JPH0210923B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a nonlinear element having a metal-insulating film-metal (MIM) structure for realizing a high-duty drive liquid crystal display.

In conventional dynamic driving of liquid crystals, the duty was limited to about 1/16, but recently a method of driving liquid crystals through nonlinear elements such as MIM elements has been proposed as a means of improving the driving duty. There is. For example, when a liquid crystal is driven through a passive element with VI characteristics as shown in Figure 1, when the voltage V _ON that turns on the liquid crystal is applied, the effective resistance on the element side is low, and the resistance on the liquid crystal side is low. Since the voltage is high, most of the applied voltage is applied to the liquid crystal side. In addition, when a voltage V _OFF that does not turn on the liquid crystal is applied, the effective resistance on the element side becomes higher than the liquid crystal, and almost _no voltage is applied to the liquid _crystal . Substantially, the ratio of the applied voltages becomes much larger, and the difference between lighting and non-lighting, that is, the margin, becomes considerably large, and the driving duty can be effectively improved to about 1/200. The MIM element that realizes this nonlinear element has a structure as shown in FIG. Glass substrate 2
After forming a Ta film or TaN on 0 and patterning it to form a Ta or TaN first metal electrode 21 and a lead part, a Ta 2 O 5 layer 22 is formed by anodic oxidation, and then a Ta ₂ O ₅ layer 22 is formed on the upper electrode. 2 metal electrodes 23 are formed. The Ta ₂ O ₅ layer 22 has a thickness of about 500 to 1000 Å, and the characteristics shown in FIG. 1 are realized by utilizing traps in this insulating film to be conducted by an electron tunneling phenomenon. For this reason, the insulating film layer needs to be sufficiently thin.

FIG. 3 shows an equivalent circuit for driving the liquid crystal 31 by the MIM element 30, where VD is the driving voltage, VC is the voltage of the common electrode of the liquid crystal, and VM is the voltage actually applied to the terminals of the liquid crystal. MIM element has nonlinear resistance RM
and capacitance CM, and the liquid crystal can be expressed by resistance RL and capacitance CL. A voltage is applied to the liquid crystal 31 via a liquid crystal drive electrode.

Figure 4 shows the actual drive waveform, and when A is ON, B
is when it is OFF. Even when voltage VD returns to zero potential, voltage VM has a large time constant of capacitance CL and resistance RL, so the applied voltage can be maintained to a certain extent, which is why the duty ratio can be increased.
If the capacitance CM is larger than CL, when VD returns to 0 potential, the voltage drops △V _{M ON} and △V _{M OFF} will become large, and the desired function will not be achieved.

Therefore, we would like to make CL≫CM, but in reality, the Ta anodic oxide film has εs=25 compared to the driving area of the liquid crystal, so
The area of the MIM part needs to be 1/10000 or less.

For example, if the size of the liquid crystal drive electrode is 300μm□, the area of MIM is 3μm□, and with the current photo-etching technology, it is extremely difficult to form a 3μm□ size on the entire surface of a 10cm-sized glass. If you try, you'll end up with something quite expensive.

The present invention aims to provide a means for improving such drawbacks, and actually uses SiO, SiO ₂ , which has a low dielectric constant, as the insulating film of the MIM.

However, as mentioned above, the insulating film of the MIM element needs to be thin in order to maintain a certain degree of conductivity.
For this purpose, a dense film with few defects such as pinholes is required. Therefore, it is commonly used on metals such as Ta.
If SiO or SiO ₂ is formed, the film quality will be poor and the above conditions will not be met. Therefore, in the present invention, a Si oxide film of good quality is obtained by first forming a Si film on a metal film such as Ta, and then oxidizing the Si film.

FIG. 5 shows a specific example of the present invention. glass substrate 5
0, an island 51 of a metal film such as Ta is formed. Next, a Si film 52 with a thickness of about 100 to 300 Å is formed by sputtering and plasma CVD at low temperature deposition.

Next, this Si film 52 is oxidized. One is to introduce O ₂ gas of about 0.1 to 10 Torr into a negative chamber and oxidize it in a plasma state. Another method may be anodic oxidation performed in a liquid such as citric acid by applying a voltage of about 100V. Since the silicon oxide film obtained by oxidizing the Si film is important, the object of the present invention can be achieved if the means are similar. Thereafter, a top metal layer 54 is formed to form the MIM device.

The dielectric constant of SiO or SiO ₂ produced in this way is around 3.5, which is about 1/1 that of Ta oxide.
It is 4. Therefore, for a 300μm□ liquid crystal dot,
The size is 12 μm□, which is a size that is sufficiently easy to manufacture using conventional technology. As a result, △V _{M ON} and △ in Figure 4
Since V _{M OFF} is small and the effective voltage for driving the liquid crystal does not drop, dynamic drive with a sufficiently high duty is possible.

As described above, in the nonlinear element of the present invention, since the insulating film constituting the MIM structure is a Si oxide film, it is possible to reduce the area of the liquid crystal drive electrode.
It becomes possible to provide an image display device with higher density.
This is because the dielectric constant of Si oxide film is different from that of other insulators.
For example, it is smaller than tantalum pentoxide, aluminum oxide, silicon nitride, etc., so if the area of the nonlinear element is the same, the capacitance of the nonlinear element will be smaller if the dielectric constant of the insulating film is smaller, and the area of the liquid crystal drive electrode will be reduced accordingly. This is because it can be made smaller.

Furthermore, even if Si oxide was simply formed directly by sputtering, it was not possible to obtain a dense film without pinholes, and this was not practical in terms of yield. By forming a thin film layer and then oxidizing it to form a Si oxide film, a dense Si oxide film without pinholes can be obtained, making it possible to realize high-density image display devices with the above-mentioned effects with high yield. It is something.

Furthermore, since the Si oxide film according to the present invention has a dense film quality, it has the effect of improving the withstand voltage as a nonlinear element and reducing the risk of element destruction due to high voltage caused by static electricity or the like.

[Brief explanation of drawings]

Figure 1 shows the VI characteristics of the MIM device, Figure 2 shows
The conventional structure of an MIM element, Figure 3 is an equivalent circuit for driving a liquid crystal with an MIM element, Figure 4 is its operating waveform,
FIG. 5 shows manufacturing process diagrams of the MIM device of the present invention. 20, 50...Glass substrate, 21, 23, 5
1,54...Ta film, 23...Ta oxide, 52...
...Si film or Si oxide film.

Claims (1)

[Claims] 1 A step of forming a metal thin film to become a first metal electrode on an insulating substrate, a step of depositing a Si thin film, a step of substantially oxidizing the Si thin film to form a Si oxide film, and a step of forming a second metal thin film on the Si oxide film. 1. A method for manufacturing a liquid crystal display device, comprising a step of forming a metal electrode, and comprising a first metal electrode, a Si oxide film, and a second metal electrode to form a nonlinear element with an MIM structure.