JP2827570B2 - Liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display using a thin film transistor as a switching element, and more particularly to a liquid crystal display having a structure capable of obtaining a large storage capacity without lowering an aperture ratio.

[0002]

2. Description of the Related Art FIG. 11 is a cross-sectional view showing one example of the prior art relating to the addition of a storage capacitor for each pixel in a conventionally known liquid crystal display using an amorphous silicon (amorphous Si) thin film transistor as a switching element. It is a figure (refer to Unexamined-Japanese-Patent No. 1-140129). FIG.
In the figure, 201 is a glass substrate, 202a and 202b are gate wirings, 203 is a gate insulating film, 204 and 205 are amorphous Sii layers and amorphous Sin layers,
06 is a transparent pixel electrode, 207 is a data line, 208 is a lower electrode of a storage capacitor, and 209 is a protective film of a transistor.
In a conventional liquid crystal display using a thin film transistor TFT as a switching element, as described above, the transparent pixel electrode 2
6, a storage capacitor lower electrode 208 is formed, and a storage capacitor C is formed with the gate insulating film 203 interposed therebetween.

In a liquid crystal display using the above-described thin film transistor TFT as a switching element, by adding a storage capacitor C, the deterioration of the storage characteristic caused by the discharge of the liquid crystal and the off current of the thin film transistor TFT is compensated.
Further, it is possible to prevent image quality deterioration such as afterimages, image sticking, and flicker caused by application of a DC component to the liquid crystal through the parasitic capacitance of the thin film transistor TFT.

[0004]

It has been found that in order to prevent the above-mentioned deterioration in image quality, a storage capacitor C of three to four times the liquid crystal capacitance of the pixel portion must be added.
For example, if a storage capacitor C that is four times the capacitance of the liquid crystal pixel portion is added to a pixel having a pixel area of 240 μm × 140 μm, a storage capacitor C of 1.7 pF is required. Retention capacity C
Assuming that silicon nitride is used for the dielectric film (gate insulating film 203) constituting silicon and the dielectric constant of silicon nitride is set to 7.0 and the film thickness is set to 0.3 μm, the area of the storage capacitor C is required to be 90 μm × 90 μm. Corresponds to 24% of the pixel area. When such a large storage capacitor C is formed in one pixel, the aperture ratio decreases, and the luminance of a liquid crystal display using the thin film transistor TFT as a switching element decreases.

In a conventional liquid crystal display using a thin film transistor TFT having a storage capacitor C as a switching element, the gate insulating film 203 also serves as a dielectric film of the storage capacitor C as shown in FIG. Further, a dielectric film constituting the storage capacitor C is formed so as to cover the storage capacitor lower electrode 208. A conventional liquid crystal display using a thin film transistor TFT with a storage capacitor C as a switching element is:
With the above-described structure, it is necessary to completely insulate the storage capacitor lower electrode 208 and the transparent pixel electrode 206 by the dielectric film forming the storage capacitor C. Cannot be made thinner. Therefore, in order to increase the storage capacitor C, the area of the storage capacitor C must be increased, so that the aperture ratio of one pixel decreases and the transmitted light decreases, so that the brightness of the liquid crystal display decreases. Furthermore, in order to correspond to a display requiring a high resolution such as a high-definition TV, the pixel area must be reduced. In the conventional structure, a storage capacitor C having a required capacitance value must be formed in one pixel. Can not.

[0006] The present invention solves the above problems,
It is an object of the present invention to provide a liquid crystal display capable of obtaining a large storage capacity without lowering the aperture ratio.

[0007]

According to the liquid crystal display of the present invention, a dielectric film constituting a storage capacitor and a dielectric film for insulating a lower electrode of the storage capacitor and a transparent pixel electrode are formed in different steps, and the liquid crystal display is formed. The dielectric film constituting the capacitor can be formed with an arbitrary thin film thickness. Then, the dielectric film constituting the storage capacitor is silicon dioxide, acid aluminum, either a single layer of chromium oxide or silicon nitride,
Silicon dioxide, tantalum oxide, aluminum oxide, oxide
What laminated | stacked ROM can be used. Further, polycrystalline silicon can be used as a semiconductor element,
The storage capacitor lower electrode may be shared with the gate line.

[0008]

In the present invention, the dielectric film forming the storage capacitor and the dielectric film insulating the lower electrode of the storage capacitor and the transparent pixel electrode are formed in different steps. It can be formed with a film thickness, and the dielectric film constituting the storage capacitor can be made thin. This makes it possible to increase the storage capacity without increasing the area occupied by the storage capacity, so that the aperture ratio of a liquid crystal display using a thin film transistor as a switching element is increased, and high luminance is obtained.

Further, since the optimum storage capacity can be selected, a liquid crystal display using a high-quality thin film transistor as a switching element without afterimage, image sticking or flicker can be obtained. Furthermore, a desired storage capacitor can be formed even if the area of one pixel is reduced in order to support a display requiring a high resolution such as a high-definition TV. Further, since a large storage capacitor can be formed, a liquid crystal material having a specific resistance of 10 ¹⁰ Ω · cm or less can be used. By using a dielectric film of silicon nitride, silicon dioxide, tantalum oxide, aluminum oxide, chromium oxide, or the like, an insulator having a sufficient selective etching property with other films constituting the liquid crystal display can be obtained. In addition, by using polycrystalline silicon for a semiconductor element, fine processing can be performed with high mobility in a high-definition, high-density liquid crystal display. Further, by sharing the storage capacitor lower electrode with the gate line, the number of intersections of wirings is reduced, and the probability of wiring short-circuit is reduced.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. (Embodiment 1) FIG. 1 shows a cross section of one pixel of Embodiment 1 of the present invention, and is a cross-sectional view taken along line AA 'of FIG. 2, and FIG. 2 is a schematic plan view thereof. Hereinafter, the manufacturing method of the first embodiment will be described. First, after cleaning the transparent substrate 1, a gate electrode 2, for example, chromium (Cr) is formed by a sputtering method. At this time, the gate electrode 2 of the next stage is simultaneously extended in the pixel to form the storage capacitor lower electrode 10. Next, the dielectric film 3 constituting the storage capacitor C, for example, silicon dioxide (S
iO ₂ ) is formed by the PCVD method. Next, a gate insulating film 4, for example, silicon nitride (Si ₃ N ₄ ), a semiconductor film 5, for example, amorphous Si, and a channel protective film 6, for example, silicon nitride (Si ₃ N ₄ ) are formed at a thickness of 100 ° by PCVD.
After continuously forming a film having a thickness of about 3000 °, the gate insulating film 4 is removed in a portion that insulates the end face of the storage capacitor lower electrode 10, and the semiconductor film 5 and the channel insulating film are left except for a portion to be a transistor. 6 is removed. Next, a transparent pixel electrode 8, for example, ITO (Indium Tin Oxide) is formed. In order to make ohmic contact with the source / drain electrodes 9, a part of the channel protection film 6 on the semiconductor film 5 is removed, and a semiconductor film 7 doped with impurities, for example, amorphous Si doped with phosphorus is formed thereon. . Further, a source / drain electrode 9, for example, aluminum (A
1) is formed to complete the structure of the first embodiment of the present invention.

In a liquid crystal display using the thin film transistor TFT having the storage capacitance C added as described above as a switching element, the gate insulating film 4 insulates the end face of the storage capacitance lower electrode 10 from the transparent pixel electrode 8. Therefore, the dielectric film 3 constituting the storage capacitor C can be formed with an arbitrary thickness. For this reason, it is possible to increase the storage capacitance value without increasing the occupation area of the storage capacitor C. Although the main cause of the dielectric breakdown is the electric field concentration at the gap, the gap is insulated by the gate insulating film 4 different from the dielectric film 3 forming the storage capacitor C. The probability is lower.

(Embodiment 2) FIG. 3 shows one of Embodiment 2 of the present invention.
It is sectional drawing of a pixel. Example 1 is the same as Example 1 except that the transparent pixel electrode 8 is formed after the source / drain electrodes 9 are formed. Even with such a configuration, the effect is equivalent to that of the first embodiment.

(Embodiment 3) FIG. 4 shows a third embodiment of the present invention.
FIG. 5 shows a cross section of the pixel, and is a cross-sectional view taken along the line AA ′ in FIG. 5, and FIG. Although the manufacturing method and the order are the same as those of the first embodiment, the storage capacitor lower electrode 10 is formed separately from the gate electrode 2 of the next stage (i + 1). Even with such a configuration, the effect is equivalent to that of the first embodiment.

