JPH0535433B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates to an image display device configured in combination with a liquid crystal.

Conventional configurations and their problems In liquid crystal display devices, in order to enable static operation of liquid crystal cells and to realize multiplexing, unit pixels consisting of nonlinear elements such as transistors and diodes and liquid crystal cells are made into two-dimensional structures. Must be arranged in a matrix.

Figure 1 shows MIS (insulated gate) as a nonlinear element.
An equivalent circuit using transistor 1 is shown.
When a gate pulse is applied to the scanning line 3, the horizontal transistors are turned on all at once, so during the period when the gate pulse is applied, y ₁ , y ₂ ...y are transmitted from the signal line 4 all at once or sequentially. _j Electrically write the image signal to the liquid crystal cell 2. Writing of the entire screen is completed by sequentially scanning the gate pulse in the vertical direction x ₁ , x ₂ . . . x _i , and multiplexing is easily achieved by scanning the gate pulse in the vertical direction again. . The signal voltage written to the liquid crystal cell 2 is discharged through the OFF resistance of the transistor 1 and the resistance of the liquid crystal cell 2, but normally these resistances are sufficiently high that changes in the potential difference between both ends of the liquid crystal cell 2 are not enough to display an image. Design methods will be taken into consideration to avoid any problems. One electrode 5 of the liquid crystal cell 2 is configured as a common electrode for all picture elements, and is maintained at an appropriate potential.

If the OFF resistance of transistor 1 or the resistance of liquid crystal cell 2 is low, or if gradation is important, an auxiliary capacitor is added in parallel to liquid crystal cell 2. A method of adding in between is known.

FIG. 2 is a plan view of an integrated substrate in which the above image display device is integrated, and FIG.
A sectional view of the main part along the line -A' is shown.

Here, we will explain the case where a-Si is used as the semiconductor material for the MIS transistor 1. The transistor 1 has a gate electrode made of, for example, Mo, which also serves as the scanning line 3, a drain (or source) electrode, made of, for example, A, which also serves as the signal line 4, and a source (or drain) electrode connected to the liquid crystal cell 2, which is a load. The liquid crystal cell 2 includes a pixel electrode 7 made of, for example, ITO, a common transparent electrode 5 also made of ITO, and a space sandwiched between transparent insulating substrates, such as glass plates 9 and 10, to seal the liquid crystal. It consists of a liquid crystal 8 to be filled. Reference numeral 11 denotes an island formed of a-Si, and reference numeral 12 denotes a gate insulating film made of, for example, Si ₃ N ₄ , both of which are constituent elements of the transistor 1 .

Various documents have been published regarding the manufacturing method and characteristics of a-Si MIS transistors, which basically consist of a gas plate 10, a transparent electrode 5, a liquid crystal 8, a transparent electrode 7, a transparent insulating layer 12, and a glass plate 9. A function and means to electrically control the optical system are required. By introducing a polarizing plate and a reflecting plate in addition to the configuration shown in FIG. 3, the image display device shown in FIG. 3 can be used as either a transmissive type or a reflective type, and the selection is determined by the light source or liquid crystal material.

In the above image display device, the picture element electrode 7 is the second
As shown in the figure, it is necessary to set the distance within a unit picture element and between adjacent unit picture elements to be smaller than the scanning line 3 and signal line 4 by a distance corresponding to the alignment accuracy of the photo-etching process. For example, in the configuration shown in FIG. 3, if the pixel electrode 7 and the signal line 4 are formed to overlap, it is obvious that the control effect of the transistor 1 will be lost. Even if the electrical short circuit is prevented by introducing the parasitic capacitance 13, it is inevitable that an extra parasitic capacitance 13 will be generated as shown in FIG. Similarly, if the picture element electrode 7 and the scanning line 3 overlap, a parasitic capacitance 14 will occur.

Since the parasitic capacitance 13 increases the load capacitance of the signal line 4, the video signal amplifier for driving the image display device needs to have a driving capacity higher than that required for charging the liquid crystal cell 2. That is, an increase in drive power and a decrease in output impedance are unavoidable.
Similarly, since the parasitic capacitance 14 increases the load capacitance of the scanning line 3, the scanning signal amplifier also requires extra driving capability. However, since the clock frequency for transferring the scanning signal is low, the increase in power consumption is small.

