JPH1039797A - Display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a display device permitting to achieve a switching characteristic of a two-terminal non-linear resistance element required for driving a liquid crystal with a wide operation range such as high-polymer distributed type liquid crystal, etc., by using zinc sulfide for a non-linear resistance layer of the two-terminal non-linear resistance element used as an active element. SOLUTION: A two-terminal non-linear resistance element 20 is composed of a lower electrode 13 electrically connected with a scanning electrode 12, a non-linear resistance layer 14 consisting of a material containing zinc sulfide as the main component, an insulation film 15, and an upper electrode 16 serving for a picture element electrode as well, which are sequentially laminated on a glass substrate 11. The non-linear resistance layer 14 is partly in contact with the upper electrode 16 via a contact hole 15a formed in the insulation layer 15, and is also heat-treated. Thus, it is possible to reduce an off-current value of the two-terminal non-linear resistance element 20 and also improve a current-voltage characteristic in steepness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active matrix type display device using a two-terminal nonlinear resistance element as a pixel switching element.

[0002]

2. Description of the Related Art Recently, OA of personal computers and the like has been developed.
(Office Automation) Portable devices are becoming more and more important, and in particular, cost reduction of display devices has become an important issue. In order to make such an OA device portable, a pair of substrates each having electrodes formed on a display medium having electro-optical characteristics is provided, and display is performed by applying a voltage between the electrodes. A display device having a configuration is generally employed. As the display medium, liquid crystal, electroluminescence, plasma, electrochromic, or the like is used. In particular, liquid crystal as a display medium can be displayed with low power consumption. Therefore, a liquid crystal display (Liquid Crystal Disp.
lay; LCD) is the most practical.

There are a simple matrix system and an active matrix system as a driving system of the liquid crystal display device. Among these drive systems, Super Twist Nematic
A simple matrix system using a stedNematic (STN) type liquid crystal cell or the like belongs to the category that can achieve the lowest cost.
However, in the future, as information becomes more multimedia, it is required that display devices have higher resolution, higher contrast, multi-gradation (multi-color, full-color), and a wider field of view. It is considered difficult to respond.

On the other hand, in an active matrix type liquid crystal display device, pixel electrodes provided in a matrix and scanning electrodes passing in the vicinity of the pixel electrodes are electrically connected via active elements (switching elements). Configuration. Therefore, in the active matrix system, the number of drivable scanning electrodes can be increased because the active elements are provided in each pixel. Accordingly, in the active matrix system, the number of pixels connected to the scanning electrodes also increases, and it is possible to achieve higher resolution, higher contrast, multiple gradations, and a wider field of view of the display device.

As the active element, a two-terminal non-linear element (two-terminal element) or a three-terminal non-linear element (three-terminal element) is used. In view of display quality, a three-terminal element is used. It is desirable. As a three-terminal element, at present, a thin film transistor (Thin Film T)
ransistor (TFT) is mainly used. However,
In the TFT, a photo process (after applying a photoresist,
Since the number of masks required for patterning by exposure and development is increased, the yield of non-defective products, that is, the yield is reduced, and the cost of products is increased.

On the other hand, as the two-terminal element, for example, a thin film diode (TFD) is used. This TFD requires only about three masks in the manufacturing process, so that the manufacturing process can be simplified as compared with the case of the TFT. As a result, the yield rate can be improved, that is, the yield can be improved, and the product can be manufactured at a low cost. It is possible to realize price increase. At present, for example, tantalum oxide (Ta ₂ O ₅ ) disclosed in Japanese Patent Publication No. Sho 61-32677 using a tantalum oxide (Ta ₂ O ₅ ) as a non-linear resistance layer is adopted as a TFD.
IM (Metal Insulator Metal) element and "New diode matrix liquid crystal display using non-stoichiometric SiNx" (1986, IEICE technical report EID8)
6-19, p. 13-16) TFD using non-stoichiometric silicon nitride, and the like.

A display device using the above-described two-terminal element as an active element is disclosed in, for example, JP-A-60-1.
There is a liquid crystal display device disclosed in Japanese Patent No. 70888. A transmission type liquid crystal display device having a structure similar to that of the above publication will be described below.

The above-mentioned transmission type liquid crystal display device is, for example, shown in FIG.
(A) As shown in (b), a scanning electrode 52 made of a conductive thin film and a lower electrode 53 branched from the scanning electrode 52 are formed on a glass substrate 51 which is a transparent insulating substrate.
A non-linear resistance layer 54 is formed thereon, and an insulating film 55 is patterned on the non-linear resistance layer 54 so that a contact hole 55 a is located above the lower electrode 53. The connection portion 56a of the upper electrode 56 made of a conductive material is formed so as to be in contact with the nonlinear resistance layer 54 via the contact hole 55a.
Therefore, a two-terminal element including the lower electrode 53, the nonlinear resistance layer 54, and the upper electrode 56 is formed on the glass substrate 51. Further, the pixel electrode 57 made of ITO (Indium Tin Oxide) or the like is partially overlapped with the end of the upper electrode 56 to be electrically connected to the two-terminal element, whereby the transmission type liquid crystal display device is manufactured. .

