JP2006162721A - Organic electroluminescence display apparatus and driving method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To apply a reverse bias current to an organic electroluminescence (OEL) element by an active element structure. <P>SOLUTION: An OEL display apparatus comprises; the OEL element 100 which is included in a plurality of pixels; a first electrode line 136 and a second electrode line 140 which flow a light emitting current to the OEL element of at least any one of pixels; first current control means 120 and 122 for controlling the light emitting current which should be flown to the OEL element by the first electrode line and the second electrode line; and second current control means 124 and 126 for flowing the reverse bias current which has a opposite direction to the light emitting current, to the OEL element. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an organic EL display device and a driving method thereof. In particular, the present invention relates to an organic EL display device using an active driving element and a driving method thereof.

  Conventionally, an organic electroluminescence display (or an organic light-emitting diode display, hereinafter referred to as “organic EL display device”) having a wide range of application possibilities such as display of a portable terminal or an industrial measuring instrument with high definition and excellent visibility. Are known. The organic EL display device includes an organic EL light emitting element having an electron transport layer, an organic EL light emitting layer, and a hole transport layer sandwiched between a first element electrode and a second element electrode in each pixel. In the organic EL light emitting device, light emission is realized by converting the current injected by the first device electrode and the second device electrode into visible light. Such an organic EL display device is a self-luminous display device that emits light by itself, and has advantages such as a wider viewing angle and a faster response speed than a non-light-emitting display device such as a liquid crystal display device. is doing. Because of such advantages, the organic EL display device is being developed as a flat panel display device for a mobile phone terminal device, a portable personal computer, and a thin television.

  As an organic EL display device, for example, an organic EL display device capable of multicolor display by a display region in which a large number of red (R), green (G), and blue (B) pixels are arranged in a matrix is known. As a conventional technique for appropriately realizing each pixel having different emission colors of R, G, and B in this display region, organic EL light emitting elements having different emission colors are arranged in each of R, G, and B pixels. A configured organic EL display device is known. In addition, a method using a fluorescent material that absorbs light in the light emission wavelength region of the organic EL light emitting layer and emits light in another visible wavelength region (hereinafter referred to as “color conversion method”) is also disclosed. (Patent Document 1 etc.). In the color conversion method, for example, an organic EL light emitting element that emits blue light is disposed not only in the B pixel but also in the R and G pixels, and the blue light is emitted from the longer wavelength in the R and G pixels. There is an example (for example, Patent Document 2) in which fluorescent conversion materials that convert green and red emission colors are further stacked.

  In such an organic EL display device capable of multi-color display, a method (dot matrix driving method) for driving each pixel independently by performing desired light emission (dot matrix driving method) is a large number of rows and columns. A TFT having an active layer (active layer) with a passive matrix driving method for driving an organic EL light emitting layer sandwiched between row and column electrodes in each pixel by combining stripe electrodes and an amorphous silicon layer, a polysilicon layer, etc. There is an active matrix driving method using an active driving element such as an element (Thin Film Transistor). In the passive matrix method, an organic EL light emitting layer is formed by a predetermined scan line (wiring also serving as a first element electrode) made of a transparent electrode and a predetermined data line (wiring also serving as a second element electrode) made of a metal electrode such as aluminum. Is sandwiched, and current is passed through the organic EL light emitting layer by performing simple matrix driving (or duty driving) on these electrodes. As a result, the pixels addressed by the scan line and the data line are caused to emit light with a desired luminance. In addition, in an active matrix driving type organic EL display device, each pixel usually includes a power supply wiring or a power supply electrode in addition to a scan line and a data line, and each pixel includes at least one current control TFT element. Yes. In the active matrix driving method, the current control TFT element is connected to the current control TFT element by controlling the current (current amount or current passing time) between the source and drain of the current control TFT element by the data line and the scan line. By controlling the luminance value and average luminance of the organic EL light emitting element, the pixel addressed by the scan line and the data line is caused to emit light with a desired luminance.

  When an organic EL display device is actually manufactured, lighting failure may occur due to various manufacturing processes. As a typical example of this lighting failure, there is a leakage failure in which the first element electrode and the second element electrode are short-circuited through the organic EL light emitting layer. When a leak failure occurs in one pixel, not only does the pixel causing the short-circuit stop light emission, but also a failure (bright line) in which brightly lit pixels emerge in a line shape may occur. This is considered to be caused by, for example, an extra current (leakage current) flowing to other pixels on the same data line. When a leak failure occurs in this way, a single pixel failure leads to a failure of the entire display device.

  As a conventional technique for repairing this leakage defect, there is a method of applying a reverse bias voltage to an organic EL light emitting element using a data line and a scan line in the passive matrix method (Patent Document 3). In this process, a reverse current (reverse bias current) flows through the organic EL light emitting layer in a short-circuited portion of a pixel having a leak failure. Then, due to the Joule heat due to the concentrated current, the short circuit of the organic EL light emitting layer of the pixel having the leak failure is eliminated, and no leak failure is observed even when light is emitted again.

Also in the active matrix driving method, a method of applying a reverse bias in a manufacturing process (Patent Document 4) and a method of applying a reverse bias by inverting the polarity of a scan line (Patent Document 5) are disclosed. FIG. 8 is an enlarged wiring diagram showing a display pixel of a conventional active matrix driving organic EL display device. Each pixel of the organic EL display device 2000 is provided with an organic EL light emitting element 200. The organic EL light emitting element 200 is connected to the drain terminal of the current control TFT element 220 and the second electrode wiring 240 connected to the ground. The current control TFT element 220 has a source terminal connected to the first electrode wiring 236 and a gate terminal connected to the drain terminal of the switching TFT element 218. The switching TFT element 218 has a gate terminal connected to the scan line 250 and a source terminal connected to the data line 260. If the contents disclosed in Patent Document 4 are described with this structure, a reverse bias voltage is applied between the first wiring electrode 236 and the second electrode wiring 240 while the switching TFT is in a conductive state in the manufacturing process. If the contents disclosed in Patent Document 5 are described with this structure, the polarity of the voltage applied to the first wiring electrode 236 and the second electrode wiring 240 after manufacturing is changed, and the first wiring electrode 236 A reverse bias voltage is applied between the second electrode wiring 240.
Japanese Patent Laid-Open No. 3-152897 JP-A-8-286033 JP 2003-234187 A JP 2004-31335 A JP 2001-109432 A

  In the method disclosed in Patent Document 4, it is necessary to pattern a wiring after applying a reverse bias to the organic EL light emitting layer in the manufacturing process, and thereafter, the reverse bias cannot be applied. Therefore, for example, there is a problem in that a leak defect repair effect cannot be obtained for a leak defect that does not occur at the time of manufacture and occurs after the start of use or after a long-term use.