The most significant adverse effect of the parasitic capacitance 14 is that the scanning signal is capacitively coupled to and superimposed on the connection point 15 between the transistor 1 and the liquid crystal cell 2. The magnitude of the change in potential at the connection point 15 due to this superimposition ΔV is determined by where the amplitude of the scanning signal is V, the parasitic capacitance is C ₁₄ , and the liquid crystal cell 2
If the capacitance of is C _LC , it is given by ΔV=V×C ₁₄ /C _LC +C ₁₄ , and the potential of connection point 15 is scanning (gate)
It undergoes a fluctuation of ΔV at the rise and fall of the pulse. As a result, when trying to drive the liquid crystal cell 2 with alternating current, the transistor 1 may be turned on even during the storage period, reducing the efficiency of using the video signal and reducing the contrast ratio of the image. Inevitable. Therefore, in order to provide sufficient writing to the liquid crystal cell 2, (1) supply a larger video signal, and (2) reduce the scanning signal to 0 (zero).
Extending the level in the negative direction (for n-channel operation); (3) providing a larger scanning signal;
In either case, power consumption for driving the image display device increases.

On the other hand, if an auxiliary capacitance C with a value sufficiently larger than the parasitic capacitance C14 and the liquid crystal cell capacitance _CLC is added between the connection point ₁₅ and the ground point or in parallel with the liquid crystal cell 2, the magnitude of the fluctuation will be ΔV=V× C ₁₄ /C ₁₄ +C _LC +C0, and the above-mentioned problems can be avoided.

However, since the load on the transistor 1 increases, a new problem arises as to whether the auxiliary capacitor C can be charged within a predetermined write period. If transistor 1 cannot cope with the increase in load capacitance, measures such as (a) increasing the scanning signal to increase the mutual conductance, and (b) increasing the planar size of transistor 1 are required. becomes. In short, if the ability to flow a current determined by the material of the nonlinear element represented by the transistor 1 is not sufficient, changes in the process technology, device structure, or circuit design will be required to have fairly severe specifications.
For example, the above (b) inevitably leads to a decrease in the aperture ratio, which is an important problem concerning the essence of the image display device.

Purpose of the Invention The present invention has been made in view of the above-mentioned current situation.
The purpose is to increase the aperture ratio without increasing the number of processes or changing specifications in circuit design.

Structure of the Invention In the present invention, the key point of the structure is to form the pixel electrodes in a self-aligned manner on the transparent substrate by utilizing the fact that the electrode materials other than the pixel electrodes are almost opaque to ultraviolet rays. , and embodiments of the present invention will be described with reference to the drawings from FIG.

DESCRIPTION OF THE EMBODIMENTS FIG. 5 is a plan view of a unit picture element of an image display device according to an embodiment of the present invention, and sectional views taken along the line B-B' are shown in FIGS. 6-8. In addition, 6th to 8th
The figure shows the structure of only 9 portions of the substrate.

In the image display device according to the present invention, nonlinear elements, scanning lines, and signal lines are formed prior to forming picture element electrodes. In many cases, semiconductor materials are used for nonlinear elements, and metal thin films are used for scanning lines and signal lines to lower resistance values. These materials are nearly opaque to ultraviolet light at the thicknesses commonly used (0.1-1 μm). Therefore, as shown in FIG. 6, after forming a scanning line 3, a signal line 4, and a transistor, which is a nonlinear element, on one main surface of a glass plate 9, for example, a transparent conductive layer 16 made of, for example, ITO is formed on the entire surface. Then, a negative photosensitive resin 17 is applied. Then, ultraviolet rays 19 are irradiated onto the other main surface of the glass plate 9. The transmittance of ultraviolet rays decreases as the wavelength of the glass plate 9 and the transparent conductive layer 16 becomes shorter, but the transmittance of ultraviolet rays is approximately 30% or more in the wavelength range of 300 to 350 nm, so if the exposure time is several times longer, the glass plate The photosensitive resin 17 is exposed to ultraviolet rays from the back side of the photosensitive resin 9 . As mentioned above, the scanning line 3 made of, for example, Mo, for example, A
A signal line 4 and a connection electrode 6 consisting of 2000~
Since the a-Si islands 11 having a thickness of 5000 Å hardly transmit ultraviolet rays, the negative type photosensitive resin 17 is selectively exposed to light except on the opaque material.