As described above, the non-linear resistance layer 54 is
5 is partially in contact with the upper electrode 56 through the contact hole 55a, so that the region of the nonlinear resistance layer 54 involved in current conduction is only the upper surface of the lower electrode 53,
As in the case where the insulating film 55 is not provided, that is, when the region of the nonlinear resistance layer 54 involved in the current conduction extends to the scan electrode 52, the problem that the leak current occurs in the step coverage portion is improved. The structure of the two-terminal element is extremely effective when the nonlinear resistance layer 54 is thinner than the lower electrode 53.

[0010]

By the way, in the above-mentioned conventional two-terminal element, the non-linear resistance layer 54 is generally made of tantalum oxide obtained by anodizing tantalum oxide used for the lower electrode. I have.

[0011] The current conduction mechanism of the above-mentioned tantalum oxide generally complies with the following equation (1), that is, Poole-Frenkel equation.

[0012]

(Equation 1)

Where n is the carrier density, μ is the mobility,
q is the carrier charge, s is the element area, d is the thickness of the nonlinear resistance layer, φ is the trap depth, k is the Boltzmann constant,
Is the absolute temperature, ε _r is the relative permittivity of the nonlinear resistance layer, and ε ₀ is the vacuum permittivity.

However, tantalum oxide has a relative dielectric constant of 2
Since it is an insulator belonging to a relatively high class of 3 to 25,
The β value that determines the switching characteristics (steepness) of the two-terminal element becomes as low as about 3. For this reason, there is a problem that it is difficult to drive a liquid crystal having a wide operating range in which the switching characteristic of the two-terminal element, that is, the steepness of the current-voltage characteristic is required.

Therefore, it has been proposed to use zinc sulfide, which has a lower dielectric constant than tantalum oxide, as the nonlinear resistance layer. Since the relative dielectric constant of zinc sulfide is 7 to 9, which is about one third of that of tantalum oxide, improvement in switching characteristics of the two-terminal element, that is, high steepness of current-voltage characteristics can be expected.

As described above, when zinc sulfide is used for the non-linear resistance layer of the two-terminal element, assuming that the current conduction mechanism of the zinc sulfide follows the Pool Frenkel equation of the above equation (1), the current-voltage characteristics are steep. The β value, which is an index of sex, becomes about 4, and the T value as used in a normal TFT-LCD is used.
It is enough to drive N liquid crystal.

By the way, liquid crystal of a nematic-cholesteric phase change type guest host (PCGH) mode, which has been recently proposed for displaying paper white with a reflection type liquid crystal display device, or a polymer, has been proposed. Dispersed liquid crystal (Polymer Dispersed Liquid Cryst
al; PDLC), for example, the liquid crystal is turned on at 5V / 1V
The operating range of the liquid crystal is wide, such as turning on / off. Therefore, in order to drive these liquid crystals, higher steepness of current-voltage characteristics (switching characteristics) is required. Therefore, if the zinc sulfide film is used as it is as the nonlinear resistance layer of the two-terminal element, the switching characteristics required for the liquid crystal having a wide operating range as described above, that is, the high steepness of the current-voltage characteristics, can be obtained. This makes it difficult to drive the liquid crystal as described above.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a vertically oriented nematic-cholesteric phase transition type using zinc sulfide for a nonlinear resistance layer of a two-terminal element. It is an object of the present invention to provide a display device capable of obtaining switching characteristics of a two-terminal element necessary for driving a liquid crystal having a wide operation range such as a liquid crystal in a guest-host mode and a polymer dispersed liquid crystal.

[0019]

Means for Solving the Problems The present inventor has found that a current value (off current value) in a low voltage region of a two-terminal element can be reduced by performing a heat treatment on the nonlinear resistance layer. That is, it has been found that when zinc sulfide is used for the nonlinear resistance layer of the two-terminal element, the switching characteristic of the two-terminal element is improved by performing heat treatment on the nonlinear resistance layer.

For example, a two-terminal element without heat treatment
FIG. 5 is a graph showing the change in the current-voltage characteristics of the two-terminal element (•) with the heat treatment depending on the heat treatment temperature. However, the heat treatment temperature is <.

As shown in FIG. 5, a two-terminal element without heat treatment has an upwardly convex curve, and has a downwardly convex curve as the heat treatment temperature is increased. That is, the higher the heat treatment temperature, the higher the sharpness of the current-voltage characteristics. This indicates that the switching characteristics of the two-terminal element are improved.

The reason why the current value (off-current value) of the two-terminal element in the low-voltage region is reduced is that, for example, defects such as vacancies and dislocations and crystal grain boundaries in the nonlinear resistance layer disappear due to heat treatment. It is conceivable that the leakage current resulting therefrom decreases.

