FIELD OF THE INVENTION

The present invention relates to a thermoelectric conversion element and a method of manufacturing the thermoelectric conversion element.

BACKGROUND OF THE INVENTION

There has been proposed a thermoelectric conversion element in which a plurality of N-type thermoelectric conversion portions and a plurality of P-type thermoelectric conversion portions are alternately arranged (for example, see Patent Document 1). This thermoelectric conversion element has a structure in which a part of each thermoelectric conversion portion is exposed on an outer surface of the thermoelectric conversion element. In addition, examples of this type of thermoelectric conversion element include a thermoelectric conversion element in which an N-type thermoelectric conversion portion is formed using an N-type oxide semiconductor material containing an oxide, and a P-type thermoelectric conversion portion is formed using a P-type semiconductor material containing metal. Incidentally, when such a thermoelectric conversion element is used in an atmosphere in which a corrosive gas such as hydrogen sulfide is dispersed, a part of the P-type thermoelectric conversion portion exposed to the outer surface of the thermoelectric conversion element is exposed to the corrosive gas. Then, the metal contained in the P-type thermoelectric conversion portion reacts with the corrosive gas, and impurities containing a corrosive gas component are formed in the part of the P-type thermoelectric conversion portion exposed on the outer surface of the thermoelectric conversion element. In this case, carrier movement in the P-type thermoelectric conversion portion is hindered, and an output voltage of the thermoelectric conversion element is lowered.

In response thereto, with regard to the above-described thermoelectric conversion element, there is a considered configuration in which the outer surface of the P-type thermoelectric conversion portion is covered with an insulator layer resistant to the corrosive gas. In this case, contact of the P-type thermoelectric conversion portion with the corrosive gas is prevented, so that the decrease in the output voltage of the thermoelectric conversion element described above is suppressed.

Patent Document 1: Japanese Patent Application Laid-Open No. 11-121815

SUMMARY OF THE INVENTION

Incidentally, a thermal expansion coefficient may be greatly different between the N-type thermoelectric conversion portion formed using the N-type oxide semiconductor material containing the oxide and the P-type thermoelectric conversion portion formed using the P-type semiconductor material containing metal in many cases. Further, in a case where the P-type thermoelectric conversion portion is covered with the insulating layer as described above, stresses applied to the P-type and N-type thermoelectric conversion portions increase when ambient temperatures of the P-type and N-type thermoelectric conversion portions greatly fluctuate. Therefore, for example, there is concern that the P-type and N-type thermoelectric conversion portions may be easily cracked after a firing process included in a manufacturing process of the thermoelectric conversion element. In addition, when a difference between a resistance value of the P-type thermoelectric conversion portion and a resistance value of the N-type thermoelectric conversion portion increases, power generation efficiency of the thermoelectric conversion element decreases accordingly.

The invention has been made in view of the above-described reasons, and an object thereof is to provide a thermoelectric conversion element having reduced generation of cracks in a thermoelectric conversion portion in a manufacturing process and having high power generation efficiency, and a method of manufacturing the thermoelectric conversion element.

A thermoelectric conversion element according to the invention includes a laminated body having a plurality of first thermoelectric conversion portions; a plurality of second thermoelectric conversion portions alternately arranged in an arrangement direction with the plurality of first thermoelectric conversion portions such that the plurality of first thermoelectric conversion portions and the plurality of second thermoelectric conversion portions are directly bonded to each other in first regions of bonded surfaces between the plurality of first thermoelectric conversion portions and the plurality of second thermoelectric conversion portions; and an insulator layer interposed between the plurality of first thermoelectric conversion portions and the plurality of second thermoelectric conversion portions in second regions of the bonded surfaces so as to surround a periphery of each of the plurality of second thermoelectric conversion portions. The laminated body has a first main surface and a second main surface located at opposed ends thereof in the arrangement direction and end surfaces located at opposed ends in a direction perpendicular to the arrangement direction, and a ratio of a first thickness of each of the plurality of first thermoelectric conversion portions to a second thickness of each of the plurality of second thermoelectric conversion portions in the arrangement direction is greater than 4 and 11 or less.

