate signal line driving circuit 102. Then, four video signals P1, P2, P3, and P0 are input to all the source signal lines (S1 to Sx).

In this way, the above-described operation is repeated, and all the gate signal lines (G1 to Gy)
When the gate signal is input to the input line, all the line periods (L1 to Ly) are completed. When all the line periods (L1 to Ly) are finished, one frame period is finished.

Thus, the current values I1, I2, and I3 corresponding to the three video signals P1, P2, and P3 input to the pixel 100 provided in the pixel portion 103 can be measured.
The obtained data is stored in the second memory 201.

  Then, the calculation circuit 202 obtains the difference between the current values I1, I2, and I3 for each pixel 100 provided in the pixel unit 103 from the current value I0 stored in the first memory 200 in Step 1 to obtain the current value. Q1 (= I1-I0), Q2 (= I2-I0), and Q3 (= I3-I0) are obtained. Then, the current values Q1, Q2, and Q3 are stored in the second memory 201, and Step 2 ends.

  Note that when there is no shorted pixel in the pixel portion 103 and an FPC or the like connected to the pixel portion 103 is correctly connected, the current value I0 is measured to be zero or almost zero. There is a case. In such a case, the operation of subtracting the current value I0 from the current values I1, I2, and I3 and the operation of measuring the current value I0 may be deleted for each pixel 100 provided in the pixel unit 103. Can be set arbitrarily.

Next, in step 3, the current-voltage characteristic (I _DS -V _GS characteristic) of the driving transistor of each pixel is acquired by the calculation circuit 202 using the above-described equation (1). In Expression (1), if I _DS → I, V _GS → P, V _TH → B, and Q = I−I0, the following Expression (4) is obtained.

In formula (4), A and B are constants. The constant A and the constant B can be obtained if there are at least two sets of (Pn, Qn) data. In other words, at least two video signals (Pn) having different magnitudes (voltage values) obtained in step 2 and at least two current values (Qn) corresponding to the video signals (Pn) are expressed by Equation (3).
By substituting into, constant A and constant B can be obtained. The constants A and B are stored in the third memory 203.

  By using the constant A and the constant B stored in the third memory 203, the value of the video signal (Pn) necessary for flowing a certain current value (Qn) can be obtained. In that case, the following formula (5) is used.

  Here, as an example, the values of the constants A and B of the pixel D, the pixel E, and the pixel F are obtained by using the equations (4) and (5), and the values shown in the graph are shown in FIG. As shown in FIG. 5, when the same video signal (here, the video signal P2 is taken as an example) is input to the pixel D, the pixel E, and the pixel F, a current indicated by Iq flows in the pixel D, and Ir in the pixel E The current indicated by Ip flows, and the current indicated by Ip flows in the pixel F. That is, even if the same video signal (P2) is input, the current values differ because the characteristics of the transistors provided in the pixels D, E, and F are different. Therefore, the present invention inputs a video signal corresponding to the characteristic of the pixel 100 to the pixel 100 using the above-described equation (4) in order to suppress the influence of such characteristic variation.

  In FIG. 5, the characteristics of the pixel D, the pixel E, and the pixel F are represented by quadratic curves using Expressions (4) and (5), but the present invention is not limited to this. FIG. 16 shows the relationship between the video signal (P) input to the pixel D, the pixel E, and the pixel F using the following formula (6) and the current value (Q) corresponding to the video signal (P). The graph made into the straight line is shown.

  By substituting the voltage value (P) and current value (Q) for each pixel obtained in step 2 into equation (6), constants a and b are obtained. Then, the obtained constant a and constant b are stored in the third memory 203 for each pixel 100, and step 3 ends.

  The graph shown in FIG. 16 is the same as the graph shown in FIG. 5, and when the same video signal (here, the video signal P2 is taken as an example) is input to the pixel D, the pixel E, and the pixel F, the pixel D is Iq. In the pixel E, a current indicated by Ir flows, and in the pixel F, a current indicated by Ip flows. That is, even if the same video signal (P2) is input, the current values are different because the characteristics of the transistors provided in the pixel 100 are different. Therefore, the present invention inputs a video signal corresponding to the characteristic of the pixel 100 to the pixel 100 using the above-described equation (6) in order to suppress the influence of such characteristic variation.

  As a method for specifying the relationship between the voltage value (P) and the current value (Q) of the video signal, it may be specified by a quadratic curve as shown in FIG. 5, or as shown in FIG. Thus, it may be specified by a straight line. Also, it may be specified by a spline curve (spline function) or a Bezier curve (Bézier function), and if the current value does not appear well on the curve, the curve (linear function) is calculated using the least square method. Optimization may be performed, and the method is not particularly limited.

  Subsequently, in step 4, the signal correction circuit 204 calculates the value of the video signal corresponding to the characteristics of each pixel 100 using the above equation (5) (or equation (6)). Then, step 4 ends, and if the calculated video signal is input to the pixel 100 in step 5, it becomes possible to flow a desired current to the light emitting element while suppressing the influence of the characteristic variation of the driving transistor, As a result, a desired light emission amount (luminance) can be obtained. Note that once the values of constant A and constant B (or constant a and constant b) obtained for each pixel 100 are once stored in the third memory 203, step 4 and step 5 may be repeated alternately.