Therefore, in the display device according to the first aspect, pixel electrodes for applying a voltage to the display medium are provided in a matrix on at least one of the pair of substrates sandwiching the display medium having electro-optical characteristics. In addition, a scanning electrode for supplying a scanning signal to each pixel electrode is formed in a stripe shape, and in the vicinity of the pixel electrode, in order to switch the pixel electrode, is electrically connected to the scanning electrode. In a display device provided with at least one or more two-terminal nonlinear resistance elements, the two-terminal nonlinear resistance element includes:
At least a lower electrode electrically connected to the scan electrode, a non-linear resistance layer, and an upper electrode electrically connected to the pixel electrode are sequentially laminated to form a laminated structure. It is made of a material containing zinc as a main component, and is characterized by being subjected to heat treatment.

According to the above structure, the nonlinear resistance layer is made of a material containing zinc sulfide as a main component having a lower dielectric constant than tantalum oxide. The steepness of the current-voltage characteristics of the used two-terminal nonlinear resistance element can be improved. Moreover, since the nonlinear resistance layer is heat-treated, the current value (off-state current value) of the two-terminal nonlinear resistance element in a low voltage region can be reduced. Therefore, the steepness of the current-voltage characteristics of the two-terminal nonlinear resistance element can be further improved.
A liquid crystal having a wide operating range, for example, a vertically aligned PCGH mode liquid crystal or PDLC can be driven. Also,
Since the steepness of the current-voltage characteristics is high and the off-state current value is small, crosstalk can be eliminated and a display device with high contrast can be provided.

According to a second aspect of the present invention, in order to solve the above-mentioned problem, in addition to the configuration of the first aspect, a display device between the lower electrode and the non-linear resistance layer or between the upper electrode and the non-linear resistance layer is provided. In any one of the embodiments, an insulating film having a contact hole for partially contacting the non-linear resistance layer and each electrode is provided.

According to the above construction, in addition to the function of the first aspect, the non-linear resistance layer and each electrode are partially contacted via the contact hole formed in the insulating film provided therebetween. Therefore, the area of the non-linear resistance layer involved in current conduction is only a part of the upper surface of the lower electrode or only a part of the lower surface of the upper electrode. , That is, at the step coverage portion, the occurrence of leakage current can be prevented.

According to a third aspect of the present invention, in order to solve the above problem, in addition to the configuration of the first or second aspect, at least one of nickel, aluminum and iron is added to zinc sulfide of the nonlinear resistance layer. It is characterized by being doped.

According to the above construction, in addition to the function of claim 1 or 2, nickel, aluminum,
By doping at least one of iron, the switching characteristics of a two-terminal nonlinear resistance element using this nonlinear resistance layer can be further improved.

According to a fourth aspect of the present invention, in order to solve the above problem, in addition to the configuration of the first, second or third aspect, the heat treatment temperature of the zinc sulfide is set in a range of 200 ° C. to 300 ° C. It is characterized by having.

According to the above construction, in addition to the function of the first, second or third aspect, the zinc sulfide of the non-linear resistance layer can be removed by 200%.
By performing the heat treatment at a temperature in the range of from about 300 ° C. to about 300 ° C., the steepness of the current-voltage characteristics can be improved without lowering the dielectric breakdown voltage and the ON current value of the nonlinear resistance layer. That is, if the heat treatment temperature is lower than 200 ° C., the steepness of the current-voltage characteristics cannot be sufficiently improved, and if the heat treatment temperature is higher than 300 ° C., the dielectric breakdown voltage and the ON current value of the nonlinear resistance layer are reduced. This causes a problem of lowering.

[0031]

BEST MODE FOR CARRYING OUT THE INVENTION

[Embodiment 1] FIG. 1 shows an embodiment of the present invention.
2 and FIG. 5 are as follows. In this embodiment, a liquid crystal display device using liquid crystal as a display medium will be described. Although a plurality of pixel electrodes are originally arranged in a matrix, in this embodiment and other embodiments, a case where the number of pixel electrodes is 2 will be described for convenience of description.

As the liquid crystal display device according to the present embodiment, a reflection type liquid crystal display device is employed. As shown in FIG. 2, the liquid crystal display device includes a liquid crystal 25 as a display medium having electro-optical characteristics, and a pair of substrates 21 and 22 opposed to each other with the liquid crystal 25 interposed therebetween. However, in this description, the number of pixels is two.

On one substrate 21, upper electrodes 16 also serving as pixel electrodes, a two-terminal nonlinear resistance element 20 for switching the upper electrode 16, and a scanning signal are supplied to the two-terminal nonlinear resistance element 20. Scanning electrode 12 for
Are provided. Hereinafter, the substrate 21 is referred to as an element-side substrate.

On the other substrate 22, the device-side substrate 21
The ITO (Indium Tin Ox) is perpendicular to the scanning electrode 12 so as to face the upper electrodes 16 provided on the substrate.
ide) Data electrodes 23 made of a film are formed. Hereinafter, the substrate 22 is referred to as a counter substrate.

Further, alignment films 24 for controlling the alignment state of the liquid crystal 25 are provided on the liquid crystal 25 side surfaces of the element side substrate 21 and the opposing side substrate 22, respectively.