In the method disclosed in Patent Document 4, a circuit that can apply a voltage whose polarity is reversed to the organic EL light emitting layer drives the organic EL display device in order to apply a reverse bias to the organic EL light emitting layer. There is a problem that the configuration of the drive circuit is complicated, which is necessary for the circuit to be operated.
An object of the present invention is to solve at least some of the above problems.

In the present invention, the configuration of the display unit of the display device is configured to allow not only the emission current but also the reverse bias current to flow through the organic EL emission layer.
That is, in the present invention, a plurality of organic EL light emitting elements corresponding to a plurality of pixels, a first electrode wiring capable of flowing a light emission current through at least some of the organic EL light emitting elements, and the first electrode wiring cooperate with each other. And a second electrode wiring that can flow a light emission current to the organic EL light emitting element, and the first electrode wiring and the second electrode wiring are used to control the light emission current that should flow to the organic EL light emitting element. A reverse bias current in a direction opposite to the light emission current can be caused to flow to the organic EL light emitting element by the first current control means electrically connected to the EL light emitting element, and the first electrode wiring and the second electrode wiring. An organic EL display device is provided that includes second current control means electrically connected to the organic EL light emitting element.

  The first and second current control means are not particularly limited, but, for example, refer to active drive elements that can control current. Typically, a polysilicon TFT element having a polysilicon layer as an active layer, an amorphous silicon TFT element having an amorphous silicon layer as an active layer, and the like, and the first and second current control means are For example, each of the active elements can be combined with each other, or these active elements can be separated and combined.

  The organic EL light emitting element used in the organic EL display device of the present invention is not particularly limited. For example, various organic EL light emitting elements having a light emitting layer sandwiched between a hole transport layer and an electron transport layer. is there. As the materials for the hole transport layer, the electron transport layer, and the light emitting layer, any materials that can obtain appropriate light emission can be used, and these materials are not limited in the present invention. A polymer type organic EL display EL light-emitting material can be used. Furthermore, a color conversion method can also be used.

  In the organic EL display device of the present invention, the first current control means controls the light emission current to be passed through the organic EL light emitting element by the first electrode wiring and the second electrode wiring, and the organic EL light emission. The second current control means is electrically connected to the element, and the second current control means is capable of causing a reverse bias current in a direction opposite to the light emission current to flow through the organic EL light emitting element by the first electrode wiring and the second electrode wiring. It is electrically connected to the organic EL light emitting element. As a result, a reverse bias current can be passed through the organic EL light emitting element without providing a means for inverting the polarity in the drive circuit, so that even if a leak failure occurs, it can be repaired by simply lighting the display device. .

  In the present invention, it is preferable that the first electrode wiring is driven so that the polarity of the voltage with respect to the second electrode wiring is not reversed. In the present invention, when a display current is passed using the first and second electrode wirings, a forward current flows for the organic EL light emitting device exhibiting diode characteristics between the first and second electrode wirings. The voltage and its polarity are adjusted. For example, immediately before the address period for addressing each pixel, the first and second electrode wirings are set to the same potential in order to discharge charges stored as parasitic capacitance between the electrodes of each organic EL light emitting element. To be controlled. In this configuration, the polarity between the first and second electrode electrodes is not reversed even in the address period. In such a case, the configuration of the power source for supplying current to the first and second electrodes in the drive circuit is simplified, and there is an advantage that a complicated drive circuit may not be used.

  In the present invention, a control wiring for transmitting a signal for controlling the first current control means and the second current control means is further provided, and the first current control means and the second current control means are in a conductive state at the same time. And a state in which a light emission current flows through the organic EL light emitting element and a state in which a reverse bias current can flow through the organic EL light emitting element by the second current control means. Is preferably switched. With this configuration, there is an advantage that, for example, the first electrode wiring and the second electrode wiring can be prevented from being short-circuited by a signal of the control wiring.

  In the organic EL display device of the present invention, the absolute value of the reverse bias voltage applied to the organic EL light emitting element when a reverse bias current is supplied to the organic EL light emitting element is the same as that of the organic EL light emitting element when the display current is supplied to the maximum. It is preferable that the absolute value of the applied forward voltage is 85% or more. If comprised in this way, sufficient leak defect repair function is realizable. Although not limited thereto, in the organic EL display device of the present invention, for example, the second current control unit may have a larger on-resistance (resistance during conduction) than the first current control unit. By applying the reverse bias voltage to the organic EL light emitting element, a sufficient leakage failure repair function can be realized even when the second current control means having a small size is used.

  In the organic EL display device of the present invention, it is preferable that the period during which a voltage capable of applying a reverse bias current is applied to the organic EL light emitting element is 20 microseconds or longer. By supplying a reverse bias current for such a period, a sufficient leakage failure repair function can be realized. Although not limited thereto, in the organic EL display device of the present invention, the period for supplying the reverse bias current is set to any period of the display period, thereby repairing the leakage defect while performing the display. An organic EL display device having the above can be realized.

  Furthermore, in the organic EL display device of the present invention, it is preferable that one of the first current control means and the second current control means is a normally-off thin film transistor and the other is a normally-on thin film transistor. . In the organic EL display device of the present invention, it is preferable that one of the first current control unit and the second current control unit is an N-channel thin film transistor and the other is a P-channel thin film transistor.

