RU2628676C1 - Thermoelectric element - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: thermoelectric element (1) includes at least two films of the base material (2) in form of a carbon material with sp³ atomic bonds hybridization, between which a film of additional material (3) is applied in form of a carbon material with sp² bonds hybridization. The thickness d, nm, of the additional material film (3) and the thickness b, nm, of the base material film (2) satisfy certain rates. Electrical contacts (4), (5) are applied to the opposite peripheral areas of the surface of the additional material film (3).

EFFECT: thermoelectric element (1) has a simpler construction and still maintains high efficiency coefficient.

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Description

The invention relates to thermoelectric instrumentation, in particular to structures and materials used in thermoelectric elements (TEE) and thermoelectric batteries (TEB).

Thermoelectricity is one of the alternative methods in the technology of producing cold, which does not use chemicals that destroy the ozone layer of the Earth, and provides many additional advantages, including the use of only solid-state devices, electronic control of the action, reversibility of the production of heating and cooling. Thermoelectric converters are used in heat recovery systems. However, cooling by thermoelectricity is not widespread due to the low efficiency compared to vapor-liquid compression. Thermoelectric efficiency (coefficient of conversion of thermal and electric energies into each other) depends on the thermoelectric parameter Z of the material from which the thermoelectric device is made. This parameter is determined by the square of the coefficient of thermo-EMF S, multiplied by the coefficient of electrical conductivity σ and divided by the coefficient of thermal conductivity X.

As a result of the development of semiconductor production, TEE and TEB appeared, consisting of semiconductor thermoelements connected in series to an electric circuit through switching elements, each of which is formed by two branches made of semiconductor p- and n-types of conductivity, respectively.

Thus, a thermoelectric element is known (see RU 2475889, IPC H01L 35/08, H01L 35/34, published 03/20/2013), including thermocouples that contain n-type semiconductors and p-type semiconductors connected to at least one electrically conductive contact material.

The disadvantage of this design is the bulkiness of the switching electrical and thermal contacts and the insufficiently high coefficient of efficiency.

Known thermoelectric element (see application JPH 10173243, IPC H01L 35/22, published 06/26/1998), including branches of n-type conductivity from graphite (crystalline carbon) and p-type conductivity in the form of a layered structure of graphite and FeC. Some electrodes (copper plates) are connected with carbon paste to the first end surfaces of the n-type and p-type branches, and the other electrode, a common copper plate, is attached to the other end surfaces of the mentioned branches. The use of such materials for branches of the TEE reduces its cost and environmental pollution.

A disadvantage of the known thermoelectric element is its low thermoelectric efficiency.

Known thermoelectric element (see RU 2223573, IPC H01L 35/32) containing a multilayer body consisting of two or more laminar bodies made of metal, and laminar bodies have an average thickness of from 0.3 to 100 nm, and the thermoelectric element is used by applying current in the direction of the thickness of the multilayer body or in the presence of a temperature difference between both ends in the direction of the thickness of the multilayer body.

The thermoelectric material developed for the known thermoelement has a higher Seebeck coefficient than in traditional semiconductors, and accordingly a higher power conversion coefficient, as well as high impact resistance, resistance to temperature deformation and the ability to shape change. However, the thermoelectric figure of merit Z of a known thermoelement is insufficient for many technical applications. It is known (see Koga T., Rabin O., Dresselhaus MS - Thermoelectric figure of merit of Bi / Pb _1-x EU _x Te superlattices. - Physical Review B, 2000, v. 62, p. 16703) that for homogeneous materials, the largest value of the thermoelectric parameter - Z≈0.003 K ^-1 - at room temperature (300 K) has an alloy of Bi ₂ Te ₃ . Such an alloy has a record thermoelectric parameter for a homogeneous material due to the fact that in electrically conductive materials, along with the usual diffusion mechanism of electron redistribution between hot and cold regions, a much more efficient mechanism for electron capture by the heat flux (phonons), known as the Gurevich effect, is possible (see Gurevich L .E. Thermoelectric properties of conductors. Journal of Experimental and Theoretical Physics, vol. 16, issue 3, pp. 193-227, 1946). The phonon flux carries electrons towards the hot end of the sample and this contributes to the thermopower coefficient. In doped bismuth (Bi ₂ Te ₃ ), this effect determines the overall coefficient of thermo-emf, which creates the above-mentioned record thermoelectric parameter.