The element-side substrate 21 is shown in FIGS.
As shown in FIG. 1, a scanning electrode 12 made of Ta (tantalum) and a lower electrode 13 branched from the scanning electrode 12 are formed on a glass substrate 11 so as to cover the scanning electrode 12 and the lower electrode 13. It has a structure in which a non-linear resistance layer 14 mainly composed of zinc sulfide, an insulating film 15 made of a photosensitive resin, and an upper electrode 16 made of aluminum also serving as a pixel electrode are sequentially laminated. For convenience of explanation,
In FIG. 1A, the non-linear resistance layer 14 and the insulating film 15 are omitted.

As shown in FIG. 1B, a contact hole 15a penetrating between the nonlinear resistance layer 14 and the upper electrode 16 is formed in the insulating film 15, and through the contact hole 15a. Connection part 16 of upper electrode 16
a is in partial contact with the nonlinear resistance layer 14.

As described above, since the non-linear resistance layer 14 and the upper electrode 16 are partially in contact with each other via the contact hole 15a formed in the insulating film 15 provided therebetween, the non-linear resistance layer 14 and the upper electrode 16 are involved in current conduction. The region of the non-linear resistance layer 14 is only a part of the upper surface of the lower electrode 13, and the stepped portion between the lower electrode 13 and the non-linear resistance layer 14, that is, the step coverage portion is compared with the case where the insulating film 15 is not provided. Generation of a leak current can be prevented.

As described above, the upper electrode 16, the nonlinear resistance layer 14, and the lower electrode 13 constitute a two-terminal nonlinear resistance element 20 which is a switching element.

Here, the manufacturing process of the liquid crystal display device having the above structure will be described below.

First, the procedure for forming the element-side substrate 21 will be described. First, a conductive thin film made of Ta (tantalum) is formed on a glass substrate 11 by sputtering or the like, and is patterned into a predetermined shape to form a scanning electrode 12.
And a lower electrode 13 branched from the scanning electrode 12. Here, Corning's # 7059 borosilicate glass is used as the glass substrate 11, and a 200 nm-thick tantalum deposited on the glass substrate 11 is used as the scanning electrode 12 and the lower electrode 13. .

Next, zinc sulfide, which is a main component of the nonlinear resistance layer 14, is formed by RF sputtering so as to cover the scanning electrode 12 and the lower electrode 13 on the glass substrate 11. Here, in the above RF sputtering, zinc sulfide was formed into a film by using zinc sulfide as a target and argon as a sputtering gas. The thickness of this zinc sulfide is 120
nm.

When a zinc sulfide film is formed, the composition of zinc sulfide (atomic ratio of zinc and sulfur) is controlled by using a rare gas containing hydrogen sulfide as a sputtering gas, or a nickel , Iron, aluminum, and the like, that is, doping impurities such as nickel, aluminum, and iron into zinc sulfide as a carrier source, thereby improving the switching characteristics of the formed two-terminal nonlinear resistance element 20. it can.

Next, the formed nonlinear resistance layer 14 is patterned to remove zinc sulfide at a terminal portion for connecting to a driving driver (not shown).

Next, the patterned non-linear resistance layer 1
4 is subjected to a heat treatment. This heat treatment is performed in a vacuum chamber of a heat treatment furnace (not shown). As described above, the heat treatment is usually performed in a vacuum.However, in order to prevent the escape of sulfur atoms of zinc sulfide during the heat treatment, the heat treatment may be performed in a sulfur atmosphere by introducing a hydrogen sulfide gas or a sulfur gas into the chamber. well,
In order to improve element characteristics, an inert gas (such as Ar), a nitrogen gas, or an oxygen gas may be introduced into the chamber. Here, the temperature of the heat treatment for the nonlinear resistance layer 14, that is, for the zinc sulfide, was set to 250 ° C.

The reason for setting the temperature of the heat treatment to 250 ° C. will be described below. In general, the heat treatment temperature for the nonlinear resistance layer 14 and the current-voltage characteristics of the two-terminal nonlinear resistance element 20 are as shown in the graph of FIG. However, the curve shows no heat treatment, the straight line and the curve show heat treatment,
The heat treatment temperature is <.

FIG. 5 shows that the steepness of the current-voltage characteristics is higher in the case where the heat treatment is performed than in the case where the heat treatment is not performed. It can also be seen that the higher the heat treatment temperature, the higher the steepness of the current-voltage characteristics. Therefore, it can be seen that, by using zinc sulfide for the nonlinear resistance layer 14, the sharpness increases as the heat treatment temperature for the zinc sulfide increases. However, if the heat treatment temperature becomes high, there is a possibility that the withstand voltage of the two-terminal nonlinear resistance element 20 is reduced. Therefore, by setting the heat treatment temperature to 250 ° C. as described above, the two-terminal nonlinear resistance element 20
The switching characteristics are optimized without lowering the breakdown voltage.