Since the photosensitive resin on the connection electrode 6 with the transistor, which is a nonlinear element, is not exposed to light in this state, normal exposure is performed from above the glass plate 9 using the glass mask 18 and ultraviolet rays 19', and a part of the transparent conductive layer 16 is exposed. and the connecting electrode 6 are partially connected to each other.

After development, as shown in FIG. 7, a photosensitive resin pattern 17' is selectively formed on the glass plate 9, that is, on the connection electrode 6 and the picture element electrode 20 formed in the process described later. As already mentioned, the edges of the opaque material and the photosensitive resin pattern 1
Since the end portions with 7' are aligned on the same line, the transparent conductive layer is etched using the photosensitive resin pattern 17' as a mask to obtain the picture element electrode 20. Incidentally, if a slight over-etching is performed at this time, it is possible to avoid a short circuit between the picture element electrode 20 and the exposed signal line 4', thereby making the present invention more reliable.

FIG. 8 is a sectional view showing another embodiment of the present invention,
As mentioned above, a nonlinear element made of an opaque material,
After forming the scanning lines and signal lines, a transparent insulating layer 21 is applied to the entire surface.
(For example, it may be an inorganic material such as SiO ₂ or Si ₃ N ₄ ,
A transparent polyimide resin or an organic material such as SP-910 manufactured by Toray Industries may be deposited thereon, and an opening 22 is provided to expose a part of the nonlinear element or connection electrode 6. Thereafter, as described above, using a negative photosensitive resin, the picture element electrodes 20 are formed in a self-aligned manner by exposing the glass plate from both sides. Naturally, in this case, overeating is unnecessary.

It is also possible to use a positive resist to form the picture element electrodes, and claims 5 and 6 are examples in which a positive photosensitive resin is used. In this case, the pixel electrodes are formed after patterning the positive photosensitive resin with a film thickness of 1 μm or more.
A transparent conductive layer of about 0.1 μm is deposited, and when the positive photosensitive resin is removed, the transparent conductive layer on the positive photosensitive resin is also removed. Although so-called lift-off is performed, there is no problem because the difference in film thickness is sufficiently large. In the embodiment described in Section 5, it goes without saying that in order to avoid short-circuiting between the picture element electrode and the opaque material, it is better to slightly reduce the amount of exposure from the back side of the glass plate.

The connection electrode 6 interposed between the nonlinear element and the picture element electrode is not an essential requirement of the present invention, and the point is that the electrical resistance between the nonlinear element and the picture element electrode does not interfere with the operation of the image display device. It is clear that the material of the frame does not matter, and the picture element electrode and the nonlinear element may be directly connected by omitting the connection electrode.

Furthermore, according to claims 5 and 6, the picture element electrodes can be formed of a metal material, and a reflective image display device can also be easily obtained.

Effects of the Invention In the image display device according to the present invention, it is possible to use all areas within a unit picture element except for scanning lines, signal lines, and nonlinear elements as picture element electrodes, and the effective aperture ratio is approximately 100%. Needless to say, a bright image can be obtained. This effect is particularly noticeable in large-screen image display devices where the alignment accuracy of the photolithography process is reduced.

Furthermore, in transmissive normally white image display devices, when the image is black, the light source from the back side of the image display device is completely blocked, so the contrast ratio is about 10 times that of conventional image display devices. A remarkable effect can be obtained.

In addition, there is almost no planar overlap between the pixel electrode and the scanning line or signal line, so there is no increase in power consumption during driving, and there is no stray capacitance between the pixel electrode and the scanning line. There is no fear that the contrast ratio will decrease due to an increase in the contrast ratio.

As is clear from the above explanation, if the scanning line and the signal line are made of a light blocking material and the nonlinear element has a layer made of a light blocking material, the nonlinear element is limited to an MIS transistor. The present invention is also effective for elements such as diodes, varistors, and MIMs, and it is also possible to use polycrystalline or amorphous silicon, which is difficult to transmit ultraviolet rays, for scanning lines and signal lines. be.

