JPH0221675A - Substrate for thin film thermopile use - Google Patents

Abstract

PURPOSE:To make it possible to obtain a thermopile having a superior thermoelectric conversion efficiency and also a high sensitivity by a method wherein a part to be formed with a thin film type thermoelectric body consists of dense ceramics and at least a part which comes into contact to the dense ceramics, out of the residual parts is constituted of porous ceramics. CONSTITUTION:A material made by a method wherein Al2O3 is contained as a main component, SiO2 and MgO are added as a firing assistant and moreover, a binder is added, is kneaded and after then, a first ceramic green sheet is molded from the kneaded material. On the other hand, a material made by adding further organic cellulose to a material identical with this material by 50wt.% is kneaded and a second ceramic green sheet is molded from the kneaded material. Then, the first ceramic green sheet 1 is superposed on the second ceramic green sheet 2 and the sheets 1 and 2 are fixed by pressure and moreover, are cut in a prescribed size. Thereby, the sheets are formed as a molding 3 and the molding is fired to obtain a substrate 3.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an improvement in a substrate used in a thin film thermopile, and particularly to one having an improved heat conduction structure.

[Conventional technology]

2. Description of the Related Art Thin film thermopiles, which are formed by forming a thin film thermoelectric material on an insulating substrate, have been well known. (For example, JP-A No. 6
1-259580, JP-A-577172, etc.).

By the way, insulating substrates are usually made of glass, ceramics, etc., but in order to stabilize the characteristics of the thin film-like thermoelectric body formed on it, it is required that the surface be smooth. . Conventionally, extremely dense ceramic materials such as A2.01 have been used as materials that are inexpensive and meet this requirement.

[Technical problem to be solved by the invention] However,
Aj! When using a substrate made of a very dense sintered body such as Therefore, the energy radiated from the heat source easily escapes to the substrate side, and the thermoelectric conversion efficiency is not sufficient. Also,
Due to its high thermal conductivity, the response intensity was also not sufficient.

Therefore, an object of the present invention is to provide a thermopile substrate that has excellent thermoelectric conversion efficiency and can obtain a highly sensitive thermopile.

[Means for solving technical problems]

The thin film thermoelectric substrate of the present invention is characterized in that the portion where the thin film thermoelectric body is formed is made of dense ceramics, and of the remaining portion, at least the portion that contacts the dense ceramics is made of porous ceramics. shall be.

[Effect]

Generally, a figure of merit Z expressed by the following formula is used as an index indicating thermoelectric conversion efficiency.

Figure of merit Z - α8/(ρ・K) In the above formula, α is the Seebeck coefficient, ρ is the specific resistance, and K is the thermal conductivity. The figure of merit Z expressed in this formula is
In order to increase the figure of merit Z, which indicates that the larger the value is, the higher the thermoelectric conversion efficiency is, it is necessary to increase the Seebeck coefficient α or to decrease the specific resistance ρ and the thermal conductivity K.

Both the Seebeck coefficient α and the specific resistance ρ are determined by the characteristics of the thin plate-like thermoelectric body. On the other hand, thermal conductivity is influenced not only by the thin film thermoelectric body but also by the substrate supporting the thermoelectric body. This is because the amount of heat obtained by the thin film thermoelectric material is conducted to the substrate side. That is, the thermal conductivity of the substrate ultimately affects the thermoelectric properties of the thermomobile.

Therefore, it is desirable to use a substrate with low thermal conductivity. However, in thin film thermopiles, as mentioned above, the part on which the thin film is formed must be smooth, so a dense substrate such as Al2O with high thermal conductivity is used. Therefore, it was necessary to use a substrate made of a sintered body.

Therefore, the inventors of the present application have proposed that the above-mentioned problems can be solved by lowering the thermal conductivity by using a substrate made of porous ceramics, and by configuring the part where the thin film thermoelectric body is formed from dense ceramics as in the past. We have discovered that this problem can be solved, and have come to form the present invention.

That is, in the present invention, the part where the thin film is formed is made of dense ceramics, so the surface is kept smooth, and at least the part of the remaining part that comes into contact with the dense ceramics is porous. Since it is made of ceramic, a thin film thermopile substrate with low thermal conductivity is realized.

[Explanation of Examples]

A material consisting mainly of Altos, to which 5iO8 and MgO are added as sintering aids, and a binder is further added is kneaded, and then a first ceramic green sheet is formed from the mixed material.

On the other hand, 50% organic cellulose was added to the same material as above.
The mixture containing % fE is kneaded, and a second ceramic green sheet is formed from the mixture.

