JP2644731B2 - Method of manufacturing voltage-dependent nonlinear resistor - Google Patents

Description

The present invention relates to an electric device, an abnormal high voltage generated in an electronic device,
The present invention relates to a method for manufacturing a voltage-dependent nonlinear resistor having a capacitor characteristic and a varistor characteristic in a laminated structure for protecting semiconductors and circuits from noise and static electricity.

Conventional technology Conventionally, SiC varistors and ZnO-based varistors with voltage-dependent non-linear resistance characteristics have been used to absorb abnormally high voltage, eliminate noise, eliminate sparks, and take measures against static electricity in various electric and electronic devices. Was. The voltage-current characteristics of such a varistor can be approximately expressed by the following equation.

I = (V / C) ^α where I is a current, V is a voltage, C is a constant unique to a varistor, and α is a voltage non-linear index.

Α of the SiC varistor is about 2 to 7, and α of the ZnO varistor.
There are as many as 50. Such varistors have excellent performance in absorbing relatively high voltages, but because of their low dielectric constant and small inherent capacitance, they can absorb relatively low voltages below the varistor voltage. Has almost no effect, and the dielectric loss tan δ is as large as 5 to 10%.

On the other hand, a semiconductor capacitor having an apparent dielectric constant of about 5 × 10 ⁴ and a tan δ of about 1% is used for removing these low-voltage noises and the like. However, when a voltage or a current exceeding a certain limit is applied due to a surge or the like, such a semiconductor capacitor is broken or loses its function as a capacitor.

Therefore, recently, those having SrTiO ₃ as a main component and having both varistor characteristics and capacitor characteristics have been developed, but the varistor voltage is low, α is large, the dielectric constant is large, and the surge withstand capability is large. No one that satisfies all these characteristics at the same time has yet been obtained.

A conventional multilayer ceramic varistor is disclosed in Japanese Patent Application Laid-Open No. S51-18849. As shown in FIG. 4, a pair of electrodes are provided on the front and back of a varistor element which has been sintered in advance. And varistors are stacked so as to connect them in parallel, and the varistor electrode 2 is exposed to the outside even at portions other than the take-out portion. Further, the surface is coated with an organic substance such as an adhesive or an exterior resin for protecting this portion and bonding the varistor element 1.

Problems to be Solved by the Invention According to this method, there was a problem that it was not suitable for lowering the value of _V1mA due to limitations on the sintering temperature and the thickness of the varistor element.

Therefore, the present invention provides a capacitor capable of satisfying all characteristics such as a low varistor voltage, a large α, a large dielectric constant, a small tanδ, and a large surge withstand voltage in order to protect semiconductors and circuits from noise, static electricity, and the like. It is an object of the present invention to provide a voltage-dependent nonlinear resistor having characteristics.

Means for Solving the Problems In order to achieve this object, a method for manufacturing a voltage-dependent nonlinear resistor according to the present invention comprises SrTiO ₃ , Ca _x Sr _1-x TiO ₃ (0.001 ≦
x ≦ 0.5), Ba _y Sr _1-y TiO ₃ (0.001 ≦ y ≦ 0.5), Mg _z Sr _1-z TiO ₃ (0.001 ≦ z ≦ 0.5) Ceramic raw sheet, Na ₂ O, NaF, Li ₂ O, LiF, K ₂ O, KF, A
g ₂ O, CuO, Cu ₂ O, alternately with a plurality of internal electrodes containing at least one or more of Tl ₂ O, and except for the portion of this internal electrode to the external electrode, the ceramic raw sheet A laminate is formed by being laminated so as to be surrounded, and after firing, an external electrode is formed on an end face of the laminate so as to be connected to an internal electrode.

Action According to this method, Na ₂ O, Na
At least one of F, Li ₂ O, LiF, K ₂ O, KF, Ag ₂ O, CuO, Cu ₂ O, Tl ₂ O diffuses into the grain boundaries of the raw ceramic sheet and selects the grain boundaries Varistor characteristics are exhibited because the resistance is increased and an energy barrier is formed at the crystal grain boundary. In addition, since the inside of the crystal grains has a low resistance and the crystal grain boundaries have a high resistance, capacitor characteristics are exhibited.