[Brief explanation of the drawing]

Figure 1 is an equivalent circuit diagram of an image display device composed of a combination of liquid crystal and MIS transistors, Figure 2 is a plan view of a unit pixel of the device, and Figure 3 is A-A in Figure 2. 4 is an equivalent circuit diagram of the image display device when parasitic capacitance occurs, FIG. 5 is a plan view of a unit pixel of the image display device according to the present invention, and FIGS. Figure 8 shows B- of the same device.
FIG. 3 is a cross-sectional view of the main part taken along line B'.

Claims (1)

[Claims] 1. A unit picture element consisting of a nonlinear element having a layer made of a light blocking material on one principal surface and a transparent conductive picture element electrode connected to one electrode of the nonlinear element. In the image display device, a liquid crystal is filled between a first transparent insulating substrate arranged in a dimensional matrix and a second transparent insulating substrate having a transparent conductive layer formed on one main surface. The scanning lines and signal lines interconnecting the unit picture elements are made of a light-blocking material, and the picture element electrodes are formed by a self-aligned photoetching process from the back side of the first transparent insulating substrate, An image display device characterized in that a connection portion between an electrode and one electrode of the nonlinear element is formed by a photoetching process from the surface of the first transparent insulating substrate. 2. A transparent insulating layer is formed on the nonlinear element, the scanning line, and the signal line, and the transparent conductive picture element includes an opening formed in the transparent insulating layer on one electrode of the nonlinear element. The image display device according to claim 1, further comprising an electrode. 3. Forming a scanning line, a signal line, and a nonlinear element having a layer made of a light blocking material on one main surface of the first transparent insulating substrate, and forming a transparent conductive layer on the first transparent insulating substrate. forming a negative photosensitive resin on the transparent conductive layer, and applying ultraviolet rays from the other main surface side of the first transparent insulating substrate to form a photosensitive resin in an area that will become a pixel electrode. and a step of exposing the photosensitive resin in a region including the picture element electrode and one electrode of the nonlinear element by irradiating ultraviolet rays from one main surface side of the first transparent insulating substrate using a photomask. , etching the transparent conductive layer using the photosensitive resin selectively left after development as a mask, and etching the first transparent insulating substrate and the second insulating substrate on which the transparent conductive layer is formed on the entire surface with a gap between them. A method for manufacturing an image display device, comprising the steps of: providing and bonding, and then injecting liquid crystal into the gap. 4. Before the step of forming a transparent conductive layer on the first transparent insulating substrate, a step of forming a transparent insulating layer on the entire surface and forming an opening in the transparent insulating layer on one electrode of the nonlinear element. 4. The method of manufacturing an image display device according to claim 3, further comprising the step of: 5. A step of forming a scanning line, a signal line, and a nonlinear element having a layer made of a light blocking material on one main surface of the first transparent insulating substrate, a step of applying a positive photosensitive resin, and a step of applying a positive photosensitive resin. A step of irradiating ultraviolet rays from the other main surface side of the first transparent insulating substrate to expose the positive photosensitive resin in the area that will become the picture element electrode, and using a photomask from the first main surface side of the first transparent insulating substrate. A step of exposing the positive photosensitive resin at the connection part connecting the picture element electrode and one electrode of the nonlinear element by irradiating ultraviolet rays, and developing it to form a positive photosensitive resin in the area other than the connection part and the picture element electrode. a step of leaving a resin; a step of forming a transparent conductive layer on the entire surface; a step of selectively removing the transparent conductive layer by removing the positive photosensitive resin; A method for manufacturing an image display device, comprising the steps of bonding a second insulating substrate on which a transparent conductive layer is formed with a gap therebetween, and then injecting liquid crystal into the gap. 6. Before the step of forming a transparent conductive layer on the entire surface, a step of forming a transparent insulating layer on the entire surface and a step of forming an opening in the transparent insulating layer on one electrode of the nonlinear element are added. A method for manufacturing an image display device according to claim 5, characterized in that: