JPH05265032A - Liquid crystal element and its driving method - Google Patents

Abstract

PURPOSE:To prevent the generation of light leakage from a picture element boundary part and to suppress the generation of abnormality in the orientation of liquid crystal by forming a conductive inter-picture-element shielding layer on a picture element electrode peripheral edge part formed on a main base in a liquid crystal element to be turned to a light shielding state at the time of impressing voltage. CONSTITUTION:Since the inter-picture-element shielding layer 102 is formed on the main base 101, alignment to a picture element electrode 107 can be determined by the accuracy of photolithography. Namely when voltage with a waveform approximately equal to voltage waveform held in the electrode 107 surrounded by the layer 102 is applied by voltage approximately equal to maximum voltage impressed to the electrode 107, a lateral direction voltage between the layer 102 and an ON picture element can be neglected and the generation of abnormality in the orientation of liquid crystal in the picture element can be suppressed. Since it is impossible to independently form the layer 102 in each picture element, a fixed voltage is simultaneously impressed to the whole surface or in each vertical/horizontal lines. Although abnormality in the orientation of liquid crystal may be generated at the impression of the fixed voltage, the generation can be neglected because a light/dark ratio is determined by the light shielding capacity of dark time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display element and a light modulation element using liquid crystal.

[0002]

2. Description of the Related Art A liquid crystal element has been actively researched and developed as a display element or a light modulation element, and a direct-view type display device using the liquid crystal element is currently widely used, and also applied to a projection type display device. Has been done.

The above-mentioned liquid crystal element generally has two electrode plates facing each other and a liquid crystal material sandwiched between them as basic constituent elements. However, in the case of a liquid crystal element having a plurality of pixels, the sizes of both electrodes are different. There are many. In particular, in a liquid crystal element having an active element such as a TFT (thin film transistor), one substrate (main substrate) is provided with an active element and a pixel electrode connected thereto, and the other substrate (counter substrate) is provided with a common counter electrode on one surface. It is provided.

FIG. 5A is a plan view showing a pixel portion of a liquid crystal element applied to a general liquid crystal display device using a TN (twisted nematic) liquid crystal and a TFT. Figure 5
FIG. 5B shows a cross section taken along the line AA ′ in FIG. A transparent pixel electrode 107, a signal electrode 104 and a counter electrode 109 are formed on the main substrate 101 and the counter substrate 108, respectively, and an alignment film 110 is applied thereon, and a TN liquid crystal material 111 is sandwiched therebetween. ing. This type of liquid crystal element is normally used in a so-called normally white mode in which light is transmitted when a liquid crystal drive voltage is not applied and light is shielded when a voltage is applied. Since such a liquid crystal element cannot apply a voltage to the gap (boundary portion 112) between the pixel electrodes, the brightness ratio of the pixel cannot be increased as it is. Further, in the peripheral portion of the pixel electrode 107, since the direction of the electric field is not perpendicular to the electrode, alignment or more (disclination or the like) occurs in the liquid crystal layer, which causes display defects such as image sticking and afterimage.

Therefore, some kind of light-shielding portion is usually provided in the pixel boundary portion 112. Generally, as shown in FIG. 5B, an inter-pixel light-shielding layer 102 is provided on a counter substrate to hide the boundary portion where transmitted light cannot be controlled and its vicinity from the pixel opening portion. In addition, especially for a portion where an abnormal orientation is likely to appear, the area of the inter-pixel light shielding layer 502 is enlarged to conceal the problematic portion (Japanese Patent Laid-Open No. HEI-1).
-266512).

[0006]

