JPS6236608B2 - - 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 a liquid between two opposing electrodes provided on a glass substrate, and utilize the unique behavior of liquid crystal molecules when a voltage is applied between the two electrodes to create a transparent space for light. This is an element that displays characters or images by changing the reflection situation. 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, resulting in a decrease in contrast. 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 MOSFETs 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 O ₃ , MnO ₂ , Sb ₂ O ₃ , etc. and sintering it at a high temperature, mirror-polishing one side, and then providing electrodes on it by vacuum evaporation. . A typical structure thereof is shown in FIG. In Figure 1, 1 is
Metal oxide varistor substrate mainly composed of ZnO, 2.
3 is an electrode provided on the substrate 1, 4 is a lead electrode for applying voltage to the electrode 3 from the outside, 5 is a glass substrate, and 6 is a transparent electrode provided on the glass substrate 5 facing the electrode 2. The electrodes 7 are lead electrodes for externally applying voltage to the electrode 6, and 8 is a liquid crystal. 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. In Fig. 2, 1 is a metal oxide varistor;
2, 3, and 6 correspond to electrodes 2, 3, and 6 in Fig. 1, respectively, 4 corresponds to the lead electrode on the metal oxide varistor side, and 7 and 7' correspond to the lead electrodes on the glass substrate side. 8 is a liquid crystal. Now, to display an image, as shown in FIG. 1, by making the voltage applied between electrodes 2-6 higher than the on-voltage of the liquid crystal, the composition state of liquid crystal molecules between electrodes 2-6 is changed, and the liquid crystal molecules passing through glass 5 are changed. This is done by changing the state of the light that reaches the electrode 2 and substrate 1, is reflected there, and passes through the glass again. Metal oxide varistors, on the other hand, allow almost no current to flow up to a certain voltage. It has the property that current suddenly starts flowing above a certain voltage (rise voltage). Therefore, in order to turn on the upper picture element in FIG. 2, _the sum ( _V V _T
It is sufficient to apply a voltage higher than +V _ON ). To be more specific, for example, (V _T +V _ON )/
2. Apply a voltage of -(V _T +V _ON )/2 to the electrode 7. As a result, a voltage of T _T +V _ON is applied between electrodes 4-7, current flows through the upper metal oxide varistor, and the upper picture element turns on. Furthermore, the rising voltage of the metal oxide varistor is (V _T +V _ON )/2 or more (in other words, V
_T > V _ON ), and if the potential of electrode 7' is set to OV, the voltage applied to the lower metal oxide varistor at this time is (V _T +V _ON )/2, and the metal oxide No current flows through the physical varistor, so only the upper picture element can be turned on 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 the electrode 4 and a voltage of - (V _T +V _ON /2 to the electrode 7'). By doing so, it is possible to eliminate crosstalk between each picture element and display an image with good contrast.By the way, when the configuration shown in Fig. 1 is used, the varistor action occurs only on the very surface of the substrate between electrodes 2 and 3. The specific structure of that part is shown in Figure 3. In Figure 3, part 1 is the substrate part of the metal oxide varistor. 2 and 3 are the electrodes provided on the substrate. , 14 are ZuO particles which are the main constituents of metal oxide varistors, 15 are grain boundary parts with high resistance that exhibit non-reformability, and 16 are impurities attached to the surface.The particle size of ZnO particles 14 is usually The diameter is around several μm.As shown in this figure, the surface has defects caused by polishing and impurities, making it extremely irregular.Now, when a voltage is applied between electrodes 2 and 3, , the current is at electrode 2-
It flows only through the shortest part between 3. Further, since the impurities 16 generally contain alkali metals, etc., the resistance may be low and flow through the impurities.
Therefore, the current path follows the route shown at 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 concave electrodes formed on the surface of a concave portion provided in the substrate 1, 2',
3' is a lead electrode, 14 is a ZnO particle, 15 is a grain boundary, and 16 is an impurity attached to the surface. When a voltage is applied between the electrodes 2 and 3 in this configuration, the current flows in a dispersed manner because the cross-sectional area of the shortest distance between the electrodes 2 and 3 is large, and as shown by the arrow 17, the current mainly flows through the 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. In Table 1, the distance between electrodes 2-3 is 200
The difference in variation in falling voltage (voltage V when 10 μA flows is assumed to be ₁₀ μA) in μm is shown.
For comparison, the characteristics when using a conventional electrode structure are also shown. All 100 on the same board
This figure shows the variation in rising voltage when a pair of electrodes is provided. Also, Table 2 shows 10μA at 70℃
The figure shows the rate of change in V ₁₀ μA when a current of 10 μA is applied continuously for 100 hours. The structure of the present invention is superior in both characteristics.

