WO1999065086A1

WO1999065086A1 - Process for production of high performance thermoelectric modules and low temperature sinterable thermoelectric compositions therefor

Info

Publication number: WO1999065086A1
Application number: PCT/US1999/012767
Authority: WO
Inventors: Xiaomei Xi; Goran S. Matijasevic; Lutz Brandt; Linh Ha
Original assignee: Ormet Corporation
Priority date: 1998-06-08
Filing date: 1999-06-08
Publication date: 1999-12-16
Also published as: AU4551399A

Abstract

Methods for the cost-effective manufacture of thermoelectric elements and modules with a multitude of thermoelectric couples are disclosed. Invention methods make possible the fabrication of very small, compact and powerful thermoelectric modules. Invention methods may also be employed to fabricate integrated thermoelectric modules in electronic and other devices. Thermoelectric compositions which comprise at least one low melting point material powders, optionally a high melting point material powder, and optionally a binder system are invented. Methods of the present invention are based on additive technology using thermoelectric pastes and patternable insulators. Also provided are compositions useful for the manufacture of thermoelectric elements. These compositions do not exhibit thermoelectric properties prior to cure. Thermoelectric materials are formed after sintering or curing the thermoelectric compositions. During curing, the low melting point material powders melt and react with each other or with the high melting point material powder to form an electrically conductive network with thermoelectric properties. A multitude of thermoelectric elements can be formed simultaneously with the processing of thermoelectric materials. Small size thermoelectric elements have been produced by applying the thermoelectric compositions into a patterned substrate using stencil printing, screen printing, pressure filling or other techniques and subsequently curing them at temperature ≤ about 300 °C.

Description

PROCESS FOR PRODUCTION OF HIGH PERFORMANCE THERMOELECTRIC MODULES AND LOW TEMPERATURE SINTERABLE THERMOELECTRIC

COMPOSITIONS THEREFOR

FIELD OF INVENTION

This invention is directed to low temperature sinterable thermoelectric compositions and uses thereof. In another aspect, the present invention relates to methods for producing thermoelectric modules. In a particular aspect, the invention relates to methods for producing thermoelectric modules with a multitude of thermoelectric elements.

BACKGROUND OF THE INVENTION

Thermoelectric modules are based on the Peltier effect, which states that a DC current applied across two dissimilar materials causes a temperature differential. A typical thermoelectric module comprises two ceramic wafers with a series of P- and N- doped thermoelectric elements sandwiched between them. One P- and one N- type thermoelectric element make up a thermoelectric couple. Thermoelectric couples are electrically in series and thermally in parallel. A thermoelectric module can contain one to several hundred couples. Its performance is proportional to the electrical current and the number of thermoelectric couples.

Thermoelectric materials are used in making thermoelectric modules to produce thermoelectric coolers (e.g., Peltier coolers), thermoelectric power generators, temperature sensors, and the like. The performance of a thermoelectric material is expressed using the figure of merit Z, which is defined as follows:

Z = S² σ / k Where S is the Seebeck coefficient (typically expressed in units of V/°K), k is the thermal conductivity of the material (typically expressed in units of W/m°K), and σ is the electrical conductivity of the material (typically expressed in units of Ω-m^"1). From this equation, one can see that in order for a thermoelectric material to have a high Z, it must have a large Seebeck coefficient (S), a large electrical conductivity σ, and a low thermal conductivity (k). In terms of a material's thermoelectric properties, materials with a larger figure of merit are more desirable. However, to be useful as thermoelectric material, many applications require that the material also have good mechanical properties (i.e. adequate strength and flexibility), chemical stability, temperature stability, processability and the like.

Known thermoelectric materials, such as Bi₂Te₃, PbTe, Bi₂Se₃, (Bi,Sb)₂Te₃, Si- Ge, etc., usually have a high Seebeck Coefficient when in their single crystal and polycrystalline structure. However, these highly ordered materials suffer from poor mechanical properties, poor processability, and sensitivity to the presence of contaminants as well as the inherent properties of some raw materials. In addition, it is hard to modify crystalline materials to achieve low thermal conductivity while maintaining high electrical conductivity. Efforts have been made in developing amorphous or highly disordered thermoelectric materials to achieve better mechanical strength and lower thermal conductivity. However, high sintering temperatures and long processing times are still needed for the fabrication of these disordered thermoelectric materials.

