JP2000305105A - Liquid crystal display element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase a liquid crystal display element in the pixel density and numerical aperture, and decrease it in the physical dimensions. SOLUTION: This liquid crystal display element is such that one p-well 212b is formed for every four pixels adjacent to each other, and n-type transistors 202 of the above-mentioned four pixels are formed in this well 212b. Moreover, a p-type transistor 201 is formed at a position on the diagonal of the n-type transistor 202. Thus, by forming the plural transistors of the same polarity in the p-well 212b, the inter-transistor distances can be set shorter without causing malfunctions of the transistors, therefore, it is possible to substratially reduce an area occupied by the transistors.

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 device provided with a semiconductor element corresponding to each pixel and used for an image display device such as a television receiver or a computer display, and more particularly to a liquid crystal display device such as a video projector and a data projector. The present invention relates to a liquid crystal display device capable of displaying a bright image even when used as a light valve in a liquid crystal projector.

[0002]

2. Description of the Related Art In recent years, liquid crystal display elements have been increasingly used in direct-view and projection image display devices. In particular, in a projection type image display device, by providing a liquid crystal display element as a light valve instead of a CRT, high brightness and compactness are achieved. This type of image display device requires a higher pixel density (high resolution) and a larger aperture ratio (high brightness) than a direct-view type image display device. Display elements are receiving attention.

[0003] As an example of a conventional liquid crystal display device, a reflection type liquid crystal display device used in, for example, an SXGA data projector will be described.

[0004] The liquid crystal display element is constituted by providing a liquid crystal layer 103 between a transparent substrate 101 and a silicon substrate 102 as shown in FIG. 11 for example. The transparent substrate 1
In FIG. 1, a transparent counter electrode 104 is formed. On the silicon substrate 102, a pixel switching transistor 111, an insulating layer 112, and a light-shielding layer 113 arranged in a matrix corresponding to each display pixel are formed, and further connected to the pixel switching transistor 111, respectively. The image signal line 114, the scanning signal line 115, and the reflection pixel electrode 116 are formed. The light-shielding layer 113 prevents light incident from the gap between the reflective pixel electrodes 116 from reaching the silicon substrate 102 and prevents a malfunction of the pixel switching transistor 111 due to a decrease in electric resistance of the silicon substrate 102. Is provided.

The above-mentioned pixel switching transistor 111
More specifically, as shown in FIG. 12, a source electrode, a gate electrode, and a drain electrode are connected to an image signal line 114, a scanning signal line 115, or a reflective pixel electrode 116, respectively.
, And the image signal voltage input from the image signal line 114 is switched and applied to the reflective pixel electrode 116 in accordance with the scanning signal input from the scanning signal line 115. Further, an auxiliary capacitance 118 is connected between the drain electrode and the common electrode 117. By providing the auxiliary capacitance 118, the liquid crystal capacitance 119 formed between the reflective pixel electrode 116 and the counter electrode 104 is substantially increased, and when the pixel switching transistor 111 is OFF, the liquid crystal capacitance 119 is reduced. The reduction in voltage due to the discharge of the stored charge is suppressed to a small level.

In the above-described liquid crystal display device, when incident light P aligned in a predetermined polarization direction enters through a polarizing plate or the like (not shown), the polarization direction is changed to the opposite electrode when passing through the liquid crystal layer 103. It changes according to the voltage (electric field) between the pixel electrode 104 and the reflective pixel electrode 116 (the polarization direction is modulated),
The emitted light Q is emitted. Therefore, when the emitted light Q passes through the polarizing plate, an image is displayed with a light amount corresponding to the change amount of the polarization direction.

By the way, in order to improve the image quality of the image display device, it is necessary to suppress a decrease in the voltage due to the discharge of the electric charge accumulated in the liquid crystal capacitor 119. For this reason, it is preferable that the auxiliary capacitance 118 provided in parallel with the liquid crystal capacitance 119 as described above is set to a capacitance as large as possible. However, in general, the auxiliary capacitance 118 is the same as the liquid crystal capacitance 119 due to restrictions on the area of electrodes that can be formed. The capacity is set to about or several times the capacity. Therefore, it is difficult to suppress the above-mentioned voltage drop to a small extent and to greatly improve the image quality.