  A normally-off thin film transistor is, for example, an enhancement type thin film transistor in which an active layer is made of polysilicon or amorphous silicon. It is a depletion type thin film transistor that is manufactured by being doped by a process such as implantation. In an N-channel thin film transistor, an n + region is formed in the source and drain regions, and when the potential of the gate terminal is increased from the potential of the source terminal to a predetermined value or more, a channel is formed and the source terminal and the drain terminal become conductive. Such a thin film transistor. In addition, in a p-channel thin film transistor, p + regions are formed in the source and drain regions, and when the potential of the gate terminal is lowered from the potential of the source terminal to a predetermined value or more, a channel is formed and the source terminal and the drain terminal are brought into conduction. Such a thin film transistor. When using a combination of normally-on and normally-off thin film transistors, or using a combination of N-channel and P-channel thin film transistors, the gate terminals of the two transistors are controlled by one control wiring, thereby providing an organic EL. A light emitting current and a reverse bias current can be supplied to the light emitting element.

  The organic EL display device of the present invention includes a plurality of scan lines and data lines for addressing each pixel and writing display image data to the addressed pixel, and is electrically connected to the scan line. An organic EL display device comprising a switching TFT element comprising a gate terminal, a source terminal electrically connected to a data line, and a drain terminal electrically connected to a control electrode, wherein the switching TFT element is a scan Based on the potential control of the gate terminal by the line, the signal of the data line is output to the control wiring through the source terminal and the drain terminal, and the first current control means outputs the first TFT element and the second TFT element. The second current control means includes a third TFT element and a fourth TFT element; The first TFT element is electrically connected to the first electrode wiring, and the drain terminal is electrically connected to the first element electrode of the organic EL light emitting element. The second TFT element has a source terminal electrically connected to the second element electrode of the organic EL light emitting element, a drain terminal electrically connected to the second electrode wiring, and the third TFT element has a source The terminal is electrically connected to the second electrode wiring, the drain terminal is electrically connected to the first element electrode of the organic EL light emitting element, and the fourth TFT element has a source terminal that is the second of the organic EL light emitting element. The device electrode is electrically connected, the drain terminal is electrically connected to the first electrode wiring, and the voltage for flowing the light emission current to the organic EL light emitting element is controlled by the control wiring of the first to fourth TFT elements. Get By simultaneously controlling the first and second TFT terminals, the source terminals and drain terminals of the first TFT element and the second TFT element are made conductive, and the source terminals and drain terminals of the third TFT element and the fourth TFT element are made insulative. The voltage applied to the EL light-emitting element and causing the reverse bias current to flow through the organic EL light-emitting element is controlled by simultaneously controlling the gate terminals of the first to fourth TFT elements by the control wiring, and the source terminals of the first and second TFT elements. It is preferable that the drain terminal is insulated and the source terminal / drain terminal of the third TFT element and the fourth TFT element are made conductive to be applied to the organic EL light emitting element.

  Here, each TFT element of the switching TFT element and the first to fourth TFT elements is a thin film transistor element, and has a source terminal, a drain terminal, and a gate terminal. Since the source terminal and the drain terminal are structurally symmetrical with each other and are given names according to their functions, the names interchanged with each other may be used. The gate terminal is a terminal that controls conduction between the source terminal and the drain terminal. Various configurations can be used for the TFT element. For example, a polysilicon TFT element having a polysilicon layer formed by crystallizing an amorphous silicon layer by laser annealing or thermal annealing as an active layer, or amorphous silicon It can be set as the organic TFT element which uses a TFT element and an organic semiconductor. In addition, various metal wirings can be used for the scan line and the data line. As this example, various metal wirings such as aluminum alloy, titanium, and tantalum can be used.

  In the present invention, a method for driving an organic EL display device is also provided. That is, in the present invention, a plurality of organic EL light emitting elements corresponding to a plurality of pixels, a first electrode wiring capable of flowing a light emission current through at least some of the organic EL light emitting elements, and the first electrode wiring cooperate with each other. And a second electrode wiring that can flow a light emission current to the organic EL light emitting element, and the first electrode wiring and the second electrode wiring are used to control the light emission current that should flow to the organic EL light emitting element. A reverse bias current in a direction opposite to the light emission current can be caused to flow to the organic EL light emitting element by the first current control means electrically connected to the EL light emitting element, and the first electrode wiring and the second electrode wiring. A driving method of an organic EL display device including a second current control unit electrically connected to an organic EL light emitting element in at least one of the pixels, wherein the organic EL display device is organic by a first electrode wiring and a second electrode wiring. Emitted to EL light emitting device A first step of controlling the states of the first current control means and the second current control means so that a current flows and no reverse bias current flows; and here, the light emission current is displayed by the organic EL display device The first current control means and the second current control means are set so as to prevent a reverse bias current from flowing through the organic EL light-emitting element through the first electrode wiring and the second electrode wiring, and prevent the light-emitting current from flowing. And a second step of controlling the state of the current control means.

  By driving in this way, it is possible to drive to repair or prevent leakage defects while continuing to display the display contents, thereby improving the reliability of the organic EL display device.

  According to the configuration of the organic EL display device of the present invention, it is possible to realize a function of applying a reverse bias to the organic EL light emitting element of each pixel without using complicated power supply driving means. This makes it possible to repair a leak that has occurred during use.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block configuration diagram showing an electrical configuration of an organic EL display device 1000 according to an embodiment of the present invention. The video signal 50 transmits the contents of images and videos in an appropriate format to the organic EL display device 1000 of the present embodiment. The video signal 50 can be changed to image data of a digital signal by the A / D converter 52. For example, when a digitized image or video is used, it is not necessary to use an A / D converter provided as a video data digital signal. This image data is temporarily stored in the memory 54. The memory 54 can be a so-called line memory or the like that can store image data applied to at least one column of pixels of the display unit (pixel matrix unit) 102 of the organic EL light emitting device. The controller 56 controls the data driver 104, the scan driver 106, and the power supply driving means 116 in accordance with the synchronization signal of the video signal 50 and other appropriate timing signals.