The heat treatment temperature (250 ° C.) is not absolute, but changes depending on the concentration of impurities added to zinc sulfide which is a main component of the nonlinear resistance layer 14. About 200 ° C ~
It is desirable to set the temperature in the range of 300 ° C. For example, if the heat treatment temperature is lower than 200 ° C., the steepness of the current-voltage characteristics of the nonlinear resistance layer 14 cannot be sufficiently improved, and if the heat treatment temperature is higher than 300 ° C., the nonlinear resistance layer 14 There is a problem that the dielectric breakdown voltage and the ON current value are reduced.

Next, an insulating film 15 is formed so as to cover the nonlinear resistance layer 14. Here, the insulating film 15 was formed to a thickness of about 300 nm using an acrylic photosensitive resin. That is, the insulating film 15 is formed by spin-coating a photosensitive resin on the non-linear resistance layer 14, and then performing exposure and development so that the contact hole 15 a comes to a position corresponding to the upper part of the lower electrode 13.

If a photosensitive resin is used for the insulating film 15 as described above, the etching step and the resist stripping step can be omitted in order to perform patterning so as to have the contact hole 15a, so that the manufacturing process can be simplified. The material of the insulating film 15 is not limited to the photosensitive resin described above, but may be any material that does not erode the nonlinear resistance layer 14 during patterning.

Finally, the upper electrode 16 is formed on the insulating film 15. Here, the upper electrode 16 is formed by depositing aluminum on the insulating film 15 by sputtering, and after a photo process,
It is formed by etching aluminum using phosphoric acid or the like as an etchant. In addition, the upper electrode 16 is provided in FIG.
As shown in (b), the contact hole 1 in the insulating film 15 is formed.
The connection portion 16a is formed so as to partially contact the non-linear resistance layer 14 via 5a.

As the material for the upper electrode 16, besides aluminum, molybdenum, titanium, silver and the like can be used. In the case of a metal having a low surface reflectance such as molybdenum,
It is desirable to improve the reflectance by stacking one layer of aluminum.

Next, a procedure for forming the opposing substrate 22 will be described. The opposing substrate 22 has striped data electrodes 23 formed on an insulating substrate made of glass or the like. Here, Corning's # 705 glass substrate was used.
Using a 9-borosilicate glass, an about 200 nm thick ITO film is formed on this glass substrate by sputtering.
After a photo step, the ITO film is etched using hydrobromic acid as an etchant, and the photoresist is stripped to obtain a sprite-like data electrode 23. No. 22 was formed.

Thereafter, on the element and electrode forming surface side of the element-side substrate 21 and the counter substrate 22 prepared as described above,
Each of the alignment films 24 is applied.

Next, seal printing is performed at a predetermined position on the surface of the substrates 21 and 22 on which the alignment film 24 is formed, so that the surface on which the alignment film 24 is formed is located inside. 22 are laminated. After that, both substrates 21
A liquid crystal 25 is injected between 22 and the injection hole is sealed to complete a reflection type liquid crystal display device. Here, a vertical alignment film is used as the alignment film 24, and a nematic liquid crystal 25 is used as the liquid crystal 25.
A cholesteric phase transition type host-guest (PCGH) mode liquid crystal was used. Thus, the reflective liquid crystal display device having the above-described configuration performs paper white display.

According to the above configuration, the heat-treated zinc sulfide, which is the main component of the nonlinear resistance layer 14, has a smaller relative dielectric constant than tantalum oxide or the like conventionally used as the nonlinear resistance layer. It has been found that the steepness of the current-voltage characteristics of the two-terminal nonlinear resistance element 20 is high and the off-current value is low. Therefore, even a liquid crystal having a wide operation range such as ON / OFF at 5 V / 1 V, such as the above-described PCGH mode liquid crystal, can be driven sufficiently. Further, by using heat-treated zinc sulfide as the nonlinear resistance layer 14, the switching characteristics of the two-terminal nonlinear resistance element 20 are improved, so that a liquid crystal display device with high contrast without crosstalk can be provided. It becomes possible.

In the present embodiment, a reflection type liquid crystal display device has been described as a liquid crystal display device. In the second embodiment, a case where the present invention is applied to a transmission type liquid crystal display device will be described.

[Second Embodiment] Another embodiment of the present invention will be described below with reference to FIGS. 3, 4 and 5. In this embodiment, a transmissive liquid crystal display device is employed as the liquid crystal display device.

The liquid crystal display device according to the present embodiment has a structure shown in FIG.
As shown in FIG. 7, the liquid crystal display device has a liquid crystal 44 as a display medium having electro-optical characteristics, and a pair of substrates 41 and 42 disposed to face each other with the liquid crystal 44 interposed therebetween. However, in this explanation,
Assume that the number of pixels is two.

On one substrate 41, pixel electrodes 37 and 37 formed in a matrix, a two-terminal nonlinear resistance element 30 for switching the pixel electrodes 37, and an upper electrode 36 And a scanning electrode 32 connected through the same. Hereinafter, the substrate 4
1 is called an element side substrate.

On the other substrate 42, the element-side substrate 41
The ITO (Indium Tin Ox) is perpendicular to the scanning electrode 32 so as to face the pixel electrodes 37 provided on the substrate.
ide) Data electrodes 43 made of a film are formed. Hereinafter, the substrate 42 is referred to as a counter substrate.