  Reference is again made to FIG. If the pixel D, the pixel E, and the pixel F are to emit light with the same luminance, it is necessary to pass the same current value Ir. For this purpose, it is necessary to input a video signal corresponding to the characteristics of the driving transistor. As shown in FIG. 5, the video signal P1 is input to the pixel D and the video signal P2 is input to the pixel E. Then, it is necessary to input the video signal P3 to the pixel F. For this purpose, in step 4, it is essential to obtain a video signal corresponding to the characteristics of each pixel and input the obtained signal to each pixel.

  The operation of measuring a plurality of current values corresponding to a plurality of different video signals using the ammeter 130 (the operation of Step 1 to Step 3) may be performed immediately before or after the actual image display. It may be performed every certain period. Further, it may be performed before predetermined information is stored in the storage means. In addition, the interpolation function F calculated by the calculation circuit 202 may be temporarily stored in the storage medium 211, and the storage medium 211 may be formed integrally with the pixel unit 103. . Then, the video signal corresponding to the characteristics of the pixel can be calculated with reference to the interpolation function F stored in the storage medium 211, so that it is not necessary to provide the ammeter 130 in the light emitting device.

  In the present embodiment, when the interpolation function F is stored in the storage medium 211, a video signal to be input to the pixel 100 is calculated at any time based on the interpolation function F, and the calculated video signal is calculated as the pixel 100. However, the present invention is not limited to this.

  For example, based on the interpolation function F stored in the storage medium 211, a video signal corresponding to the number of gradations of the image to be displayed is calculated in advance for each pixel 100 in the calculation circuit 202, and the calculated video signal May be stored in the storage medium 211. For example, if an image is displayed with 16 gradations, 16 video signals for the 16 gradations are calculated in advance for each pixel 100. The calculated video signal is stored in the storage medium 211. By doing so, since the information of the video signal input when displaying a certain gradation for each pixel 100 is stored in the storage medium 211, an image can be displayed based on that information. That is, an image can be displayed based on information stored in the storage medium 211 without providing the calculation circuit 202 in the light emitting device.

When a video signal corresponding to the number of gradations of the displayed image is calculated in advance for each pixel 100 by the calculation circuit 202, a video signal that has been subjected to gamma correction with a gamma value is stored in the storage medium 211. It may be memorized.
Note that the gamma value used may be common to the pixel units or may be different for each pixel. Then, a clearer image can be displayed.

  The present invention can also be applied to a light emitting device having a pixel configuration different from that shown in FIG. In this embodiment, an example will be described with reference to FIGS. 6, 18B, and 18C.

  A pixel (i, j) illustrated in FIG. 6 includes a light emitting element 311, a switching transistor 312, a driving transistor 313, an erasing transistor 315, and a storage capacitor 314. The pixel 100 is arranged in a region surrounded by the source signal line (Si), the power supply line (Vi), the gate signal line (Gj), and the erasing gate signal line (Rj).

  The gate electrode of the switching transistor 312 is connected to the gate signal line (Gj). One of the source region and the drain region of the switching transistor 312 is connected to the source signal line (Si), and the other is connected to the gate electrode of the driving transistor 313. The switching transistor 312 is a transistor that functions as a switching element when a signal is input to the pixel 100.

  The capacitor 314 is provided to hold the gate voltage of the driving transistor 313 when the switching transistor 312 is in a non-selected state (off state). In this embodiment mode, the capacitor 314 is provided. However, the present invention is not limited to this, and the capacitor 314 may not be provided.

  The source region of the driving transistor 313 is connected to the power supply line (Vi), and the drain region is connected to the light emitting element 311. The power supply line (Vi) is connected to the power supply 131 via the ammeter 130, and is always given a constant power supply potential. The power supply line (Vi) is connected to the capacitor 314. The driving transistor 313 is a transistor that functions as an element (current control element) for controlling a current supplied to the light emitting element 311.

  The light emitting element 311 includes an anode and a cathode, and an organic compound layer provided between the anode and the cathode. In the case where the anode is connected to the drain region of the driving transistor 313, the anode is a pixel electrode and the cathode is a counter electrode. Conversely, when the cathode is connected to the drain region of the driving transistor 313, the cathode is the pixel electrode and the anode is the counter electrode.

  The gate electrode of the erasing transistor 315 is connected to the erasing gate signal line (Rj). One of the source region and the drain region of the erasing transistor 315 is connected to the power supply line (Vi) and the other is connected to the gate electrode of the driving transistor 313. The erasing transistor 315 is a transistor that functions as an element for erasing (resetting) a signal written in the pixel 100.