FIG. 2 is a timing chart showing the timing for driving the organic EL display device according to the embodiment of the present invention. In the organic EL display device 1000 of the present invention, although not limited, a plurality of sub-frames SF _{1 to} SF _K having different light emission periods are used in a frame which is a minimum unit of time constituting one image. A time division gray scale driving method can be implemented. In this case, the first current control means (first TFT element 120, second TFT element 122) or second current is controlled by the switching TFT element 118 (FIG. 3) provided in each pixel by driving by the data driver 104 and the scan driver 106. The current control means (third TFT element 124 and fourth TFT element 126) is controlled to control light emission and non-light emission in each of the subframes SF _{1 to} SF _K. Therefore, in each subframe, the actual period of the organic EL light emitting device 100 is determined according to the address periods A _{1 to} A _K for performing this control and the states of the first and second control means controlled during the address period. There are light emission periods E _{1 to} E _K during which light emission can be performed. In the address periods A _{1 to} A _K , each pixel is addressed, and a signal is written from the data line 160 to the pixel that specifies whether the pixel should emit light in the subframe. Note that the number (K) of the light emission periods E _{1 to} E _K and the length of each period can correspond to the number of bits used for gradation display. For example, in order for each pixel to display 256 gradations from gradation level 0 (non-lighting) to 255 (maximum luminance), K is set to 8 and the light emission period Es + 1 for all s from 1 to K−1. Can be set to be twice the length of the light emission period Es, and is proportional to an arbitrary gradation level of gradation levels 0 to 255 by a combination of these light emission periods E _{1 to} E _K. Light emission luminance can be obtained.

  FIG. 3 is an enlarged wiring diagram showing the display pixels of the organic EL display device 1000 according to the embodiment of the present invention. One scan line 150 and one data line 160 are arranged to correspond to each pixel. In addition, the organic EL light emitting device 100 is provided corresponding to a portion where each of the pixels intersects the scan line 150 and the data line 160. A switching TFT element 118 is disposed in the pixel. The switching TFT element 118 has a gate terminal G connected to the scan line 150, a source terminal S connected to the data line 160, and a drain terminal D connected to the control wiring 130. Since the voltage of the gate terminal of the switching TFT element 118 is controlled by the scan line 150, the signal of the data line 160 is output to the control wiring 130 of the pixel in the selected row.

  The control wiring 130 is connected to the gate terminals of the four TFT elements. These four TFT elements are a first TFT element 120, a second TFT element 122, a third TFT element 124, and a fourth TFT element 126. The first TFT element 120 and the second TFT element 122 operate as first current control means in the present invention, and the third TFT element 124 and the fourth TFT element 126 operate as second current control means in the present invention.

  The source terminal S of the first TFT element 120 is electrically connected to the first electrode wiring 136. Therefore, the voltage of the source terminal S of the first TFT element 120 is controlled by the power supply driving means 116. The drain terminal D of the first TFT element 120 is electrically connected to a first element electrode (not shown) of the organic EL light emitting element 100. The source terminal S of the second TFT element 122 is electrically connected to a second element electrode (not shown) of the organic EL light emitting element 100, and the drain terminal D of the second TFT element 122 is electrically connected to the second electrode wiring 140. Connected to. The second electrode wiring 140 is kept at the ground. The source terminal S of the third TFT element 124 is electrically connected to the second electrode wiring 140, and the drain terminal D of the third TFT element is electrically connected to the first element electrode of the organic EL light emitting element 100. Further, the source terminal S of the fourth TFT element is electrically connected to the second element electrode of the organic EL light emitting element 100, and the drain terminal D of the fourth TFT element is electrically connected to the first electrode wiring 136.

In order to cause a light emission current to flow through the organic EL light emitting element 100 during the light emission periods E _{1 to} E _K , it is necessary to apply a forward bias voltage to the organic EL light emitting element 100. Applied by being controlled by a 4 TFT element. That is, the voltage of the control wiring 130 causes the source terminal / drain terminal of the first TFT element 120 and the second TFT element 122 to be in a conductive state, and at the same time, the source terminal / drain terminal of the third TFT element 124 and the fourth TFT element 126 is connected. A voltage is applied that is in an insulated state and becomes a forward bias. Applied to the organic EL light emitting device 100. Here, the first electrode wiring 136 is switched by the power supply driving means 116 between the voltage V _E required for light emission and the same potential as the second electrode wiring 140 (in this embodiment, the ground level). FIG. 2D shows this state. The first electrode wiring 136 is set to 0 volt in the address periods A _{1 to} A _K and is set to V _E in the light emission periods E _{1 to} E _K. As a result, the first electrode wiring 136 and the second electrode wiring 140 can cause a light emission current to flow through the organic EL light emitting device 100. FIG. 4 is an explanatory diagram showing the current path by enlarging the wiring diagram of the display pixel of the organic EL display device 100, and the path through which the display current 132 flows is indicated by a dotted line.

  In addition, in order to cause a reverse bias current to flow through the organic EL light emitting device 100, it is necessary to apply a reverse bias voltage to the organic EL light emitting device 100. This voltage is also controlled and applied by the first to fourth TFT elements. That is, even when the first electrode wiring 136 is set to a positive voltage with respect to the second electrode wiring 140 in order to flow the light emission current, the voltage of the control wiring 130 is controlled to control the first TFT element 120. In addition, the source terminal and the drain terminal of the second TFT element 122 are in an insulated state, and the source terminal and the drain terminal of the third TFT element 124 and the fourth TFT element 126 are in a conductive state. When there is no leak failure in the organic EL light emitting device 100, no reverse bias current flows even if such a reverse bias voltage is applied to the organic EL light emitting device 100, but there is a leak failure in the organic EL light emitting device 100. Then, a reverse bias current flows through the organic EL light emitting device 100. FIG. 5 is an explanatory diagram illustrating the current path by enlarging the wiring diagram of the display pixel, and the path of the reverse bias current 134 is indicated by a dotted line.

Next, referring to FIG. 2 again, a method for driving the organic EL display device 1000 of the present embodiment will be described in more detail. First, in the address period, the scan driver 106 (FIG. 1) sequentially selects the scan lines 150 and turns on the switching TFT elements 118 of all the pixels connected to each scan line 150 for a predetermined time (conductive state). After that, the operation (selection operation) to turn OFF (insulation state) is performed. When the voltage for turning on the switching TFT element 118 is V ₂ and the voltage for turning on the switching TFT element 118 is V ₁ , a scan to which V ₂ is applied as shown in FIG. Line 150 is switched sequentially.

