JPH0430004B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a matrix type liquid crystal display device in which display characteristics are improved by forming nonlinear switching elements.

[Prior Art] Conventionally, nonlinear elements used in display devices include metal-insulator-metal (M = etal-
Nonlinear elements with I = nsulator - M = tal (abbreviated as MIM) structure (hereinafter referred to as MIM) have a simple element configuration, so compared to other nonlinear elements, the manufacturing process is shorter and the element design is easier. It has many advantages.

It is thought that current flows through this MIM element due to tunnel effect, Schottky effect, Poole-Frenkel effect, etc., and it exhibits nonlinear voltage-current characteristics as shown in FIG.

Insulators include Al, Ta, Nb, Ti, Si, Mo,
Oxides such as W and Hf, oxides of the metals doped with nitrogen, inorganic materials such as chalcogenide glass, and even organic materials such as polyimide resin can be used.

If the insulating film is sandwiched with metal, it becomes MIM.
structure, and this metal includes the metal and Ni,
Cr, Au or an alloy thereof can be used.

When a voltage is applied to a MIM element, the conduction mechanism differs depending on the thickness of the insulating film, and it is said that the tunnel effect is dominant at 50 to 100 Å, and the Schottki effect and Poole-Frenkel effect are dominant at 100 to 1000 Å. The liquid crystal display device which is the object of the present invention
When combining MIM elements, it is considered desirable to use a region that exhibits the Poole-Frenkel effect in view of the liquid crystal driving method, and in that region, the voltage-current characteristics are expressed by the Poole-Frenkel equation: I=KV exp (β√) (1) [In the formula (1), I is a current, V is an applied current, and k and β are proportionality constants representing ease of current flow and nonlinearity, respectively. ] It is expressed as .

When a liquid crystal display device incorporating this MIM element is driven using the voltage averaging method used to drive a normal matrix type liquid crystal display device, the nonlinearity of the MIM element causes the voltage actually applied to the liquid crystal to decrease. ON/
The OFF effective value ratio is the ON/OFF of the voltage averaging method itself.
It becomes larger than the effective value ratio, and more efficient matrix driving becomes possible. When an MIM element is combined with a liquid crystal display device, the equivalent circuit for one pixel is as shown in Figure 2: CMIM for capacitance and RMIM for nonlinear resistance.
It can be considered that the MIM element 1 in which the capacitance CL0 and the resistance RLC are connected in parallel are connected in series.

A voltage is applied to both ends of this, but the effective voltage actually applied to the liquid crystal part 2 is MIM
Time constant of element 1, time constant of liquid crystal part 2 and MIM
CMIM for the capacitance of element 1 and the capacitance of liquid crystal part 2
The ratio to CLC is determined by the combination of CLC/CMIM,
When the time constant of liquid crystal portion 2 and the value of CLC/CMIM are large, and the time constant of MIM element 1 is an appropriate value, the time effective voltage will be the largest.In theory, the greater the nonlinearity of MIM element 1, the higher the matrix drive. You will be able to get more digits.

To explain the structure of a conventional MIM element here,
For example, as shown in FIGS. 3 and 4, a glass substrate 3 is coated with an oxide film 4 to serve as an etch stop, then a metal thin film 5 is formed, and after patterning the metal thin film 5 into a desired shape, an insulating thin film 6 is formed on the surface. form. Furthermore, a thin metal film is applied and patterned.
This is the counter electrode 7 of the MIM element. At this time, the area of the MIM element is the area of the portion where the metal electrode 5 and the counter electrode 7 overlap each other. To make a liquid crystal display device, next, a pixel electrode 8 is formed using a transparent conductive film, a liquid crystal alignment layer is formed on the surface, a counter substrate is formed with a constant distance maintained, and a cell is formed, and a liquid crystal is sealed in the space. Attach a polarizing plate to create a TN liquid crystal display device.

[Problems with conventional technology] When trying to make a matrix type liquid crystal display device using an MIM element with such a structure, the pixel size of 0.3 to 0.5 mm is often used in conventional matrix type liquid crystal display devices. The dimensions of an MIM element suitable for pixels of such dimensions are 3 to 6 μm square. In the current photolin graph technology, this 3 to 6 μm square area is the boundary area between LSI and VLSI, and since it is a matrix type display device, the display area is 5 to 10 cm in size, which takes up a considerable area. This necessitates the formation of devices with dimensions in the submicron region, which is accompanied by considerable difficulty. Furthermore, if a matrix type liquid crystal display device having pixels of even smaller dimensions is to be manufactured, VLSI technology must be used completely, which is not desirable in terms of cost.