Known thermoelectric elements are generally fabricated by slicing an ingot of thermoelectric material(s) into bulk thermoelectric elements and bonding them onto electrodes by soldering or like technique. Such ingots are conventionally produced using high temperature alloying, powder sintering, poly-crystallization zone melting, amorphous production, or like techniques. However, these methods have problems in that the process is complicated, requiring high temperatures and long treatment times. Thus productivity is low and the cost is high. In addition, process automation is difficult since the thermoelectric elements are produced by slicing only one at a time from the ingot. This too leads to high production costs. Finally, assembly of thermoelectric modules requires placement and attachment of the individual, sometimes very small thermoelectric elements. Thus it is very difficult to fabricate thermoelectric modules with a multitude of thermoelectric elements.

An additional problem encountered with conventional production of thermoelectric modules is the notably lower yield of thermoelectric elements when the thickness of the thermoelectric elements is less than 1.5 mm. This is due to the difficulty in cutting ingot thermoelectric materials. Miniaturization of thermoelectric elements is very difficult. As a result, the number of thermoelectric couples that can be fabricated in a thermoelectric module is limited. Thus, the efficiency of the thermoelectric modules is rather low. In summary, it is very difficult to produce compact, high performance thermoelectric modules using conventional methods.

In recent years, some encouraging results have been obtained with ceramic thick film thermoelectric materials. Ceramic thick film thermoelectric pastes have been produced by incorporating thermoelectric material powders, and glass frit into a binder system to form a paste. Thermoelectric materials and elements can be achieved by sintering the ceramic thick film thermoelectric pastes at > 500°C for a suitable period of time to form a polycrystalline structure. A Seebeck coefficient of 250 μV/K and figure of merit (Z) of 1.2 x 10^"3 /degree K have been achieved using this ceramic thick film technology. These materials allow patterning using selective deposition.

However, the high sintering temperature and lengthy processing time has limited their use to ceramic applications only.

Encouraging results have also been achieved in deposition of thin film thermoelectric materials by condensing Bi, Te, Sb, or like elements on an insulated substrate. The deposition is carried out in an ultra-high vacuum chamber with a residual pressure below 10^"9 torr. Small thermoelectric devices can be made by this thin film deposition technique. However, the high vacuum, high processing temperature, and the long processing time make the resulting thin film thermoelectric elements very expensive. Low temperature liquid phase sinterable compositions with electrically conductive characteristics were known in the art (see, for example, Capote, et al., United States Patent No. 5,376,403), however, such compositions were not shown to be useful as thermoelectric materials. Based on the prior art regarding such conductive compositions, one of skill in the art would have no reasonable basis upon which to make the assumption that the impure and only partly crystalline materials that result from low temperature liquid phase sintering techniques would result in thermoelectric materials with any practical level of utility.

Accordingly, there is still a need in the art for low temperature sinterable thermoelectric materials and new processing methods employing same which will enable cost-effective production of high performance thermoelectric materials with good mechanical strength. In addition, there is still a need in the art for new processing methods which enable cost-effective production of compact thermoelectric modules with a multitude of thermoelectric elements.

OBJECTS OF THE INVENTION

To circumvent problems associated with known thermoelectric materials and processing techniques for producing thermoelectric modules, it is an object of this invention to provide compositions which can be processed at low temperatures to form thermoelectric materials and elements, as well as methods for using such material(s).

Another object of this invention is to provide processing methods for cost- effective production of thermoelectric modules with a multitude of thermoelectric couples. Yet another object of this invention is to provide processing methods for producing very small sized thermoelectric elements.

Still another object of this invention is to provide methods for producing very small, compact thermoelectric modules.

A further object of the invention is to provide thermoelectric compositions which permit the production of thermoelectric elements with various sizes and shapes employing a variety of processing methods.

A still further object of the invention is to provide thermoelectric compositions and processing methods which permit the production of a multitude of very small size thermoelectric elements employing simple processing techniques.

These and other objects of the present invention will become apparent upon review of the specification and appended claims.

BRIEF DESCRIPTION OF THE INVENTION

In accordance with the present invention, there are provided methods for the cost-effective production of thermoelectric elements. Invention methods employ composite thermoelectric pastes instead of ingot thermoelectric materials to produce thermoelectric elements. Thermoelectric elements are obtained by depositing the thermoelectric pastes into pattern holes that have been selectively formed in a pattemable insulator, followed by curing and/or sintering of the deposited pastes. Location, shape and size of the individual thermoelectric elements are thereby determined by the pattern of the holes.