Therefore, in order to suppress the discharge itself of the electric charge accumulated in the liquid crystal capacitor 119, for example, as shown in FIG. 1, a p-type transistor 201 driven by scanning signals of opposite polarities is provided for each pixel. It is conceivable to provide a pair of transistors with the n-type transistor 202 in parallel. That is, since the p-type transistor 201 and the n-type transistor 202 generate photocurrents in the opposite directions to each other, the movement of the charges is cancelled, so that discharge due to the photocurrent can be substantially prevented or reduced. Also, 2
By providing two transistors, the breakdown voltage of each transistor can be set low, so that each transistor can be miniaturized to reduce the size of the liquid crystal display element,
It is also possible to increase the aperture ratio (increase the luminance).

The above-mentioned pair of transistors may be formed, for example, as shown in FIG. That is, assuming that the entire image display area of the silicon substrate 121 is an n-well, the p-type transistor 201 is formed on the silicon substrate 121 by the p ⁻ region 201 a and the p ⁺ region 201.
It can be formed by providing b. On the other hand, n
The type transistor 202 can be formed by forming a p-well 122 on a silicon substrate 121 and providing an n ⁻ region 202a and an n ⁺ region 202b in the p well 122. In the figure, reference numeral 203 denotes a first scanning signal line, 204 denotes a second scanning signal line, 205 denotes an image signal line, and 206 denotes a reflection pixel electrode. In addition, in the figure, only members related to the p-type transistor 201 and the n-type transistor 202 are mainly illustrated for convenience.

[0010]

However, as described above, each pixel has a different channel type.
In the case of forming a pair of transistors, it is difficult to reduce the size of a pixel to achieve high definition of a display image and downsizing of a liquid crystal display element. That is, in the layout design of a semiconductor, it is necessary to follow various rules provided for avoiding malfunction of a semiconductor element, and in particular, it is necessary to set a distance between adjacent transistors to a minimum limit or more.

Specifically, for example, the p-type transistor 20
1 and the voltage applied to the n-type transistor 202 is 1
When the voltage is about 5 V, the distances S1 and S2 (the distance from each transistor to the boundary of the well) shown in FIG. 13 need to be set to at least about 2 μm. Therefore, for example, a p-type transistor 201 and an n-type transistor 202
Is 2.5 × 6 μm and the shape of the pixel is a square, as is apparent from FIG.
The size cannot be made smaller than the corner, and the size of the pixel is further increased when an auxiliary capacitance is formed. This is the same even when the fine processing technology of the 0.35 to 0.8 μm class, which is the most advanced semiconductor technology, is used.

Here, for example, a light valve having a diagonal size of 0.9 inches used in a projection type image display device and capable of displaying a so-called high-definition (HDTV) image having 1080 × 1920 pixels. It is necessary to set the pixel size to about 10 μm square.

In view of the above, the present invention provides a liquid crystal display device capable of suppressing discharge of electric charges accumulated in a liquid crystal capacitor, and achieving high pixel density, large aperture ratio, and miniaturization. It is an object.

[0014]

In order to solve the above-mentioned problems, the present invention comprises a substrate, a pixel electrode formed for each pixel on the substrate, and a pixel electrode opposed to the pixel electrode. A liquid crystal display comprising a counter electrode, a liquid crystal layer provided between the pixel electrode and the counter electrode, and a plurality of semiconductor elements of different polarities or types formed on the substrate for each pixel. An element, on the substrate, p
A well of at least one polarity of n-type or n-type is partially formed over a plurality of pixels adjacent to each other;
The semiconductor element of the same polarity or the same type among the semiconductor elements of the plurality of pixels adjacent to each other is formed in the well.

As the semiconductor elements having different polarities or types, for example, a p-type transistor and an n-type transistor, or a p-type or n-type transistor and a diode are used.