As a result, it is possible to obtain a voltage-dependent nonlinear resistor that can simultaneously satisfy the characteristics of a low varistor voltage, a relatively large α, a large dielectric constant, a small tan δ, and a large surge resistance.

Further, the voltage-dependent nonlinear resistor according to the present invention has a dielectric constant 5 to 20 times as large as that of a ZnO-based laminated varistor, and is extremely effective against a steep rising pulse such as noise or static electricity.

Furthermore, the internal electrodes are all surrounded by a raw ceramic sheet except for the parts that are taken out, and there are few voids, so there is little deterioration in electrode characteristics due to intrusion of moisture or deterioration of exterior resin, etc., humidity resistance, and high temperature load. Excellent characteristics.

 Hereinafter, the present invention will be described specifically with reference to examples.

First, the main raw materials are weighed so as to have the composition shown in Table 1 below, and mixed by a ball mill or the like for 24 hours. And
After being dried, it is calcined at 800 to 1200 ° C. for 2 hours, crushed and dried again, and then an organic binder, a dispersant and a plasticizer are added to form a slurry. This is formed into a green sheet having a predetermined thickness by a sheet molding method (eg, doctor blade method).

On the other hand, to the internal electrode material made of an alloy such as gold, platinum, palladium, silver, and molybdenum, a substance capable of increasing the resistance of the grain boundaries shown in Table 1 below is added to form a paste, and the raw sheet An internal electrode is applied on one side by a screen printing method or the like, and a predetermined number of the raw sheets are stacked,
Raw sheets on which electrodes are not printed are stacked on top and bottom, pressed and cut to a predetermined size.

Then, 1350 to 15 in a reducing gas atmosphere of N ₂ : H ₂ = 9: 1.
Bake at 00 ° C for 5 hours and then in air at 800-1100 ° C for 3 hours.
Fired for hours. Next, silver electrodes are applied to both end surfaces exposing the internal electrodes, and baked at 580 ° C.

As shown in FIGS. 1 to 3, all of the devices thus obtained are encapsulated in a varistor element having a capacitor characteristic except for a portion of the internal electrode 6 containing a high-grain-boundary material, which is taken out to the outside. Then, the structure is surrounded only by the same laminated sintered body 5 in which the electrodes are integrated. Since there are few voids and it is difficult for moisture to enter, the characteristic deterioration of the internal electrodes 6 due to the exterior resin is small. . Also, in the figure, 7 and 8 are end face electrodes.

Next, the characteristics of the device obtained as described above are shown in Table 2 below.

The dielectric constant is a value calculated from the capacitance at 1 kHz, and the surge withstand capability is that the change in V _1mA (voltage when a current of ₁ mA flows) after applying a pulse current of 8 × 20 μsec is ± 10%.
% Was evaluated based on the peak value of the applied current.

In this embodiment, only the doctor blade method is shown as the sheet forming method, but any other film forming method may be used.

The additives in the composition and the amount of the additives may be any as long as they exhibit the characteristics of both the capacitor and the varistor. Further, in the present embodiment, after lamination, the mixture was fired in a reducing atmosphere. However, the blended raw materials were fired in a reducing atmosphere in advance, and then pulverized, sheet-formed, electrode printed, laminated, cut, and fired in the air. Thus, it was confirmed that the same effect was obtained even if the end face electrode was formed. Further, in the present embodiment, only palladium, silver-palladium, platinum-rhodium, platinum-iridium, platinum-molybdenum, platinum-tungsten are shown as internal electrodes, but these are gold, silver, palladium, platinum, rhodium, Any material may be used as long as it is mainly composed of one kind of metal of iridium, molybdenum, tungsten, nickel, iron, chromium, and copper or an alloy made of these metals.

The range of the composition of the main component is defined as x, y, z is 0.0
If it is less than 01, no effect is exhibited, and if it exceeds 0.5, the grain growth is suppressed, so that the varistor voltage is high, the dielectric constant is small, and the surge withstand capability is extremely small.

