JPH04180201A - Oxide semiconductor for thermistor and its material - Google Patents

Abstract

PURPOSE:To lower a thermistor constant with reference to a resistivity and to make a resistance value variable in a wide temperature range by a method wherein three kinds of cobalt, copper and iron as constituent metal elements are mixed in respectively specific ratios. CONSTITUTION:This material is composed of the sintered mixed substance of metal compounds; and mixture ratios of its constituent metal elements are set within a hexagonal bold-line frame. That is to say, it is formed by mixing the following as main components: a spinel oxide which contains three kinds of metal elements of iron(Fe), cobalt(Co) and copper(Cu) in ratios indicated by this hexagon and which uses iron and cobalt, both having a high thermistor constant and a high resistivity as main components; and a spinel oxide which uses cobalt and copper, both having a low thermistor constant and a low resistivity, as main components. Thereby, it is possible to produce an oxide semiconductor, for thermistor use, whose thermistor constant B is low with reference to a resistivity rho.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an oxide semiconductor for a thermistor that can be used in a wide temperature range. The present invention is utilized for manufacturing a thermistor with a low thermistor constant B and a large specific resistance ρ.

The present invention is applied to a thermistor that can be used over a wide temperature range of -50°C to +400°C.

The present invention is suitable for use in a thermistor for a microwave oven that can cover two temperature ranges, one for defrosting and one for cooking.

〔overview〕

The present invention provides an oxide semiconductor for a thermistor made of a sintered mixture of metal oxides, which has three constituent metal elements: konolte, copper, and iron.
By mixing each species in a specific proportion obtained experimentally, the thermistor constant B is made low relative to the resistivity ρ,
The resistance value changes over a wide temperature range.

[Conventional technology]

Conventionally, as a general-purpose disk type thermistor, Mn sC
Composite oxide thermistor materials containing metal elements such as O 2 and Ni, whose crystal structure is a spinel structure have been mainly used.

The electrical characteristics of the thermistor material are represented by a specific resistance ρ and a thermistor constant B, where the thermistor constant B represents the temperature gradient of resistance and is determined by the activation energy corresponding to the band gap of the thermistor material. Therefore, as the thermistor constant B increases, the change in resistance value with respect to temperature increases.

In addition, there is a correlation between the specific resistance ρ and the thermistor constant B, as shown in the range A' in Figure 2, and the conventionally used general-purpose thermistor materials have a specific resistance ρ of several 10 to several 100. Ω・cm, thermistor constant B is 2500 to 50
00K has been used.

In a general thermistor, the resistance value as a sensor is in the range of 100Ω to IMΩ, preferably 500Ω to 500Ω, in relation to the resistance value in the circuit. In this case, -50
In order to use the material in a wide temperature range from .degree. C. to +400.degree. C., the B constant, which is the temperature coefficient of the above-mentioned material, generally becomes as large as 3000 K or more. For example, if a material with a B constant of 3000 K is used and the resistance is -50°C and 500Ω, the temperature at which the usable resistance value is 500Ω or more is 200°C or lower. For this reason, conventional sensors have a temperature range of
Two or more separate elements were required to achieve temperatures between 0°C and +400°C.

Composite oxide materials in which Cu is added to metal elements such as Mn, Co, and Ni are also known as materials with a B constant of 3000 K or less, but both the specific resistance ρ and thermistor constant B are low, making them suitable for use over a wide temperature range. It was not suitable as a thermistor material for temperature sensors [References ■
Hitachi, Ltd., collection of papers commemorating the 20th anniversary of the founding of the Central Research Institute, 1962].

[Problem to be solved by the invention]

As mentioned above, conventional materials include materials with a B constant of 3000 or less, but they have a low resistivity and are suitable for this purpose at 150.
As a chip-type thermistor for glass sealing used in sensors above ℃, the dimensions and shape are extremely long and thin.
It is not possible to obtain a resistance value of 500Ω or more as an element.

In other words, it can be used in a chip-type thermistor that can be sealed with glass, and its usable temperature range is from 150°C to
A material is required that has a constant and resistivity that can be used up to +400°C or at least 300°C. More specifically, it has a B constant of 2500 K or less,
A material with an order of magnitude higher resistivity than conventional resistivity is required (see Figure 1).

The present invention was made against this background, and an object of the present invention is to provide an oxide semiconductor for a thermistor and a material thereof, which has a low thermistor constant B with respect to a high value of specific resistance ρ.

[Means to solve the problem]

The present invention is characterized in that it consists of a sintered mixture of metal oxides, and that the mixing ratio of its constituent metal elements is within the bold line frame shown in FIG.

That is, three types of metal elements, iron (Fe), cobalt (Co), and copper (Cu), are contained in the proportions shown in the rough outline in Figure 1, and iron and cobalt, which have a high thermistor constant and specific resistance during firing, are used. It is characterized by being formed mainly of spinel oxide containing cobalt and copper, which have a low thermistor constant and specific resistance, as the main components.

Thermistor oxide materials basically have a spinel structure, and generally, when the B constant is low, the resistivity is also low.

When the crystal/structure contained in the material is a single phase, the characteristics aimed at by the invention cannot be obtained as in the conventional example.

The inventors discovered that in a multicomponent system, a component with a high B constant and high resistivity ρ and a component with a low B constant and low resistivity ρ exist simultaneously inside the element, and current appears to flow selectively through the low component. It was realized that a material with a lower constant and higher resistivity ρ could be obtained. As a result of examining various materials, especially FeC0Cu
Among spinel oxides, spinel oxides mainly composed of FeCo-based materials with high B and high ρ characteristics and spinel oxides mainly composed of CoCu-based materials with low B and low ρ characteristics are produced in certain composition ranges. I found it.