With the above configuration, the distance between semiconductor elements of the same polarity or of the same type formed in the same well is equal to the distance between semiconductor elements of different polarities or of different types formed via the well boundary. Even if it is arranged to be shorter than the distance, malfunction of the semiconductor element can be prevented, so that the area occupied by the semiconductor element can be substantially reduced. Therefore, it is possible to easily increase the pixel density and reduce the size of the pixel, or to increase the aperture ratio by reducing the size of the pixel.

The well may be formed over four pixels adjacent to each other. In this case,
Since the number of semiconductor elements formed at narrow intervals in a well is large, it is easy to greatly reduce the size of a pixel. Further, the well may be formed over two pixels adjacent to each other. Such a configuration has three problems due to restrictions on the layout of the wiring pattern.
This is effective when one or more transistors cannot be brought close to each other.

A reflective liquid crystal display element may be formed by using a reflective electrode that reflects visible light as the pixel electrode. On the other hand, a transparent electrode that transmits visible light may be used as the pixel electrode. Type liquid crystal display element. In the case where a reflective liquid crystal display element is formed, it is easy to increase the pixel density and downsize by reducing the pixel size as described above, while forming a transmissive liquid crystal display element. In this case, the aperture ratio can be easily increased by reducing the area occupied by the semiconductor element.

Further, by reducing the area occupied by the semiconductor element substantially as described above, the capacitance of the auxiliary capacitance means can be easily set to, for example, a liquid crystal capacitance or more. It is also possible to easily suppress a decrease in voltage due to discharge of electric charges.

[0020]

(Embodiment 1) As Embodiment 1 of the present invention, a reflective liquid crystal display element used in a projection type liquid crystal display device will be described.

First, the circuit of the liquid crystal display device will be described. As shown in FIG. 1, the liquid crystal display element includes a p-type transistor 201 and an n-type transistor 2 for each pixel.
02 is provided. The gate electrodes of these transistors are connected to the first scanning signal line 203 or the second scanning signal line 204, respectively. The source electrodes are both connected to the image signal line 205, and the drain electrodes are both connected to the reflective pixel electrode 206. The reflective pixel electrode 206 is connected to the opposite electrode 207 by the liquid crystal capacitor 20.
8 are formed. In addition, an auxiliary capacitance 210 is connected between the drain electrodes of the p-type transistor 201 and the n-type transistor 202 and the common electrode 209.

The first scanning signal line 203 or the second scanning signal line 204 supplies scanning signals of opposite polarities to the p-type transistor 201 and the n-type transistor 202. In response to this scanning signal, the image signal line 2
The image signal voltage input from the switch 05 is switched and applied to the reflective pixel electrode 206. As described above, by providing a pair of transistors of the p-type transistor 201 and the n-type transistor 202 driven in parallel by the scanning signals of opposite polarities,
Since photocurrents are generated in the respective transistors in directions opposite to each other, the movement of charges is canceled out, so that discharge due to the photocurrent is substantially prevented or reduced. In addition, since the withstand voltage of each transistor can be set low by providing two transistors, each transistor can be miniaturized to reduce the size of a pixel, thereby achieving high pixel density and miniaturization.

Next, the structure of the liquid crystal display device will be described.

The liquid crystal display element is shown in FIG. 2 (A in FIG. 3 described later).
As shown in FIG. 2A, a liquid crystal layer 213 is provided between the transparent substrate 211 and the p-type silicon substrate 212. As the liquid crystal layer 213, for example, a twisted nematic liquid crystal mode (TN) having a twist angle of about 40 to 70 ° or a vertical alignment mode (VA) using a nematic liquid crystal having a negative dielectric anisotropy is used. Applied. On the transparent substrate 211, a transparent counter electrode 207 is provided.
Are formed. The p-type silicon substrate 212 has pixel switching p-type transistors 201 arranged in a matrix corresponding to each display pixel, and n
A type transistor 202 is formed. More specifically, on the p-type silicon substrate 212, an n-well 212a is formed over the entire image display region, and a p-well 212b is partially formed in the n-well 212a. The p-type transistor 201 has a p ^- region 201a and ap ⁺ region 201 in the n-well 212a.
It is formed by providing b. On the other hand, n-type transistor 202 has n ⁻ region 202a and n ⁺ region 202 in partially formed p well 212b.
It is formed by providing b. Note that these p-type transistor 201 and n-type transistor 2
The arrangement pattern of No. 02 will be described later in detail.