In accordance with another embodiment of the invention, there are provided methods of forming thermoelectric modules using a variety of related approaches, including an additive process whereby individual circuit trace-containing layers are fabricated followed by the formation thereon of one or more thermoelectric element containing layers; a laminating process whereby individual circuit trace-containing layers and thermoelectric layers are formed and then laminated together to form single or multi-stage thermoelectric modules; and combinations of the two methods.

To overcome the shortcomings of conventional thermoelectric materials, the present invention also provides compositions useful for the preparation of thermoelectric materials and thermoelectric elements. Invention compositions contain at least one low melting point material, optionally one or more high melting point materials, an optional binder system and an optional dopant. Thermoelectric materials are formed in situ by sintering or curing the thermoelectric precursor material compositions using low temperature reactive-liquid-phase-sintering process. During sintering, the low melting point material(s) melt and react with each other and/or with the high melting point material(s) to form an electrically conductive composite network with thermoelectric properties. The resulting composite structure is a mixture of ordered and disordered phases and thus has good mechanical properties as well as low thermal conductivity. These thermoelectric materials can be processed at temperatures less than or equal to about 300°C in minutes. In addition, unlike traditional methods where the thermoelectric crystalline material is first formed and then sliced into thermoelectric elements, thermoelectric elements employing invention compositions can be produced simultaneously with the processing of the thermoelectric materials.

The advantages and efficiencies of the present invention will become more apparent by referring to the following detailed description of the invention in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is a typical example of a thermoelectric module produced using the invention methods.

Figures 2A, 2B, 2C, 2D, 2E, 2F and 2G diagram a process which exemplifies an embodiment of the invention method for producing thermoelectric elements using thermoelectric pastes.

Figures 3A, 3B, 3C, 3D, 3E, 3F and 3G diagram a process which illustrates an example means for electrically connecting the thermoelectric elements to form a thermoelectric module using an additive technique.

Figures 4A, 4B, 4C and 4D diagram a process which illustrates an example means for electrically connecting the thermoelectric elements to form a thermoelectric module using a laminating technique.

Figures 5A, 5B, 5C, 5D, 5E, 5F and 5G diagram a process which illustrates an example means for electrically connecting the thermoelectric elements to form a thermoelectric module using a combination of the additive and laminating techniques.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the present invention, there are provided methods for creating thermoelectric elements and precursors thereof, said method comprising:

a) selectively imparting a pattern to a pattemable insulator layer, thereby forming pattern holes therethrough,

b) selectively depositing P- and N-type thermoelectric pastes into portions of said pattern holes, c) optionally, curing and/or sintering said P- and N-type thermoelectric pastes,

wherein said pattern holes into which said p-type thermoelectric paste is deposited are not the same as the pattern holes into which the N-type thermoelectric paste has been deposited, such that a layer of thermoelectric elements is formed containing one or more thermoelectric couples.

As will be understood by those of skill in the art, until curing and/or sintering, thermoelectric elements have not been formed and are thus considered "precursors."

The pattemable insulator layer provides a supporting frame for the deposition of thermoelectric material precursor compositions, as described in greater detail below. The pattemable insulator layer will generally be retained in the thermoelectric module due to the low temperature required to cure/sinter invention compositions. Alternatively, a removable resist material can be used which, upon curing of the thermoelectric material precursor compositions is dissolved away. The insulator layer can also be burned out during the sintering process, as is the case where ceramic thick film thermoelectric pastes are used to prepare the thermoelectric elements.

As will be readily understood by those skilled in the art, there are a number of pattemable insulating materials that can be employed in the present invention. As used herein, "pattemable insulating materials" include any electrically insulating material which is pattemable using photoimaging and subsequent development, plasma etching, sand blasting, laser drilling, mechanical drilling, chemical etching, or other techniques known in the art.

Suitable materials for use in the present invention as pattemable insulators include, for example, photopattemable epoxies, epoxy-acrylates, polyimide-based resins, epoxy-based resins, thermoplastics, phenolic-based resins, methacrylates, cyclic hydrocarbons, and the like. These materials can be commercially obtained in liquid or dry sheet form. As is readily understood by those of skill in the art, the pattemable insulator may be applied to the underlying circuit-traced insulator by a number of suitable methods including, but not limited to, laminating (e.g., roll lamination, etc.), and like techniques for dry sheet/film form pattemable insulators. Suitable application methods for pattemable insulators in liquid form include screen printing, curtain coating, stencil printing, doctor blading, spraying, spin coating, roller coating, extrusion, and the like, to the desired thickness. In a preferred embodiment of the invention, the pattemable insulator layer will be from about 5 μm to about 10 mm in thickness.