In the present embodiment, only one kind of each of the main raw material component of the element body and the substance capable of increasing the crystal grain boundary of the element body is shown.
_{TiO 3, Ca x Sr 1-} x TiO 3 (0.001 ≦ x ≦ 0.5), Ba y Sr 1-y TiO 3 (0.001 ≦ y ≦ 0.5), Mg z Sr 1-z TiO 3 (0.00
A plurality of types (1 ≦ z ≦ 0.5) may be added at the same time. In addition, substances capable of increasing the resistance of the crystal grain boundaries of the element body include Ng ₂ O, NaF, Li ₂ O, LiF, K ₂ O, KF, Ag ₂ O, CuO, Cu
Multiple types of ₂ O and Tl ₂ O may be added at the same time.

The device thus obtained was subjected to a wet / medium load test at 85 ° C. and 95% RH at a power application rate of 95%. The change rate of the varistor voltage after 1500 hours was + 3.5%, which was the conventional value. The value was 1/3 or less, and the moisture resistance was significantly improved. In addition, even in a high-temperature load test at 125 ° C, the rate of change was 1/4 or less of the conventional rate, and it was confirmed that the high-temperature resistance was excellent.

Effects of the Invention According to the present invention as described above, a substance capable of increasing the crystal grain boundary of a ceramic green sheet contained in an internal electrode during firing is diffused into the crystal grain boundary, and the crystal grain boundary is selectively formed. A varistor characteristic is exhibited because the resistance is increased and an energy barrier is formed at the crystal grain boundary, and a voltage that can simultaneously satisfy characteristics such as a low varistor voltage, a relatively large α, a large dielectric constant, a small tanδ, and a large surge withstand voltage. A dependent nonlinear resistor is obtained.

A substance included in the internal electrode and capable of increasing the resistance of the crystal grain boundary of the ceramic green sheet promotes sintering of the laminate and can reduce the porosity. In addition to preventing intrusion, there is little deterioration in characteristics due to deterioration of exterior resin and the like, and it has excellent moisture resistance and high temperature load characteristics.

In addition, since the inside of the crystal grains has a low resistance and the crystal grain boundaries have a high resistance, capacitor characteristics are exhibited.

Except for the part where the internal electrode is taken out, all parts are surrounded by the raw ceramic sheet and there are few voids.Therefore, there is little deterioration of the electrode characteristics due to intrusion of moisture from the outside or deterioration of the exterior resin, etc. And high temperature load characteristics.

Furthermore, the dielectric constant is 5-20 compared to the ZnO-based multilayer varistor.
It is twice as large, and is extremely effective against a steep rising pulse such as noise or static electricity.

Therefore, according to the present invention, it is possible to obtain a voltage-dependent nonlinear resistor having capacitor characteristics capable of protecting a semiconductor and a circuit from noise and static electricity, and the effect is extremely large.

[Brief description of the drawings]

FIG. 1 is a perspective view of a voltage-dependent nonlinear resistor according to the present invention, FIG. 2 is a sectional view taken along a cutting line AA 'of FIG.
FIG. 3 is a sectional view taken in the direction of the arrow, and FIG.
FIG. 4 is a sectional view taken along the line B 'and viewed in the direction of the arrow, and FIG. 4 is a perspective view of a conventional voltage-dependent nonlinear resistor. 5: laminated sintered body, 6: internal electrode containing a grain boundary high resistance material, 7, 8: end face electrode.

Claims (2)

(57) [Claims] (1) SrTiO ₃ , Ca _x Sr _1-x TiO ₃ (0.001 ≦ x ≦ 0.
5), a plurality of ceramics mainly composed of at least one of Ba _y Sr _1-y TiO ₃ (0.001 ≦ y ≦ 0.5) and Mg _z Sr _1-z TiO ₃ (0.001 ≦ z ≦ 0.5) Sheet and
Na ₂ O, NaF, Li ₂ O, LiF, K ₂ O, KF, Ag ₂ O, CuO, Cu ₂ O, Tl
Alternately with a plurality of internal electrodes containing at least one kind of ₂ O, and, except for a portion where the internal electrodes are taken out to external electrodes, are laminated so as to be surrounded by the ceramic raw sheet to form a laminate. Then, after firing this laminate, a method of manufacturing a voltage-dependent non-linear resistor, wherein an external electrode is formed on an end face of the laminate so as to be connected to an internal electrode. 2. The internal electrode is composed mainly of one of gold, silver, paridium, platinum, rhodium, iridium, molybdenum, tungsten, nickel, iron, chromium and copper, or an alloy of these metals. The method for manufacturing a voltage-dependent nonlinear resistor according to claim 1.