The gate electrodes 216 and 216 are provided at the center (gate) of the p-type transistor 201 and the n-type transistor 202 via insulating layers 214 and 215, respectively.
217 are provided. These gate electrodes 216,
217 denotes a first scanning signal line 20 in a cross section (not shown).
3 or a projection formed on the second scanning signal line 204. The p ⁺ region 201b and the n ⁺ region 202b which are the sources of the p-type transistor 201 and the n-type transistor 202 are connected to the image signal line 2
05 is connected. On the other hand, the p ⁺ region 201b and the n ⁺ region 202b serving as drains have first relay electrodes 2
18, the second relay electrode 219, and the reflective pixel electrode 206 are connected via the contact hole electrode 220. Further, an auxiliary capacitance electrode 210a is connected to the first relay electrode 218. This auxiliary capacitance electrode 210
a, the insulating layer 210b, and the n-well 212a also serving as the common electrode 209 form an auxiliary capacitance 210 that substantially increases the liquid crystal capacitance 208. This auxiliary capacity 21
0 is set to, for example, a capacity equal to or larger than the liquid crystal capacity 208 (about several times). Further, the p-type transistor 201 and the n-type transistor 202
An insulating layer 221 is provided between and the reflective pixel electrode 206.

The p-type transistor 201 and the n-type transistor 202 are arranged as shown in FIG. That is, one p-well 212b is formed for every four pixels adjacent to each other, and the n-type transistors 202 of the four pixels are formed in the p-well 212b. Further, the n-type transistor 202 in each pixel
A p-type transistor 201 is formed at a position diagonally above. Note that, for convenience, only members related to the p-type transistor 201 and the n-type transistor 202 are illustrated in FIG.

As described above, when four n-type transistors 202 are formed in one p-well 212b formed for every four pixels, transistors having the same polarity are adjacent to each other. In this case, in order to prevent malfunction of each transistor, the distances S11 and S12 shown in FIG.
(Distance from each transistor to boundary of well) is 2μ
m or more, but the distance S13 (the distance between transistors of the same polarity in the same well)
Can be set to about 0.5 to 0.6 μm.
Therefore, for example, if the size of the p-type transistor 201 and the n-type transistor 202 is 2.5 × 6 μm and the shape of the pixel is a square, the size of the pixel can be reduced to about 10 μm square, as is apparent from FIG. .

Therefore, this liquid crystal display device has, for example,
A diagonal dimension generally used for a projection type image display device is 0.9 inches, and is called a high-definition (H
DTV) can be used as a light valve of 1080 × 1920 pixels capable of displaying an image. Further, since the area occupied by the transistor can be substantially reduced, it is easy to form an auxiliary capacitor having a large area. On the other hand, when the pixel shape is rectangular,
Further, the pixel density can be increased and the size of the liquid crystal display element can be easily reduced.

The p-type transistor 20 for each pixel
The 1 and n-type transistors 202 are not limited to those arranged at diagonal positions as described above, but may be arranged along the same side as shown in FIG. 4, for example.

(Embodiment 2) As Embodiment 2 of the present invention, a liquid crystal display element in which one p-well is formed for every two adjacent pixels will be described. The circuit configuration of this liquid crystal display element is the same as that of the first embodiment (FIG. 1). In the following embodiments, components having the same functions as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

As shown in FIG. 5, this liquid crystal display element
One p-well 212 for every two pixels adjacent to each other
The n-type transistors 202 of the two pixels are formed in the p-well 212b. In such a configuration, the vertical dimension of the pixel in the figure cannot be reduced, but the horizontal dimension can be reduced, so that the pixel size can be reduced or the auxiliary capacitance can be reduced. It can be easily enlarged. Such a configuration is effective when three or more transistors cannot be brought close to each other due to restrictions on the layout of the wiring pattern.

The arrangement is not limited to the above arrangement. For example, as shown in FIG. 6, the p-type transistor 201 and the n-type transistor 202 in the vertical direction in FIG. . Also, for example, FIG.
As shown in FIG. 5, the n-type transistors 202 of the vertically adjacent pixels in the same drawing may be formed in the same p-well 212b.

(Embodiment 3) As Embodiment 3 of the present invention, an example of a liquid crystal display element using a diode instead of the n-type transistor 202 of Embodiment 1 will be described.

In this liquid crystal display element, as shown in FIG. 8, for each pixel, a p-type transistor 201 and a diode 232 whose anode is connected to the bias signal line 231 and to which a reverse bias voltage is always applied are provided. Is provided. By providing the diode 232 in this manner, the leakage current is also reduced, and the p-type transistor 20
When 1 is in the OFF state, the voltage drop due to the discharge of the charge accumulated in the liquid crystal capacitance 208 can be suppressed to a small level.

As shown in FIG. 9 (a cross-sectional view taken along the line BB in FIG. 10), the diode 232 has n in the p-well 212b.
^- it is formed by regions 232a and n ⁺ region 232b is provided. Here, the n-well 212a is
It also serves as the common electrode 209 of the storage capacitor 210 and also serves as the bias signal line 231 of the diode 232.
Also, the p-type transistor 201 and the diode 232
Are arranged as shown in FIG. That is, one p-well 212b for every four pixels adjacent to each other
Are formed, and the diodes 232 of the four pixels are formed in the p well 212b.

With the above structure, the diode 232 occupies a smaller area than the transistor, has a smaller number of wires, and has the p-well 212b.
The distance between the diodes 232 within 0.5 to 0.6 μm
Since it can be set to the degree, it is possible to further easily reduce the size of the pixel and increase the auxiliary capacitance.

The present invention is not limited to the combination of the p-type transistor and the diode as described above, but may be a combination of an n-type transistor and a diode.

Further, the present invention is not limited to the case where one p-well is formed for every four pixels adjacent to each other as described above, and one p-well is formed for every four pixels adjacent to each other as in the second embodiment. May be formed. Further, various arrangement patterns similar to those described in the first and second embodiments can be modified.

In the first to third embodiments, an n-well 212a is formed on a p-type silicon substrate 212, and a p-well 212b is formed in the n-well 212a partially over a plurality of pixels adjacent to each other. However, the types of semiconductors and the types of p and n are not limited to those described above. That is, a similar effect can be obtained by forming a well of at least one polarity partially over a plurality of pixels adjacent to each other and forming a plurality of transistors and diodes of the same polarity in the well.

Further, a p-type transistor and n
Two or more pairs with the type transistor may be provided.

Further, the present invention is not limited to the method of forming a transistor on a single crystal silicon substrate as described above. For example, a transistor or a diode may be formed by forming a polysilicon layer or an amorphous silicon layer on an insulating substrate. Is also good.

The present invention is not limited to the reflection type liquid crystal display device used in the projection type liquid crystal display device as described above, but may be a transmission type liquid crystal display device. A reflective or transmissive liquid crystal display element used for the present invention may be configured. In particular, when a transmissive liquid crystal display element is formed, the size of a transistor or the like can be substantially reduced, so that the aperture ratio can be increased.

[0043]

The present invention is embodied in the form described above and has the following effects.

That is, a well of at least one polarity of p-type or n-type is partially formed on a substrate over a plurality of pixels adjacent to each other, and in the well,
By forming semiconductor elements of the same polarity or the same type among the semiconductor elements in the plurality of pixels adjacent to each other, the interval between the semiconductor elements can be set narrow without causing a malfunction of the semiconductor elements. The effect that the area occupied by the semiconductor element can be reduced in size, and therefore the size of the pixel can be reduced, so that the pixel density can be easily increased, the size can be reduced, and the aperture ratio can be easily increased. To play.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating a circuit configuration of a liquid crystal display element in Embodiment 1.

FIG. 2 is a longitudinal sectional view illustrating a structure of a liquid crystal display element of Embodiment 1.