  When the erasing transistor 315 is turned on, the capacitance held in the capacitor 314 is discharged. Then, the signal written in the pixel 100 is erased (reset), and the light emitting element does not emit light. That is, when the erasing transistor 315 is turned on, the pixel 100 is forced to emit no light. By providing the erasing transistor 315 in this manner, the pixel 100 can be forced to emit no light to have various effects. For example, in the case of the digital method, since the lighting time of the light emitting element can be arbitrarily set, a high gradation image can be displayed. In the case of the analog method, the pixel can be brought into a non-light emitting state every time the frame period is switched, so that a moving image can be clearly displayed without leaving an afterimage.

The power supply line (Vi) is connected to the power supply 131 via the ammeter 130. Note that the ammeter 130 and the power source 131 may be formed on a different substrate from the substrate on which the pixel portion 103 is formed, and may be connected to the pixel portion 103 through a connector or the like, or can be manufactured. For example, the pixel portion 103 may be formed over the same substrate.
The numbers of ammeters 130 and power supplies 131 are not particularly limited and can be set arbitrarily.

  The current value measured by the ammeter 130 is sent to the correction circuit 210 as data. The correction circuit 210 includes a storage medium 211, a calculation circuit 202, and a signal correction circuit 204. Note that the configuration of the correction circuit 210 is not limited to the configuration illustrated in FIG. 6, and an amplifier circuit or the like may be provided. The configuration of the correction circuit 210 can be freely designed by the designer.

  In the pixel portion (not shown), the pixels (i, j) shown in FIG. 6 are provided in a matrix. The pixel portion is provided with source signal lines (S1 to Sx), gate signal lines (G1 to Gy), power supply lines (V1 to Vx), and erasing gate signal lines (R1 to Ry). ing.

  FIG. 18B shows a pixel in which a reset line Rj is added to the pixel shown in FIG. 2 and a capacitor 114 is connected to the reset line Rj instead of the power supply line Vi. In this case, the capacitor 114 serves to reset the pixel (i, j). Further, FIG. 18C shows a pixel in which a reset line Rj and a diode 150 are added to the pixel shown in FIG. 2, and the diode plays a role of resetting the pixel (i, j).

  Note that the structure of a pixel of a light-emitting device to which the present invention is applied is a structure having a light-emitting element and a transistor. There is no particular limitation on the connection relationship between the light-emitting element and the transistor in the pixel, and any connection relationship may be used. The pixel structure described in this embodiment is an example.

Here, taking the pixel shown in FIG. 6 as an example, its operation will be briefly described.
Either a digital method or an analog method can be applied to the pixel. Here, an operation when a digital method combined with a time gray scale method is applied will be described. Note that the time gray scale method is a method of performing gray scale expression by controlling the lighting period of the light emitting element, as reported in detail in Japanese Patent Application Laid-Open No. 2001-343933. Specifically, one frame period is divided into a plurality of subframe periods having different lengths, and light emission or non-light emission of the light-emitting element in each period is selected, so that the length of the lighting period in one frame period is The gradation is expressed with the difference. That is, the gradation is expressed by controlling the length of the lighting period by the video signal.

  In the digital method, as described above, the operation is mainly performed in the linear region, but the operation may be performed in the saturation region. When operating in the linear region, the amount of current changes when the organic compound layer deteriorates. On the other hand, when operating in the saturation region, it is easily affected by variations in characteristics of the driving transistor.

  In the present invention, the influence of the characteristic variation of each pixel is suppressed by correcting the video signal input to each pixel. That is, in a light emitting device to which an analog method is applied, correction of a video signal corresponds to correction of an amplitude value of the video signal. In a light-emitting device to which a digital method combined with a time grayscale method is applied, correction of a video signal corresponds to correction of the length of a lighting period of a pixel to which the video signal is input.

  In a light emitting device to which a digital method combined with a time gray scale method is applied, it is preferable to use the equation (6) indicated by a straight line. However, in the digital method, since it is not necessary to measure the non-light emitting state, the value of the constant b in the equation (6) is preferably zero. The characteristic of each pixel may be measured only once to obtain the value of the constant a.

  The present invention having the above-described structure can provide a light-emitting device capable of displaying a clear multi-gradation and a driving method thereof, in which the influence of variations in transistor characteristics is prevented in a light-emitting device driven in an analog manner. . Furthermore, the present invention can provide a light-emitting device and a driving method thereof that can suppress a change in the amount of current flowing between both electrodes of the light-emitting element due to a change with time and can display clear multi-gradation.

  Note that this embodiment can be freely combined with the embodiment mode.

  In this embodiment, an example of a cross-sectional structure of a pixel will be described with reference to FIG.

  In FIG. 7, an n-channel transistor formed by a known method is used as a switching transistor 4502 provided over a substrate 4501. Although the double gate structure is used in this embodiment, a single gate structure may be used, and a triple gate structure or a multi-gate structure having more gates may be used. Alternatively, a p-channel transistor formed by a known method may be used.

  As the driving transistor 4503, an n-channel transistor formed by a known method is used. A drain wiring 4504 of the switching transistor 4502 is electrically connected to a gate electrode 4506 of the driving transistor 4503 by a wiring (not shown).

