JPS6322443B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a voltage nonlinear resistor suitable for a display switching element of a liquid crystal display element. Liquid crystal display elements sandwich liquid crystal between two opposing electrodes on a glass substrate, and use the unique behavior of liquid crystal molecules when a voltage is applied between both electrodes to transmit or reflect light. It is an element that changes the situation and displays characters or images. A pair of opposing electrodes and the liquid crystal part sandwiched between them are called picture elements. Increasing the number of picture elements increases the number of characters that can be displayed. However, in a general matrix driving system, as the number of picture elements increases, the influence of crosstalk between picture elements increases, and the contrast deteriorates. As a method to improve this, a method is known in which a switching element is connected in series to each picture element. In order to increase the resolution of characters, it is necessary to reduce the size of each picture element and form one display panel with thousands to tens of thousands of picture elements. Therefore, the switching elements connected to these picture elements are small elements (specifically 200 microns x 200 microns or smaller) and are formed all at once on a single substrate like an integrated circuit. Something like this is desirable. As such a switching array, MOSFET
Arrays or metal oxide varistor arrays are known. A MOSFET array is formed by integrating NOSFETs on a single Si substrate using integrated circuit technology. However, with current manufacturing technology, the yield is low, and tens of thousands of pieces are produced on a single board.
When you try to form MOSFETs, you will end up with a percentage of them that do not work properly. If such a switching array is used, there will be a portion of the display panel that does not function properly, making it impossible to provide a clear display as a display element. On the other hand, varistor arrays have zinc oxide as the main component, and
A sintered body made by adding Bi ₂ O ₃ , Co ₂ C ₃ , MnO ₂ , Sb ₂ O _{3 ,} etc. and sintering it at a high temperature. One side of the sintered body is polished to a mirror finish, and an electrode is provided on it by vacuum evaporation. It is.
A typical structure thereof is shown in FIG. In FIG. 1, 1 is a metal oxide varistor substrate mainly composed of ZnO, 2 and 3 are electrodes provided on the substrate, 4 is a lead electrode for applying voltage to the electrode 3 from the outside,
5 is a glass substrate, 6 is a transparent electrode provided on the glass substrate 5 to face the electrode 2, and 7 is a lead electrode for applying a voltage to the electrode 6 from the outside.
In reality, a number of such components are formed. Next, the operation of this device will be explained. FIG. 2 shows a circuit configuration in which there are two components shown in FIG. 1. 1 to 7 in FIG. 2 indicate the same components as those with the same symbols in FIG. In other words, 1 is a metal oxide varistor, 2, 3, and 6 are parts corresponding to the electrodes, and 4 is a lead electrode on the metal oxide varistor side.
7 and 7' correspond to lead electrodes on the glass substrate side, and 8 is a liquid crystal. Now, in order to display an image, in Fig. 1, by making the voltage applied between electrodes 2-6 higher than the on-voltage of the liquid crystal,