The element-side substrate 41 is shown in FIGS.
As shown in FIG. 2, a scanning electrode 32 made of Ta (tantalum) and a lower electrode 33 branched from the scanning electrode 32 are formed on a glass substrate 31 so as to cover the scanning electrode 32 and the lower electrode 33. It has a structure in which a nonlinear resistance layer 34 mainly composed of zinc sulfide, an insulating film 35 made of a photosensitive resin, and an upper electrode 36 made of molybdenum are sequentially laminated. A pixel electrode 37 made of an ITO film is formed on the insulating film 35 so as to partially overlap the upper electrode 36. For convenience of explanation, FIG.
The non-linear resistance layer 34 and the insulating film 35 are omitted.

As shown in FIG. 3B, a contact hole 35a penetrating between the non-linear resistance layer 34 and the upper electrode 36 is formed in the insulating film 35, and the contact hole 35a is formed through the contact hole 35a. Connection part 36 of upper electrode 36
a is in partial contact with the nonlinear resistance layer 34.

As described above, since the non-linear resistance layer 34 and the upper electrode 36 are partially in contact with each other via the contact hole 35a formed in the insulating film 35 provided therebetween, the non-linear resistance layer 34 and the upper electrode 36 are involved in current conduction. Since the region of the non-linear resistance layer 34 is only a part of the upper surface of the lower electrode 33, the lower electrode 33 and the non-linear resistance layer 34 are compared with the case where the insulating film 35 is not provided.
, That is, at the step coverage portion, the occurrence of leakage current can be prevented.

As described above, the upper electrode 36, the nonlinear resistance layer 34, and the lower electrode 33 constitute the two-terminal nonlinear resistance element 30 as a switching element.

Here, the manufacturing process of the liquid crystal display device having the above structure will be described below.

First, a procedure for forming the element-side substrate 41 will be described. First, a conductive thin film made of Ta (tantalum) is formed on a glass substrate 31 by sputtering or the like, and is patterned into a predetermined shape to form a scanning electrode 32.
Then, a lower electrode 33 branched from the scanning electrode 32 is formed. Here, as the glass substrate 31, a # 7059 borosilicate glass manufactured by Corning Incorporated is used.
On 1, as the scanning electrode 32 and the lower electrode 33, a 200 nm thick tantalum is used.

Next, zinc sulfide, which is the main component of the nonlinear resistance layer 34, is formed by radio frequency (RF) sputtering so as to cover the scanning electrode 32 and the lower electrode 33 on the glass substrate 31. Here, in the RF sputtering, zinc sulfide was formed using zinc sulfide as a target and argon as a sputtering gas.

The thickness of the zinc sulfide was about 120 nm.

When a zinc sulfide film is formed, the composition ratio of zinc sulfide (atomic ratio of zinc to sulfur) is controlled by using a rare gas containing hydrogen sulfide as a sputtering gas, or nickel is previously contained in a target. By mixing elements such as iron, aluminum and the like, the switching characteristics of the formed two-terminal nonlinear resistance element 30 can be improved.

Next, the formed nonlinear resistance layer 34 is patterned to remove zinc sulfide at a terminal portion for connecting to a driving driver (not shown).

Next, the patterned non-linear resistance layer 3
4 is subjected to a heat treatment. This heat treatment is performed in a vacuum chamber of a heat treatment furnace (not shown). As described above, the heat treatment is usually performed in a vacuum.However, in order to prevent the escape of sulfur atoms of zinc sulfide during the heat treatment, the heat treatment may be performed in a sulfur atmosphere by introducing a hydrogen sulfide gas or a sulfur gas into the chamber. well,
In order to improve element characteristics, an inert gas (such as Ar), a nitrogen gas, or an oxygen gas may be introduced into the chamber. Here, the temperature of the heat treatment for the nonlinear resistance layer 34, that is, for the zinc sulfide, was set to 250 ° C.

The reason why the temperature of the heat treatment is set to 250 ° C. is the same as that of the first embodiment, and therefore the description is omitted here.

Next, an insulating film 35 is formed so as to cover the nonlinear resistance layer 34. Here, the insulating film 35 was formed to a thickness of about 300 nm using an acrylic photosensitive resin. That is, the insulating film 35 is formed by spin-coating a photosensitive resin on the non-linear resistance layer 34, and then performing exposure and development so that the contact hole 35a comes to a position corresponding to the upper part of the lower electrode 33.

By using the photosensitive resin for the insulating film 35 as described above, the etching step and the resist peeling step can be omitted in order to perform patterning so as to have the contact hole 35a, so that the manufacturing process can be simplified. . Note that the material of the insulating film 35 is not limited to the above-described photosensitive resin, and may be any material that does not erode the nonlinear resistance layer 34 during patterning.