On the other hand, in addition to dimensional problems when manufacturing MIM devices, it is extremely difficult to obtain completely symmetrical devices using conventional MIM device manufacturing methods, and there are problems such as non-uniformity of the oxide film used as an insulator, and metal-oxidation problems. Due to the unevenness of the membrane interface, the MIM element has an asymmetry in which the V-I characteristics change when the polarity of the voltage applied to it changes.
If a liquid crystal is driven with a symmetrical alternating waveform through an element, an asymmetrical alternating waveform will be applied to the liquid crystal, and a DC component will remain, significantly shortening the life of the liquid crystal display device.

The present invention overcomes the above problems, and by forming a nonlinear element using the side portion of a metal electrode, the capacitance ratio of the element to the pixel can be minimized, and two nonlinear elements can be formed. By connecting the elements in series, a switching element with symmetrical characteristics can be formed.

[Example] The present invention will be explained below with reference to Examples.

Example 1 In ₂ O ₃ , SnO ₂ ,
The pixel electrode 10 is formed of a transparent conductive film such as ITO (In ₂ O ₃ +SnO ₂ ) or NiCr/Au thin film. →FIG. 5a Next, a tantalum thin film with a thickness of 1000 to 10000 Å is formed and patterned into a predetermined shape, and then the surface is oxidized to form a lead portion and one metal electrode 11 of the MIM element and an insulating film 12. →Figure 5b When patterning tantalum, taper etching of tantalum is performed by plasma etching with a mixture of 5 to 50% CF ₄ gas and O ₂ gas.

Next, a zinc oxide thin film layer 13 with a thickness of 1500 to 7000 Å is applied to the entire surface.
Then, a positive resist layer 14 having a thickness of about 1 to 2 μm is formed. →Figure 5c In this state, the back side of the Pyrex glass substrate 9,
That is, when exposure is performed from the opposite side of the positive resist layer 14, the lead portion and the tantalum portion of the metal electrode 11 of one of the MIM elements serve as a mask, and when developed, the resist 14 remains as shown in FIG. 5d.

Next, the zinc oxide thin film layer 13 is etched as shown in FIG. 5e. At this time, the etching conditions for the zinc oxide thin film layer 13 are controlled so that the side etching amount is 1000 to 10000 Å.

Next, a thin NiCr/Au film 15 with a thickness of 1000 to 10000 Å
form. Figure 5 f At this time, the lead part and
It is preferable to use a method that improves the step coverage at the tapered portion of the metal electrode 11 and the insulating film 12 of the MIM element (for example, vapor deposition using a rotation-revolution type substrate mounting jig or sputtering).

Next, by removing the remaining part of the zinc oxide thin layer 13, the upper resist 14 and NiCr/
The Au thin film 15 is also removed to form the state shown in FIG. 5g.

Next, unnecessary portions of the NiCr/Au thin film 15 are removed to complete the MIM device and expose the picture electrode 10. →Figure 5h At this time, the completed MIM element and pixel electrode 10
An example of the planar layout of is shown in FIG. 6.

The area of the MIM element is determined by the length of the tapered portion of the insulating film 12 and the width of the NiCr/Au thin film 15 of the counter electrode.

That is, as shown in FIG. 5h, the first MIM element as a non-linear element is formed by the side part of the metal wiring electrode 11, the insulating film 12, and one side part of the thin film 15 which is the connection electrode, The second MIM element is formed by the other side of the connection electrode 15, an insulating film 12', and an island-shaped metal electrode 12'.

FIG. 7 shows a cross-sectional view of a liquid crystal display device having the MIM element of this example.

Polyimide resin is applied to the surface of the Pyrex glass substrate 9 on which the MIM element and the pixel electrode 15 are formed, and a liquid crystal alignment process is performed by baking and rubbing with cotton cloth. Separately, a Pyrex glass counter substrate 17 on which a striped transparent electrode 16 is formed and subjected to a liquid crystal alignment treatment by rubbing with a polyimide resin is prepared, and the liquid crystal 18 is sealed by adhering the substrate at a distance of 5 to 20 μm. . At this time, rubbing is performed so that the liquid crystal molecules are twisted 90 degrees between the upper and lower substrates 9 and 17. Polarizing plates 19 and 20 are arranged outside this liquid crystal cell so that the polarization axis matches the alignment state of the liquid crystal to form a TN type liquid crystal display device.

FIG. 8 is an equivalent circuit diagram of a matrix type liquid crystal display device having non-linear switching elements. i.e. two MIMs acting as bidirectional diodes.
A capacitor 82 whose dielectric is a combination of elements 81 and the liquid crystal of the pixel portion is connected in series between an X-direction wiring 83 and a Y-direction wiring 84. This combination of one pixel is repeated a predetermined number of times in the X direction and the Y direction, and is arranged in an XY matrix.

