JP2578806B2 - 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.

Further, an oxide semiconductor in which cobalt oxide and lithium are combined is an example of a valence control theory generally described as one of the conduction mechanisms of an oxide semiconductor material.
Featured by RWEY et al. (Philips Reserch
(Report 5173 (1950)) However, the study by VERWEY et al. Has been completed at the academic stage only, prior to the development of the application as a thermistor, and the study as a thermistor material was described by Hisao Futaki ( (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, there has been a demand for a thermistor material having a low specific resistance and a high B constant for the purpose of improving responsiveness, such as for a water temperature gauge of an automobile or a temperature sensor of an iron. However, 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) 69.0 to 96.0 at%, copper (Cu) 0.4 to
5.0 atomic%, lithium (Li) 2.5-22.0 atomic%, nickel (Ni) 0.5-5.5 atomic%, and silicon (Si) 0.0-2.0 atomic% (excluding 0.0 atomic%), total 100 atomic% It is made.

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 is cobalt oxide (CoO)
Is the basic composition, and when tricobalt tetroxide (Co ₃ O ₄ ) is generated, the high B
Unable to achieve the constant.

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

Commercially available raw materials such as cobalt oxide, copper oxide, lithium oxide, nickel oxide and silicon dioxide were blended so as to have a composition of each atomic% as shown in the table below. As an example of the thermistor production process, these blended compositions were wet-mixed with a ball mill, the slurry was dried and then calcined at a temperature of 800 ° C., and the calcined product was again wet-pulverized and mixed with 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. 25 ° C and
Measure the resistance at 50 ° C (R ₂₅ and R ₅₀ respectively),
The specific resistance ρ ₂₅ at 25 ° C. was calculated from the following equation (1), and the B constant was calculated from the following equation (2).

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, 5, 6, 8, 9, 12, 13, 15, 16, 17
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. In addition, zirconia cobblestone was used for mixing and pulverization.

Advantageous Effects of the Invention As described above, according to the present invention, by further adding silicon to cobalt, copper, lithium, and nickel, it is intended to further reduce the specific resistance and the B constant more than the ternary material. Further, since silicon is easily vitrified with lithium, it is necessary to compensate for the amount of lithium that forms a solid solution with cobalt.
Although a slight increase in the B constant is observed as an effect of the addition of silicon, it is unclear whether or not the glass phase contributes.

As described above, the present invention provides an oxide semiconductor for a thermistor having a low specific resistance and a negative temperature coefficient of resistance having a high B constant. However, as a sensor, it has high detection accuracy and high response to temperature. And the power can be saved. In addition, 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 69.0 to 96.0 atomic% of cobalt and 0.4% of copper as constituent metal elements.
~ 5.0 atomic%, lithium 2.5 ~ 22.0 atomic%, nickel 0.5
An oxide semiconductor for a thermistor, characterized by containing a total of 100 atomic% of five kinds of -5.5 atomic% and silicon 0.0-2.0 atomic% (excluding 0.0 atomic%).