JPH03187279A - Bi-te thermoelectric conversion thin film and its thermoelectric conversion element - Google Patents

Abstract

PURPOSE:To optimize the thermoelectric performance of a film to the direction of the hot flow during film formation by forming the thermoelectric semiconductor film on a substrate out of a Bi-Te crystal in c face orientation. CONSTITUTION:A Bi-Te thermoelectric semiconductor consisting of, for example, Bi-Sb-Se polycrystal in c face orientation is made on a substrate 1. In this case, as the Bi-Te thermoelectric conversion film 2 is made of the Bi-Te thermoelectric semiconductor consisting of Bi-Te polycrystal in c face orientation, since faces are disposed with the c axis direction, in which thermal conductivity is small, parallel with the direction of hot flow, the performance index controlling the performance as a thermoelectric conversion element can be improved. Hereby, making use of this thermoelectric film as a thermoelectric semiconductor chip, the whole thermoelectric conversion element can be miniaturized and highly integrated with the thermoelectric performance equivalent to a bulk maintained.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a Bi-Te (bismuth-tellurium)-based thermoelectric conversion thin film and a thermoelectric conversion element thereof, and is particularly applicable to thermoelectric conversion in the electrical industry, energy industry, and aerospace field. B used in thermoelectric conversion elements for power generation and electronic cooling/heating
This invention relates to a 1-Te-based thermoelectric conversion thin film and a thermoelectric conversion element using the same.

[Prior Art] Thermoelectric conversion materials used in thermoelectric conversion devices generally include those called thermoelectric semiconductors that have high carrier mobility and low lattice thermal conductivity. In other words, thermoelectric semiconductors are desirably ones that have large Bertier and Seebeck effects and small losses due to Joule heat and thermal conduction, that is, have a large figure of merit 2, and materials that are suitable for the operating temperature of the device are selected and used.

8l-Te series thermoelectric semiconductors including Bi-Sb-Te-3e series are used as thermoelectric semiconductors that have a relatively low operating temperature and a high figure of merit.

Old-Sb-Te-3 used for thermoelectric conversion as mentioned above
The thermoelectric performance of e-based semiconductor single crystals is described in, for example, Journal
or the physics and chemis
try or so ds, 49 [101 (1988
) (English) P, 1237-1247, it is generally known to be anisotropic. Therefore, since the bulk semiconductor chips used to form thermoelectric conversion elements are made of single crystals, pseudo-single crystals, or polycrystals with a texture, their thermoelectric performance is different from that of single crystals. It becomes anisotropic reflecting the influence of orientation. However, when arranging them to form a thermal lightning conversion element, the optimal chip orientation can be selected depending on the direction of heat flow used, so the element is formed by selecting the chip orientation.

On the other hand, when attempting to downsize and highly integrate the entire device by constructing the device with a thin-film semiconductor chip, the polycrystalline material that makes up the chip generally forms a texture during film formation, so the direction of heat flow is The orientation with respect to the substrate that determines the film is fixed during film formation, and it is not possible to optimize the chip orientation after film formation, as was done for conventional bulk chips, which makes it difficult to put it into practical use. This is the current situation.

[Problems to be Solved by the Invention] As described above, when a B 1-3b-Te-Se based thermoelectric conversion element is constructed with a thin film chip, the thermoelectric performance of the chip is deteriorated due to the texture (preferential orientation) of the film. becomes anisotropic, but since its orientation with respect to the substrate, which determines the direction of heat flow, is determined during film formation, its orientation relative to the direction of heat flow is determined after film formation, as in the case of conventional bulk semiconductor chips There is a problem that optimization cannot be achieved.

The present invention was made to solve this problem.
The object of the present invention is to provide a B 1-Te-based thermoelectric conversion thin film and a thermoelectric conversion element thereof, in which the thermoelectric performance of the thin film is optimized in the direction of heat flow during film formation.

[Means for Solving the Problems] The Bi-Te thermoelectric conversion thin film according to the present invention uses a Bi-Te thermoelectric semiconductor composed of, for example, a B1-Sb-Te-3e polycrystalline body oriented in the C-plane. It is formed on a substrate. In this case, the C-plane oriented thermoelectric semiconductor film having the above structure has its thickness direction as the direction of heat waves and current.

Further, the Bi-Te based thermoelectric conversion element according to the present invention has a C-plane oriented Bi-Sb-T having a thickness of 1001 m or less.
It is formed by using an e-3e polycrystalline thermoelectric conversion thin film as a thermoelectric semiconductor chip.

[Function] In this invention, since the old-Te-based thermoelectric conversion thin film is formed of a thermoelectric semiconductor consisting of a B1-Te-based polycrystal with C-plane orientation, the C-axis direction, which has low thermal conductivity, is Since they are arranged parallel to the direction of heat flow, they contribute to improving the figure of merit that governs the performance of the thermal lightning conversion element. In this C-plane oriented thermal lightning conversion thin film, optimization of thermal lightning performance is achieved during film formation, with the film thickness direction being the direction of heat waves and current. Therefore, this film is suitable as a thermoelectric semiconductor chip for a high-performance thermal lightning conversion element.

〔Example〕

FIG. 1 shows an embodiment of the present invention, BI-Sb-Te-
FIG. 9 is a schematic explanatory diagram of a 9c-based polycrystalline thermoelectric conversion thin film. In the figure, 1 is a substrate, and 2 is a thermoelectric conversion thin film formed on the substrate 1 and made of a C-plane oriented Bi-Sb-Te-Se polycrystalline thermoelectric semiconductor. The thick arrow shown in the figure shows the direction of the C-axis, and the thin arrow shows the direction of heat waves and current during thermoelectric conversion operation.

The film forming conditions for thermoelectric conversion thin film [2] were to use argon ion beam sputtering method, and to operate at an operating pressure of 2.0 x 10-' Tor.
r, beam voltage LOOOV, beam current 10 mA, and substrate temperature 200°C. By this film forming method, a thermoelectric conversion thin film H2 consisting of an aggregate in which each crystal grain 3 is oriented in the C-plane can be obtained. Note that the thermoelectric conversion thin film is not limited to the old-9b-Te-Se system, but may have any composition as long as it is a 131-Te system thermoelectric semiconductor.

Figure 2 shows a 2-layer Bi- film formed as described above.
Xv of Sb-Te-Se polycrystalline thermoelectric conversion thin film (n type)
A diffraction pattern. In the figure, the horizontal axis is the diffraction angle, and the vertical axis is the X-ray intensity. The X-rays used to measure the X-ray diffraction pattern were produced by monochromating copper characteristic X-rays generated from a copper target using a monochromator. Incidentally, FIG. 3 shows an X-ray diffraction pattern in a non-oriented state measured using a powder sample having the same composition as the thin film used in the measurement in FIG. 2 for comparison. The horizontal and vertical axes are the same as in FIG. Comparing FIGS. 2 and 3, it can be seen that the peak labeled 008,0015 in FIG. 2 is significantly larger than the same peak in the pattern of FIG. This means that the thermoelectric conversion thin film used for the measurement in Figure 2 is
This means that it has a C-plane oriented polycrystalline structure as shown in the example in the figure.

By the way, the old-T including the B l-Sb-Te-3e system
In the case of a single crystal of e-based thermoelectric semiconductor, its Seebeck coefficient α
Although the value of is almost isotropic, its resistivity ρ and thermal conductivity are extremely anisotropic, and if the crystal structure is expressed as a hexagonal crystal, ρ33/ρ1□-4 to 6, 1□ / to 33-2
~2.5 is known. In addition to the above-mentioned documents, this is disclosed in three or four papers published from 1957 to 1961, although not listed. however,
The subscripts 11.33 of ρ and ni represent the direction parallel to the 0-plane and the direction perpendicular to the 0-plane, respectively.

Therefore, the C weight according to the present invention is Bi-5b-
Te-Se based thermoelectric conversion thin film has a C-axis direction with low thermal conductivity aligned in the direction of heat flow, so it has a figure of merit of 2 which governs the performance as a thermoelectric conversion element (when the operating temperature is fixed). (-α2/ to ρ). In this way, by forming a thermoelectric conversion thin film with a texture of C-plane oriented crystal grains in the film thickness direction, we have achieved a figure of merit 2 of 2 x 1O-3 (K'-') or more. The usefulness was confirmed.

FIG. 4 shows the original form 1-1 formed using the C-plane oriented thermoelectric conversion thin film 2 according to the present invention as a thermoelectric semiconductor chip.
FIG. 2 is a schematic explanatory diagram of a Te-based thermoelectric conversion element.

In the figure, for example, an n-type thermoelectric thin film consisting of the thermoelectric conversion thin film (hereinafter referred to as thermoelectric thin film) 2 explained in the embodiment of FIG. 2a, a p-type thermoelectric thin film 2b is provided.

For example, the p-type thermoelectric thin film 2b is placed on the electrode 4C,
A pair of n-type thermoelectric thin films 2a are formed at predetermined intervals.

Furthermore, for example, n-type thermoelectric thin film 2a + p-type thermoelectric thin film 2b
Electrodes 4b and 4d are formed to cover a pair of electrodes, and a thermal lightning conversion element is formed such that a thermoelectric thin film is sandwiched between the upper and lower electrodes. Therefore, one unit of this element is constituted by, for example, the electrodes 4a, 4b, and 4C, and the n-type thermoelectric thin film 2a and the p-type thermoelectric thin film 2b sandwiched therebetween. Such width number 1 Jffl ~ number 10
By alternately connecting unit thermoelectric thin films of - through upper and lower electrodes, it is possible to form a thermoelectric conversion element with a large number of chips per unit area, that is, with a large energy transport density.

In the configuration shown in Figure 4, for example, when the upper side is the heat-absorbing surface and the lower side is the heat-generating surface, the direction of current will be as shown by the arrow, and the direction of heat flow (temperature gradient) will also be as shown by the arrow in the frame. works. Therefore, the direction of current in the thermoelectric thin film is the direction of its thickness.

In general, the performance of a unit semiconductor chip depends only on its shape ratio, that is, its cross-sectional area/height (thickness), so if this shape ratio is constant, the thickness will be thinner, and the device will be smaller. and the effect of reducing material costs is significant. By using thin film formation processes such as vapor deposition and sputtering, it is possible to form semiconductor thin films with a thickness of 100 mm or less, which cannot be achieved (or is not practical in terms of yield) with bulk manufacturing processes such as melt molding and sintering. is easy, and C-plane oriented Bi-Te prepared by such a thin film formation process
Thermoelectric thin films can provide thermoelectric conversion elements that can be downsized and highly integrated, and can significantly reduce material costs.

[Effects of the Invention] As described above, according to the present invention, C-plane oriented Bi-T
An e-based polycrystalline thermoelectric conversion thin film was achieved by applying ordinary thin film formation process technology, and its usefulness was confirmed. By using this thermoelectric thin film as a thermoelectric semiconductor chip, it becomes possible to downsize and highly integrate the entire thermoelectric conversion element while maintaining thermoelectric performance equivalent to that of the bulk, thereby reducing material costs and, ultimately, the element price. It can be significantly lower than the type. Furthermore, conventional devices that use bulk semiconductor chips cannot be used in large numbers due to the size of the device itself, so they can only be used at low voltages and high currents. However, by using the thin film type small chip of the present invention, it is possible to significantly change the chip shape ratio (Ifr surface height) and the number of series arrays, so it can be used at high voltage and low current. This has the effect of expanding the range of electronic circuits that can be combined with the element.

[Brief explanation of drawings]

FIG. 1 shows an embodiment of the present invention with C-plane oriented B.
A schematic explanatory diagram of l-9b-Te-Se based polycrystalline thermoelectric conversion thin film, Figure 2 is the X-ray diffraction pattern of the thermoelectric thin film of 21a+ film thickness of the example in Figure 1, and tJ3 diagram is the measurement of Figure 2. X-ray diffraction pattern of a powder sample having the same composition as the sample, 4th
The figure is a schematic explanatory diagram of an original old-Te type thermoelectric conversion element showing an embodiment of the present invention. In the figure, 1 is a substrate, 2, 2a, and 2b are thermoelectric conversion thin films, and 3 is a crystal grain, and 4a, 4b, 4c, and 4d. 4e is an electrode.

Claims (3)

[Claims] (1) Bi characterized in that the thermoelectric semiconductor film formed on the substrate is made of a Bi-Te-based polycrystalline body oriented in the c-plane.
-Te-based thermoelectric conversion thin film. (2) The Bi-Te based thermoelectric conversion thin film according to claim 1, wherein the thickness direction of the thermoelectric semiconductor film is the direction of heat waves and current. (3) C-plane oriented Bi with a thickness of 100 μm or less
- A Bi-Te-based thermoelectric conversion element comprising a Sb-Te-Se-based polycrystalline thermoelectric conversion thin film as a thermoelectric semiconductor chip.