JPS62282409A - Voltage-dependent nonlinear resistor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a voltage-dependent nonlinear resistor having a laminated structure and having capacitor characteristics and varistor characteristics for protecting semiconductors and circuits from voltage, noise, and static electricity.

Conventional technology SiC varistors and ZnO having voltage-dependent nonlinear resistance characteristics have been used to absorb abnormally high voltages, remove noise, eliminate sparks, and counter static electricity in various electrical and electronic devices.
Type baristas were used. The voltage-current characteristics of such a varistor can be approximately expressed by the following equation.

1=(V/C) Here, I is current, V is voltage, C is a constant specific to the varistor, and α is a voltage nonlinear index.

The α of SiC varistors is about 2 to 7, and the α of some ZnO-based varistors is as high as 60. Although such varistors have excellent performance in absorbing relatively high voltages, their low dielectric constant and small inherent capacitance make them difficult to absorb relatively low voltages below the varistor voltage. shows almost no effect, and the dielectric loss -δ is as large as 5 to 10%.

On the other hand, semiconductor capacitors with an apparent dielectric constant of about 5×10 4 and −δ of about 1% are used to remove these low-voltage noises. However, if a voltage or current exceeding a certain limit is applied to such a semiconductor capacitor due to a surge or the like, it may break down and no longer function as a capacitor.

Recently, a device with 5rTiOf as its main component that has both varistor and capacitor characteristics has been developed, but it has a low varistor voltage, a large α, a large dielectric constant, and a large surge resistance. A product that satisfies all of the above characteristics at the same time has not yet been obtained.

Furthermore, as a conventional multilayer ceramic varistor, there is one disclosed in Japanese Patent Application Laid-Open No. 51-18849, which has a pair of varistor elements on the front and back sides of a varistor element 1 which has been sintered in advance, as shown in Fig. 4. The electrodes 2 are formed, and electrodes 3 and 4 are attached so as to connect them in parallel.The structure is such that the electrodes 2 of the varistor are exposed to the outside even in areas other than the lead-out portion. Furthermore, the surface is coated with an organic substance such as an adhesive or an exterior resin to protect this part and to adhere the varistor element 1. Therefore, it is not suitable for reducing the values of v and In due to limitations on the sintering temperature and the thickness of the varistor element.

In addition, the one disclosed in Japanese Patent Publication No. 58-23921 is a multilayer varistor whose main component is ZnO-based and whose desired characteristics are a rise voltage of 4 V or more that can be adjusted arbitrarily.
It is effective as a small varistor due to its voltage nonlinearity, leakage current, power load characteristics, and surge resistance characteristics, but its low dielectric constant makes it almost ineffective in protecting semiconductors and circuits from noise and static electricity. Not shown.

Problems to be solved by the invention In order to protect semiconductors and circuits from noise, static electricity, etc., varistor voltage is low, α is large, dielectric constant is large, −δ is small, and surge resistance is large. The aim is to satisfy all of the above characteristics at the same time, and to make it possible to achieve compact size, light weight, and high-density packaging.

□Means to solve the problem□In order to solve the above-mentioned problem, the present invention provides a plurality of electrodes inside the laminated sintered body, and increases the resistance of the element body and the grain boundaries of the element body. Forms a layered structure with substances that can
The internal electrode is surrounded by the element body except for the part taken out to the outside, and the internal electrode and the element body which is sintered and has capacitor characteristics and varistor characteristics are laminated together before sintering and integrated. It is characterized by a structure obtained by sintering after oxidation.

action In the present invention, an organic binder and a dispersant are added to the raw material powder.

Add a plasticizer to make a raw sheet film, apply a substance capable of increasing the resistance of the crystal grain boundaries of the element to both sides of the raw sheet, print internal electrodes on top of it, and stack it. After being crimped, it is cut into a predetermined size and sintered.

Therefore, during sintering, substances that can increase the resistance of the grain boundaries of the element diffuse into the grain boundaries, selectively increasing the resistance of the grain boundaries, and forming energy barriers at the grain boundaries, which improves the varistor properties. manifest. In addition, since the inside of the crystal grain has low resistance and the grain boundary has high resistance, capacitor characteristics are exhibited.

Therefore, all of the internal electrodes have capacitor characteristics except for the part taken out to the outside. There are few parts, so there is little deterioration of electrode characteristics due to moisture intrusion or exterior resin, and it has excellent moisture resistance and high temperature load characteristics.

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

First, the main raw materials were blended to have the composition shown in Table 1 below, mixed in a ball mill for 23 hours, dried, calcined at 850'C for 2 hours, crushed again, dried, and then , an organic binder, a dispersant, and a plasticizer are added to form a slurry. A raw sheet having a predetermined thickness is made from this by a sheet forming method (for example, a doctor blade method).

On the other hand, organic binders (such as ethyl cellulose) are added to substances that can make grain boundaries highly resistive (such as NΔ20.NaF, Li2O, LiF, IC20°KF, λg20.CuO, Cu2O, TJ?, O, etc.).
is added to make a paste, which is applied to both sides of the raw sheet and dried.

This raw sheet is cut into a predetermined size, and the internal electrode material (for example, gold) is formed by screen printing or the like.

Metals such as platinum, palladium, silver, molybdenum, and their alloys) are applied, and a predetermined number of sheets are stacked, and raw sheets with no electrodes printed are stacked on top and bottom and pressed together.

Then, cut into a predetermined size, N2: H2==9:
6 at 1350'C to 1500''C in a reducing atmosphere of 1
Calcinate for 2 hours, then at 900-1180°C in air for 2 hours.
Baked for an hour. Next, silver electrodes are applied to both end faces of the internal electrode ftK and baked with a sintering process.

As shown in FIGS. 1 to 3, the device obtained in this way is enclosed in a varistor cord having capacitor characteristics except for the portion of the internal electrode 6 taken out to the outside.
It has a structure in which the electrodes are surrounded only by the same laminated sintered body 6, and there are few voids and moisture does not easily enter, so there is little deterioration of the characteristics of the internal electrodes 6 due to the exterior resin. Further, in the figure, 7 and 8 are end face electrodes, and 9 is a layer of a substance that increases the total grain boundary resistance.

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

The dielectric constant is the value calculated from the capacitance at 1K [Iz], and the surge resistance is the voltage after applying a pulse current of 8 x 20μ (□voltage when a current of 1mm is applied). )
The applied current is evaluated based on the highest value when the change is within ±1°.

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

Moreover, the additives in the composition and the amounts added thereof may be of any type as long as they exhibit the characteristics of both a capacitor and a varistor. Furthermore, in this example, the raw materials were fired in a reducing atmosphere after being laminated, but the blended raw materials were fired in advance in a reducing atmosphere. It was confirmed that the same effect can be obtained even if the entire end electrode is formed by firing with Only molybdenum, platinum-tungsten is shown, but this includes gold, silver, palladium, platinum, rhodium, iridium, molybdenum, tungsten, nickel, iron, chromium,
Any material may be used as long as it is made of one metal among copper or an alloy of these metals.

In addition, the range of the main raw material components of the element body was defined as x, y
When , z is less than 0.001, no effect of addition is seen, while when o, s '2 is exceeded, the grain growth of the element body is suppressed.
This is because the varistor voltage is high, the dielectric constant is low, and the surge resistance is significantly deteriorated.

In addition, in this example, only one type of substance capable of increasing the resistance of the main raw material component of the element body and the crystal grain boundaries of the element body is shown, but as the main raw material component of the element body, 5r
TiO,,CaxSr, -xTie.

(o, o01-xTiO3(0.001≦x≦0.5
), BaySr, -yTie3 (0.001≦y
≦0.5) 1Mg z S r + , -z T
10 s (0.001≦z≦0.6), a plurality of types may be added at the same time. In addition, substances that can make the grain boundaries of the element high in resistance include Na2O, N
aF, Li2O, LiF, K2O, KF.

Multiple types of Mug20, CuO, CuzO, and TN20 may all be added at the same time.

When the device thus obtained was subjected to a mixed load test under the conditions of 86°C and 90% RH with a charge rate of 96%,
The rate of change in varistor voltage after 1000 hours was +25%, which was lower than conventional values, and the moisture resistance properties were significantly improved. It was also confirmed that the characteristics were improved in a high temperature load test at 125°C.

Effects of the Invention As shown above, if the present invention is implemented, the following characteristics can be simultaneously satisfied: low varistor voltage, relatively large α, high dielectric constant, low −δ, and large surge resistance. Can be done.

Furthermore, compared to conventional laminated ceramic varistors, there are fewer voids, which prevents moisture from entering, improving moisture resistance, and because the internal electrodes do not come into direct contact with the exterior resin, high-temperature load characteristics are improved. Furthermore, it has a dielectric constant 6 to 20 times greater than that of a ZnO-based multilayer varistor, and is extremely effective against steep-rising pulses such as noise and static electricity.

Therefore, according to the present invention, it is possible to obtain an element that is small, lightweight, can be mounted at high density, and can protect semiconductors and circuits from noise and static electricity, and its practical effects are extremely large.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a perspective view of a voltage-dependent nonlinear resistor 4 according to the present invention, and FIG. 2 is a cross-section taken along the cutting line Mu' in FIG. 1 and viewed in the direction of the arrow. Figure 3 is the section line B-B in Figure 1.
FIG. 4 is a cross-sectional view taken along the line ' and viewed in the direction of the arrow, and FIG. 4 is a perspective view of a conventional voltage-dependent nonlinear resistor. 6... Sintered body, 6... Internal electrode, 7.
8... Edge electrode, 9... Layer of substance that makes grain boundaries high in resistance. Name of agent: Patent attorney Toshio Nakao and one other person
Sorry cQ″′ faction castle

Claims (4)

[Claims] (1) A plurality of internal electrodes, an element body, and a substance capable of increasing the resistance of the crystal grain boundaries of the element body form a laminated structure, and the parts other than the portions of the internal electrodes that are taken out to the outside are surrounded by the element body. Voltage-dependent nonlinear resistor with capacitor characteristics. (2) The elementary bodies are SrTiO_3, Ca_xSr_1_-_
xTiO_3 (0.001≦x≦0.5), Ba_yS
r_1_-_yTiO_3 (0.001≦y≦0.5)
, Mg_zSr_1_−_zTiO_3 (0.001≦
z≦0.5), the voltage dependent nonlinear resistor according to claim 1, wherein the voltage dependent nonlinear resistor has at least one type selected from the group consisting of: z≦0.5). (3) Substances that can increase the resistance of the grain boundaries of the element body are Na_2O, NaF, Li_2O, LiF, K_2
O, KF, Ag_2O, CuO, Cu_2O, Tl_2
2. The voltage-dependent nonlinear resistor according to claim 1, comprising at least one type of O. (4) Internal electrodes include gold, silver, palladium, platinum, rhodium, iridium, molybdenum, tungsten, nickel,
Claim 1 whose main component is one of iron, chromium, and copper, or an alloy of these metals.
Voltage-dependent non-linear resistor as described in section.