In another embodiment of the present invention, there are provided methods for forming a thermoelectric module, said methods comprising: a) fabricating conductive traces on a first insulating plane, thereby forming a first trace-containing layer, b) forming on said first trace-containing layer a layer of thermoelectric elements created as described herein, c) optionally: i) forming an intermediate trace-containing layer by applying conductive traces on first and second sides of an insulating plane, ii) affixing said first side of said intermediate trace-containing layer to said layer of thermoelectric elements, iii) affixing to said second side of said intermediate trace- containing layer a next layer of thermoelectric elements, and iv) optionally repeating steps (i) - (iii), d) fabricating conductive traces on the layer of thermoelectric elements formed during step (B) or affixed during the last iteration of step (iii), if carried out, thereby forming a second layer of conductive traces, and e) affixing a bottom insulating plane to said second layer of conductive traces, thereby forming a second trace-containing layer, wherein said thermoelectric element(s) is electrically connected to said conductive traces on said first, second and any intermediate insulating planes such that a thermoelectric module is formed.

By this method, single, or if optional step (c) is carried out, multi-stage thermoelectric modules can be formed.

The insulating planes provide mechanical support for the thermoelectric elements and electrically conductive traces. As used herein, "insulating plane" includes, but is not limited to electrically insulating materials such as polymers, including, but not limited to, polymer-based composites, including, for example, fiber-reinforced composites and particle-reinforced composites, insulated metals or metal matrix composites, ceramics and the like. Suitable fibers for fiber-reinforced materials include, glass, carbon, ceramic, and like fibers. Suitable particles for particle reinforced materials include ceramic particles, glass beads, and like particles. Preferred materials are insulated materials with good thermal conductivity, such as insulated metals or metal composites, ceramics, thermally conductive polymer composites, insulated graphite, insulated composites containing graphite fibers, diamond, and the like.

The conductive trace-containing layers provide means to electrically connect the thermoelectric elements and thus form a thermoelectric module. As contemplated by the present invention, conductive traces can be formed by a variety of techniques, such as, for example, etching metal laminates, vapor deposition of metals, deposition of conductive pastes, and such other techniques as are known in the art, as well as a combination of such techniques. Suitable conductive pastes include, but are not limited to, polymer or ceramic thick film pastes, solder pastes, transient liquid phase sintering pastes as described herein, and the like. Suitable metal laminates for etching and/or vapor deposition include, but are not limited to, copper, aluminum, gold, silver, nickel and the like. In a preferred embodiment, the conductive traces are able to form reliable electrically conductive bonds with the thermoelectric elements during the curing or sintering process.

In yet another embodiment of the present invention, methods are provided for forming thermoelectric modules, said methods comprising: a) fabricating conductive traces on a first and a second insulating plane, thereby forming first and second trace-containing layers, b) applying a pattemable insulating layer to said first trace-containing layer, c) forming on said pattemable insulating layer a layer of thermoelectric elements as described herein, d) optionally, i) forming an intermediate trace-containing layer by applying conductive traces on first and second sides of an insulating plane, ii) affixing a first side of said intermediate insulating plane to said layer of thermoelectric elements, iii) forming on said pattemable insulating layer a layer of thermoelectric elements as described herein, and iv) optionally, repeating steps i-iii, e) laminating the second trace-containing layer to said layer of thermoelectric elements, and f) optionally heating said laminate under conditions suitable to sinter the thermoelectric material precursor compositions, thereby forming a thermoelectric module.

In still another embodiment of the present invention, methods are provided for forming thermoelectric modules, said methods comprising: a) fabricating conductive traces on a first and a second insulating plane, thereby forming first and second trace-containing layers, b) forming a layer of thermoelectric elements as described herein, c) optionally, i) forming one or more intermediate trace-containing layers by applying conductive traces on first and second sides of an insulating plane, and ii) forming one or more layers of thermoelectric elements as described herein, d) laminating said layer of thermoelectric elements, and any optional trace-containing layers alternating with any optional layers of thermoelectric elements, between said first and second trace-containing layers, and e) optionally heating said laminate under conditions suitable to sinter the thermoelectric paste precursor materials, thereby forming a thermoelectric module.

As used herein in the context of forming thermoelectric modules, "laminating" refers to the application of sufficient pressure and heat to adhere adjacent layers of the module to one another.

In a further embodiment of the present invention, there are provided articles of manufacture incorporating one or more compositions described herein and/or one or more thermoelectric elements and/or modules manufactured according to the methods described herein.

