JPS647673B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a solid-state image display device constructed by combining a liquid crystal and a semiconductor integrated circuit, and an image display device with improved characteristics and reliability by employing a transparent insulating substrate and transparent electrodes. The purpose is to provide

FIG. 1 shows an example of an image display device constructed by combining a liquid crystal and a MOS transistor array. A unit picture element is composed of a MOS transistor 1, a storage capacitor 2, and a liquid crystal cell 3, and the operating principle of the image display device is as follows. For example, when a gate signal is applied to the x _i terminal and the horizontal MOS transistor group is turned on, the video signal terminal charges the capacitor 2 from the y _i terminal through the transistor 1. Even when the gate signal disappears and MOS transistor 1 is turned off, as long as the charge stored in capacitor 2 continues to apply voltage to liquid crystal cell 3, liquid crystal cell 3 adjusts the magnitude of dynamic scattering according to the voltage. Since the light passing through the liquid crystal cell 3 is changed, the light passing through the liquid crystal cell 3 can be modulated by the video signal. The charge stored in the capacitor 2 leaks through the off resistance of the transistor 1 and the resistance of the liquid crystal cell 3 until the next gate signal is applied and reset.

As shown in Figure 1, it is possible to construct a television by arranging unit pixels in a matrix and scanning them in the x and y directions, and as mentioned earlier, turning on transistor groups in the horizontal direction. By writing the video signal group into the capacitor group and sequentially scanning the gate signal group in the vertical direction, so-called line scanning, an effect equivalent to that of a CRT can be obtained.

FIG. 2 shows a plan view when the unit picture elements shown in FIG. 1 are integrated into an integrated circuit. The size of a unit picture element is, for example, 200×150 μm.

The MOS transistor consists of a source 4, a drain 5, and a polycrystalline silicon gate 6, and 8 is a metal reflective electrode that forms the wiring path 7 made of polycrystalline silicon and the capacitor 2 through a thin oxide film.

FIG. 3 shows a cross-sectional view taken along line AA in FIG. 2.
12 is a silicon oxide film covering the surface of the sapphire substrate 11, and 10 is a gate oxide film. The polycrystalline silicon gate 6 and wiring path 7 made of polycrystalline silicon are doped with impurities to provide conductivity. The metal reflective electrode 8 is in ohmic contact with the drain 5, which is a diffusion layer, through the opening 9 of the silicon oxide film 12.

A liquid crystal 1 that generates a dynamic scattering mode between a sapphire substrate 11 on which an integrated circuit is formed and a glass plate 13 on which a transparent electrode 14 is formed on one main surface.
6, the liquid crystal cell 3 consisting of the transparent electrode 14 and the metal reflective electrode 8 is constructed. Light 15 incident from above the glass plate 13 enters the liquid crystal cell 3
The metal reflective electrode 8 receives appropriate scattering within the
It is reflected by the light and reaches the observer's eyes. In Fig. 3, the light 15 that is incident parallel to the plane of the paper is reflected by the metal reflective electrode 8 and exits parallel to the plane of the paper again, so there is no light that comes out in a direction perpendicular to the plane of the paper, and it appears black to the observer, and the liquid crystal display When dynamic scattering occurs, the light is diffusely reflected by the liquid crystal molecules and comes out in a direction perpendicular to the plane of the paper, so the observer will see that it appears white. In other words, a reflective image display device is obtained.

Improving a reflective image display device as shown in FIG. 3 to a transmissive type provides the following advantages. (1) It can be used in dark places because it is illuminated from the back using power light instead of external light. (2) Since FE (phase change) type liquid crystal can be used, the operating voltage can be lowered, which is expected to extend the life of the liquid crystal material and improve the yield of semiconductor integrated circuits. (3) It is easy to handle colorization. This is because it is difficult to realize the three primary colors of R, G, and B with a reflective electrode, whereas with a transparent electrode, it is extremely easy to color the filter with resin.

Therefore, among the materials shown in FIG. 3, the metal reflective electrode 8 and polycrystalline silicon 6, 7, which are materials that do not transmit light, are replaced with transparent conductive metal oxide ITO (Indium-ITO).
Attempts were made to replace it with tin-oxide). The results are as follows. (1) It is not possible to completely replace polycrystalline silicon with ITO; at least a polycrystalline silicon gate 6 is required. This is because when ITO is used as the gate electrode of a MOS transistor, instability occurs in the on-voltage V _T of the transistor, and this is thought to be because the composition ratio of ITO changes due to heat treatment. (2) Diffusion layer and
It is difficult to make ohmic contact with ITO, resulting in extra voltage drop loss. (3) Although the metal reflective electrode is not necessary, it is not desirable to eliminate the metal electrode for connection with the outside. Because ITO
Since wire bonding is not possible, wireless bonding has to be applied, but as the number of picture elements increases, the number of bonding locations increases, resulting in a lack of reliability.