The data driver 104 applies a voltage for controlling the opening / closing of the first current control means 120, 122 and the second current control means 124, 126 to the data line 160. For example, the voltage to be applied to the data line 160 to turn on the first current control means 120 and 122 and the second current control means 124 and 126 is V _H , and the voltage to turn off is V _L It is assumed that the pixels in the first row and the second row in the column to which the data line 160 belongs emit light and the pixels in the third row do not emit light. In this case, as shown in FIG. 2B, the data driver 104 drives the data line 160 so that the voltage of the data line 160 is changed in accordance with the timing at which the scan line 150 of each row is selected. . That is, the data driver 104 sequentially outputs a voltage corresponding to data to be emitted at each pixel in the column direction connected to each data line 160. This voltage is written in the control wiring 130 through the switching TFT element 118 that is turned on at an appropriate timing.

Next, the principle of driving in the light emission period will be described. In the address period A _s (s = 1 to K), V _H or V _L is written in the control wiring 130 depending on whether or not the organic EL light emitting element 100 of the pixel emits light. This voltage is held for the second power supply wiring 140 by the storage capacitor 142. For this reason, the open / closed states of the first current control means 120 and 122 and the second current control means 124 and 126 are not changed until the next address period As _{+ 1} . Then, in the light emitting period E _s after the address period A _s, the first electrode wiring 136 is the V _E by the power drive means 116. In this way, in the pixel in which the control wiring 130 is set to V _H , a light emission current flows in the organic EL light emitting element 100 (FIG. 4), and in the pixel in which the control wiring 130 is set to V _L , the organic EL light emitting element. A reverse bias current flows through 100 (FIG. 5).

Here, whether or not the light emission current is allowed to flow in each of the light emission periods E _{1 to} E _K is determined according to the image data to be displayed by the organic EL display device 1000 of the present embodiment. For example, in the embodiment using the time-division gray scale driving method, when the image data is data that should cause the pixel to emit 100%, the pixel emits light in all the light emission periods E _{1 to} E _K. As described above, V _H is applied to the data line 160 by the data driver 104 in all the address periods A _{1 to} A _K. When the image data is data that does not cause the pixel to emit light at all, _VL is applied to the data line 160 in all address periods A _{1 to} A _K. In order to obtain the brightness of the intermediate tone between them, depending on the lightness, some address period A ₁ to A _K is V _H is outputted by the data driver 104 selected, in other address periods V _L is output.

For example, the first current control means (first and second TFT elements) described above is configured such that, for example, when the potential obtained by subtracting the source terminal voltage from the gate terminal voltage (hereinafter referred to as “V _GS ”) is 0 volts, A normal state in which conduction between the source terminal and the drain terminal occurs only when the drain terminal is kept in an insulated state and V _GS is set to a voltage equal to or higher than a predetermined positive threshold (or lower than a predetermined negative threshold). An off TFT element can be obtained. As an example of the TFT element of the first current control means, an enhancement type TFT element can be used. The second current control means (third and fourth TFT elements) may be a normally-on TFT element in which the connection between the source terminal and the drain terminal is made conductive even when V _GS is 0 volt. it can. As an example of the TFT element of the second current control means, a depletion type TFT element can be used.

  Further, as described above, in order to operate the first TFT element and the third TFT element in a complementary manner, and to operate the second TFT element and the fourth TFT element in a complementary manner, the first TFT element and the second TFT in the first current control means. For example, the element may be an N-channel TFT element, and the third TFT element and the fourth TFT element of the second current control unit may be, for example, a P-channel TFT element. For example, the source and drain regions in the semiconductor layers of the first and second TFT elements are made N + regions, and the source and drain regions in the semiconductor layers of the third and fourth TFT elements are made P + regions. it can.

Here, voltage conditions for appropriately driving each organic EL light emitting element will be described. The voltage V _E or 0 volt applied to the first electrode wiring 136 in the light emission period is applied to the source terminal of the first TFT 120 and the source terminal of the fourth TFT 126. Further, due to the action of the storage capacitor 142, the potential of the control wiring 130 is maintained in the previous address period even in the light emission period. For example, the first TFT 120 is an N-channel TFT, and when the gate terminal is set to a voltage higher than V _{TH1 with} respect to the source terminal, the source terminal and the gate terminal are electrically connected, and the fourth TFT 126 is a P-channel TFT. In the case where the source terminal and the gate terminal are electrically connected when the gate terminal is set to a voltage equal to or lower than V _{TH4 with} respect to the source terminal, the first TFT 120 is appropriately turned on or off during the light emission period. In order to be OFF, the two inequalities V _L −V _E <V _TH1 <V _H −V _E are considered in consideration that the voltage of the first electrode wiring 136 can be V _E or 0 volts.
V _L <V _TH1 <V _H
Both of these need to hold. Therefore,
V _L <V _TH1 <V _H −V _E
Must be established. Similarly, in order for the fourth TFT 120 to be appropriately turned OFF or ON,
V _L <V _TH4 <V _H −V _E
Must be established. Therefore, if V _TH4 <V _TH1 , then V _L <V _TH4 ,
V _TH1 <V _H −V _E ,
Must meet,
V _L <V _TH4
V _H > V _TH1 + V _E
(However, V _TH4 <V _TH1 )
Must be set to be

Further, when the switching TFT 118 is an N-channel TFT and the source terminal and the gate terminal are conductive when the potential of the gate terminal is higher than the potential of the source terminal by V _THS or more, V ₁ <V ₂
V ₁ −V _H <V _THS <V ₂ −V _H
V ₁ −V _L <V _THS <V ₂ −V _L
Must be established at the same time.
Therefore,
V ₁ −V _L <V _THS <V ₂ −V _H ,
That is,
V ₁ <V _THS + V _L
V ₂ > V _THS + V _H ,
It is necessary to.

As an example satisfying the above conditions, for example, when V _E = 18.0 volts, V _TH1 = 3.0 volts, V _TH4 = −3.0 volts, and V _THS = 3.0 volts, V _L = − 3.5 volts, V _H = 21.5 volts, V ₁ = -1.0 volts, a V ₂ = 25.0 volts.