This is done by changing the alignment state of the liquid crystal molecules between them, and changing the state of light that passes through the glass 5, reaches the electrode 2 and the substrate 1, is reflected there, and passes through the glass again. On the other hand, metal oxide varistors have the property that almost no current flows until a certain voltage, and the current suddenly starts flowing above a certain voltage (rise voltage). Therefore, in order to turn on _the upper picture element _in FIG. All you have to do is apply a voltage of . To be more specific, for example, if a voltage of (V _T +V _ON )/2 is applied to electrode 4 and a voltage of (V _T +V _ON )/2 is applied to electrode 7, then the rising voltage of the metal oxide varistor becomes (V _T +V ON )/2. _ON )/2 or more (in other words, V _T >V _ON ), it is possible to turn on only the upper picture element without turning on the lower picture element. Next, to turn on the lower picture element, apply a voltage of (V _T +V _ON )/2 to 4 and 7'. With this configuration, crosstalk between each picture element can be eliminated and images can be displayed with good contrast. By the way, the varistor action in the configuration shown in FIG. 1 utilizes the characteristics of only the very surface of the substrate between the electrodes 2 and 3. The specific structure of that part is shown in FIG. In FIG. 3, the portion 1 is the substrate portion of the metal oxide varistor. 2,3
14 is an electrode provided on the substrate, 14 is a ZnO particle which is a main component of the metal oxide varistor, and 15 is a high-resistance grain boundary portion exhibiting non-ohmic properties. 16 is an impurity attached to the surface. The particle size of the ZnO particles 14 is usually around several μm. As shown in this figure, the surface is extremely irregular with defects and impurities caused by polishing. Now, when a voltage is applied between electrodes 2 and 3, current flows only through the shortest portion between electrodes 2 and 3. Furthermore, since the impurities 16 generally contain alkali metals, the resistance may be low and flow may occur through the impurities. Therefore, the current path follows a path as shown by arrow 17. As can be seen from this, a varistor having such a structure is susceptible to changes depending on the state of surface defects and impurities, causing variations in initial characteristics, and also tends to change characteristics during use. Therefore, it is not sufficient to be used as a switching array of tens of thousands of picture elements. In view of the above points, the present invention provides a varistor array with less variation in initial characteristics and excellent long-term reliability. FIG. 4 shows the element structure of the present invention. 1 is a metal oxide varistor substrate part, 2 and 3 are through-type electrodes formed on the surface of a through hole provided in the substrate 1, 2',
3' is a lead electrode, 14 is a ZnO particle, 15 is a grain boundary,
16 is an impurity attached to the surface. Although the shape of the through-hole in which the electrodes 2 and 3 are provided may be circular, a rectangular shape is preferable when a large amount of current is to flow. When a voltage is applied between electrodes 2 and 3 in this configuration, the current flows in a dispersed manner because the cross-sectional area of the shortest distance between electrodes 2 and 3 is wide, and as shown by arrow 17, the current mainly flows through burnout. It begins to flow inside the junction board. Therefore, compared to the structure shown in FIG. 3, it is possible to obtain an element with less variation in initial characteristics and excellent stability. Table 1 shows the distance between electrodes 2 and 3.
This shows the difference in the variation in the rise voltage (voltage V when 10 μA flows is assumed to be ₁₀ μA) when the diameter is 200 μm.
For comparison, the characteristics when using a conventional electrode structure are also shown.