[Effect]

Iron (Fe), Balt (Co), and Copper (Cu)
When fired at the mixing ratio in the area surrounded by the solid line in Figure 1, when transitioning from the high temperature range to the low temperature range, the thermistor constant and ratio are increased in the element body part where the thermistor constant and resistivity are high, as shown in Figure 3. Elements with low resistance are precipitated. In this state, when a voltage is applied to the picture electrode, the current passes through the precipitated part with low specific resistance, but because the path of this part with low specific resistance is narrow, it is the same as the element body with high specific resistance. Therefore, the sintered and mixed element body as a whole has a high specific resistance, and an element body whose thermistor constant is low relative to the specific resistance is formed.

This makes it possible to produce an oxide semiconductor for thermistors that has a low thermistor constant relative to the specific resistance, and therefore corresponds to the surface area of the temperature range required for defrosting and the temperature range required for cooking for use in microwave ovens. The thermistor can be constructed from one element, which simplifies the circuit configuration and reduces manufacturing costs.

〔Example〕

Next, embodiments of the present invention will be described based on the drawings.

FIG. 1 is a diagram showing the mixing ratio of metal elements in an example of the present invention.

Iron oxide (Fe203) and cobalt oxide (Co) are used as raw materials.
Using copper oxide (Cub) and copper oxide (Cub), the respective metal elements were blended so as to have the compositions shown in FIG. 1 and the table.

These blended compositions were wet mixed in a ball mill for 24 hours, filtered and dehydrated, and dried at 100°C. After loosening this dried product, it was calcined in air at 900° C. for 10 hours, and the powder was wet-pulverized in a ball mill for 48 hours, and then dried to obtain an oxide powder.

Add polyvinyl alcohol to this oxide powder by weight.
The mixture was added to a concentration of 5%, granulated, and press-molded at a pressure of 1 ton/7 to form a disc with a diameter of 21 mm and a thickness of 7 mm.

The disc-shaped molded product thus obtained was heated to 950°C in air.
A sintered body was obtained by firing at a temperature of 1100°C to 1100°C for 10 hours.

A wafer with a thickness of 1 mm is cut from the inside of this sintered body with high sintering density and no deformation, and silver (Ag) is coated on both sides.
After providing an electrode containing as a main component, a thermistor element was cut out into a chip shape of 0.5 mm square. This was sealed and sealed in a glass tube using a Dimet wire as a terminal to obtain a glass-encapsulated thermistor.

The samples of the glass-encapsulated thermistors thus obtained and their individual characteristics are shown in the table. The specific resistance in the table is the value determined from the measurement results of the zero-load resistance value at 25°C, and the thermistor constant B is the value determined from the zero-load resistance value at 25°C and 50°C. FIG. 2 shows the relationship between the thermistor constant and specific resistance.

Further, the numbers attached in the figure indicate the sample numbers in the table, and the sample numbers marked with * indicate the samples used as comparative examples.

FIG. 3 shows an example of the temperature characteristics of the resistance value of sample No. 7. As shown in the figure, 400℃
The resistance value is within the range of 100Ω to IMΩ from 150° C. to 150° C., and the material characteristic is that the curve is upwardly convex, that is, the B constant increases on the high temperature side. This is extremely preferable as a temperature sensor for a wide temperature range using a thermistor.

As seen in Figure 2 and the table, iron (
Fe) 5.0 to 35.0 atomic%, cobalt (Co)
15.0 to 55.0 at%, copper (Cu) 7.5 to 35.
By mixing and sintering three types of 0 atomic % within a composition range containing a total of 100 atomic %, a low resistivity of 60 to 5,000 Ω/kap and a low thermistor constant of 1,200 to 2,000 K are achieved. It is possible to produce a material for a thermistor element having the following properties.

(Hereinafter, in the margin of this page) [Effects of the Invention] As explained above, according to the present invention, it is possible to produce an oxide semiconductor for a thermistor having a thermistor constant B that is low with respect to the specific resistance ρ. Therefore, a thermistor for use in a microwave oven that can handle both the temperature range required for defrosting and the temperature range required for cooking can be constructed from one material.

Furthermore, since the two thermistors are combined into one, the circuit configuration is simplified, which has the effect of reducing the manufacturing cost of electronic equipment.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the mixing ratio of metal elements in Examples of the present invention. FIG. 2 is a diagram showing the relationship between the thermistor constant and specific resistance of oxide semiconductors for thermistors in a conventional example and an example of the present invention. FIG. 3 is a diagram showing the temperature characteristics of sample 7 in an example of the present invention. FIG. 4(a) and FIG. 4(a) are diagrams showing the external appearance and cross section of a thermistor element in an embodiment of the present invention. Patent Applicant Mitsubishi Mining Cement Co., Ltd. Agent Patent Attorney Nao Takashi Ide Co (/Atom 01.) Threat f1 to 12111111 Figure 1 25-50″C/lB constant (K) Conventional example 2J Yoshikayu 11 Fig. 2

Claims (2)

[Claims] 1. An oxide semiconductor for a thermistor comprising a mixed sintered body of metal oxides, characterized in that the mixing ratio of the constituent metal elements is within the thick line frame shown in FIG. 2. An oxide material for a thermistor, characterized in that the mixing ratio of metal elements is within the bold line frame shown in FIG.