  The above-described embodiment has been described as an example. In the present invention, for example, analog driving that adjusts the opening degree of the first to fourth TFT elements in accordance with the voltage value given by the data line can be used instead of time-division gray scale driving. In this case, for example, the source terminal and the drain terminal of the third and fourth TFT elements are insulated from each other in the voltage range in which the source terminal and the drain terminal of the first and second TFT elements are electrically connected. The ON resistance between the source terminal and the drain terminal of the second TFT element depends on the voltage between the control electrode 130 (the gate electrode of the first and second TFT elements) and the voltage between the first electrode wiring 136 in the voltage range. You may comprise so that it may change. At this time, the voltage of the data line in which the source terminal and the drain terminal of the first and second TFT elements are insulated to be non-lighted is set to be conductive between the source terminal and the drain terminal of the third and fourth TFT elements. By using a low voltage, a reverse bias voltage can be applied to the organic EL light emitting element. Further, the configuration of each TFT element is not limited to a configuration in which the channel portion is not doped, but a TFT device in which the channel portion is doped may be used in order to control the threshold value of the TFT element in accordance with the driving voltage. good. Of course, as the TFT element, an amorphous silicon TFT element, an organic semiconductor TFT element, or the like can be used in addition to the TFT element using polysilicon. In addition, the multi-coloring of the organic EL light-emitting elements can use organic EL light-emitting elements having different emission colors for each of R, G, and B, or a color conversion method. The organic EL light-emitting element can be either a low molecular type or a high molecular type.

Furthermore, with reference to drawings, the Example of the organic electroluminescent display apparatus of this invention is described.
As an example of the organic EL display device of the present invention, an organic EL display device having 240 rows and 960 columns (320 × RGB), that is, 230,400 pixels in the display unit 102 was manufactured. The pixel pitch was 110 × 330 μm.

  The configuration of this embodiment of the organic EL display device is shown in FIGS. FIG. 6 is a layout diagram showing a planar layout of TFT elements and wirings of an organic EL display device according to an example of the present invention. FIG. 7 is a cross-sectional view showing a configuration of a display pixel portion of the organic EL display device according to the embodiment of the present invention, and shows a cross section of the AA portion of FIG. In FIG. 6, a configuration that is actually opaque and cannot be observed is also shown through. Further, the configuration of the electrode and the light emitting layer of the organic EL light emitting element is omitted here. For the sake of simplicity, the same reference numerals as those in FIG. The circuit configuration is as shown in FIG.

The organic EL display device of this example was performed by the following steps. In the first step, a base coat 306 of SiO ₂ that prevents elution of impurities was applied to the entire surface of one side of the borosilicate glass substrate 330. Then, as a second step, an amorphous silicon layer was formed using silane gas by plasma CVD. In the third step, the amorphous silicon layer was subjected to laser annealing using an excimer laser to obtain a polysilicon film. Then, as a fourth step, the polysilicon film was patterned into an island shape to obtain polysilicon films of the switching TFT element 118 and the first to fourth TFT elements 120, 122, 124, and 126. In FIG. 7, polysilicon films 302 and 304 in the second TFT element 122 and the third TFT element 124 are shown. Then, as a fifth step, silicon nitride (SiN _x ) was formed while introducing nitrogen into the silane gas by plasma CVD, and an insulating film 308 was obtained. This insulating film 308 functions as a gate insulating film on the polysilicon film of the TFT element. Then, as a sixth step, an aluminum alloy was formed on the insulating film 308 and patterned as the wiring 130A in FIG. 6 to form a gate terminal portion of each TFT element and a part of the control wiring 130. At this time, the scan line 150 is patterned to be formed of the same layer. Then, as the seventh step, the TFT elements (switching TFT elements, first TFT elements, and second TFT elements) manufactured for the N channel are covered, and the TFT elements (third TFT element, fourth TFT element) that are manufactured for the P channel are not covered. A resist pattern is formed, and boron (B) ions are implanted to form P + portions of the source and drain regions of the P-channel TFT element via the insulating film 308 (for example, the source region 304S of the polysilicon film 304). And drain region 304D). Furthermore, as an eighth step, a resist pattern that covers the third TFT element and the fourth TFT element, does not cover the channel TFT element, the first TFT element, and the second TFT element is formed, and phosphorus (P) ions are implanted to insulate N + portions of the source and drain regions of the N-channel TFT element are formed through the film 308 (for example, the source region 302S and the drain region 302D of the polysilicon film 302). In these ion implantation processes, the aluminum alloy in the gate portion of each TFT element has a function of preventing ions from being implanted into the channel portion (active region, for example, intrinsic semiconductor regions 302I and 304I) of the polysilicon film. Also have. As a ninth step, in order to form the storage capacitor 142 in the wiring 130A, a silicon nitride film was formed and patterned so as to leave only the upper portion of the storage capacitor 142. This silicon nitride film is not shown in FIGS. As a tenth step, a passivation layer 310 to be an interlayer insulating film was formed from a photosensitive acrylate resin and patterned. Further, as an eleventh step, an opening was provided in the insulating film 308 to form contact portions for connection to the source terminal and drain terminal of each TFT element. As a twelfth step, a metal layer 312 made of an aluminum alloy was formed and patterned. The metal layer 312 becomes the first electrode wiring 136 and the second electrode wiring 140, and also the wiring 130B (FIG. 6) which becomes a part of the control wiring 130 together with the data line 160 and the wiring 130A. In FIG. 7, the cross section of the part used as the 2nd electrode wiring 140 is described. As a thirteenth step, the second passivation layer 314 was also formed from a photosensitive acrylate resin and patterned. This pattern was set so as not to leave passivation in the contact portion for taking out the first and second element electrodes of the organic EL light emitting element 100 from the metal layer 312 and the storage capacitor 142. Furthermore, as a 14th step, an electrode layer 316 to be a first element electrode was formed and patterned so as to have a pixel shape of the organic EL light emitting element. Thereafter, as a fifteenth step, an electron transport layer, a light emitting layer, and a hole transport layer were formed in this order by mask film formation to obtain an organic EL light emitting device. Since the emission colors are three colors of R, G, and B, mask formation was performed three times by shifting the position using a mask for forming an organic EL light emitting element only for each color pixel. In this embodiment, two types of organic EL display devices having different light emitting layer thicknesses are manufactured. After forming a transparent electrode layer 320 serving as a second element electrode as a 16th step and patterning it into a pixel shape, a resin layer 322 serving as a moisture-proof protective layer was formed as a 17th step. In this manner, an example of an organic EL display device that extracts light emitted from the transparent electrode layer 302 was obtained.