In addition, the thermoelectric conversion element according to the invention may further include a first electrode on the first main surface of the laminated body; and a second electrode on the second main surface of the laminated body. Each of the first electrode and the second electrode may include a NiCr layer in which at least a part thereof is in contact with the first main surface or the second main surface of the laminated body.

In addition, in the thermoelectric conversion element according to the invention, the first and second electrodes may be disposed inside a projection area of the second thermoelectric conversion portions in the arrangement direction on each of the first main surface and the second main surface.

In addition, in the thermoelectric conversion element according to the invention, a smallest thickness of a part of the NiCr layer in the arrangement direction may be 1 μm or less.

In addition, in the thermoelectric conversion element according to the invention, the first and second electrodes may include a metal film.

In addition, in the thermoelectric conversion element according to the invention, each of the first thermoelectric conversion portions may comprise an oxide semiconductor, each of the second thermoelectric conversion portions may comprise a semiconductor containing a metal, and the insulator layer may comprise an oxide insulator.

In addition, in the thermoelectric conversion element according to the invention, the oxide semiconductor may be an N-type semiconductor containing a complex oxide, a semiconductor containing the metal may be a P-type semiconductor containing Ni, Mo, and the composite oxide, the oxide insulator may contain Y2O3—ZrO2, and the composite oxide may contain Sr, La, and Ti.

In addition, in the thermoelectric conversion element according to the invention, the oxide insulator may further contain Mn.

A method of manufacturing a thermoelectric conversion element from another viewpoint includes the steps of forming a first insulator paste layer provided with a first slit on an oxide thermoelectric conversion material sheet, forming a metal thermoelectric conversion material paste layer covering the first slit on the first insulator paste layer, forming a second insulator paste layer around a periphery of the metal thermoelectric conversion material paste layer on the first insulator paste layer, covering the metal thermoelectric conversion material paste layer and the second insulator paste layer with a third insulator paste layer provided with a second slit, producing a laminated body including the oxide thermoelectric conversion material sheet, the metal thermoelectric conversion material paste layer, the first insulator paste layer, the second insulator paste layer, and the third insulator paste layer, and firing the laminated body such that thicknesses of the oxide thermoelectric conversion material sheet and the metal thermoelectric conversion material paste layer are set such that a ratio of a first thickness of the oxide thermoelectric conversion material sheet to a second thickness of the metal thermoelectric conversion material paste layer is greater than 4 and 11 or less after the firing of the laminated body.

In addition, the method of manufacturing the thermoelectric conversion element according to the invention may further include forming an electrode after the firing of the laminated body.

In addition, in the method of manufacturing the thermoelectric conversion element according to the invention, the electrode may be formed using a sputtering method.

According to the invention, the ratio of the thickness of the first thermoelectric conversion portion to the thickness of the second thermoelectric conversion portion in the arrangement direction of the first thermoelectric conversion portions and the second thermoelectric conversion portions is greater than 4. In this way, for example, when the thermal expansion coefficient of the second thermoelectric conversion portions is larger than the thermal expansion coefficient of the first thermoelectric conversion portions, the stress applied to the first thermoelectric conversion portions and the second thermoelectric conversion portions immediately after the firing process included in the process of manufacturing the thermoelectric conversion element is alleviated. Therefore, generation of cracks in the first thermoelectric conversion portions and the second thermoelectric conversion portions immediately after the firing process is reduced. In addition, according to the invention, the ratio of the thickness of the first thermoelectric conversion portion to the thickness of the second thermoelectric conversion portion in the arrangement direction of the first thermoelectric conversion portions and the second thermoelectric conversion portions is greater than 4 and 11 or less. In this way, for example, when the first thermoelectric conversion portions include a composite oxide containing Sr, La, and Ti, and the second thermoelectric conversion portions includes Ni, Mo, and the composite oxide, the resistance value of the first thermoelectric conversion portions can be brought close to the resistance value of the second thermoelectric conversion portions, and thus the power generation efficiency of the thermoelectric conversion element is improved accordingly.

