JPS5831502A - Thin film thermistor - 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 thermistor that detects temperature by mechanically contacting an object whose temperature is to be detected, such as a thermistor that detects the temperature of food inside a pot through the bottom of the pot when cooking food in a pot. It is related to.

Conventionally, this temperature detection has been carried out by mechanically bringing a thermocouple 2 into contact with the pot bottom 1 and detecting the thermoelectromotive force of the thermocouple 2, as shown in FIG.

At this time, the thermocouple 2 was fixed to the support container 3 in order to bring the thermocouple 2 into strong mechanical contact with the pot bottom 1.

However, the thermoelectromotive force usually has the drawback that only a small value can be obtained. For example, an alumel-chromel thermocouple has excellent heat resistance (60 to 100°C in air) and is inexpensive, but it generates an electromotive force of only -40 μv/°C. Copper-constantan thermocouples and platinum-platinum/rhodium thermocouples not only provide a thermoelectromotive force of only (30 to eo) μV/'C, but also have low heat resistance (copper-constantan thermocouples) and are expensive. There were drawbacks such as (platinum-platinum-rhodium thermocouple). Various other thermocouples exist, but all of them have the drawbacks mentioned above. As mentioned above, when controlling the amount of heat generated by a heat source by electrically detecting a small thermoelectromotive force, a large electrical amplification is required, which increases the price and requires a complicated electrical circuit. There are also 3 drawbacks such as
He lived a good life.

On the other hand, when temperature is detected using a thermistor instead of the above thermocouple, the rate of change in resistance value with respect to temperature is (1 to 7%).
/°C) can be obtained. Therefore, it does not require a complicated electric circuit and has the advantage of being low cost. In this case, the thermistor element is selected to be as small as possible and to have a low heat capacity. This is because miniaturization allows for faster thermal response. Such small-sized thermistor elements include bead-type thermistor elements using composite oxide sintered bodies such as Fe, Ni, Go, and Mn as the temperature-sensitive resistor, or composite oxides such as those mentioned above, Go, Si, and S.
There is a thin film thermistor element that uses a thin film such as iC as a temperature sensitive resistor. However, bead-type thermistor elements are usually used.

Because it has a shape similar to a sphere or a spheroid,
Even if this thermistor element was fixed to the support container 3, there was a drawback that the thermal resistance became large. In other words, even though the thermal capacity of the thermistor element itself is small, it is difficult to reduce the thermal resistance at the connection part with the support container 3 due to its complicated shape, and as a result, the thermal response becomes slow. There were drawbacks.

On the other hand, since the thin film thermistor element can be connected to the support container 3 by brazing as shown in FIG. 2, it has the advantage of providing high-speed response. However, in this case, the following drawbacks also occurred. That is, the above-mentioned thin film temperature sensitive resistor film 6 is formed, and the lead wire 7 is further connected to the electrode film 6. A film 8 was formed and the support container 3 was connected to the support container 3 via a brazing material layer 9 by brazing. However, since metals such as W and Mo have high melting points and are easily oxidized, the metallized film 8 is usually formed at a high temperature of 1400 °C or higher in a reducing atmosphere containing a bow or the like. Therefore, the manufacturing process is complicated and requires special equipment, as well as being expensive.

Further, as the electrode film 6, a thick film electrode film with excellent heat resistance is often used, but a thick film electrode film easily deteriorates in a reducing atmosphere.
In addition, the heat resistance is 100°C or less in air, so thick film electrode films are not suitable for the process of forming metallized films, and conversely, metallized films are also It is not suitable for firing at high temperatures of ~100°C). Therefore, in the configuration shown in FIG. 2, a metallized film must also be used for the electrode film 6. This not only increases the price, but also has the disadvantage that when connecting the lead wire 7 to the electrode film 6, it is difficult to perform the commonly used welding connection since the metallized film has a high melting point.

The present invention provides a thin film thermistor that overcomes these conventional drawbacks.

The gist of the present invention is to show a thin film thermistor chip and a support container formed by forming an electrode film 6 and a temperature sensitive resistor film 6 on one surface of a flat ceramic insulating substrate 4, as shown in FIG. 3 which is an embodiment. 3, a titanium film 10 or a zirconium film 10 is formed on the other surface of the ceramic insulating substrate 4, and the titanium film 10 or zirconium film 1o and the support container 3 are brazed together. At the point of connection. The soldered connection is made via the brazing material layer 9.

Alumina, mullite, steatite, etc. are often used for the ceramic insulating substrate 4. Normally, this type of ceramic insulating substrate 4 and the brazing material 9 do not wet each other, that is, there is almost no chemical bonding force between them.