The organic EL display device of the manufactured example has a thickness of the organic EL light emitting layer of 60 nm and a voltage (driving voltage) applied to the first electrode wiring of 18 volts. A number of samples (sample A) from which luminance of m ² can be obtained and a number of organic EL display devices (sample B) of other examples that were similarly manufactured except that the thickness of the organic EL light emitting layer was set to 30 nm were prepared. did. In the organic EL display device of Sample B, a luminance of 200 cd / m ² was obtained when the drive voltage was 15 volts. From each of the organic EL display devices of Sample A and Sample B, one having a pixel that causes a leak failure in any pixel of the display unit was selected.

Next, using two types of organic EL display devices of Sample A and Sample B of this example, an experiment was performed to obtain voltage conditions necessary for repairing a leak failure. In the experiment, DC V ₂ was applied to all the scan lines 150 and all the data lines 160 were set to V _L so that a reverse bias was applied to all the pixels. Whether or not the leakage failure is repaired by setting the voltage (reverse bias voltage) applied to the first electrode wiring 136 to a different voltage every 5% from 0% to 100% relative to the driving voltage. Was observed. Experiments were performed using 10 organic EL display devices of Sample A and Sample B for each voltage condition. As a result, as shown in Table 1, when the reverse bias voltage was 75% of the drive voltage, there were 0 samples in which the leakage failure was completely repaired, but the reverse bias voltage was 80% of the drive voltage. In the range from 100 to 100%, the number of samples in which the leakage failure was completely repaired increased with the voltage. That is, if the reverse bias voltage is 80% of the drive voltage, 8 out of 10 leak failures are completely repaired, and if the reverse bias voltage is 85% of the drive voltage, leak failures in all 10 samples are detected. Fully repaired. This was the same for both sample A and sample B.

Subsequently, using two types of organic EL display devices of Sample A and Sample B of this example, an experiment was performed to obtain time conditions necessary for repairing a leak failure. In this experiment, in order to fix the reverse bias voltage to 85% of the original drive voltage, the voltage applied to the first electrode wiring 136 was set to 85% of the drive voltage. That is, the voltages applied to the first electrode wiring 136 were 15.3 volts (sample A) and 12.75 volts (sample A), respectively. Then, DC V ₂ was applied to all of the scan lines 150, and all of the data lines 160 were set to V _{H so that the} organic EL display device was lit at a driving voltage of 85%. Thereafter, all the data lines 160 are set to V _L for a predetermined time, and a reverse bias voltage of 85% of the drive voltage is applied only during that time, and a waveform that returns all the data lines 160 to V _H again is applied to the data lines 160 once. It was applied to observe whether the leak failure was repaired. Here, the time for maintaining all the data lines 160 at V _L (that is, the time for applying the reverse bias voltage to the organic EL light emitting element) is 10, 15, 20, and 30 μs, and 10 units for each condition. The same observation was performed using the organic EL display device.

As a result, as shown in Table 2, as the application time of the reverse bias voltage is increased, the number of organic EL display devices whose leak defects are completely repaired is increased. Specifically, the number of organic EL display devices in which leakage failure is completely repaired under the condition where the application time of the reverse bias voltage is 10 μs is 0 for both samples A and B, but under the condition where the application time is 15 μs. Under the conditions of 8 units (sample A) and 7 units (sample B) and the application time of 20 μs and 30 μs, the leakage defects of all the organic EL display devices were completely repaired in both samples A and B.

  As an additional experiment, all organic EL display devices in which the leak failure was completely repaired were operated for 1000 hours. In this operation, the driving method described with reference to FIG. 2 was used, and a frame rate of 60 Hz, a maximum luminance of 200 cd / m 2, and time-division gradation driving (8 bits) were performed. As the display data, data that switches to a random luminance every certain time between a gradation level 0 (non-lighting) and a gradation level 255 (maximum luminance level) was used. In this case, as described above, in the display other than the gradation level 255, since there is a subframe to which the reverse bias is applied during the light emission period, the reverse bias is applied to the organic EL light emitting element during the operation. In this experiment, pixels that did not emit light due to a leak failure were not confirmed during 1000 hours of operation.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications, changes and combinations can be made based on the technical idea of the present invention. .

FIG. 1 is a block configuration diagram showing an electrical configuration of an organic EL display device according to an embodiment of the present invention. FIG. 2 is a timing chart showing timing for driving the organic EL display device according to the embodiment of the present invention. FIG. 3 is an enlarged wiring diagram showing the display pixels of the organic EL display device according to the embodiment of the present invention. FIG. 4 is an explanatory diagram illustrating the current path when the display current is passed by enlarging the wiring diagram of the display pixel of the organic EL display device according to the embodiment of the present invention. FIG. 5 is an explanatory diagram illustrating the current path when the reverse bias current is supplied by enlarging the wiring diagram of the display pixel of the organic EL display device according to the embodiment of the present invention. FIG. 6 is a layout diagram showing a planar layout of TFT elements and wirings of an organic EL display device according to an example of the present invention. FIG. 7 is a cross-sectional view showing a configuration of a display pixel portion of the organic EL display device according to the example of the present invention. FIG. 8 is an enlarged wiring diagram showing display pixels of a conventional organic EL display device.