【table】

[Table] The device having the structure of the present invention was prepared as follows. First, 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, the flat surface of this sintered body was thoroughly polished to a mirror surface, washed with a solvent, and a resist was applied. Next, only the concave electrode formation portion was exposed, developed, and the resist was removed, followed by selective etching of the portion where the resist was removed. By this etching operation, recesses were formed in predetermined portions of the surface of the varistor substrate. Then, electrodes were formed only on the surfaces of the recesses by sputtering. Then, remove the resist once, apply the resist again, and expose only the electrode molded area on the surface.
After development, the exposed portions of the resist were removed, and surface electrodes were formed on the removed portions by vacuum deposition. By removing the resist again, an element having the structure shown in FIG. 4 was obtained. 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. It is. Also, as a metal oxide varistor substrate, after sintering,
By diffusing monovalent elements such as Li or Cu onto the surface and increasing the resistance of the ZnO layer on the surface based on the principle of valence control, or by forming a high-resistance film on the substrate surface, this The effect of the invention can be further improved. 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 surface electrode for driving a liquid crystal, and 53 is a concave electrode, which is electrically connected to the surface electrode 52 by a lead electrode 54. Reference numeral 55 designates the other concave electrode that pairs with 53, and is connected to a scanning lead electrode through a lead electrode 56. 57 is a glass substrate, 58 is an opposing transparent electrode having the same shape as the electrode 52 provided on the glass substrate, 59 is a lead electrode for applying a voltage to the electrode 58 from the outside, and 60 is a liquid crystal.
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, 53 and 55 are a pair of concave electrodes,
54 and 56 are lead electrodes, respectively. In the case of such a structure, the electrode 56-
If a voltage is applied between electrodes 59 and 59, a voltage can be applied between electrodes 52 and 58 via the varistor formed between electrodes 53 and 55, causing the liquid crystal sandwiched between electrodes 52 and 58 to operate in a switching manner. can be done. If the surface electrodes are made large and the concave electrodes of the electrodes 53 and 55 are made small, the blank space 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 a structure in which a large number of picture elements are constructed. In the figure, the same parts as in FIG. 5 are given the same reference numerals. i.e. 52, 52', 52'', 5
2 is a surface electrode, 53, 53', 53'', 53 and 5
Reference numerals 5, 55', 55'' and 55 are pairs of concave electrodes, respectively, and electrodes 55'' and 55 are connected to the scanning lead wire 11 and the electrodes 55'' and 55 are connected to the scanning lead wire 12, respectively. In this case, each pair of concave electrodes 5
3,55 distance 53'-55', 53''-55'',
The distance between 53 and 55 is the distance between other electrodes,
For example, between 53-11, 52-11, 52-5
2', 52-53', 52-12, etc., and are arranged so that the distance is shorter than the distance to electrodes that are not electrically connected with a conductor. With this configuration, it is possible to switch a large number of picture elements without causing crosstalk due to varistor action formed between unintended electrodes. As described in detail above, by devising the electrode structure, the present invention makes it possible to utilize stable voltage nonlinearity inside the sintered body while using electrodes formed on the same substrate surface. It is particularly useful as a varistor array for liquid crystal display devices.

[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 a schematic diagram explaining the conventional electrode configuration. 4 is a schematic diagram showing the electrode structure of the voltage nonlinear resistance element of the present invention,
FIG. 5 is a sectional view showing the structure of the element, and FIGS. 6 and 7 are plan views showing the arrangement of electrodes. 51...Metal oxide varistor substrate, 52...Liquid crystal driving electrode, 53, 55...Concave electrode, 54,
56, 59...Lead electrode, 57...Glass substrate, 58...Transparent surface electrode, 60...Liquid crystal.

Claims (1)

[Claims] 1. A metal oxide varistor substrate having a characteristic that the resistance value decreases as the voltage increases, a plurality of recesses are provided on one surface of the substrate, a recessed electrode is provided on the inner surface of the recess, and the recessed A voltage nonlinear resistor characterized by utilizing voltage nonlinearity between electrodes. 2. A plurality of pairs of recesses are provided on one surface of a metal oxide varistor substrate having a characteristic that the resistance value decreases as the voltage increases, and recessed electrodes are provided on the inner surface of the recesses, and one of the recessed electrodes of each pair is connected to a surface electrode for driving a liquid crystal provided on the surface of the metal oxide varistor, and connecting the other concave electrode to a scanning electrode also provided on the surface of the metal oxide varistor; By utilizing the voltage non-linearity of the metal oxide varistor between the pair of concave electrodes, the liquid crystal in the portion sandwiched between the transparent counter electrodes provided on the glass substrate facing the plane electrode can be switched. A voltage nonlinear resistor characterized in that it is driven by.