(Embodiment 4) FIG. 6 shows Embodiment 4 of the present invention.
It is sectional drawing of a pixel. The structure of the thin film transistor TFT is different from the first to third embodiments. First, after cleaning the transparent substrate 1, a gate electrode 2, for example, Cr is formed by a sputtering method. At this time, the gate electrode 2 of the next stage is
Is extended into the pixel to form the storage capacitor lower electrode 10.
Next, a dielectric film 3 constituting the storage capacitor C, for example, silicon dioxide (SiO ₂ ) is formed by the PCVD method. Next, a gate insulating film 4, for example, silicon nitride (Si ₃ N ₄ ),
Semiconductor film 5, for example, amorphous Si, impurity-doped semiconductor film 7, for example, phosphorus-doped amorphous S
i is continuously formed by the PCVD method, and then the storage capacitor lower electrode 1 is formed.
The gate insulating film 4 is removed except for the portion that insulates the end face of the transistor 0, and the semiconductor film 5 and the impurity-doped semiconductor film 7 are removed except for the portion that becomes a transistor. next,
A transparent pixel electrode 8, for example, ITO is formed. Example 4 A source / drain electrode 9, for example, Al was formed, and a semiconductor film 7 doped with unnecessary impurities in a channel portion was removed.
The structure of is completed. Such a thin film transistor TFT
The effect of the present invention can also be obtained with the above structure. Further, similarly to the second embodiment, the effect of the present invention can be obtained by a structure in which the order of forming the transparent pixel electrode 8 and the source / drain electrode 9 is changed.

(Embodiment 5) FIG. 7 shows one of Embodiment 5 of the present invention.
FIG. 8 is a cross-sectional view taken along line AA ′ of FIG. 8, showing a cross section of a pixel, and FIG. 8 is a schematic plan view thereof. This embodiment is a manufacturing method when polycrystalline silicon is used as a semiconductor film of a thin film transistor TFT. First, the transparent substrate 10
After cleaning 1, polycrystalline Si 105 is formed by, for example, an LPCVD method. Next, a gate insulating film 104, for example, silicon dioxide (SiO ₂ ) is formed by, for example, a thermal oxidation method. Next, a gate electrode 102, for example, a polycrystalline Si film doped with impurities is formed by, for example, an LPCVD method. At this time, the storage capacitor lower electrode 110 is formed at the same time. Using the gate electrode 102 as a mask, impurities are diffused into the polycrystalline Si 105 by, for example, ion implantation to form source / drain regions 107. Polycrystalline Si10
5. After removing the gate insulating film 104 other than on the source / drain regions 107, the dielectric film 1 forming the storage capacitor C
03, for example, silicon dioxide (SiO ₂ ) is formed, and the end face protective film 106, for example, silicon nitride (Si ₃ N ₄ ) is formed. After a transparent pixel electrode 108, for example, silicon nitride ITO is formed, a portion of the gate insulating film 104 in contact with the source / drain electrode 109 is removed, and a source / drain electrode 109, for example, Al is formed. Complete.

(Embodiment 6) FIG. 9 shows a sixth embodiment of the present invention.
It shows a cross section of a pixel, and is a cross-sectional view taken along line AA 'in FIG. 10, and FIG. 10 is a schematic plan view thereof. Although the manufacturing method and the order are the same as those of the fifth embodiment, the storage capacitor lower electrode 10 is formed separately from the gate electrode of the next stage. Such a configuration is equivalent to the other embodiments.

In the above embodiment, the storage capacitor C is formed.
Dielectric films 3 and 103 are made of silicon dioxide., A
The same effect can be obtained by using an oxide film of a metal such as l or Cr.
Can be further,Silicon nitride, silicon dioxide, tantalum oxide
, Aluminum oxide, chromium oxideLayered in multiple layers
May be used. In addition, source / drain electrodes 9 and 10
Although Al was used as 9, Cr, titanium (Ti),
Ta, Al-copper (Cu) alloy, Al-Si-Cu alloy,
Alternatively, these may be laminated. More transparent
Although ITO was used for the pixel electrodes 8 and 108, tin oxide,
Indium oxide may be used.

In the first to fourth embodiments of the present invention, Cr was used as the gate electrode 2, but Al, titanium (T
i), Ta, Al-Cu alloy, Al-Si-Cu alloy,
Alternatively, these may be laminated. In the fifth and sixth embodiments, polycrystalline Si doped with impurities is used as the gate electrode 102. However, Cr, Al, Ti, T
a, an Al-Cu alloy, an Al-Si-Cu alloy, or a laminate thereof.

Further, in the first to fourth embodiments, silicon nitride is used as the gate insulating film 4, but silicon dioxide may be used. The same effect can be obtained by using an oxide film of Ta, Al, Cr or the like. Further, these films may be stacked in multiple layers. In the fifth and sixth embodiments, silicon dioxide is formed by thermal oxidation as the gate oxide film 104. However, silicon dioxide and silicon nitride may be formed by PCVD or sputtering.

