JPH0210924B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for manufacturing a liquid crystal display.

More specifically, the present invention relates to a method for manufacturing a liquid crystal display in which a non-linear element is coupled to each display pixel.

In recent years, the application of liquid crystal displays has progressed, and they are now being used in large quantities as displays for wristwatches, calculators, and various other small electronic devices. In order to further expand the field of application of this liquid crystal display, it is essential to increase the display capacity. However, in conventional liquid crystal displays, the rise in voltage-contrast characteristics is not very steep, so as the number of digits in multiplex drive is increased, the difference in the effective value applied to the selected point and the non-selected or half-selected point increases. However, even if improvements were made to the liquid crystal composition and the structure of the liquid crystal display, multiplex driving of several tens of orders of magnitude was the limit. Therefore, in order to increase the display capacity of a liquid crystal display, an active strix type liquid crystal display in which a switching element is combined with a liquid crystal display has been considered. Various approaches have been taken, such as baristas.

As such a switching element, we applied the nonlinearity of metal-insulator-metal (MIM) structure.
The use of MIM elements has the advantage that the element structure is simple, so element design is easy, and the manufacturing process is simpler than other elements.

It is thought that current flows in this MIM element due to the tunnel effect at the metal-insulator interface, the Schottky effect, or the bulk effect in the insulator, and it exhibits nonlinear voltage-current characteristics as shown in Figure 1. Insulators include Al, Ta, Nb, Ti,
Oxides such as Si, oxides of the metals doped with other elements such as nitrogen, inorganic materials such as chalcogenide glass, and even organic thin films can also be used.

When an oxide film is used as an insulator, the conduction mechanism differs depending on the film thickness, and at 50 to 100 Å, there is a tunnel effect,
It is said that the Schottki effect and the Poole-Frenkel effect are dominant in the range of 100 to 1000 Å. In the combination of liquid crystal displays that is the object of the present invention, it is considered desirable to use a region exhibiting the Poole-Frenkel effect in view of the liquid crystal driving method, and in that region, the voltage-current characteristics described above are・Frenkel formula I=KV _exp (β√ ...(1) [In formula (1), I is current, V is applied voltage, K, β
is a proportionality constant that represents the ease of current flow and nonlinearity. ] It is expressed as . When a liquid crystal display incorporating this MIM element is driven by the voltage averaging method used for matrix driving of ordinary liquid crystal displays,
Due to the nonlinearity of the MIM element, the ON/OFF effective value ratio actually applied to the liquid crystal may be affected by the voltage averaging method itself.
It is larger than the ON/OFF effective value ratio, making it possible to drive a matrix with more digits.

When a MIM element is combined with a liquid crystal display, the equivalent circuit for one pixel is as shown in Figure 2.
MIM in which C _MIM and nonlinear resistance component R _MIM are connected in parallel
It can be considered that the element 1 and the liquid crystal portion 2, in which the capacitance C _LC and the resistance R _LC are connected in parallel, are connected in series. Then, a driving voltage is applied across these ends, and depending on the value of the ratio L _LC /C _MIM of the capacitance C _MIM of the MIM element 1 and the capacitance C _LC of the liquid crystal 2,
The voltage waveform actually applied to the liquid crystal 2 becomes different, and both in calculation and in practice, the larger the value of the capacitance ratio C _LC /C _MIM , the larger the ON/OFF voltage ratio applied to the liquid crystal. The number of drivable digits increases.

As shown in FIG. 3, the conventional MIM device has a structure in which a glass substrate 3 is covered with an oxide film 4 and a metal thin film 5 is coated on the glass substrate 3.
After forming and patterning, an insulating thin film 6 is formed on the surface. Furthermore, a metal thin film 7 is formed and patterned to create an MIM structure. in this case,
The area of the MIM element is the area of the intersection of metal electrode 5 and metal electrode 7. 4th to drive the liquid crystal
As shown in the figure, an electrode 8 is formed so as to be electrically conductive with the metal electrode 7, and a voltage is applied between the counter electrode provided on the counter substrate sandwiching the liquid crystal with a certain gap. control the array of

In this conventional method, manufacturing of a substrate equipped with an MIM element involves (1) patterning of the metal thin film 5, (2) patterning of the metal thin film 7, and (3) electrode 8 for driving the liquid crystal.
It required several patterning steps and three photolithography steps, and the manufacturing cost was high.

The present invention reduces the photolithography process by one process and reduces costs by simultaneously patterning the liquid crystal drive electrode during the photoetching process when forming one metal electrode of the MIM element. It is something.

The present invention will be described below with reference to Examples.