Therefore, the inventor of the present invention intervened a metal layer between the diffusion layer and the ITO, and made it possible to form a highly reliable transparent electrode (ITO) with a large aperture ratio, thereby facilitating the easy formation of high-precision, high-quality capacitors. By doing this, a transmissive image display device with a novel structure was obtained.Examples of the present invention will be described with reference to FIGS. 4 to 6.

As shown in FIG. 4, a first oxide film 19 is formed on the surface of the transistor 1, an opening is provided above the drain 5, and metal is selectively left in the opening and its periphery to form 8'. Next, wiring paths 17 are selectively formed using ITO, and a second oxide film 20 is deposited on the entire surface.
The electrode 18 of the liquid crystal cell is selectively formed of ITO on the metal film 8' of the oxide film 20 covering the metal film 8'.
It goes without saying that the capacitor 2 is formed of the ITO 17, 18 and the second oxide film 20. 1st
The oxide film 19 is not necessary if the MOS transistor is a self-aligned type, but if it is not a self-aligned type, it is automatically formed in the gate oxidation process.

Figure 5 shows a plan view of the surrounding area.
21 is a metal electrode, and 25 is a ground line made of a diffusion layer. Cross-sectional views along lines B-B' and C-C' are shown in FIGS. 6a and 6b. The opening 22 is provided in the first oxide film 19, and the wiring path 17' overlaps the metal electrode 21 so that the diffusion layer 25 and the wiring path 17' made of ITO are connected via the metal electrode 21. It is formed by The opening 23 is similarly provided in the first oxide film 19, and the metal electrode 21 is formed to overlap the polycrystalline silicon 6'. A wire bond 26 is made to the metal electrode exposed through the opening 24 provided in the second oxide film 20, and a gate signal is supplied from the outside.

As is clear from the above description, the present invention is characterized in that extremely good ohmic contact can be obtained because metal is interposed between the diffusion layer and the ITO. Al is the most common metal electrode material, but there is already a lot of experience in the semiconductor industry regarding the good ohmic properties of the combination of Al-ITO and Al-diffused layers. It can be said that good ohmic contact was obtained between the ITO and the diffusion layer. Needless to say, heat treatment is required.

Another advantage is that the metal used to connect the diffusion layer and ITO is used to simultaneously form the bonding pads necessary for connection to an external circuit, so the process is not complicated. Picture element electrode 1 made of ITO
Since the connection 8 is made through the opening formed in the insulating layer 20 after the metal wiring 8' is formed, the metal wiring is never etched during the formation of the picture element electrode, and the picture element electrode is Since the process is performed on the top of the substrate, the quality of the film is not impaired.

In the above embodiment, sapphire is used as the transparent insulating substrate, single crystal silicon is used as the semiconductor, ITO is used as the transparent electrode, and Al is used as the metal layer, but the present invention is not limited to these specific materials. It is clear from the gist. Further, according to the present invention, a storage capacitor can be formed with high precision using a pair of stable and high-quality transparent electrodes, and a transmissive liquid crystal display device with stable operation and good image quality can be realized. It becomes possible.

[Brief explanation of the drawing]

FIG. 1 is an equivalent circuit diagram of an image display device consisting of a liquid crystal and a semiconductor integrated circuit, FIGS. 2 and 3 are a plan view and a sectional view of a unit pixel of the same device, and FIG. 4 is an embodiment of the present invention. FIGS. 5 and 6 a and b are a plan view and a sectional view showing wiring paths and signal extraction in the peripheral area according to an embodiment of the present invention. 1... MOS transistor, 2... Capacitor for charge storage, 3... Liquid crystal cell, 8... Metal reflective electrode, 16... Liquid crystal, 8'... Metal on selectively left diffusion layer, 17, 17'... Transparent electrode forming a wiring path, 18... Transparent electrode forming one electrode of a liquid crystal cell, 20... Insulating film.

Claims (1)

[Claims] 1. On one light-transmitting insulating substrate constituting a liquid crystal cell, a pair of transparent electrodes, a capacitor made of a transparent insulating film sandwiched between the pair of transparent electrodes, and a MOS transistor made of the transparent insulating film are provided as structural units. Metal electrodes arranged in a two-dimensional matrix and making ohmic contact with the source or drain of the MOS transistor are formed, the transparent insulating film is formed to cover the metal electrodes, and a pixel electrode is formed on the transparent insulating film. An image display device characterized in that one of the transparent electrodes is formed to be the metal electrode and the one of the transparent electrodes to be the picture element electrode is connected through an opening formed in the transparent insulating film. .