JPH04313284A - Thin-film thermoelectric element - Google Patents

Abstract

PURPOSE:To obtain a thin-film thermoelectric element which can be used up to a high temperature region with a high sensitivity by using a transition metal silicide as a thermoelectric material. CONSTITUTION:A thin-film thermoelectric element is obtained by forming a thin-film pattern 2 of a p-type transition metal silicide and a thin-film pattern 3 of an n-type transition metal silicide where a positive hole concentration and an electron concentration are controlled by a mixed ratio of a transition metal silicide showing a p-type conduction and that showing an n-type conduction on a substrate 1.

Description

[Detailed description of the invention]

[0001] This invention relates to an infrared sensor, a temperature sensor,
This invention relates to thin film thermoelectric elements used in thermal sensors and the like.

0002

[Prior Art] Conventionally, infrared sensors, temperature sensors,
2. Description of the Related Art A so-called thermopile type thermoelectric element, in which a large number of thermocouples are connected in series, has been developed for use as a thermal sensor.

Generally, a thermopile type thermoelectric element has a structure in which a large number of thermoelectric materials are connected in series, and thermoelectromotive force generated from a temperature difference is added, and a large thermoelectromotive force can be obtained.

[0004] Thereby, it can be used as a highly efficient thermoelectric conversion element or a highly sensitive infrared, temperature, or thermal sensor that detects minute temperature differences. In particular, thin film thermoelectric elements are mainly used for sensor applications in order to achieve miniaturization, high sensitivity, and high response speed. In a conventional thin film thermoelectric element, thin wire patterns made of an n-type thermoelectric material and thin wire patterns made of a p-type thermoelectric material are alternately connected in series on a substrate.

Constantan-nichrome (Japanese Patent Publication No. 61-4015) is used as a thermoelectric material for such conventional thin-film thermoelectric elements.
No. 4), Si, Ge (Japanese Unexamined Patent Publication No. 57-7172), Bi
-Sb-Te (JP-A-53-132282, JP-A-6
Metal-based or semiconductor-based materials such as No. 1-22676) have been used.

[0006]

[Problems to be Solved by the Invention] These conventional thermoelectric materials have the advantage of high electrical conductivity and high thermoelectric conversion efficiency, but they have a small Seebeck coefficient, a large temperature change in the Seebeck coefficient, and cannot be used at high temperatures. It has the following disadvantages. In addition, metal-based thermoelectric materials such as copper-constantan are easy to form into thin films, but have the disadvantage of small thermoelectromotive force and low sensitivity, while compound semiconductor materials such as Bi-Sb-Te have relatively high sensitivity. However, it has drawbacks such as poor adhesion to the substrate, difficulty in etching, and high cost.

By the way, transition metal silicides exhibit conductivity forms ranging from metal conductivity to semimetallic conductivity and semiconductor conductivity, and have long been used as resistor materials with excellent oxidation resistance. But F
Except for eSi2, FeS has a small Seebeck coefficient of less than 100 μV/K and is used as a thermoelectric material.
i2 only. Among transition metal silicides, FeSi
2 is an intrinsic semiconductor and exhibits p and n conduction and thermoelectric properties by adding and controlling impurities, but other transition metal silicides are generally not intrinsic semiconductors and have Fermi energy near the valence band or conduction band. Many are degenerate. Therefore, although the electrical conductivity is high, the Seebeck coefficient is small.

An object of the present invention is to obtain an inexpensive thin film thermoelectric element that has high sensitivity, can be used up to a high temperature range, and exhibits little change in Seebeck coefficient up to a high temperature range.

[0009]

[Means for Solving the Problems] The present invention focuses on transition metal silicides that have high adhesion to Si substrates or SiO2 substrates and good selective etching properties as thin film thermoelectric elements. However, as mentioned above, transition metal silicides other than FeSi2 tend to have high electrical conductivity and low Seebeck coefficient.

In general, semiconductors tend to show a tendency that the lower the carrier concentration, the higher the Seebeck coefficient and the lower the electrical conductivity, and conversely, the higher the carrier concentration, the lower the Seebeck coefficient and the higher the electrical conductivity. As mentioned above, most transition metal silicides are degenerate semiconductors with very high hole or electron carrier concentrations and exhibit the latter characteristic.

[0011] There is a figure of merit as an index of thermoelectric conversion efficiency, and the highest region of this figure of merit is a carrier concentration of about 1025/m3. Therefore, the inventors formed an intermetallic compound containing both a hole-conducting (p-type) transition metal silicide and an electron-conducting (n-type) transition metal silicide with a high carrier concentration to appropriately dissipate carriers. The concentration was controlled by

It has been found that a thin film thermoelectric element free from the above-mentioned drawbacks can be obtained by forming a thin film of transition metal silicide having optimum carrier concentrations for p-type and n-type on a substrate.

The thin film thermoelectric element of the present invention contains both a transition metal silicide exhibiting p-type conduction and a transition metal silicide exhibiting n-type conductivity, and the hole concentration and electron concentration are controlled by the mixing ratio of the two. Thin film pattern of p-type transition metal silicide and n
It is characterized by forming a thin film pattern of type transition metal silicide on a substrate.