Example 2 The manufacturing process is almost the same as Example 1, but in the oxide film formation process, the pixel electrode 22, the lead part, and the MIM are placed on the glass substrate 21 as shown in FIG. 9a.
After forming the metal electrode 23 on one side of the element,
After sputtering Ta, thermal oxidation is performed in oxygen at 400 to 500° C. to form an oxide film 24 on the entire surface. Furthermore, the MIM device is completed by the same process as in Example 1, as shown in FIG. 9b.

Although the embodiments have been described above, the present invention is not limited to the above embodiments. For example, the substrate may be made of any material used in ordinary liquid crystal display devices, such as not only Pyrex glass but also soda lime glass. Can be used.

Further, regarding the method of forming the insulating film, after forming a metal thin film, various oxidation methods such as anodic oxidation, thermal oxidation, plasma oxidation, or implantation of oxygen ions can be used. Further, various film forming techniques such as direct sputtering, CVD, plasma CVD, electron beam evaporation, induction heating evaporation, ion beam evaporation, and coating methods can be used for oxides and organic materials.

Furthermore, regarding the zinc oxide thin film mentioned in the implementation, any material may be used as long as it transmits light during exposure and can be selectively etched with the photoresist, insulator film, and substrate material, such as magnesium oxide, It is also possible to use inorganic materials such as calcium oxide and silicon nitride, and organic materials such as polyimide resin. According to Example 1, the tartar that will become the lead portion and one electrode 11 of the MIM element in FIG. 2500 assuming that the side etching amount of the zinc oxide thin film 13 is 3000 Å.
A MIM device was formed by attaching a NiCr/Au thin film with a thickness of 1.5 μm. The width of the other electrode 15 of the MIM element made of NiCr/Au thin film is 30 μm, and in combination with a 300 μm square pixel electrode, a matrix type liquid crystal display device is fabricated.
= 1.5Vrms, Vsat = 2.0Vrms liquid crystal is enclosed, 1/
When driving was performed using a voltage averaging method of 5 bias and 1/512 duty, a contrast of ON: 90% or more and OFF: 10% or less was obtained in the voltage range of 12 to 15 VP-P.

[Effects] As described above, the present invention includes a pair of substrates in which liquid crystal is sealed, a pixel electrode disposed on the substrates, a wiring electrode disposed adjacent to the pixel electrode, and a wiring electrode made of the same metal as the wiring electrode. an island-like metal electrode electrically connected to the pixel electrode, an insulating thin film covering the wiring electrode and the island-like metal electrode, and connecting the wiring electrode and the island-like metal electrode via the insulating thin film. A first non-linear element part is formed by a side part of the wiring electrode, the insulating thin film, and one side part of the connecting electrode, and the other side part of the connecting electrode and the insulating thin film are connected to each other. A second non-linear element part is formed by the side part of the island-shaped metal electrode, and the first non-linear element part and the second non-linear element part are connected in series. Since the formation area of the linear element can be minimized, two non-linear switch elements, which are much smaller than the pixel electrode, can be formed in series compared to the conventional art.
Therefore, even if the number of pixels increases and the pixel area decreases, it is possible to obtain sufficient ON/OFF ratio contrast and obtain a symmetrical response to AC signals.

[Brief explanation of drawings]

Figure 1 shows the nonlinear characteristics of the MIM element. Second
The figure shows an equivalent circuit when a MIM element and liquid crystal are combined. FIG. 3 is a cross-sectional view and a sketch of a conventional MIM element, and FIG. 4 is a plan view showing the arrangement of a conventional MIM element and one pixel. FIG. 5 is an explanatory diagram of the manufacturing process of the MIM element according to the present invention. FIG. 6 is a plan view of one pixel of a liquid crystal display device according to Example 1 of the present invention, and FIG. 7 is a sectional view of the liquid crystal display device. FIG. 8 is an equivalent circuit of the matrix type liquid crystal display device of Example 1. Figure 9 shows Example 2
It is a figure explaining the manufacturing process in.

Claims (1)

[Claims] 1 A liquid crystal is sealed in a pair of substrates, a pixel electrode placed on the substrate, a wiring electrode placed adjacent to the pixel electrode, and a wiring electrode made of the same metal as the wiring electrode and electrically connected to the pixel electrode. It has an island-shaped metal electrode connected to it, an insulating thin film covering the wiring electrode and the island-shaped metal electrode, a connection electrode connecting the wiring electrode and the island-shaped metal electrode via an insulating thin film, and A first non-linear element part is formed by the wiring electrode side part, the insulating thin film, and one side part of the connection electrode, and the other side part of the connection electrode, the insulating thin film, and the side part of the island metal electrode. A second nonlinear element portion is formed by the first
A liquid crystal display electrode characterized in that a non-linear element portion and the second non-linear element portion are connected in series.