  Since the driving transistor 4503 is an element for controlling the amount of current flowing through the light-emitting element 4510, a large amount of current flows, and the driving transistor 4503 is also an element with a high risk of deterioration due to heat or hot carriers. Therefore, a structure in which an LDD region is provided in the drain region of the driving transistor 4503 or in both the source region and the drain region so as to overlap with the gate electrode through the gate insulating film is extremely effective. FIG. 7 shows an example in which LDD regions are formed in both the source region and the drain region of the driving transistor 4503 as an example.

  In this embodiment, the driving transistor 4503 is illustrated with a single gate structure, but a multi-gate structure in which a plurality of transistors are connected in series may be used. Further, a structure may be employed in which a plurality of transistors are connected in parallel to substantially divide a channel formation region into a plurality of portions so that heat can be emitted with high efficiency. Such a structure is effective as a countermeasure against deterioration due to heat.

  A wiring (not shown) including the gate electrode 4506 of the driving transistor 4503 partially overlaps with the drain wiring 4512 of the driving transistor 4503 through an insulating film, and a storage capacitor is formed in that region. This storage capacitor has a function of holding a voltage applied to the gate electrode 4506 of the driving transistor 4503.

  A first interlayer insulating film 4514 is provided over the switching transistor 4502 and the driving transistor 4503, and a second interlayer insulating film 4515 made of a resin insulating film is formed thereover.

  Reference numeral 4517 denotes a pixel electrode (anode of the light emitting element) made of a highly light-transmitting conductive film, which is formed so as to partially cover the drain region of the driving transistor 4503 and is electrically connected thereto. As the pixel electrode 4517, a compound of indium oxide and tin oxide (called ITO) or a compound of indium oxide and zinc oxide is preferably used. Of course, other light-transmitting conductive films may be used.

  Next, after an organic resin film 4516 is formed over the pixel electrode 4517 and a portion facing the pixel electrode 4517 is patterned, an organic compound layer 4519 is formed. Although not shown here, an organic compound layer 4519 corresponding to each color of R (red), G (green), and B (blue) may be separately formed. As a light-emitting material for the organic compound layer 4519, a π-conjugated polymer material is used. Typical polymer materials include polyparaphenylene vinylene (PPV), polyvinyl carbazole (PVK), and polyfluorene. In addition, the organic compound layer 4519 has two structures of a single layer structure and a stacked structure, but the present invention may produce either structure. An organic compound layer 4519 (a layer for performing light emission and carrier movement therefor) may be formed by freely combining known materials and structures.

  For example, although an example in which a polymer material is used as the organic compound layer 4519 is described in this embodiment, a low molecular organic light emitting material may be used. It is also possible to use an inorganic material such as silicon carbide for the charge transport layer or the charge injection layer. Known materials can be used for these organic light emitting materials and inorganic materials.

  When the cathode 4523 is formed, the light emitting element 4510 is completed. Note that the light-emitting element 4510 here refers to a stacked body including a pixel electrode 4517, an organic compound layer 4519, a hole injection layer 4522, and a cathode 4523.

  By the way, in this embodiment, a passivation film 4524 is provided on the cathode 4523. As the passivation film 4524, a silicon nitride film or a silicon nitride oxide film is preferable. This purpose is to cut off the light emitting element 4510 from the outside, and has both the meaning of preventing deterioration due to oxidation of the light emitting material and the meaning of suppressing degassing from the organic light emitting material. This increases the reliability of the light emitting device.

  As described above, the light-emitting device described in this embodiment includes a pixel portion including a pixel having the structure illustrated in FIG. 7, a selection transistor having a sufficiently low off-current value, a driving transistor resistant to hot carrier injection, Have Therefore, a light emitting device having high reliability and capable of displaying a good image can be obtained.

  In the case of the light-emitting element having the structure described in this embodiment, light generated in the organic compound layer 4519 is emitted in the direction of the substrate 4501 over which a transistor is formed as indicated by an arrow. Note that light emitted from the light-emitting element 4510 is emitted in the direction of the substrate 4501 is referred to as bottom emission.

  Next, a cross-sectional structure of the light-emitting device in which light emitted from the light-emitting element is emitted in a direction opposite to the substrate 4510 (top emission) will be described with reference to FIGS.

  In FIG. 17A, a driving transistor 1601 is formed over a substrate 1600. The driving transistor 1601 includes a source region 1604a, a drain region 1604c, and a channel formation region 1604b. In addition, a gate electrode 1603a is provided over the channel formation region 1604b with the gate insulating film 1605 provided therebetween. Note that the driver transistor 1601 can have a known structure as well as the structure shown in FIG.

  An interlayer film 1606 is formed over the driving transistor 1601. Next, a transparent conductive film such as ITO is formed and patterned into a desired shape to form a pixel electrode 1608. Here, the pixel electrode 1608 functions as an anode of the light-emitting element 1614.

  The interlayer film 1606 forms contact holes that reach the source region 1604a and the drain region 1604c of the driving transistor 1601, forms a laminated film of Ti and Al containing Ti, and Ti, and patterns it into a desired shape. . Accordingly, a wiring 1607 and a wiring 1609 are formed.

