JPH0262004A - Thermistor - Google Patents

Abstract

PURPOSE:To obtain a thermistor whose reliability is excellent by a method wherein four kinds of metals, Co, Li, Cu and Ti, are contained as constituent metal elements and 85% or higher of a content of Li is melted and solidified inside a crystal grain of cobalt oxide of an NaCl type. CONSTITUTION:A thermistor is formed on a sintered and mixed substance of a metal oxide. A total of 100atomic% of four kinds of Co, Li, Cu and Ti are contained as constituent metal elements. At least 85% or higher of a content of Li is melted and solidified inside a crystal grain of cobalt oxide of an NaCl type. Then, it is possible to realize the thermistor whose stability is more excellent than that of a conventional thermistor in a direct-current load test and a wet load test. Thereby, the thermistor whose reliability is excellent can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a thermistor having a large negative temperature coefficient of resistance and which can be used as a highly responsive and highly accurate temperature sensor.

Conventional technology Conventionally, oxide semiconductors made by combining cobalt oxide and lithium have been developed using the old (V
It has been taken up by Arway et al. (Ph1li
ps Re5search Report61了a (1
950)).

However, the study by Vertvey et al. is only at the academic stage, and the solid solution amount of lithium is 1 wt%.
The following was a product that had not yet been developed for use as a thermistor.

In Japan, two reports (Hitachi, Ltd., Collection of papers commemorating the 20th anniversary of the founding of the Central Research Institute, pages 30-46)
, 1960), but the thermistor characteristics are low in both specific resistance and B constant, and are not suitable as a thermistor, but are described as similar to this.

On the other hand, as a result of re-examination by the present inventors, an excellent thermistor material with a low specific resistance and a high B constant can be obtained by combining cobalt oxide and lithium with a specific crystal structure. I found out that it can be done.

Problems to be Solved by the Invention The above-mentioned thermistor material exhibited the best characteristics in a composition range containing 3 to 35% lithium with respect to Coba #l-. That is, as a disk thermistor, 16
Even when left at a high temperature of 0°C, very stable results were obtained compared to conventional spinel crystal type thermistors made of transition metal oxides whose main components are cobalt, manganese, copper, and nickel. However, the DC load test
Particularly in a DC load test in humidity, the problem was that they were not as good as conventional general-purpose thermistors. After analyzing the cause of this defect, we found that lithium, which was thought to be solidly dissolved in cobalt oxide, segregates at grain boundaries or crystal junctions, and the lithium ions move under direct current load.

The present invention solves these problems and aims to provide a thermistor that is highly reliable as a sensor.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention, as a result of various improvement studies, consists of a sintered mixture of metal oxides.
Its constituent metal elements include cobalt (Co), lithium (L), copper (Cu), and titanium (Ti) with a total of 100 atoms, and at least 86 or more of the lithium content is converted to N to Cl. It is characterized by being a solid solution within the crystal grains of type cobalt oxide.

Function By satisfying this ceramic microstructure, it exhibits better stability than conventional thermistors even in DC load tests and humidity load tests.

Example An embodiment of the present invention will be described below.

First, using commercially available cobalt nitrate and lithium carbonate as starting materials, Co: Li: Cu: Ti=sa:
The mixture was dissolved in an atomic ratio of 10:3:3, evaporated to dryness, calcined at a temperature of 600'C, and the calcined product was wet-pulverized in a ball mill. After drying this slurry, add and mix polyvinyl alcohol as a binder, take the required amount and pressure mold it into a disk shape to make many molded products.
It was baked at 0'C for 2 hours. Electrodes containing human g as a main component were provided on both sides of the disk-shaped sintered body thus obtained, and a sample was prepared.

In the above process, several types of samples were prepared by changing the slurry drying method, conditions, and firing conditions.
~95 section RH, humid load with load power 0.4W, and 15
A high temperature storage test (2000 hours) at 0°C was conducted.

In addition, elemental analysis of the device was performed using atomic absorption spectroscopy, dividing the device into device components and eluted components. The results are summarized in the table below.

(Those marked with * are comparative examples and are outside the scope of claims.) In this table, the values shown in the grain section of the lithium content are the total amount minus the elution amount. The value shown in the section (fields and junctions) is the amount of eluted components. Here, as for the product specifications of the thermistor, samples AA, B, and C in the above table satisfy the resistance value change rate in the humidity load test, which is within ±6 coefficients. That is, if the lithium content of 86 atoms or more is dissolved in the crystal grains of UAC6 type cobalt oxide, the specifications can be fully satisfied.

In addition, the specific resistance and B constant of these samples (25°C and 60°C
) are all 1010Ω'cm±1
B constant: 5430±3%.

Here, cobalt has 65 to 99 atoms, and lithium has 35 atoms.
A composition in the range of ~1 atomic ratio is preferable in order to satisfy low resistivity and high B constant, and can further satisfy the electrical characteristics required by the device as a sensor. This is as previously disclosed by the present inventors in Japanese Patent Application No. 63-61049.

Effects of the Invention As described above, the present invention provides a thermistor that has a low specific resistance, a high B constant, and a negative temperature coefficient of resistance, and is excellent in reliability even in high temperature storage tests and humidity load tests. However, as a sensor, it is possible to achieve high accuracy, high responsiveness, and high reliability with respect to temperature, and new applications can be expected.

Claims (1)

[Claims] It consists of a sintered mixture of metal oxides, and its constituent metal elements include cobalt (Co), lithium (Li), and copper (C
u) and titanium (Ti) at a total of 100 atomic %, and at least 85% of the lithium content is N.
A thermistor characterized in that it is a solid solution in the crystal grains of aCl type cobalt oxide.