The liquid crystal alignment abnormality occurs at the peripheral portion of the pixel electrode when a voltage is applied, and the normally white mode liquid crystal element shields light when a voltage is applied. It cannot be expanded to size. When the light-shielding portion between pixels is provided on the counter substrate, an overhanging portion corresponding to the viewing angle is required for the pixel electrode. In addition, it is necessary to consider the deviation when bonding the substrates, and the opening area must be significantly narrowed with respect to the area of the pixel electrode. The higher the positioning accuracy required in the substrate bonding process, the more difficult the manufacturing becomes. Since it is almost unnecessary to consider the viewing angle in a liquid crystal element or the like used in a projection display device, the aperture ratio can be improved by improving the substrate bonding accuracy, but the electrode interval is narrow because the entire substrate is downsized. Therefore, the liquid crystal alignment abnormality is likely to occur inside the pixel. When the inter-pixel light-shielding layer is provided on the main substrate, the alignment with the pixel electrode can be determined by the precision of photolinography, so high precision can be easily obtained.
Pixels to which light-shielding layer between pixels and saturation voltage are applied (on-pixel)
When a horizontal electric field is applied between the pixel electrode and the pixel electrode, liquid crystal alignment abnormality occurs inside the pixel electrode. Due to the above reasons, the light utilization efficiency cannot be improved in this type of device, which causes an increase in power consumption. For this reason, a means that can secure the aperture ratio without deteriorating the display quality is required, and it is desirable that it be realized without raising the substrate bonding accuracy more drastically than in the past.

The present invention solves the above-mentioned problems and prevents the leakage of light at the pixel boundary portion and at the same time conceals the liquid crystal alignment abnormality occurring at the peripheral edge portion of the pixel electrode by narrowing the pixel opening portion more than necessary. It is an object of the present invention to improve the performance of a liquid crystal element by realizing the liquid crystal device without the need for high positioning accuracy in the substrate bonding process.

[0008]

According to the present invention, a liquid crystal material is held in a gap between a main substrate having a pixel electrode and active elements and wirings connected to the pixel electrode and a counter substrate having a counter electrode. In a liquid crystal element which is sometimes in a light-shielded state, a conductive inter-pixel light-shielding layer is provided on a peripheral portion of a pixel electrode on a main substrate. In addition, in this liquid crystal element, a voltage having an effective voltage substantially equal to the maximum voltage applied to the pixel electrode surrounded by the pixel light shielding layer and having a waveform substantially equal to the voltage waveform held by the pixel electrode is applied to the pixel light shielding layer. The effect can be maximized by giving.

[0009]

By providing the inter-pixel light shielding layer 102 on the main substrate 101 as shown in FIGS. 1 (a) and 1 (b), the alignment with the pixel electrode 107 can be determined by the accuracy of photolithography, and the height can be easily increased. Accuracy can be obtained. The counter substrate 108
Since there is no light-shielding layer, high precision is not required when the substrates are bonded together, and manufacturing is not difficult.

By providing the inter-pixel light-shielding layer 102 with a voltage having an effective voltage substantially equal to the maximum voltage applied to the pixel electrode surrounded by it and having a waveform substantially equal to the voltage waveform held by the pixel electrode, The lateral voltage between the light-shielding layer and the ON pixel becomes a magnitude that does not pose a problem, and it is possible to prevent abnormal liquid crystal alignment from occurring in the pixel. Since the inter-pixel light-shielding layer 102 cannot be provided independently for each pixel, a constant voltage is applied to the entire surface all at once or for each line either vertically or horizontally. In this case, a horizontal electric field is generated between a pixel to which no voltage is applied or the applied voltage is close to the threshold voltage (on-pixel), and liquid crystal alignment abnormality is also generated, but the pixel brightness ratio is dark. This is not a problem because it is determined by the light-shielding ability at the time (when on). Due to other factors, the inter-pixel light shielding layer 1
Even if the film thickness of 02 is inevitably thin and the light-shielding ability is considered to be insufficient, there is also an advantage that a sufficient light-shielding ability is obtained because the alignment of the liquid crystal is in the state of light-shielding by voltage application. ..

With the above operation, the aperture ratio can be improved without lowering the pixel contrast ratio and without improving the alignment accuracy as compared with the prior art.

[0012]