For this reason, it has been difficult to connect the ceramic insulating substrate 4 with brazing. However, since the thermistor chip of the present invention has the titanium film 10 or the zirconium film 1o formed on the other surface, the brazing material 9 is wetted with the brazing material 9, so that the brazing material is formed in the support container 3. Titanium film 1o or zirconium film 1o
can be easily formed by a vacuum evaporation method or a sputtering method. In the case of the vacuum evaporation method, titanium or zirconium is evaporated in a vacuum of 10-5 torr or less to form these films, but at this time the thermistor chip is only heated to about 300°C, so the electrode film is As 5, a thick film electrode film can be used. The sputtering method is almost the same as vacuum deposition except that it is processed in a vacuum of 10-1 to 10 torr, so a thick electrode film can be used. That is, the structure of the present invention can be adapted to the process of forming a thick film electrode film. Therefore, not only is the cost low, but also the lead wire 7 can be easily connected to the electrode film 6 by welding.

Note that it is possible to form another metal film instead of the titanium film 10 or the zirconium film 10, but it must have strong adhesion to the ceramic insulating substrate 4 and have a melting point higher than the melting point of the brazing material 9. Considering the fact that most of this metal film does not diffuse into the brazing material e during brazing, the titanium film 10 or the zirconium film 10 is preferable.

That is, gold, silver, copper, platinum, and the like have a drawback that their adhesion to the ceramic insulating substrate 4 is weak, and almost all of them diffuse into the brazing material 9 during brazing.

Furthermore, tungsten, molybdenum, and the like have the drawback of weak adhesion. Also, aluminum, zinc, tin, etc. have a drawback of having a low melting point. On the other hand, titanium and zirconium are optimal in that they satisfy all of the above conditions.

The material of the support container 3 is J-var alloy and titanium.

Preferably, it is selected from the group of tantalum, platinum, stainless steel, iron-nickel alloy, etc. This means that the thermal expansion coefficient of the ceramic insulating substrate 4 is (SO~90)
7/°C, it is desirable that the support container 3 has a similar value.

The solder material 9 may be copper solder or silver solder, but silver-copper eutectic silver solder is better. This is because this silver brazing material is easy to process into a foil shape and is often used industrially in a foil shape. This is because brazing connection can be easily achieved by placing a foil brazing material between the two and heating it to ~80°C in a vacuum.

Example An electrode film 6 of Au-P is formed on one surface of the alumina substrate 4.
After forming a StC temperature sensitive resistor film 6, a titanium film 1 is formed.
o was formed by vacuum evaporation. Thereafter, a brazing connection was made to a support container 3 made of stainless steel via a silver-copper eutectic silver brazing material 9. Next, the platinum wire 7 was connected to the Au-Pt electrode film 6 by welding. 90 of the thermistor formed in this way
% response time was measured. eo% response time is initially T1℃
When the temperature of the bottom of the pot in Figure 1, which was maintained at
- T1) The time required to reach °C, T1 - room temperature, T2
= ~10°C. As a result, the eo% response time was 3 to 5 seconds, showing almost the same high-speed response as the configuration shown in FIG. Further, the adhesive strength of the alumina substrate 4 to the support container 3 was 1 to 6 ooy/-, indicating a strength sufficient for practical use. Furthermore, even when a thermal shock test was conducted in air at 360° C. and in room temperature water for 10 cycles, no mechanical deterioration of the brazed joint was observed, and there was almost no change in thermal response.

FIG. 3 is a sectional view showing the structure of a thin film thermistor according to an embodiment of the present invention.

3... Support container, 4... Ceramic insulating substrate, 6... Electrode film, 6... Temperature sensitive resistor film, 7... ... Lead wire, 9 ... Brazing material layer, 10 ... Titanium film or zirconium film.

Claims (1)

[Scope of Claims] (1) A thin-film thermistor chip formed by forming an electrode film and a temperature-sensitive resistor film on one surface of a flat ceramic insulating substrate and a support container are connected, and the ceramic insulating A thin film thermistor in which a titanium film or zirconium film is formed on the other surface of the substrate, and the titanium film or zirconium film is connected to a support container by brazing. (?) The material of the support container is Kovar alloy and titanium. The thin film thermistor according to claim 1, which is one selected from the group consisting of metal/tal, platinum, stainless steel, and iron-nickel alloy. (3) The thin film thermistor according to claim 1, wherein the solder material is a silver-steel eutectic silver solder.