Further, in the embodiment of the present invention, the storage capacitor C
Of the storage capacitor lower electrode 1
Although the example formed in the range inside from 0,110 was shown,
The effect remains the same even if it is larger than the storage capacitor lower electrodes 10 and 110 or if it constitutes a part of the semiconductor element. Further, the example has been described in which the end surfaces of the storage capacitor lower electrodes 10 and 110 and the transparent pixel electrodes 8 and 108 are also insulated by the gate insulating films 4 and 104. However, the effects of the present invention can be achieved by using other insulating films. can get.

[0021]

As described above, according to the present invention, the dielectric film forming the storage capacitor and the dielectric film insulating the lower electrode of the storage capacitor and the transparent pixel electrode are formed in different steps, so that the storage capacitor is formed. Since the dielectric film can be formed at an arbitrary thickness and the storage capacitance value can be increased without increasing the occupation area of the storage capacitor, the aperture ratio of the liquid crystal display using the thin film transistor as a switching element is increased. High brightness can be obtained.

In addition, since an optimum storage capacitance value can be selected, a liquid crystal display using a high quality thin film transistor as a switching element free from afterimages, image sticking and flicker can be obtained. Furthermore, a desired storage capacitor can be formed even if the area of one pixel is reduced in order to support a display requiring a high resolution such as a high-definition TV.

Further, since a large storage capacitor can be formed, a liquid crystal material having a specific resistance of 10 ¹⁰ Ω · cm or less can be used.

Further, the dielectric film constituting the storage capacitor, the two <br/> silicon oxide, acid aluminum, is a single layer, such as chromium oxide
Or silicon nitride, silicon dioxide, tantalum oxide, aluminum oxide
Since a layer obtained by stacking nickel and chromium oxide is used, it is possible to obtain an insulator having a sufficient selective etching property with respect to other films constituting the liquid crystal display. Furthermore, since polycrystalline silicon is used for the semiconductor element, fine processing can be performed with high mobility. In addition, since the lower electrode of the storage capacitor is shared with the gate electrode, intersections of the wiring are reduced,
The probability of wiring short-circuit is reduced, and the yield is improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of one pixel showing a first embodiment of the present invention.

FIG. 2 is a plan view of one pixel according to the first embodiment of the present invention.

FIG. 3 is a cross-sectional view of one pixel showing a second embodiment of the present invention.

FIG. 4 is a cross-sectional view of one pixel showing a third embodiment of the present invention.

FIG. 5 is a plan view of one pixel showing a third embodiment of the present invention.

FIG. 6 is a cross-sectional view of one pixel showing Example 4 of the present invention.

FIG. 7 is a cross-sectional view of one pixel showing Example 5 of the present invention.

FIG. 8 is a plan view of one pixel showing a fifth embodiment of the present invention.

FIG. 9 is a sectional view of one pixel, showing Example 6 of the present invention.

FIG. 10 is a plan view of one pixel showing a sixth embodiment of the present invention.

FIG. 11 is a cross-sectional view of one pixel in the related art relating to addition of a storage capacitor for each pixel in a liquid crystal display using a thin film transistor as a switching element.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 transparent substrate 2 gate electrode 3 dielectric film constituting storage capacitor 4 gate insulating film 5 semiconductor film 6 channel protection film 7 semiconductor film doped with impurities 8 transparent pixel electrode 9 source / drain electrode 10 lower electrode of storage capacitor

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G02F 1/136 500

Claims (4)

(57) [Claims] 1. A semiconductor device comprising a plurality of gate lines and a plurality of data lines intersecting the plurality of gate lines, and a transparent pixel electrode and a semiconductor element connected to the transparent pixel electrode at each intersection of the gate line and the data line. A first substrate having a charge storage capacitor formed between the transparent pixel electrode and a storage capacitor lower electrode opposed to the transparent pixel electrode with a dielectric film interposed therebetween, and a display electrode on the substrate surface In a liquid crystal display in which a liquid crystal is sandwiched between a second substrate and a second substrate, a lower portion of the storage capacitor facing the transparent pixel electrode is formed in a step different from the step of forming a dielectric film forming the storage capacitor. A liquid crystal display, wherein a dielectric film for insulating an end face of an electrode and the transparent pixel electrode is formed thicker than a dielectric film constituting the storage capacitor. 2. A dielectric film constituting the storage capacitor, silicon dioxide, acid aluminum, either a single layer of chromium oxide or silicon nitride, silicon dioxide, tantalum oxide, Al
The liquid crystal display according to claim 1, wherein the liquid crystal display has a structure in which minium and chromium oxide are laminated. 3. A semiconductor device formed on a first substrate, comprising:
2. The liquid crystal display according to claim 1, wherein the liquid crystal display is made of polycrystalline silicon. 4. The liquid crystal display according to claim 1, wherein a lower electrode of the storage capacitor facing the transparent pixel electrode is shared with a gate line.