【table】

[Table] Each table shows the variation in rising voltage when 100 pairs of electrodes are provided on the same substrate. Table 2 shows the rate of change in V ₁₀ μA when a current of 10 μA was continuously applied for 100 hours at 70°C. The element having the structure of the present invention is superior in all characteristics.

[Table] The device having the structure of the present invention was prepared as follows. ZnO (97 mol%), Bi ₂ O ₃ (0.5 mol %), Co ₂ O ₃
(0.5 mol%), MnO ₂ (0.5 mol%), Sb ₂ O ₃ (1.0 mol%), and Cr ₂ O ₃ (0.5 mol%) were mixed, fired into a disk shape, and heated at 1200°C. It was baked for 2 hours. Next, after thoroughly polishing the flat part of this sintered body to a mirror surface, it is washed with a solvent, a resist is applied, a penetration part is created at a predetermined location using a laser beam, and an electrode is formed on the surface of the penetration part by sputtering. Then, the resist was removed once. Next, apply resist to the entire surface again,
Only the portion of the electrode to be formed on the surface was exposed to light using a mask, then the exposed portion was developed and removed, and the electrode on the surface was formed by vacuum evaporation to obtain an element having the structure shown in FIG. Although a metal oxide varistor with a specific composition was used in this example, the effect of the present invention is derived from its electrode structure, and it is clear that the same effect can be achieved even if the composition is different. be. Further, in this embodiment, a specific method was used to realize a predetermined electrode structure, but it is clear that other methods may be used. Further, there may be a void inside the through-hole, or the entire through-hole may be filled with the electrode material. However, if there is a gap, a plate to prevent liquid crystal leakage will be required on the back side when actually assembling the panel. Next, the structure and operation of a varistor array for a liquid crystal display element using the voltage non-linear element of this structure will be explained. FIG. 5 shows an example of the structure of the element of the present invention. In the figure, 51 is a metal oxide varistor substrate, 52 is a liquid crystal driving electrode, and 53 is a through-type electrode, which is electrically connected to the surface electrode 2 by a lead electrode 54. Reference numeral 55 designates another penetrating electrode that pairs with the electrode 53, and is connected to a scanning lead electrode through a lead electrode 56. 57 is a glass substrate, 58
Reference numeral 59 indicates an opposite transparent surface electrode having the same shape as the electrode 52 provided on the glass substrate, and 59 indicates a lead electrode for applying a voltage to the electrode 58 from the outside. Next, FIG. 6 shows a top view of various electrode shapes provided on the metal oxide varistor substrate. Numbers are assigned corresponding to FIG. That is, 52 is a surface electrode, 5
3 and 55 are a pair of through electrodes, and 54, 5
6 are lead electrodes, respectively. With such a structure, if voltage is applied between electrodes 56-59 in FIG. 5, voltage can be applied between electrodes 52-58 via the varistor formed between electrodes 53-55, and the electrodes The liquid crystal 60 sandwiched between 52 and 58 can be operated in a switching manner. Large surface electrodes are used, and through-type electrodes 53, 55 are used.
By making small, blank spaces around the electrodes 53 and 55 that cannot be displayed can be made to have virtually no effect on characters or images. Next, FIG. 7 shows an example of configuring a large number of picture elements. In the figure, the numbers correspond to those in FIG.
55″ and 55 are pairs of through electrodes,
55, 55' are connected to the scanning lead wire 11, 55'', 5
5 is connected to a scanning lead wire 62. In this case, the distance between each pair of through electrodes 53 and 55 is 53'-55'53''-55'', 53-55
The distance between them is the distance between other electrodes, for example 53-
53', between 53-52', 52-52', 52-5
It is arranged so that the distance is shorter than the distance between electrodes that are not electrically connected with a conductor, such as between 3' and 52 and 55''. With this configuration, it is possible to prevent unintentional formation between electrodes. A large number of picture elements can be switched without causing crosstalk due to the varistor action.In addition, in the case of this configuration, the scanning electrodes 61 and 62 can be formed on opposite sides of the substrate, so that the degree of integration can be increased. As described in detail above, the present invention makes it possible to maintain stable voltage nonlinearity inside the sintered body while using electrodes formed on the same substrate surface by devising the electrode structure. It has been made available for use, and is particularly useful as a varistor array for liquid crystal display elements.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view showing the basic structure of a liquid crystal display element using a varistor, Figure 2 is a wiring diagram showing the circuit configuration of a liquid crystal display element using a varistor, and Figure 3 is an explanatory diagram showing a conventional electrode configuration. , FIG. 4 is an explanatory diagram showing the electrode configuration of the voltage non-linear resistor of the present invention, FIG. 5 is a sectional view showing the structure of the voltage non-linear resistor, and FIG.
7 are plan views showing the electrode structure of the same element. 51... Zinc oxide varistor substrate, 52... Surface electrode for driving liquid crystal, 53, 55... Penetration electrode, 5
4, 56...Lead electrode, 57...Glass substrate,
58... Transparent surface electrode, 59... Lead electrode, 60
……liquid crystal.

Claims (1)

[Claims] 1. A metal oxide varistor substrate having a property that the resistance value decreases as the voltage increases, has a plurality of pairs of through parts, and has an electrode on the inner surface of the through part, one of the through electrodes of each pair, The metal oxide varistor substrate is connected to a surface electrode for driving the liquid crystal provided on one surface, and the other through-type electrode is connected to the surface electrode for scanning provided on the substrate surface of the metal oxide varistor. The voltage non-linearity of the metal oxide varistor between the pair of through-type electrodes is utilized to create a gap between the transparent opposing electrodes provided on the glass substrate facing the surface electrode. A voltage non-linear resistor characterized in that a liquid crystal in a portion of the resistor is driven in a switching manner.