According to the process of the present invention, thermoelectric elements with sizes as small as about 10 μm in diameter can be produced. This allows the miniaturization of the thermoelectric modules and the production of compact thermoelectric modules containing large numbers (thousands or tens of thousands) of thermoelectric couples, which has heretofore been impossible. With large numbers of thermoelectric couples in a small thermoelectric module, high performance thermoelectric modules are possible even with commercially available thermoelectric materials, whose figure of merit (Z, a measure of thermoelectric efficiency) is not very high. In addition, because the thermoelectric elements are produced by deposition of thermoelectric material precursor compositions into defined locations using screen printing, pressure filling, doctor blading, automatic dispensing, stencil printing, or like techniques, a large number of thermoelectric elements can be produced in a single operation. The processing cost incurred upon preparation of invention thermoelectric modules is thus substantially reduced as the steps of ingot thermoelectric material processing, cutting of the thermoelectric ingot, and soldering of the thermoelectric elements onto the conductive traces are eliminated.

Furthermore, with processes of the present invention, automation of thermoelectric module production is possible. This will both reduce the cost and increase the reliability of the products. In addition, if polymer thick film thermoelectric materials are used, low processing temperatures are possible.

Invention methods can be also used to fabricate integrated thermoelectric modules in electrical devices, systems, packagings, etc., by integrating the fabrication of the thermoelectric modules with the fabrication of the electrical devices, systems, packagings, etc. The integrated thermoelectric modules can act as thermoelectric coolers, thermoelectric power generators or temperature stabilizers as desired.

As will be readily understood by those skilled in the art, invention methods can be carried out by various insubstantial modifications of the methods herein described. Such variations are contemplated by the inventors as within the scope of the present invention. Figures 1-5 illustrate examples of various embodiments of invention methods and articles produced thereby. The embodiments described below and shown in the figures are merely illustrative and non-limiting. For example, Figure 1 shows a thermoelectric module comprising a first insulating plane 11, a layer of conductive traces 12 on the first insulating plane 11, a pattemable insulator layer 13, P- and N-type thermoelectric elements, 14 and 15, positioned in the pattemable insulator layer 13, a second insulating plane 17, and a layer of conductive traces 16 on the second insulating plane 17. The first and second insulating planes 11 and 17 provide mechanical support for the thermoelectric elements and electrically conductive traces. Thermoelectric elements are formed in the patterned regions by curing or sintering the thermoelectric pastes.

An example of invention methods for fabricating a layer of thermoelectric elements is illustrated in Figures 2 A through 2D. The process begins with the formation of a pattemable insulator layer 13 (Fig. 2A). A desired pattern is fabricated on the pattemable insulator layer 13 by one or more methods described herein or other techniques known to the art (Fig. 2B). P- or N-type thermoelectric pastes are then deposited into the patterned holes by one or more methods described herein, or other techniques known to the art, thereby forming P- and N-type thermoelectric elements, 14 and 15 respectively. (Figs. 2D and 2E). In order to deposit each type of thermoelectric paste individually, the locations for the other thermoelectric paste have to be masked or protected using temporary plugs, suitably patterned screens or stencils, or like techniques. As shown in Fig. 2D, the P-type thermoelectric paste is deposited when the locations for N-type thermoelectric elements are masked or protected. The mask or the protector is then removed. The N-type thermoelectric paste is then deposited into the locations positioned for N-type thermoelectric elements 15, while the locations for P-type thermoelectric elements 14 are masked or protected (Fig. 2E). After removal of the mask or the protector, the deposited thermoelectric pastes are cured or sintered to form P- and N- type thermoelectric elements 14 and 15. Of course, the curing/sintering step may alternatively take place after the module is completely assembled. A thermoelectric module is fabricated when the P- and N- type thermoelectric elements are connected, electrically in series and thermally in parallel. As described herein, invention methods employ several techniques for electrically connecting thermoelectric elements in order to form thermoelectric modules. The following embodiments provide illustrative examples of three different connecting techniques: the additive technique, the laminating technique, and the combination of additive and laminating techniques.

As shown in Figures 3A through 3G, an additive technique may be employed for electrically connecting thermoelectric elements to form a thermoelectric module. The process begins with the fabrication of a layer of conductive traces 12 on an insulating plane 11 by methods described herein, or other techniques known to those skilled in the art (Fig. 3 A). A pattemable insulator 13 is then affixed onto the conductive traces using suitable techniques as described herein for either liquid or dry film pastes, or other techniques known to those skilled in the art (Fig. 3B). A desired pattern is imparted to the pattemable insulator layer as described herein, or using other techniques known in the art (Fig. 3C). In Figures 3D and 3E, P- and N- type thermoelectric elements 14 and 15 are fabricated in the patterned regions using the same methods as shown in Figures 2D and 2E and described herein.