Next, an upper electrode 36 is formed on the insulating film 35 by molybdenum. Here, the upper electrode 36 is formed by sputtering molybdenum on the insulating film 35 (with a film thickness of about 15
0 nm), and after the photo step, molybdenum is etched by using a mixed solution of phosphoric acid, nitric acid, and acetic acid as an etching solution to cover the contact holes 35a of the insulating film 35 in an island shape. Thus, the upper electrode 36 is formed such that the connection portion 36a is electrically connected to the nonlinear resistance layer 34 via the contact hole 35a of the insulating film 35, as shown in FIG.

Finally, a pixel electrode 37 made of ITO is formed on the insulating film 35 so as to partially overlap the upper electrode 36. Here, the pixel electrode 37 is formed by depositing ITO by sputtering, passing through a photo process, and then etching the ITO film so as to partially overlap the upper electrode 36 using hydrobromic acid or the like as an etchant. It is formed by patterning.

Next, a procedure for forming the opposing substrate 42 will be described. The opposing substrate 42 has a stripe-shaped data electrode 43 formed on an insulating substrate made of glass or the like. Here, Corning's # 705 glass substrate was used.
Using a 9-borosilicate glass, an about 200 nm thick ITO film is formed on this glass substrate by sputtering.
After a photo step, the ITO film is etched using hydrobromic acid as an etchant, and the photoresist is stripped to obtain a sprite-like data electrode 43. The opposing substrate as shown in FIG. 42 were formed.

In the present embodiment, the liquid crystal 44 is a polymer-dispersed liquid crystal (PDL) capable of bright display without a polarizing plate.
C) is used. As a result, the two substrates 41 and 42 created
Therefore, it is not necessary to form an alignment film, and rubbing is not required.

Next, seal printing is performed on the surfaces of the substrates 41 and 42 on which thin films such as elements and electrodes are formed, and the substrates 41 and 42 are formed such that the surfaces on which the thin films are formed are inside.
Is bonded. After that, the liquid crystal 44 is injected between the two substrates 41 and 42, the injection hole is sealed, the monomer is polymerized by irradiation of ultraviolet rays, and the liquid crystal droplets are formed in the polymer, so that the transmission type PDLC is formed. Complete the display device.

According to the above-described structure, the heat-treated zinc sulfide, which is the main component of the nonlinear resistance layer 34, has a smaller relative dielectric constant than tantalum oxide or the like conventionally used as the nonlinear resistance layer. It has been found that the steepness of the current-voltage characteristic of the terminal nonlinear resistance element 30 is high and the off-current value is low. Therefore, even a liquid crystal having a wide operating range, such as the above-mentioned PDCL, which is turned on / off at 5 V / 1 V, for example, can be driven sufficiently. Further, by using the heat-treated zinc sulfide as the nonlinear resistance layer 34, the switching characteristics of the two-terminal nonlinear resistance element 30 are improved, so that a crosstalk does not occur and a liquid crystal display device with high contrast can be provided. It becomes possible.

In the first and second embodiments, the heat treatment for the non-linear resistance layers 14 and 34, that is, the heat treatment for zinc sulfide is performed immediately after the non-linear resistance layers are formed. The timing of the heat treatment is not particularly limited, and may be performed, for example, after the upper electrodes 16 and 36 are formed.

In Embodiments 1 and 2, 2
As a structure of the terminal nonlinear resistance elements 20 and 30, an insulating film 1 is interposed between the nonlinear resistance layers 14 and 34 and the upper electrodes 16 and 36.
5 and 35 are formed, but the invention is not limited to this. For example, an insulating film is provided between the non-linear resistance layer and the lower electrode, and the non-linear resistance layer and the lower electrode are partially connected via a contact hole. May be configured to come into contact with.

Further, in each embodiment, a liquid crystal display device using liquid crystal as a display medium has been described as a display device. However, the present invention is not limited to this, and any display medium having electro-optical characteristics may be used. The present invention may be applied to a display device using electroluminescence, plasma, electrochromic, or the like.

[0085]

As described above, according to the display device of the first aspect of the present invention, a pixel for applying a voltage to at least one of a pair of substrates sandwiching a display medium having electro-optical characteristics is provided. The electrodes are provided in a matrix, and a scanning electrode for supplying a scanning signal to each pixel electrode is formed in a stripe shape. In the vicinity of the pixel electrode, the scanning electrode is used to switch the pixel electrode. In the display device provided with at least one or more two-terminal nonlinear resistance elements electrically connected to the scan electrode, the two-terminal nonlinear resistance element includes at least a lower electrode electrically connected to the scan electrode and a nonlinear resistance layer. And an upper electrode electrically connected to the pixel electrode to form a laminated structure sequentially laminated, the nonlinear resistance layer is made of a material containing zinc sulfide as a main component, Process is the configuration that has been subjected.