FIG. 3 is a plan view illustrating an arrangement of a transistor in Embodiment 1;

FIG. 4 is a plan view illustrating a modification of the arrangement of the transistors in Embodiment 1.

FIG. 5 is a plan view showing an arrangement of transistors in Embodiment 2.

FIG. 6 is a plan view illustrating a modification of the arrangement of the transistors in Embodiment 2.

FIG. 7 is a plan view showing another modification of the arrangement of the transistors in the second embodiment.

FIG. 8 is a circuit diagram illustrating a circuit configuration of a liquid crystal display element in Embodiment 3.

FIG. 9 is a longitudinal sectional view illustrating a structure of a liquid crystal display element in Embodiment 3.

FIG. 10 is a plan view showing an arrangement of a transistor and the like in Embodiment 3;

FIG. 11 is a longitudinal sectional view showing the structure of a conventional liquid crystal display element.

FIG. 12 is a circuit diagram showing a circuit configuration of a conventional liquid crystal display element.

FIG. 13 is a plan view showing a possible transistor arrangement when p-type and n-type transistors are provided for each pixel;

[Explanation of symbols]

201 p-type transistor 201a p ⁻ region 201b p ⁺ region 202 n-type transistor 202a n ⁻ region 202b n ⁺ region 203 first scan signal line 204 second scan signal line 205 image signal line 206 reflective pixel electrode 207 counter electrode 208 liquid crystal capacitance 209 common electrode 210 auxiliary capacitance 210a auxiliary capacitance electrode 210b insulating layer 211 transparent substrate 212 p-type silicon substrate 212a n-well 212b p-well 213 liquid crystal layer 214,215 insulating layer 216,217 gate electrode 218 first relay electrode 219 second relay electrode 220 contact hole electrode 221 insulating layer 231 bias signal line 232 diode 232a n ⁻ region 232b n ⁺ region

Continued on the front page (72) Inventor Kazuhiro Nishiyama 1006 Kazuma Kadoma, Osaka Pref. Matsushita Electric Industrial Co., Ltd. 2H092 HA05 JA23 JA29 JA38 JA42 JA46 JB42 JB56 JB63 JB69 KA03 KA07 MA35 MA37 NA07 NA24 NA25 NA27 PA12 5C094 AA05 AA10 AA15 BA03 BA16 BA43 CA19 DA13 EA04 EA10 FB14 HA08

Claims (9)

[Claims] A substrate; a pixel electrode formed on the substrate for each pixel; a counter electrode provided to face the pixel electrode; and a counter electrode provided between the pixel electrode and the counter electrode. A liquid crystal layer, and a plurality of semiconductor elements having different polarities or types formed on each of the pixels on the substrate, wherein a p-type or an n-type is formed on the substrate. A well of at least one polarity is partially formed over a plurality of pixels adjacent to each other, and a semiconductor element of the same polarity or the same type among the semiconductor elements in the plurality of pixels adjacent to each other is formed in the well. A liquid crystal display element characterized by being formed. 2. The liquid crystal display element according to claim 1, wherein said semiconductor elements having different polarities are a p-type transistor and an n-type transistor. 3. The liquid crystal display device according to claim 1, wherein said different types of semiconductor devices are a p-type or n-type transistor and a diode. 4. The liquid crystal display device according to claim 1, wherein said well is formed over four pixels adjacent to each other. 5. The liquid crystal display device according to claim 1, wherein said well is formed over two pixels adjacent to each other. 6. The liquid crystal display device according to claim 1, wherein said pixel electrode is a reflective electrode that reflects visible light. 7. The liquid crystal display device according to claim 1, wherein said pixel electrode is a transparent electrode that transmits visible light. 8. The liquid crystal display device according to claim 1, wherein said substrate contains single crystal silicon. 9. The liquid crystal display device according to claim 1, further comprising auxiliary capacitance means having one electrode connected to said pixel electrode, wherein a capacitance of said auxiliary capacitance means is opposite to said pixel electrode. A liquid crystal display element, wherein the liquid crystal display element is set to be equal to or larger than a liquid crystal capacitance formed between the electrodes.