JP2578807B2 - Oxide semiconductor for thermistor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxide semiconductor for a thermistor having a negative temperature coefficient of resistance which is excellent in temperature detection accuracy and can be used as a highly responsive temperature sensor. .

Conventional technology Conventionally, Mn-Co-Ni
-Cu oxide thermistor materials whose crystal structure has a spinel structure have been mainly used.
The electrical characteristics of the thermistor material are generally represented by the specific resistance and the thermistor constant B. The thermistor constant (hereinafter referred to as B constant) indicates the temperature gradient of the resistance.
Specifically, it is determined by the activation energy corresponding to the band gap of the thermistor material. Therefore, the larger the B constant, the larger the change in resistance value with respect to temperature. Conversely, from the viewpoint of the change in resistance value, the temperature detection accuracy is higher and the response is better. Also, there is a correlation between the specific resistance and the B constant as shown in the figure, and the current general-purpose thermistor material has an area surrounded by 2 in the figure, that is, a specific resistance of several tens to several hundreds KΩ · cm, and a B constant of 2500.
~ 5000K is used.

In addition, as an oxide semiconductor that combines cobalt oxide and lithium, an example of the valence control theory generally described as one of the conduction mechanisms of an oxide semiconductor material is an old example of VERW.
Featured by EY et al. (Philips Reserch Re
port 5173 (1950)) However, the study by VERWEY et al. is at the research stage only, before the application development as a thermistor, and the study as a thermistor material was described by Hisao Niki ( (Hitachi, Ltd., Central Research Laboratory, 20th anniversary commemorative papers, pp. 30-46, Showa 37). According to the examination results of Futaki, both the specific resistance and the B constant are low, and are not suitable as a thermistor but are described as being equivalent thereto.

Problems to be Solved by the Invention Conventionally, for a water temperature gauge of an automobile or for a temperature sensor of an iron, the temperature detection accuracy is high, and the specific resistance for the purpose of improving the response is low. Although a high thermistor material has been demanded, the general purpose thermistor material shown in the above figure could not satisfy this demand.

An object of the present invention is to provide a thermistor material that satisfies this demand, that is, an oxide semiconductor for a thermistor.

Means for Solving the Problems In order to achieve the above-mentioned demands, the present invention has been achieved by reviewing and improving the aforementioned Co-Li-based oxide semiconductor. The oxide semiconductor for a thermistor of the present invention is composed of a sintered mixture of a metal oxide, and its metal element is cobalt (Co) 67.5 to 97.8 atomic% and copper (Cu) 1.0 to 1.0.
It contains four types of 7.0 at%, lithium (Li) 2.0 to 22.0 at%, and nickel (Ni) 0.1 to 0.5 at% (excluding 0.5 at%), for a total of 100 at%.

Action With this configuration, an oxide semiconductor for a thermistor having a low specific resistance and a high B constant in the region 1 surrounded by the solid line in the figure can be obtained. Here, this semiconductor has a basic composition of cobalt oxide (CoO), and when tricobalt tetroxide (Co ₃ O ₄ ) is generated, a high B constant can be achieved by the contribution of hopping conduction. Can not.

Examples Hereinafter, examples of the present invention will be described.

Commercial raw materials such as cobalt oxide, copper oxide, lithium oxide and nickel oxide were blended so as to have a composition of each atomic% as shown in the table below. To illustrate the thermistor manufacturing process, these compounded compositions are wet-mixed with a ball mill, and the slurry is dried and calcined at a temperature of 800 ° C.
The calcined product was again wet-pulverized and mixed by a ball mill.
The slurry thus obtained is dried, polyvinyl alcohol is added and mixed as a binder, a required amount is taken and pressure-molded into a disc shape to form a large number of molded products, and these are subjected to a nitrogen gas flow at 1200 ° C. to 1300 ° C. for 2 hours. Fired. Electrodes mainly composed of Ag were provided on both surfaces of the disk-shaped sintered body thus obtained. The resistance values (R ₂₅ and R ₅₀ ) at 25 ° C. and 50 ° C. of these samples were measured, and the specific resistance ρ ₂₅ at 25 ° C. was obtained from the following equation (1), and the B constant was obtained according to the following (2). It was calculated from the equation.

The results are summarized in the table below.

As described above, a region 1 surrounded by a solid line in the drawing is a region having a low specific resistance and a high B constant which are the objects of the present invention. This area is obtained by replacing the electrical characteristics requested by the device side with the thermistor material characteristics (specific resistance and B constant) in order to achieve high detection accuracy and high response as a sensor.

In the preceding table, sample numbers 1, 4, 5, and 6 are not included in the area 1 surrounded by the solid line. That is, it is out of the scope of the present invention because it does not satisfy the demands of the device maker.

For this sample, we used what was fired after dry molding,
The device may be a bead type device and is not limited by the device manufacturing method.

As described above, according to the present invention, an oxide semiconductor for a thermistor having a low specific resistance, a high B constant and a negative temperature coefficient of resistance is provided. Accuracy and high response can be achieved, and power can be saved. Further, since it is a thermistor material having a low specific resistance and a high B constant, which has never existed in the past, it is expected that a completely new use as a sensor will be developed.

[Brief description of the drawings]

The figure shows the characteristic correlation of a thermistor material having a negative temperature coefficient of resistance.

Claims (1)

(57) [Claims] 1. A sintered mixture of a metal oxide, comprising 67.5 to 97.8 atomic% of cobalt and 1.0% of copper as constituent metal elements.
~ 7.0 atomic%, lithium 2.0 ~ 22.0 atomic%, nickel 0.1
100 kinds of 4 kinds of up to 0.5 atom% (excluding 0.5 atom%)
An oxide semiconductor for a thermistor, characterized by containing at least atomic%.