Explanation of symbols

50 Video Signal 52 A / D Converter 54 Memory 56 Controller 1000 Organic EL Display Device 100 Organic EL Light Emitting Element 102 Display Unit (Pixel Matrix Unit)
104 data driver 106 scan driver 116 power source driving means 118 switching TFT element 120 first TFT element (N-channel enhancement type TFT element, first current control means)
122 2nd TFT element (N-channel enhancement type TFT element, first current control means)
124 3rd TFT element (P-channel depletion type TFT element, second current control means)
126 4th TFT element (P-channel depletion type TFT element, second current control means)
130 Control wiring 132 Light emission current 134 Reverse bias current 136 First electrode wiring 140 Second electrode wiring 142 Storage capacitor 150 Scan line 160 Data line 302, 304 Polysilicon layer 306 Base coat 308 Insulating film 310 Passivation 312 Metal layer 314 Passivation 316 Electrode layer 318 Electron transport layer, light emitting layer, hole transport layer 320 Transparent electrode 322 Resin layer 330 Glass substrate 2000 Organic EL display device (conventional example)
200 Organic EL Light Emitting Element 218 Switching TFT Element 220 Current Control TFT Element 236 First Electrode Wiring 240 Second Electrode Wiring 250 Scan Line 260 Data Line

Claims (9)

A plurality of organic EL light emitting elements corresponding to a plurality of pixels;
A first electrode wiring capable of causing a light-emitting current to flow through at least some of the organic EL light-emitting elements;
A second electrode wiring capable of causing a light-emitting current to flow in the organic EL light-emitting element in cooperation with the first electrode wiring;
First current control means electrically connected to the organic EL light-emitting element for controlling a light-emitting current to be passed through the organic EL light-emitting element by the first electrode wiring and the second electrode wiring; ,
A second electrode electrically connected to the organic EL light emitting element, wherein a reverse bias current in a direction opposite to the light emission current is allowed to flow through the organic EL light emitting element by the first electrode wiring and the second electrode wiring. An organic EL display device comprising:   The organic EL display device according to claim 1, wherein the first electrode wiring is driven so that a polarity of a voltage with respect to the second electrode wiring is not reversed. A control wiring for transmitting a signal for controlling the first current control means and the second current control means;
The first current control unit and the second current control unit are configured so as not to be in a conductive state at the same time, and are controlled by a signal of the control wiring to transmit the light emission current to the organic EL light emitting element. 3. The organic EL display device according to claim 1, wherein a state of flowing and a state of allowing the reverse bias current to flow through the organic EL light emitting element are switched by the second current control unit.   The absolute value of the reverse bias voltage applied to the organic EL light emitting element when the reverse bias current is supplied to the organic EL light emitting element is the order in which the organic EL light emitting element is applied when the display current is supplied to the maximum. The organic EL display device according to claim 1, wherein the organic EL display device is set to 85% or more of the absolute value of the directional voltage.   The organic EL display device according to claim 1, wherein a period during which a voltage capable of causing a reverse bias current to flow is applied to the organic EL light emitting element is 20 microseconds or more.   6. The organic EL according to claim 1, wherein one of the first current control means and the second current control means is a normally-off thin film transistor and the other is a normally-on thin film transistor. Display device.   7. The organic EL according to claim 1, wherein one of the first current control unit and the second current control unit is an N-channel thin film transistor and the other is a P-channel thin film transistor. Display device. Each pixel includes a plurality of scan lines and data lines for addressing each pixel and writing display image data to the addressed pixel, and a gate terminal electrically connected to the scan line, and the data line electrically The organic EL display device according to claim 3, further comprising a switching TFT element including a source terminal that is electrically connected and a drain terminal that is electrically connected to the control electrode,
The switching TFT element outputs a signal of the data line to the control wiring via the source terminal and the drain terminal based on potential control of the gate terminal by the scan line,
The first current control means includes a first TFT element and a second TFT element,
The second current control means includes a third TFT element and a fourth TFT element,
The control wiring is electrically connected to gate terminals of the first to fourth TFT elements,
The first TFT element has a source terminal electrically connected to the first electrode wiring, a drain terminal electrically connected to the first element electrode of the organic EL light emitting element,
The second TFT element has a source terminal electrically connected to the second element electrode of the organic EL light emitting element, and a drain terminal electrically connected to the second electrode wiring,
The third TFT element has a source terminal electrically connected to the second electrode wiring, a drain terminal electrically connected to the first element electrode of the organic EL light emitting element,
The fourth TFT element has a source terminal electrically connected to the second element electrode of the organic EL light emitting element, and a drain terminal electrically connected to the first electrode wiring,
The voltage for flowing the light-emitting current to the organic EL light-emitting element is controlled by simultaneously controlling the gate terminals of the first to fourth TFT elements by the control wiring, and the source terminals and drains of the first TFT element and the second TFT element. By applying a conductive state between the terminals and insulating between the source terminal and the drain terminal of the third TFT element and the fourth TFT element, it is applied to the organic EL light emitting element,
The voltage for causing the reverse bias current to flow through the organic EL light emitting element is controlled by simultaneously controlling the gate terminals of the first to fourth TFT elements by the control wiring, and the source terminals of the first TFT element and the second TFT element. The organic EL according to claim 3, wherein the organic EL light emitting element is applied to the organic EL light emitting element by making an insulating state between the drain terminals and conducting between the source terminal and the drain terminal of the third TFT element and the fourth TFT element. Display device. A plurality of organic EL light emitting elements corresponding to a plurality of pixels, a first electrode wiring capable of causing a light emission current to flow through at least some of the organic EL light emitting elements, and the organic EL in cooperation with the first electrode wiring A second electrode wiring capable of causing a light-emitting current to flow through the light-emitting element, and controlling the light-emitting current to be passed through the organic EL light-emitting element by the first electrode wiring and the second electrode wiring. A reverse bias current opposite to the light emission current is applied to the organic EL light emitting element by the first current control means electrically connected to the EL light emitting element, and the first electrode wiring and the second electrode wiring. And a second current control means electrically connected to the organic EL light emitting element, and a driving method of an organic EL display device including at least one of the pixels,
The first current control unit and the second current control unit prevent the light emission current from flowing through the organic EL light emitting element and the reverse bias current from flowing through the first electrode wiring and the second electrode wiring. A first step of controlling the state of the light emitting current, wherein the light emission current is determined according to image data to be displayed by the organic EL display device,
The first current control unit and the second current control unit prevent the reverse bias current from flowing through the organic EL light emitting element by the first electrode wiring and the second electrode wiring, and prevent the light emitting current from flowing. And a second step of controlling the state of the driving method.

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