A layer of conductive traces 16 is applied to the surface of the pattemable insulator layer using suitable techniques as described herein, or other techniques known to those skilled in the art (Fig. 3F). The conductive traces 16 connect the P- and N- type thermoelectric elements so that they are electrically in series and thermally in parallel. Finally, the production of the thermoelectric module is completed when an insulating plane is affixed, as shown in Fig. 3G.

As illustrated in Figures 4A through 4D, a laminating technique may be employed for electrically connecting thermoelectric elements to form thermoelectric modules. The process begins with fabricating a layer of conductive traces 12 and 16 on first and second insulating planes 11 and 17, respectively, as described hereinabove. (Fig. 4A) Next, a layer of P- and N- type- thermoelectric elements 14 and 15, respectively (Fig. 4B), is fabricated separately in a pattemable insulator layer 13 using the same techniques shown in Figures 2A to 2E and described herein. The layer of thermoelectric elements is then aligned with and applied to the layers of the conductive traces 12 and 16 on the first and second insulating planes, and all are laminated together by pressing under sufficient heat and/or pressure to adhere adjacent layers to one another. A thermoelectric module is formed when the resulting layered construct is heated to fully cure or sinter the thermoelectric elements thus forming good electrical contact between the thermoelectric elements and the conductive traces.

Multistage thermoelectric modules can be achieved by laminating more than one layer of thermoelectric elements with one or more intermediate trace-containing layers and heating the laminate to fully sinter/cure the thermoelectric elements and form electrical contact.

A method for electrically connecting thermoelectric elements to form thermoelectric modules using a combination of the additive and laminating techniques is illustrated in Figures 5 A through 5G. The process begins with fabrication of a layer of conductive traces 12 and 16 on first and second insulating planes 11 and 17, respectively, as described hereinabove. (Fig. 5A) In the next step (Fig. 5B), a pattemable insulator layer 13 is applied to the surface of the first conductive trace- containing layer 12 as depicted in Figure 3 and described hereinabove. A desired pattern is then formed on the insulator layer. (Fig. 5C).

Figures 5D and 5E illustrate the thermoelectric pastes deposited into the patterned insulator layer in order to form a layer of thermoelectric elements. This is achieved when P-type thermoelectric paste is deposited into the pattern holes for P- type thermoelectric elements, while pattern holes for N-type thermoelectric elements are masked or protected (Fig. 5D). The mask or protector is removed after the deposition process. N-type thermoelectric paste is then deposited while the filled P- type thermoelectric elements are masked or protected (Fig. 5E). The deposition process is finished when the mask or protecting layer on top of the P-type thermoelectric elements is removed. As shown in Fig. 5F, the second insulating plane 17 with conductive traces 16 is laminated onto the layer of thermoelectric elements. Pressure may be applied in order to achieve better contact between the conductive traces and the thermoelectric elements. To achieve good electrical, and mechanically strong contacts between the thermoelectric elements and the conductive traces, it is advantageous to form an electrically conductive bond between the thermoelectric elements and the conductive traces by a curing or sintering process. The thermoelectric module is thus obtained by curing/sintering the deposited thermoelectric pastes at a desired temperature to complete the formation of the thermoelectric elements (Fig. 5F). If ceramic thick film thermoelectric pastes are used, the polymer-based pattemable insulating layer 13 may be burned out during the sintering process due to the comparatively high sintering temperature (>500°C). The structure of the resulting thermoelectric module is shown in the Fig. 5G.

Multistage thermoelectric modules can be fabricated in the same fashion by laminating several alternating thermoelectric layers and conductive layers on top of each other and subsequently sintering the laminate at suitable temperatures.