A thermoelectric element is known (see US 6670539, IPC H01L 35/18, H01L 35/34, H01L 35/12, published December 30, 2003) containing additional bismuth material, an alloy with bismuth, bismuth in other metals and a mixture of the above materials (possibly , including additional additives), placed in extended parallel pores of the main porous material with pore sizes of 5-15 nm. The base material is taken in the form of unoxidized porous aluminum, porous glass or porous silica gel. The base material is used in the form of bulk material. Electrical contacts are attached to the end surfaces of the additional material in the pores of the core.

The record value of the parameter Z = 0.08 K ^-1 (at a temperature of 77 K) achieved at that time in the known thermoelectric element is now insufficient for many applications; in addition, the thermoelectric element has a relatively low efficiency.

Known thermoelectric element (see patent RU 2376681, IPC H01L 35/12, H01L 35/32, published December 20, 2009), coinciding with this technical solution for the largest number of essential features and adopted for the prototype. The thermoelectric prototype element consists of a base material having extended parallel recesses, and additional material located therein having various electrical and thermal conductivities, and electrical contacts to the additional material. A carbon material with sp ³ hybridization of atomic bonds was taken as the main material of the thermoelectric element, and a carbon material with sp ² hybridization of bonds was taken as an additional material. The recesses are made in the form of grooves in which the depth, width and distance between the axes of the nearest grooves satisfy certain relations:

2 nm≤d≤10 nm,

1≤I / b≤100,

where d is the depth of the groove, nm;

b is the width of the groove, nm;

I is the distance between the axes of the nearest grooves, nm,

and electrical contacts are located along the bottom of the grooves and on the opposite surface of the additional material.

The thermoelectric prototype element has an increased efficiency due to high thermoelectric efficiency, and also provides miniaturization of the device, since the nanometric dimensions of the grooves and less than the micrometric dimensions of the distance between the grooves make it possible to create mini-thermoelectric batteries from such thermoelements that satisfy user requirements.

The disadvantages of the thermoelectric prototype element are the technological difficulty of creating grooves of the required size and the difficulty of placing additional material and electrical contacts to the additional material in them.

The objective of this technical solution was the development of such a thermoelectric element, which would have a simpler design to manufacture and at the same time maintain a high efficiency.

The problem is solved in that the thermoelectric element includes a base material in the form of a carbon material with sp ³ hybridization of atomic bonds and an additional material in the form of a carbon material with sp ² hybridization of bonds. New is the implementation of the base material in the form of at least two films between which there is a film of additional material, the thickness d, nm, the film of additional material and the thickness b, nm, the film of the basic material satisfying the relations:

and electrical contacts are applied to opposite peripheral regions of the surface of the film of additional material.

The proposed technical solution is illustrated in the drawing, where

in FIG. 1 shows a real TEE in a vertical section;

in FIG. Figure 2 shows a fuel cell, consisting of many individual fuel cells, in a vertical section.

The present thermoelectric element 1 includes (see Fig. 1) two films of the base material 2 in the form of a carbon material with sp ³ hybridization of atomic bonds, between which there is a film of additional material 3 in the form of a carbon material with sp ² hybridization of bonds. On the opposite peripheral regions of the surface of the film of additional material 2, electrical contacts 4, 5 are applied. One of the contacts 3 or 4 is hot and the other is cold. The thickness d, nm, the film of additional material 3 and the thickness b, nm, the film of the base material 2 satisfy the above relations (1), (2).

Depicted in FIG. 2, the thermoelectric battery includes a substrate 6 in the form of a plate of materials selected from the requirements of the manufacturing technology on which the thermoelectric elements 1 are stacked.