Example Tantalum pentoxide 10, indium oxide 11,
Thin films are formed in the order of tantalum 12 [FIG. 5a].
Next, the tantalum thin film 12 is etched so that the tantalum part 13, which will become one of the metal electrodes and lead parts of the MIM element, and the tantalum part 14, which has the same shape as the display pixel, remain [FIG. 5b]. Subsequently, the indium oxide layer 11 is etched using the tantalum 13 and 14 as a mask, and the transparent electrode 15 for driving the liquid crystal is patterned (FIG. 5c).

Next, only the surface of tantalum 13, which will become one metal electrode and lead portion of the MIM element, is anodized to form tantalum pentoxide 16 (FIG. 5d).
At this time, if only the tantalum 13 in the lead part is energized and anodized, the tantalum 13 in the display pixel part
is not oxidized and remains tantalum.

Next, a tantalum thin film is sputtered over the entire surface to form the other metal electrode 17 of the MIM element (FIG. 5e). At this time, tantalum pentoxide 16
In order to prevent the transparent electrode 15 from being completely etched, it is necessary to perform etching by a method that allows selective etching of tantalum, tantalum pentoxide, and indium oxide. For example, by performing plasma etching with Freon gas. You can achieve your purpose. at this point
At the same time as the MIM element is completed, the transparent electrode 15 for driving the liquid crystal is exposed, and one substrate of the liquid crystal display is completed. A liquid crystal display is completed by subjecting this substrate to an alignment treatment, combining it with a counter substrate having a counter electrode for driving a liquid crystal, which has also been subjected to an alignment treatment, and filling it with liquid crystal.

Although the embodiments have been described above, the present invention is not limited to the above embodiments. For example, as one metal electrode and insulator material of the MIM element, Ta-
It is possible to use not only the Ta ₂ O ₅ type but also the aforementioned metals and their oxides, such as Al, Nb, Ti, Si, etc., and furthermore, the above metals and their oxides can be used for the purpose of controlling the electrical characteristics of the MIM element. It is also possible to dope other elements such as nitrogen into the material. For example, by doping Ta with nitrogen, the specific resistance of the Ta film increases, but temperature changes in electrical characteristics can be controlled. In this case, the resistance value of the metal part (corresponding to tantalum 13 in the example) in the lead part of the MIM element becomes high, but the presence of the underlying transparent electrode lowers the resistance value of the entire lead part, which is advantageous. .

Regarding transparent electrodes, we are not limited to indium oxide, but also tin oxide-doped indium oxide, antimony-doped tin oxide, etc., which have lower specific resistance.
Various transparent conductive films such as NiCr/Au thin film can be used. The other metal electrode of the MIM element can be made of any material as long as it is basically a conductor and can be selectively etched with the transparent conductive film and the insulator of the MIM element. metals can be used.
This selective etching is a selective etching of metals and oxides, and can be easily performed.

As described above, the present invention includes a step of depositing a transparent conductive film and a first metal thin film on a transparent substrate, and a step of depositing a transparent conductive film and a first metal thin film on a transparent substrate, and a step of depositing the transparent conductive film and the first metal thin film into display pixel shapes, lead part shapes, and first metal electrode parts. a step of simultaneously patterning the patterned lead portion and the first metal electrode portion to form an insulating film;
depositing a second thin metal film;
Since the process of patterning the metal electrode part in the shape of This simplifies the process, reduces costs, reduces manufacturing defects, and significantly improves yield.

Further, a transparent conductive film is laminated and formed on the lead portion made of the first metal thin film, for example, the first metal thin film.
When Ta is used as the metal thin film, the resistance value of the transparent conductive film can be made to be about the same as Ta, so the electrical resistance of the lead part becomes smaller.
This has the effect that the wiring capacitance is significantly reduced and the signal voltage is efficiently applied to the display pixels.

[Brief explanation of drawings]

FIG. 1 shows the nonlinear characteristics of the MIM element. FIG. 2 shows an equivalent circuit when an MIM element and a liquid crystal are combined. FIG. 3 is a cross-sectional view and sketch of a conventional MIM element, and FIG. 4 is a plan view showing the arrangement of a conventional MIM element and one pixel. Figure 5 shows
FIG. 3 is a diagram illustrating the manufacturing process of an MIM element and a transparent electrode in the present invention.

Claims (1)

[Claims] 1 Step of depositing a transparent conductive film and a first metal thin film on a transparent substrate, and simultaneously patterning the transparent conductive film and the first metal thin film into a display pixel shape, a lead part shape, and a first metal electrode part shape. a step of oxidizing the patterned lead portion and the first metal electrode portion to form an insulating film; depositing a second metal thin film and forming the second metal thin film into a second metal electrode shape; The first metal electrode consists of a patterning process.
A method of manufacturing a liquid crystal display, characterized in that a nonlinear element with an MIM structure is formed by an insulating film-second metal electrode, and the second metal electrode is connected to the display pixel.