In accordance with another embodiment of the present invention, there are provided compositions useful for the preparation of thermoelectric materials and thermoelectric elements (using the above-described fabricating methodology or prior art methodology), said compositions comprising:

(a) two or more different finely divided materials, wherein at least one of said materials is a low melting point material having a melting point of < 300°C,

(b) optionally, a binder system, and (c) optionally, a dopant, wherein said combination produces P- or N-type thermoelectric materials upon curing. The Seebeck coefficient of thermoelectric materials produced from invention compositions is greater than or equal to about 10μV/°K. Preferably the Seebeck coefficient of thermoelectric materials produced from invention compositions is greater than or equal to about 20μV/°K. The present invention provides novel compositions and methods for producing thermoelectric materials by using low temperature (i.e., temperatures less than or equal to about 300°C) reactive-liquid-phase-sintering. Invention compositions do not exhibit thermoelectric properties before sintering or curing and are sometimes referred to herein as "precursors" or "thermoelectric precursor materials," thereby denoting invention compositions which have not yet been subjected to sintering or curing. Thermoelectric materials are formed from invention compositions in situ during sintering or curing when the low melting point materials melt and react with each other and/or with the high melting point materials to form a conductive composite network with thermoelectric properties. By depositing invention compositions into a mold or onto a substrate in a suitable pattern, thermoelectric elements can be formed simultaneously with the curing or sintering of the thermoelectric materials. The thermoelectric materials can be formed by curing or sintering at low temperature (less than or equal to about 300°C) in minutes. In a preferred embodiment of the present invention, thermoelectric materials can be formed by curing or sintering invention compositions at low temperature (less than or equal to about 300°C) for a time in the range of about 1 up to about 60 minutes. Thermoelectric materials thus formed from invention compositions exhibit better mechanical properties than their single crystal counterpart due to their composite structure.

Compared with the conventional thermoelectric materials and thermoelectric elements, invention thermoelectric compositions and the thermoelectric elements produced therefrom include the following advantages: (1) Low processing temperature (less than or equal to about 300°C),

(2) Short processing time (usually in minutes),

(3) Capability of producing a multitude of very small size thermoelectric elements,

(4) Simultaneous production of thermoelectric materials and elements, and (5) Improved mechanical properties, (6) Automatable processing,

(7) Mass element formation instead of single element formation.

Thermoelectric compositions of the present invention comprise at least one finely divided low melting point material and one or more additional finely divided materials of either relatively high melting point (i.e., a melting point greater than about 300°C) and/or relatively low melting point material. Thus, if no high melting point material is used, at least two low melting point materials are needed so that the reaction can occur. If a high melting point material is used, only one low melting point material is required.

As used herein, "powder" and "finely divided" each denote particle sizes in the range of about lμm up to about 1mm, unless otherwise noted.

As used herein, "low melting point materials" are defined as materials which will melt at temperatures of less than or equal to about 300°C. The primary requirement for the low melting point materials useful for inclusion in invention compositions is that the low melting point materials can melt and react with each other, or with the optional high melting point materials to form compounds with good thermoelectric properties and an electrically conductive composite network. Thus, low melting point materials contemplated for use in compositions of the present invention include P, S, Bi, In, Pb, Sn, Se, Ga, Cd, Zn, alloys or mixtures of two or more of them, and the like. Low melting point materials may also contain a small portion (i.e., less than or equal to about 10 wt% ) of other materials, such as Ag, Cu, Au, Sb, Te, which provide good alloy characteristics while keeping the low melting temperature of less than or equal to about 300°C. In preferred embodiments of the present invention, low melting point materials include P, S, Se, Zn-Sn alloy, Pb-Sn-Bi alloy, Bi-Sn alloy, Pb-Sn alloy, Pb-Sn-Sb alloy, Pb-Sn-Bi-Sb alloy, Pb-Sn-Bi-Te alloy, and the like, or mixtures of one or more of these materials. In preferred embodiments of the present invention, the particle size is in the range of about 1 μm up to about 20 μm. As used herein, "high melting point materials" are defined as materials which will not melt at temperatures of less than or equal to about 300°C. The principal requirement for high melting point materials useful in invention compositions is the ability to react with the low melting point materials and thereby form thermoelectric materials. Thus, the optional high melting point materials contemplated for use in compositions according to the present invention include Ag, As, Au, Al, Cu, Sb, Si, Te, Ni, Zn, Fe, Ge, Mo, Mn, Co, Mg, Ti, CuS, Cu₂S, Bi₂Te₃, Bi₂Se₃, PbTe, and the like, as well as mixtures of two or more thereof. In preferred embodiments of the present invention, high melting point materials include, but are not limited to As, Te, Ni, Sb, Si, Ge, Cu, CuS, Fe and the like, as well as mixtures of two or more thereof. In one embodiment of the present invention, the particle size is in the range of about lμm up to about 100 μm. In preferred embodiments of the present invention, the particle size is in the range of about 1 μm up to about 20 μm.

The present inventors have determined that choice and ratio of low and high melting point materials employed in invention compositions, as well as the particle size thereof, effects the Seebeck coefficient of the final thermoelectric materials. Accordingly, the property of the final thermoelectric materials as either N or P type is also thus effected.