EXAMPLE FIG. 2 (a) is a plan view showing an example of a liquid crystal element to which the present invention is applied, and FIG. 2 (b) is a sectional view taken along the line AA 'in FIG. 2 (a). FIG. The glass substrate 101 serving as the main substrate has a scan electrode 1 made of chromium.
03, signal electrode 104, active element 106 made of polycrystalline silicon, transparent ITO (Indium Tin Oxi)
de: indium tin oxide), the inter-pixel light-shielding layer 102 made of chromium is further formed via the insulating layer 105, and the counter electrode 109 made of ITO is formed on the glass substrate to be the counter substrate 108. .. Here, the inter-pixel light shielding layer 102 is composed of one continuous conductor, and has an overlap of about 2 μm on the peripheral edge of the pixel electrode 107. Polyimide alignment film 110 on both substrate surfaces
Is applied and baked, and when they are bonded together, they are aligned so that the alignment directions on the surfaces of the substrates are approximately 90 ° with each other, and then the substrates are bonded together with a gap of about 5 μm. Was injected and sealed to obtain a liquid crystal element. In such an element, a scanning voltage was applied to the scanning electrode 103, a signal voltage was applied to the signal electrode 104, a common voltage was applied to the counter electrode 109, and the same voltage as the signal electrode to which the voltage was applied was applied to the inter-pixel light shielding layer 102. When such a driving voltage is applied and display is performed in the normally white mode, the aperture ratio is 35% in a pixel of 80 μm pitch.
As described above, it was possible to easily realize a clear image with a light / dark ratio of 100: 1 or more. Although the liquid crystal alignment abnormality was slightly observed in the peripheral portion of the off pixel, it was not observed at all in the on pixel, confirming the effect of the present invention. For comparison, a liquid crystal display device having a conventional structure was manufactured and confirmed. When the aperture ratio was 35%, the light / dark ratio was 10: 1 or less, and in order to obtain the light / dark ratio of 100: 1, the aperture ratio must be reduced to 15% or less. did not become.

The voltage applied to the inter-pixel light-shielding layer 102 is a rectangular wave of about 90% or more of the liquid crystal saturation voltage, and the effective voltage for the ON pixel must be a value that does not exceed the threshold voltage of the liquid crystal. In addition, since the phase of the waveform applied to the pixel voltage is deviated at the position where the scanning is started and the position where the scanning is ended, it is desirable to select the optimum phase for the voltage applied to the inter-pixel light shielding layer. The inter-pixel light-shielding layer 102 is formed in FIG. 2 in order to reduce the inter-wiring capacitance and reduce the influence on the active elements.
As shown in (a), it is necessary to take a structure that minimizes the overlap between the wiring and the active element.

FIG. 3 is a plan view showing an embodiment of a liquid crystal element to which the present invention is applied. On the main substrate 101, a scan electrode 103 made of chromium, a signal electrode 104, an active element 106 made of polycrystalline silicon, and a pixel electrode 10 made of ITO.
7. Further, the inter-pixel light shielding layer 102 made of chrome was formed via the insulating layer 105, and the counter electrode made of ITO was formed on the glass substrate serving as the counter substrate. Here, the inter-pixel light shielding layer 102 is composed of a plurality of conductors that are continuous along the scanning electrode wiring 103, and is approximately 2 μm around the periphery of the pixel electrode 107.
Has an overlap with a width of m. After coating and baking polyimide alignment films on the surfaces of both substrates, they are aligned so that the alignment directions on the surfaces of the substrates are approximately 90 ° when the substrates are bonded together, and then the substrates are made to have a gap of about 5 μm. Were bonded together, and a TN liquid crystal material was injected and sealed to obtain a liquid crystal element. In such an element, a scanning voltage was applied to the scanning electrode 103, a signal voltage was applied to the signal electrode 104, and a common voltage was applied to the counter electrode, and the same voltage as the signal electrode to which the voltage was applied was applied to the inter-pixel light shielding layer 102. In this element, so-called scanning line inversion driving is performed in which the positive and negative of the signal voltage are inverted at each scanning, and the inter-pixel light-shielding layer 102 accordingly produces an effective voltage for the on-pixel for each light-shielding layer electrode. A voltage that does not exceed the threshold voltage of is given. When such a drive voltage was applied and display was performed in the normally white mode, a clear image having an aperture ratio of 35% or more and a light / dark ratio of 130: 1 or more at a pitch of 80 μm could be easily realized. .. When the pixel portion was observed under a microscope with a microscope, it was slightly observed in the gap between the adjacent pixel light-shielding layers and the peripheral portion of the off pixel, but in the on pixel, more than the orientation leading to the reduction of the light-dark ratio was observed. Therefore, the effect of the present invention was confirmed.

FIG. 4 is a plan view showing an embodiment of a liquid crystal element to which the present invention is applied. On the main substrate 101, a scan electrode 103 made of chromium, a signal electrode 104, an active element 106 made of polycrystalline silicon, and a pixel electrode 10 made of ITO.
7. Further, the inter-pixel light shielding layer 102 made of chrome was formed via the insulating layer 105, and the counter electrode made of ITO was formed on the counter substrate. Here, the inter-pixel light shielding layer 102
Is composed of a plurality of conductors continuous along the signal electrode wiring 104 and has an overlap of about 2 μm on the peripheral edge of the pixel electrode 107. After coating and baking polyimide alignment films on the surfaces of both substrates, they are aligned so that the alignment directions on the surfaces of the substrates are approximately 90 ° when the substrates are bonded together, and then the substrates are made to have a gap of about 5 μm. Were bonded together, and a TN liquid crystal material was injected and sealed to obtain a liquid crystal element. In such an element, a scanning voltage was applied to the scanning electrode 103, a signal voltage was applied to the signal electrode 104, and a common voltage of the counter electrode was applied, respectively, and the inter-pixel light shielding layer 102 was applied with almost the same voltage as the signal electrode to which the voltage was applied. In this element, so-called signal line inversion driving for inverting the positive / negative of the signal voltage is performed for each adjacent signal electrode, and the inter-pixel light-shielding layer 102 accordingly produces an effective voltage for the ON pixel for each light-shielding layer electrode. A voltage that does not exceed the threshold voltage of is given. When such a drive voltage was applied and display was performed in the normally white mode, it was possible to easily realize a clear image with an aperture ratio of 35% or more and a light / dark ratio of 120: 1 or more in a pixel having a pitch of 80 μm. .. When the pixel portion was observed, some alignment defects were not observed in the ON pixels, although some were observed in the gaps between the light-shielding layers between pixels and the peripheral portions of the OFF pixels, confirming the effect of the present invention.

In the above example, chromium is used as the electrode material for the scanning electrodes, the signal electrodes, and the light-shielding portions between pixels. However, the suitable material is not limited to this, and any light-shielding conductive pair such as aluminum or molybdenum can be used. It may be used, and the material of the pixel electrode and the counter electrode is not limited to ITO as long as it is a light transmissive conductive material.

[0017]

As described above, according to the present invention, in a liquid crystal element having an active element, light leakage at a pixel boundary portion is prevented, and liquid crystal alignment abnormality ((discrete It is possible to hide the (nation) liquid crystal defect) with high alignment accuracy without narrowing the pixel opening. As a result, high-quality display can be realized without lowering the light utilization rate of the device, which is a great advantage particularly when the liquid crystal display device is downsized and the density is increased.

[Brief description of drawings]

FIG. 1 is a diagram showing an outline of the present invention.

FIG. 2 is a diagram showing an embodiment of the present invention.

FIG. 3 is a diagram showing an embodiment of the present invention.

FIG. 4 is a diagram showing an embodiment of the present invention.

FIG. 5 is a diagram showing an example of a conventional element.

[Explanation of symbols]

 101 main glass substrate 102 light shielding layer between pixels 103 scanning electrode 104 signal electrode 105 insulating layer 106 active element 107 pixel electrode 108 counter glass substrate 109 counter electrode 110 alignment film 111 liquid crystal layer 112 pixel electrode boundary part

Claims (2)

[Claims] 1. A liquid crystal element in which a liquid crystal material is sandwiched in a gap between a main substrate having a pixel electrode, an active element and a wiring connected to the pixel electrode, and a counter substrate having a counter electrode, and is in a light shielding state when a voltage is applied. 2. A liquid crystal element according to, wherein a conductive inter-pixel light shielding layer is provided on a peripheral portion of a pixel electrode on a main substrate. 2. A liquid crystal material is sandwiched between a main substrate having pixel electrodes, active elements and wirings connected to the pixel electrodes, and a counter substrate having counter electrodes, and a conductive inter-pixel light-shielding layer is mainly used. A scan voltage, a signal voltage is applied to the scan electrodes of the liquid crystal element, which is shielded when a voltage is applied, a signal voltage is applied to the signal electrode, and a common voltage is applied to the counter electrode. A method for driving a liquid crystal element, wherein an effective voltage substantially equal to a maximum voltage applied to a pixel electrode surrounded by an inter-pixel light shielding layer and a voltage having a waveform substantially equal to a voltage waveform held by the pixel electrode are applied.