This TEE is produced by applying a chemical vapor deposition method in a vacuum — by CVD — first a film of the base material 2 in the form of a carbon material with sp ³ hybridization of atomic bonds. Then, on the film of the base material 2, the film of the additional material 3 in the form of a carbon material with sp ² hybridization of bonds is applied by the same method. Contacts 4, 5 from materials selected from the requirements of the manufacturing technology and providing electrical connection with the additional material 3 are applied to the peripheral regions of the surface of the additional material 3. Contacts 4, 5 may have a vertical size selected from the requirements of the manufacturing technology, and should provide the possibility of further the output on the bus terminal leads 4, 5. The procedure for applying contacts 4, 5 is selected from the requirements of the manufacturing technology. Then a film of the base material 2 is applied, covering the additional material 3 and the contacts 4, 5.

To create a fuel cell, first a TEE 1 is made on a substrate 6. Then, on the film of the base material 2, covering the film of the additional material 3 and the contacts in the already created TEE 1, the following film of the additional material is applied 3. Then, on the film deposited, as indicated above, the additional material 3, contacts 4, 5 are applied and then on top of the film of the base material 2. This process is repeated as many times as necessary to create the required thermoelectric battery.

This TEE 1 begins to work when a temperature difference is applied between contacts 4 and 5. If contact 5 and / or the adjacent area of additional material 3 are cooled, and contact 4 and / or the adjacent area of additional material 3 is heated, then in the external circuit between pins 4-5 will flow an electric current. TEE 1 in this case operates in the thermoelectric generator mode. If an electric current is passed through an external circuit directed from pin 4 to pin 5, then pin 5 and the region of additional material 3 adjacent to it will become colder than they were before the current was passed. TEE 1 at the same time operates in the thermoelectric refrigerator mode.

Examples of specific performance

Example 1. A TEE was created according to the claims. A CVD film of the main material — a carbon material with sp ³ hybridization of atomic bonds (diamond-like film) with a thickness of b = 80 nm — was applied on a substrate (silicon wafer) by CVD. Then, a CVD film of an additional material — a carbon material with sp ² hybridization of bonds (graphite-like film) with a thickness of d = 40 nm — was applied to the main material by CVD. Films lie in parallel planes. A second film of the base material with a thickness of b = 80 nm was applied to the film of additional material by CVD. One contact was applied to one peripheral region of the surface of the film of additional material; a second contact was applied to the opposite peripheral region of the surface of the film of additional material. In this case, the ratios d = 40 nm and b / d = 2 were maintained. The contacts provided electrical connection with additional material due to the fact that they consisted of a chromium sublayer 1 nm thick and a gold layer 30 nm thick on top of it. Next, the contacts were displayed on the bus. As a result, the efficiency of thermoelectric conversion was achieved Z = 0.1 K ^-1 (at T = 77 K), which, according to the authors, is only 2 times less than in the prototype, with a significant simplification of manufacturing. The simplification is that no grooves were required. Groove manufacturing technology requires sophisticated lithographic equipment. Another simplification was that no contact was required at the bottom of the groove. Currently, there is no standard equipment and technology to ensure the implementation of such an operation.

Example 2. In the second embodiment, the dimensions of the thermocouple structure were d = 20 nm, and the ratio b / d = 10. All other parameters remained the same as in example 1. The resulting value Z = 0,044 K- ¹ , which is slightly less than in the prototype, with a strong simplification of manufacture.

Using this design allows you to overcome the disadvantages of the TEE prototype, which are the technological difficulty of creating grooves of the required size and the difficulty of placing additional material and electrical contacts to the additional material in them. The problem of developing such a TEC that would have a simpler design to manufacture and at the same time maintain a high efficiency, and also provides miniaturization of the device, has been solved. the nanometer film thicknesses of the additional material and less than micrometric distances between the layers of the additional material make it possible to create mini-TEBs from such TEEs that satisfy user requirements.

Claims (4)

A thermoelectric element comprising a base material in the form of a carbon material with sp ³ hybridization of atomic bonds and an additional material in the form of a carbon material with sp ³ hybridization of bonds, characterized in that the main material is made in the form of at least two films between which a film of additional material is located wherein the thickness d, nm, the film of additional material and the thickness b, nm, film of the base material satisfies the relations: 2 nm ≤ d ≤ 50 nm, 1≤b / d≤100, and electrical contacts are applied to opposite peripheral regions of the surface of the film of additional material.

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