Therefore, since the nonlinear resistance layer is made of a material mainly composed of zinc sulfide having a lower dielectric constant than that of tantalum oxide, a two-terminal using the nonlinear resistance layer mainly composed of zinc sulfide is used. The steepness of the current-voltage characteristics of the nonlinear resistance element can be improved. Moreover, since the nonlinear resistance layer is heat-treated, the current value (off-state current value) of the two-terminal nonlinear resistance element in a low voltage region can be reduced.
Therefore, the steepness of the current-voltage characteristics of the two-terminal nonlinear resistance element can be further improved, so that a liquid crystal having a wide operating range, for example, a vertically aligned PCGH mode liquid crystal,
The PDLC can be driven. Further, since the steepness of the current-voltage characteristics is high and the off-state current value is small, there is an effect that a crosstalk is eliminated and a display device with high contrast can be provided.

As described above, according to the display device of the second aspect of the present invention, in addition to the configuration of the first aspect, any one of a portion between the lower electrode and the nonlinear resistance layer or a portion between the upper electrode and the nonlinear resistance layer is provided. On the other hand, an insulating film having a contact hole for partially contacting the nonlinear resistance layer and each electrode is provided.

Therefore, in addition to the effect of the first aspect, the non-linear resistance layer and each electrode are partially contacted via the contact hole formed in the insulating film provided therebetween. Therefore, the region of the nonlinear resistance layer involved in current conduction is only a part of the upper surface of the lower electrode or only a part of the lower surface of the upper electrode. , That is, a step current, that is, a step coverage portion, can be prevented from being generated.

According to a third aspect of the present invention, as described above, in addition to the configuration of the first or second aspect, at least one of nickel, aluminum, and iron is doped into zinc sulfide of the nonlinear resistance layer. Configuration.

Therefore, in addition to the effect of the constitution of claim 1 or 2, nickel, aluminum,
By doping at least one of iron, there is an effect that the switching characteristics of a two-terminal nonlinear resistance element using this nonlinear resistance layer can be further improved.

As described above, in the display device according to the fourth aspect of the present invention, in addition to the configuration of the first, second or third aspect, the heat treatment temperature for the nonlinear resistance layer 14 is set in the range of 200 ° C. to 300 ° C. Configuration.

Therefore, in addition to the effect of the first, second or third aspect, zinc sulfide in the non-linear resistance layer is reduced by 200%.
By performing the heat treatment at a temperature in the range of ° C to 300 ° C, the steepness of the current-voltage characteristics can be improved without lowering the dielectric breakdown voltage and the ON current value of the nonlinear resistance layer.

[Brief description of the drawings]

FIGS. 1A and 1B schematically show the vicinity of a pixel electrode and a switching element of a liquid crystal display device using liquid crystal as a display medium of the display device of the present invention, wherein FIG. 1A is a plan view, and FIG. FIG.

FIG. 2 is a schematic perspective view of two pixels of a liquid crystal display device using liquid crystal as a display medium of the display device of the present invention.

3A and 3B schematically show the vicinity of a pixel electrode and a switching element of another liquid crystal display device using liquid crystal as a display medium of the display device of the present invention, wherein FIG. 3A is a plan view and FIG.・
FIG. 3 is a cross-sectional view taken along line B.

FIG. 4 is a schematic configuration perspective view of two pixels of another liquid crystal display device using liquid crystal as a display medium of the display device of the present invention.

FIG. 5 is a graph showing a change in a current-voltage characteristic depending on a heat treatment temperature of a nonlinear resistance layer.

6A and 6B schematically show the vicinity of a pixel electrode and a switching element of a conventional liquid crystal display device, wherein FIG. 6A is a plan view, and FIG. 6B is a cross-sectional view taken along line CC in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Glass substrate 12 Scan electrode 13 Lower electrode 14 Non-linear resistance layer 15 Insulating film 15a Contact hole 16 Upper electrode (pixel electrode) 20 2-terminal nonlinear resistance element 30 2-terminal nonlinear resistance element 31 Glass substrate 32 Scan electrode 33 Lower electrode 34 Non-linear resistance Layer 35 Insulating film 35a Contact hole 36 Upper electrode 37 Pixel electrode

Claims (4)

[Claims] A pixel electrode for applying a voltage to the display medium is provided on at least one of a pair of substrates sandwiching a display medium having electro-optical characteristics in a matrix, and a scanning signal is applied to each pixel electrode. Are formed in a stripe shape, and a two-terminal nonlinear resistance element electrically connected to the scan electrode is provided near the pixel electrode for switching the pixel electrode. In one or more display devices, the two-terminal non-linear resistance element includes at least a lower electrode electrically connected to the scan electrode, a non-linear resistance layer, and an upper electrode electrically connected to the pixel electrode. Wherein the non-linear resistance layer is made of a material containing zinc sulfide as a main component and is heat-treated. . 2. A contact hole for partially contacting the non-linear resistance layer and each electrode is provided between one of the lower electrode and the non-linear resistance layer or between the upper electrode and the non-linear resistance layer. The display device according to claim 1, further comprising an insulating film. 3. The display device according to claim 1, wherein zinc sulfide of said non-linear resistance layer is doped with at least one of nickel, aluminum and iron. 4. A heat treatment temperature for the nonlinear resistance layer,
The display device according to claim 1, wherein the temperature is set in a range of 200 ° C. to 300 ° C. 5.