  Subsequently, an insulating film made of an organic resin material such as acrylic is formed, and an opening is formed at a position corresponding to the pixel electrode 1608 of the light-emitting element 1614 to form the insulating film 1610. Here, in order to avoid problems such as deterioration of the organic compound layer and disconnection due to a step difference in the side wall of the opening, the opening is formed to have a sufficiently gentle tapered side wall.

  Then, after forming the organic compound layer 1611, a counter electrode (cathode) 1612 of the light emitting element 1614 was formed in order of a cesium (Cs) film having a thickness of 2 nm or less and a silver (Ag) film having a thickness of 10 nm or less. It is formed by a laminated film. By making the thickness of the counter electrode 1612 of the light emitting element 1614 extremely small, light emitted from the organic compound layer 1611 passes through the counter electrode 1612 and is emitted in a direction opposite to the substrate 1600. Then, a protective film 1613 is formed for the purpose of protecting the light emitting element 1614.

  FIG. 17B is a cross-sectional view having a structure different from that in FIG. Note that in FIG. 17B, the same portions as those in FIG. 17A are described using the same reference numerals. In FIG. 17B, the structure up to the formation of the driving transistor 1601 and the interlayer film 1606 is the same as that shown in FIG.

  Contact holes reaching the source region 1604 a and the drain region 1604 c of the driving transistor 1601 are formed in the interlayer film 1606. Thereafter, a laminated film made of Ti, Al containing Ti and Ti is formed, and then a transparent conductive film typified by ITO or the like is formed. A laminated film made of Ti, Ti containing Ti, and Ti, and a transparent conductive film typified by ITO or the like are patterned into a desired shape to form a wiring 1607, a wiring 1608, a wiring 1609, and a pixel electrode 1620. Note that the pixel electrode 1620 functions as an anode of the light-emitting element 1624.

  Subsequently, an insulating film made of an organic resin material such as acrylic is formed, an opening is formed at a position corresponding to the pixel electrode 1620 of the light emitting element 1624, and an insulating film 1610 is formed. Here, in order to avoid problems such as deterioration and disconnection of the organic compound layer due to the step of the side wall of the opening, the opening is formed to have a sufficiently gentle tapered side wall.

  Next, after the organic compound layer 1611 is formed, the counter electrode (cathode) 1612 of the light-emitting element 1624 is formed by sequentially forming a cesium (Cs) film having a thickness of 2 nm or less and a silver (Ag) film having a thickness of 10 nm or less. It is formed by a laminated film. By making the thickness of the counter electrode 1612 of the light emitting element 1624 extremely small, light emitted from the organic compound layer 1611 passes through the counter electrode 1612 and is emitted in a direction opposite to the substrate 1600. Next, a protective film 1613 is formed for the purpose of protecting the light emitting element 1624.

  As described above, the light-emitting device that emits light in the direction opposite to the substrate 1600 does not need to visually recognize the light emission of the light-emitting element 1614 through the element such as the driving transistor 1601 formed over the substrate 1600. Therefore, the aperture ratio can be increased.

  The pixel having the structure illustrated in FIG. 17B includes a wiring 1619 connected to a source region or a drain region of the driving transistor and a pixel electrode 1620 in comparison with the pixel having the structure illustrated in FIG. Since it can be formed by patterning using a common photomask, the number of photomasks required in the manufacturing process can be reduced and the process can be simplified.

  Note that this embodiment can be freely combined with Embodiment Mode and Embodiment 1.

  In this example, the appearance of the light-emitting device of the present invention will be described with reference to FIG.

  8A is a top view of the light-emitting device, FIG. 8B is a cross-sectional view taken along the line AA ′ in FIG. 8A, and FIG. 8C is a cross-sectional view taken along the line B- in FIG. It is sectional drawing in B '.

  A sealant 4009 is provided so as to surround the pixel portion 4002 provided over the substrate 4001, the source signal line driver circuit 4003, and the first and second gate signal line driver circuits 4004a and 4004b. A sealing material 4008 is provided over the pixel portion 4002, the source signal line driver circuit 4003, and the first and second gate signal line driver circuits 4004a and 4004b. The pixel portion 4002, the source signal line driver circuit 4003, and the first and second gate signal line driver circuits 4004a and 400b are sealed together with a filler 4210 by a substrate 4001, a sealant 4009, and a sealant 4008. ing.

  In this embodiment, one set (two) of gate signal line driving circuits is provided. However, the present invention is not limited to this, and the number of gate signal line driving circuits and source signal line driving circuits is determined by the designer. Can be determined arbitrarily.

  In addition, the pixel portion 4002, the source signal line driver circuit 4003, and the first and second gate signal line driver circuits 4004a and 4004b provided over the substrate 4001 include a plurality of transistors. In FIG. 8B, a driver circuit transistor (here, an n-channel transistor and a p-channel transistor are illustrated) 4201 included in the source signal line driver circuit 4003 formed over the base film 4010 and the pixel portion A driving transistor (transistor for controlling current to the light-emitting element) 4202 included in 4002 is illustrated.