As shown in FIG. The illustrated molded body 3 is obtained by overlapping the second ceramic green sheets 1 and 2, pressing them together, and cutting them into a predetermined size. This molded body 3 is fired at a temperature of 1400°C to 1600°C, and
．． A substrate of the example having a thickness of 5W is obtained.

As shown in FIG. 1, the obtained substrate 4 is formed so that a dense ceramic portion 5 with a thickness of 0°11 and a porous ceramic portion 6 with a thickness of 0.4W form a layer.
It is constructed to have a thickness of 0.5 mm as a whole.

For comparison, a sintered substrate with a thickness of 0.5 mm was prepared using a ceramic green sheet made only of the first material.
Prepared as a comparative example.

As shown in FIG. 3, 10X2X
O,5M, 10μm thick CutOF! A film 7 is formed. A similar CuxOyl film was also formed on the substrate of the comparative example.

Next, as shown in FIG. 4, Ag is vapor-deposited from both ends to two points in order to form electrodes 8.9. Similar electrodes are formed on the substrate of the comparative example as well.

The thermoelements of Examples and Comparative Examples obtained as described above were set in the apparatus shown in FIG. 5, and their thermoelectromotive force was measured.

In addition, in FIG. 5, 11 indicates a constant temperature layer, and the cough constant temperature layer 1
The temperature inside 1 was adjusted to 25°C. This constant temperature layer 11
Inside is a heater 1 for providing a temperature difference between the electrodes 8 and 9.
2 and 13 are arranged.

An electrode 14.15 for measuring the thermoelectromotive force of the thermopile is arranged between the heater 2.13 and the electrode 8.9 on the thermopile side. During measurement, the thermopiles are stacked upside down as shown in the figure so that the electrodes 8 and 9 on the thermopile side are in contact with the electrodes 14 and 15, and in this state, a temperature difference is created between the heaters 2 and 13. and the thermoelectromotive force was measured.

The results are shown in the table below.

Table As is clear from the table above, it can be seen that the Seebeck coefficient, which is an index of thermoelectromotive force, is considerably higher in the Examples than in the Comparative Examples. This is because the thermal conductivity of the substrate is suppressed compared to the comparative example, so heat dissipation through the substrate is suppressed. In this way, by using the substrate of this example with low thermal conductivity, a thermopile with high thermoelectromotive force and high efficiency can be easily obtained.

Note that in the above embodiment, the first. The substrate was produced by laminating and firing the second ceramic green sheet, but a porous sintered plate was prepared in advance and the porous sintered plate was immersed in ceramic slurry, or the slurry was applied to the surface of the porous sintered plate. A substrate with a similar structure can also be obtained by a method in which the slurry is applied and then baked, or a porous molded body is immersed in a slurry and then baked.

Further, in the above embodiment, the dense ceramic layer is arranged on one side of the porous ceramic layer, but the substrate may be configured so that the dense ceramic layer is arranged on both sides of the porous ceramic layer. . In this case, since both sides of the porous ceramic layer are covered with dense ceramic layers, the strength of the substrate can be increased.

In other words, it is not necessarily necessary to make all of the remaining parts other than the part on which the thin film is formed of porous ceramics, and it is not necessary to make only a small part (the part where the thin film contacts the dense ceramic part on which the thin film is formed). The effects of the present invention can be obtained if the substrate is made of porous ceramics, and the physical structure of the substrate is not limited to that shown in the drawings, as long as such effects can be obtained. In terms of preventing heat dissipation, it is preferable to make it thicker than other parts.

〔Effect of the invention〕

As described above, according to the present invention, the thermal conductivity of the substrate is effectively reduced, and the smoothness of the part where the thin film thermoelectric body is formed is maintained, so that the strength and performance stability can be improved. It becomes possible to realize a thin film thermopile with excellent thermoelectric conversion efficiency and high sensitivity while maintaining the same characteristics.

[Brief explanation of the drawing]

FIG. 1 is a side view of one embodiment of the present invention, FIG. 2 is a side view of the ceramic molded body used to obtain the embodiment of FIG. 1, and FIG. 3 is a thin film thermoelectric FIG. 4 is a side view showing a state in which a body is formed, FIG. 4 is a side view showing a state in which electrodes are formed, and FIG. 5 is a schematic side view for explaining the thermoelectromotive force measuring device. In the figure, 4 is a substrate, 5 is a dense ceramic part,
6 indicates a porous ceramic portion, and 7 indicates a thin film thermoelectric body. Figure 5

Claims (1)

[Claims] In a thermopile substrate on which a thin film thermoelectric body is formed, a portion on which the thin film thermoelectric body is formed is made of dense ceramics, and at least the remaining portion is made of dense ceramics. 1. A substrate for a thin film thermopile, characterized in that a portion in contact with the substrate is made of porous ceramics.