[0014]

[Operation] In the thin film thermoelectric element of the present invention, the hole concentration and electron concentration are controlled by the mixing ratio of the transition metal silicide exhibiting p-type conduction and the transition metal silicide exhibiting n-type conduction, respectively.
A thin film pattern of p-type transition metal silicide and a thin film pattern of n-type transition metal silicide are formed on a substrate. Therefore p
By controlling the carrier concentration of transition metal silicides with electrical conductivity of , n to an optimal value, a thin film pattern with good thermoelectric properties is formed on the substrate, and it can be used with high sensitivity up to high temperatures. A thin film thermoelectric element whose Seebeck coefficient changes little with temperature can be obtained.

[0015]

[Embodiment] An embodiment of the present invention will be explained in the order of manufacturing steps based on FIGS. 1 to 3.

<Preparation of p-type semiconductor target> First,
27 mol % Cr with purity 99.99% or higher, purity 9
More than 9.99% Co, 7 mol % and purity 99.
Powders containing 999% or more of 66 mol % Si were mixed, pre-pressed into a disk shape, and then heated at 2000 k in Ar.
HIP (hot isostatic pressing) is performed at 1000° C. and 1000° C. Thereafter, the surface of the sintered body is polished to obtain a p-type semiconductor target.

<Preparation of n-type semiconductor target> First,
4 mol% Cr with purity 99.99% or higher, purity 99
．． More than 99% Co, 30 mol % and purity 99.
Powders containing 999% or more of 66 mol % Si were mixed, pre-pressed into a disk shape, and then heated at 2000 k in Ar.
HIP is carried out at 1000°C. Thereafter, the surface of the sintered body is polished to obtain an n-type semiconductor target.

<Formation of p-type semiconductor thin film pattern>
A thin film is formed over the entire surface of the substrate by RF sputtering using a mold semiconductor target. The sputtering conditions at this time are as follows.

Substrate temperature: 300° C. High frequency output: 500 W to 1.5 kW Rate: 1 to 10 μm/hr Subsequently, the p-type semiconductor thin film at unnecessary locations is removed by forming a photoresist film, mask exposure, development, and lift-off. A p-type semiconductor thin film pattern is formed.

FIG. 1 shows the state of the substrate at this time. Figure 1
In (A) is a plan view, (B) is a schematic front view,
1 is a glass substrate, and 2 is a p-type semiconductor thin film pattern.

<Formation of n-type semiconductor thin film pattern>
Using a mold semiconductor target, an n-type semiconductor thin film is formed over the entire surface of the substrate by RF sputtering. The sputtering conditions at this time are as follows.

Substrate temperature: 300° C. High frequency output: 500 W to 1.5 kW Rate: 1 to 10 μm/hr After that, unnecessary n-type semiconductor thin film is removed by forming a photoresist film, mask exposure, development, and lift-off. Form an n-type semiconductor thin film pattern.

FIG. 2 shows the state of the substrate at this time. Figure 2
(A) is a plan view, and (B) is a schematic front view. As shown in this figure, an n-type semiconductor thin film pattern 3 is formed by partially overlapping the already formed p-type semiconductor thin film pattern 2 at the hot/cold junction, and the p-type semiconductor thin film pattern 3 is formed as shown in the figure. 2 and n-type semiconductor thin film pattern 3 are connected in series.

<Other Pattern Formation> Thereafter, the entire substrate is heat treated in a vacuum at 600 to 800° C. in order to stabilize the film. As shown in FIG. 3, a heat collecting black body 4 made of platinum black or the like is formed in the center of the substrate, and lead-out electrodes 5, made of an electrode material such as Ni are placed at predetermined locations on the substrate.
form 5.

In the embodiments shown above, the number of thermocouples is reduced to make the drawings clearer, but each pattern can be made finer. For example, in the structure shown in Figure 3, a thermoelectric element with 150 pairs of thermocouples was created on a 5 mm square substrate, and the sensitivity was measured while performing temperature compensation using a thermistor.
It was 110V/W at the bottom.

[0026]

[Effects of the Invention] According to the present invention, by controlling the carrier concentration of transition metal silicides exhibiting p-type and n-type electrical conductivity, it is possible to form a thin film with good thermoelectric properties, and with high sensitivity. A thin film thermoelectric element can be obtained that can be used up to a high temperature range and has a small change in Seebeck coefficient up to a high temperature range.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a state in the middle of manufacturing a thin film thermoelectric element according to an example, in which (A) is a plan view and (B) is a schematic front view.

FIG. 2 is a diagram showing a state in the middle of manufacturing a thin film thermoelectric element according to an example, in which (A) is a plan view and (B) is a schematic front view.

FIG. 3 is a diagram showing a completed thin film thermoelectric element, (A)
is a plan view, and (B) is a schematic front view.

[Explanation of symbols]

1-Glass substrate 2-p type semiconductor thin film pattern 3-n type semiconductor thin film pattern 4- Heat collecting blackbody 5-electrode

Claims (1)

[Claims] 1. A p-type transition metal silicide containing both a transition metal silicide exhibiting p-type conductivity and a transition metal silicide exhibiting n-type conductivity, with hole concentration and electron concentration controlled respectively by the mixing ratio thereof. A thin film thermoelectric element comprising a thin film pattern of n-type transition metal silicide and a thin film pattern of n-type transition metal silicide formed on a substrate.