  In this embodiment, a p-channel transistor or an n-channel transistor manufactured by a known method is used as the driver circuit transistor 4201, and a p-channel transistor manufactured by a known method is used as the driving transistor 4202. Used. In addition, the pixel portion 4002 is provided with a storage capacitor (not shown) connected to the gate electrode of the driving transistor 4202.

  An interlayer insulating film (planarization film) 4301 is formed over the driver circuit transistor 4201 and the driving transistor 4202, and a pixel electrode (anode) 4203 electrically connected to the drain of the driving transistor 4202 is formed thereon. The As the pixel electrode 4203, a transparent conductive film having a large work function is used. As the transparent conductive film, a compound of indium oxide and tin oxide, a compound of indium oxide and zinc oxide, zinc oxide, tin oxide, or indium oxide can be used. Moreover, you may use what added the gallium to the said transparent conductive film.

  An insulating film 4302 is formed over the pixel electrode 4203, and an opening is formed over the pixel electrode 4203 in the insulating film 4302. In this opening, an organic compound layer 4204 is formed on the pixel electrode 4203. A known organic light emitting material or inorganic light emitting material can be used for the organic compound layer 4204. The organic light emitting material includes a low molecular (monomer) material and a high molecular (polymer) material, either of which may be used.

  As a method for forming the organic compound layer 4204, a known vapor deposition technique or coating technique may be used. The structure of the organic compound layer may be a stacked structure or a single layer structure by freely combining a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, or an electron injection layer.

A conductive film having a light-blocking property over the organic compound layer 4204 (typically, a conductive film containing aluminum, copper, or silver as its main component or a stacked film of these and another conductive film)
A cathode 4205 made of is formed. In addition, it is desirable to remove moisture and oxygen present at the interface between the cathode 4205 and the organic compound layer 4204 as much as possible. Therefore, it is necessary to devise such that the organic compound layer 4204 is formed in a nitrogen or rare gas atmosphere and the cathode 4205 is formed without being exposed to oxygen or moisture. In this embodiment, the above-described film formation is possible by using a multi-chamber type (cluster tool type) film formation apparatus. The cathode 4205 is given a predetermined voltage.

  As described above, a light-emitting element 4303 including the pixel electrode (anode) 4203, the organic compound layer 4204, and the cathode 4205 is formed. A protective film 4209 is formed over the insulating film 4302 so as to cover the light emitting element 4303. The protective film 4209 is effective in preventing oxygen, moisture, and the like from entering the light emitting element 4303.

  Reference numeral 4005 a denotes a lead wiring connected to the power supply line, which is electrically connected to the source region of the driving transistor 4202. The lead wiring 4005 a passes between the sealant 4009 and the substrate 4001 and is electrically connected to the FPC wiring 4301 included in the FPC 4006 through the anisotropic conductive film 4300.

As the sealing material 4008, a glass material, a metal material (typically a stainless steel material), a ceramic material, or a plastic material (including a plastic film) can be used. Plastic materials include FRP (Fiberglass-Reinforced Plastics) plate, PVF (polyvinyl fluoride)
A film, mylar film, polyester film or acrylic resin film can be used. A sheet having a structure in which an aluminum foil is sandwiched between PVF films or mylar films can also be used.

  However, when the light emission direction from the light emitting element is directed toward the cover material, the cover material must be transparent. In that case, a transparent material such as a glass plate, a plastic plate, a polyester film or an acrylic film is used.

  Further, as the filler 4103, in addition to an inert gas such as nitrogen or argon, an ultraviolet curable resin or a thermosetting resin can be used. PVC (polyvinyl chloride), acrylic, polyimide, epoxy resin, silicone resin, PVB (Polyvinyl butyral) or EVA (ethylene vinyl acetate) can be used. In this example, nitrogen was used as the filler.

  Further, in order to expose the filler 4103 to a hygroscopic substance (preferably barium oxide) or a substance capable of adsorbing oxygen, a recess 4007 is provided on the surface of the sealing material 4008 on the substrate 4001 side to adsorb the hygroscopic substance or oxygen. A possible substance 4207 is placed. In order to prevent the hygroscopic substance or the substance 4207 capable of adsorbing oxygen from scattering, the concave part cover material 4208 holds the hygroscopic substance or the substance 4207 capable of adsorbing oxygen in the concave part 4007. Note that the concave cover material 4208 has a fine mesh shape, and is configured to allow air and moisture to pass therethrough but not a hygroscopic substance or a substance 4207 capable of adsorbing oxygen. By providing the hygroscopic substance or the substance 4207 capable of adsorbing oxygen, deterioration of the light-emitting element 4303 can be suppressed.

  As shown in FIG. 8C, the conductive film 4203a is formed so as to be in contact with the lead wiring 4005a at the same time as the pixel electrode 4203 is formed.

  The anisotropic conductive film 4300 has a conductive filler 4300a. By thermally pressing the substrate 4001 and the FPC 4006, the conductive film 4203a on the substrate 4001 and the FPC wiring 4301 on the FPC 4006 are electrically connected by the conductive filler 4300a.

  An ammeter and a correction circuit included in the light-emitting device of the present invention are formed over a substrate (not shown) different from the substrate 4001, and are electrically connected to the power supply line and the cathode 4205 formed over the substrate 4001 through the FPC 4006. It is connected to the.

  Note that this embodiment can be implemented by being freely combined with the embodiment mode and Embodiments 1 and 2.

  In this embodiment, the appearance of a light emitting device of the present invention, which is different from that of Embodiment 3, will be described with reference to FIG. More specifically, the ammeter and the correction circuit are formed on a substrate different from the substrate on which the pixel portion is formed, and the pixel portion is formed by means such as a wire bonding method or a COG (chip on glass) method. The appearance of the light emitting device when connected to the wiring on the substrate is described with reference to FIG.

  FIG. 9 shows an external view of the light emitting device of this embodiment. A sealant 5009 is provided so as to surround the pixel portion 5002 provided over the substrate 5001, the source signal line driver circuit 5003, and the first and second gate signal line driver circuits 5004a and 5004b. A sealing material 5008 is provided over the pixel portion 5002, the source signal line driver circuit 5003, and the first and second gate signal line driver circuits 5004a and 5004b. Therefore, the pixel portion 5002, the source signal line driver circuit 5003, and the first and second gate signal line driver circuits 5004a and 500b are filled with a filler (not shown) by the substrate 5001, the sealant 5009, and the sealing material 5008. Z).

  In this embodiment, two gate signal line drive circuits are provided, but the present invention is not limited to this, and the number of gate signal line drive circuits and source signal line drive circuits can be arbitrarily determined by the designer.

  A recess 5007 is provided on the surface of the sealing material 5008 on the substrate 5001 side, and a hygroscopic substance or a substance capable of adsorbing oxygen is disposed.

  A wiring routed on the substrate 5001 (routed wiring) passes between the sealant 5009 and the substrate 5001 and is connected to a circuit or an element outside the light-emitting device through the FPC 5006.

The ammeter and the correction circuit are different from the substrate 5001 (hereinafter referred to as a chip).
5020, attached to the substrate 5001 by means such as a COG (chip on glass) method, and electrically connected to a power supply line and a cathode (not shown) formed on the substrate 5001.

  In this embodiment, the chip 5020 is mounted on the substrate 5001 by a wire bonding method, a COG method, or the like, so that the light emitting device can be configured with one substrate, the device itself is compact, and the mechanical strength is also high. Go up.

  The method for connecting the chip on the substrate can be performed using a known method. Further, an ammeter and circuits and elements other than the correction circuit may be attached on the substrate 5001.

  This embodiment can be implemented by being freely combined with the embodiment mode and Embodiments 1 to 3.

  Since the light-emitting device is a self-luminous type, it is superior in visibility in a bright place and has a wide viewing angle compared to a liquid crystal display. Therefore, it can be used for display portions of various electronic devices.

  As an electronic device using the light emitting device of the present invention, a video camera, a digital camera, a goggle type display (head mounted display), a navigation system, a sound reproduction device (car audio, audio component, etc.), a notebook type personal computer, a game device, A portable information terminal (mobile computer, mobile phone, portable game machine, electronic book, or the like), an image playback device equipped with a recording medium (specifically, a recording medium such as a digital video disc (DVD)) A device having a display capable of displaying). In particular, since a wide viewing angle is important for a portable information terminal that often has an opportunity to see a screen from an oblique direction, it is desirable to use a light emitting device. Specific examples of these electronic devices are shown in FIGS.

  FIG. 10A illustrates a light-emitting device, which includes a housing 3001, a support base 3002, a display portion 3003, speaker portions 3004, a video input terminal 3005, and the like. The light emitting device of the present invention can be used for the display portion 3003. Since the light-emitting device is a self-luminous type, a backlight is not necessary and a display portion thinner than a liquid crystal display can be obtained. Note that the light emitting device includes all display devices for displaying information such as for personal computers, for receiving TV broadcasts, and for displaying advertisements.

  FIG. 10B illustrates a digital still camera, which includes a main body 3101, a display portion 3102, an image receiving portion 3103, operation keys 3104, an external connection port 3105, a shutter 3106, and the like. The light emitting device of the present invention can be used for the display portion 3102.

  FIG. 10C illustrates a notebook personal computer, which includes a main body 3201, a housing 3202, a display portion 3203, a keyboard 3204, an external connection port 3205, a pointing mouse 3206, and the like. The light emitting device of the present invention can be used for the display portion 3203.

  FIG. 10D illustrates a mobile computer, which includes a main body 3301, a display portion 3302, a switch 3303, operation keys 3304, an infrared port 3305, and the like. The light-emitting device of the present invention can be used for the display portion 3302.

  FIG. 10E illustrates a portable image reproducing device (specifically, a DVD reproducing device) provided with a recording medium, which includes a main body 3401, a housing 3402, a display portion A3403, a display portion B3404, and a recording medium (DVD or the like). A reading unit 3405, an operation key 3406, a speaker unit 3407, and the like are included. Although the display portion A 3403 mainly displays image information and the display portion B 3404 mainly displays character information, the light-emitting device of the present invention can be used for the display portions A, B 3403, and 3404. Note that an image reproducing device provided with a recording medium includes a home game machine and the like.

  FIG. 10F illustrates a goggle type display (head mounted display), which includes a main body 3501, a display portion 3502, and an arm portion 3503. The light emitting device of the present invention can be used for the display portion 3502.

  FIG. 10G illustrates a video camera, which includes a main body 3601, a display portion 3602, a housing 3603, an external connection port 3604, a remote control receiving portion 3605, an image receiving portion 3606, a battery 3607, an audio input portion 3608, operation keys 3609, and the like. . The light-emitting device of the present invention can be used for the display portion 3602.

  Here, FIG. 10H illustrates a mobile phone, which includes a main body 3701, a housing 3702, a display portion 3703, an audio input portion 3704, an audio output portion 3705, operation keys 3706, an external connection port 3707, an antenna 3708, and the like. The light-emitting device of the present invention can be used for the display portion 3703. Note that the display portion 3703 can suppress power consumption of the mobile phone by displaying white characters on a black background.

  If the light emission luminance of the organic light emitting material is increased in the future, the light including the output image information can be enlarged and projected by a lens or the like and used in a front type or rear type projector.

  In addition, the electronic devices often display information distributed through electronic communication lines such as the Internet and CATV (cable television), and in particular, opportunities to display moving image information are increasing. Since the organic light emitting material has a very high response speed, the light emitting device is preferable for displaying moving images.

  Further, since the light emitting part consumes power in the light emitting device, it is desirable to display information so that the light emitting part is minimized. Therefore, when a light emitting device is used for a display unit mainly including character information, such as a portable information terminal, particularly a mobile phone or a sound reproduction device, it is driven so that character information is formed by the light emitting part with the non-light emitting part as the background. It is desirable to do.

  As described above, the applicable range of the present invention is so wide that it can be used for electronic devices in various fields.

1 is a circuit diagram of a light emitting device of the present invention. 1 is a circuit diagram of a light emitting device of the present invention. 4A and 4B illustrate a driving method of a light-emitting device of the present invention. FIG. 11 is a timing chart of signals input to the light-emitting device of the present invention. The figure which shows the relationship between a video signal and an electric current value. FIG. 4 is a diagram illustrating a circuit diagram of a pixel of a light-emitting device of the present invention. The figure which shows the cross-section (lower surface emission) of the light-emitting device of this invention. The figure which shows the external appearance of the light-emitting device of this invention. The figure which shows the external appearance of the light-emitting device of this invention. FIG. 14 illustrates an example of an electronic device in which a light-emitting device of the present invention is provided. 3A and 3B illustrate a connection structure between a light-emitting element and a driving transistor, and diagrams illustrating voltage-current characteristics of the light-emitting element and the driving transistor. FIG. 9 shows voltage-current characteristics of a light-emitting element and a driving transistor. The figure which shows the relationship between the gate voltage and drain current of a driving transistor. FIG. 11 is a diagram illustrating a circuit diagram of a pixel portion of a light-emitting device. FIG. 6 is a timing chart of signals input to the light-emitting device. The figure which shows the relationship between a video signal and an electric current value. The figure which shows the cross-section (upper surface emission) of the light-emitting device of this invention. The figure which shows the voltage-current characteristic of a light emitting element and a driving transistor, and the circuit diagram of a pixel.

Claims (5)

A pixel portion having a plurality of pixels each including a light emitting element and a transistor electrically connected to the light emitting element;
Current measuring means for measuring a current value when all of the light emitting elements are in a non-lighting state and a current value when each of the light emitting elements is in a lighting state;
A correction circuit for deriving an interpolation function using a difference between a current value in the lighting state and a current value in the non-lighting state, and correcting a video signal input to each pixel using the interpolation function; Have
The current measuring means and the correction circuit are provided on a substrate different from the substrate on which the pixel portion is provided,
The light emitting device, wherein the substrate provided with the current measuring means and the correction circuit is attached to the substrate provided with the pixel portion. A pixel portion having a plurality of pixels each including a light emitting element and a transistor electrically connected to the light emitting element;
Current measuring means for measuring a current value when all of the light emitting elements are in a non-lighting state and a current value when each of the light emitting elements is in a lighting state;
A correction circuit for deriving an interpolation function using a difference between a current value in the lighting state and a current value in the non-lighting state, and correcting a video signal input to each pixel using the interpolation function; Have
The current measuring means and the correction circuit are provided on a substrate different from the substrate on which the pixel portion is provided,
The substrate provided with the current measuring means and the correction circuit is configured such that the pixel unit is externally sealed with a sealing material and one of a glass material, a metal material, a ceramic material, and a plastic material, A light-emitting device which is attached to the provided substrate. In claim 1 or claim 2,
The light-emitting device, wherein the substrate on which the current measuring unit and the correction circuit are provided is a chip. In any one of Claims 1 thru | or 3,
The substrate provided with the current measuring means and the correction circuit is attached to the substrate provided with the pixel portion using a wire bonding method or a COG (chip-on-glass) method. A light emitting device characterized. An electronic apparatus comprising the light emitting device according to claim 1 in a display portion.

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