In another embodiment of the present invention, there are provided compositions as described herein which further comprise one or more of a binder system and/or a dopant in addition to the above-described low melting point material(s) and optional high melting point material(s).

The optional binder system contemplated for use in the practice of the present invention compositions may function in one or more of the following ways. Without wishing to be bound by theory, it is presently believed that one function of binder is to act as a carrier in which the finely divided materials are dispersed. Another possible function is to bind the thermoelectric materials together and also bond the thermoelectric elements to the substrate after sintering or curing. Yet another possible function is to act as a fluxing agent.

As used herein, "binder system" means one or more of a solvent, a fluxing agent, or a polymer resin system. In embodiments of the present invention wherein the binder system is included and comprises a solvent, the solvent can be any one of known solvents, such as a ketone (e.g., acetone), an alcohol (e.g., ethanol), a glycol (e.g., ethylene glycol), an aromatic solvent (e.g., benzene), an ester (e.g., methyl acetate), an ether (e.g., diethyl ether), or the like. In embodiments of the present invention composition wherein the binder system is included and comprises a polymer resin system, the resin may be any resin which can be cross-linked by a curing agent. Resins which meet this requirement include epoxies, phenolics, novolacs, polyurethanes, polyimides, bismaleimides, maleimides, cyanate esters, polyesters, polyvinyl alcohol, polyureas and the like. Presently, the preferred resin is an epoxy.

The optional dopant contemplated for use in the present invention functions to alter the Seebeck coefficient of the final thermoelectric materials. Accordingly, the property of the final thermoelectric materials as either N or P type is also thereby effected. In embodiments of the present invention that include a dopant, the dopant may be Ag₂S, Sbl₃ or the like. In one embodiment of the present invention, the dopant comprises a powder of one of the above materials, wherein the powder particle size is in the range of about lμm up to about 100 μm. In another aspect of the present invention, the dopant powder particle size is in the range of about 1 μm up to about 20 μm.

The proportion of components incorporated into compositions according to the present invention may be varied over a considerable range and still yield useful thermoelectric materials. For example, in one embodiment of the present invention there are provided compositions for the preparation of thermoelectric materials and thermoelectric elements, said compositions comprising:

(a) two or more different finely divided materials, wherein said finely divided materials comprise: (i) in the range of about 15 up to about 100 wt% of at least one finely divided low melting point material having a melting point of < 300°C, (ii) in the range of about 0 up to about 85 wt% of a finely divided high melting point material having a melting point of > 300°C,

(b) in the range of 0 up to about 85 wt% of a binder system, and (c) in the range of 0 up to about 10 wt % of a dopant, wherein said combination produces thermoelectric materials upon curing.

In another embodiment of the present invention, there are provided compositions for the preparation of thermoelectric materials and thermoelectric elements, said composition comprising:

(a) in the range of about 30 up to about 85 wt% of at least one finely divided low melting point material having a melting point of < 300°C,

(b) in the range of about 5 up to about 45 wt% of at least one finely divided high melting point material having a melting point of > 300°C, (c) in the range of about 15 up to about 40 wt% of a binder system, and

(d) in the range of about 0 up to about 5 wt % of a dopant, wherein said combination produces thermoelectric materials upon curing.

The low temperature liquid phase sinterable compositions defined herein are the first example of such compositions with useful thermoelectric properties.

Although low temperature liquid phase sinterable compositions were previously known to result in materials with electrically conductive properties, only the present inventors have discovered low temperature liquid phase sinterable compositions with utility for the production of thermoelectric materials. Compositions of the present invention yield, upon low temperature sintering, thermoelectric materials of practical value as a result of judicious selection of both composition and constituent morphology characteristics such as particle size. The criteria employed in the selection of compositions that would likely have utility as thermoelectric materials are entirely different than those utilized for the formulation of the conductive materials previously known. For example, with respect to conductors, it is desirable to minimize the amount of intermetallic formation since intermetallics are much poorer electrical conductors than most metals and metal alloys. However, for thermoelectric materials, it is desirable to maximize the amount of intermetallic formation due to the fact that the thermoelectric effect is a consequence of specific intermetallic structures. In addition, thermoelectric materials must have an active functionality that responds in a predictable manner to changes in specific conditions. For example, resisitivity will change predictably with temperature. In contrast, conductors are required only to display a reliable electrical connective function and are not required to respond in a specific manner to changes in environment. Finally, to achieve a maximum Z value, thermoelectric materials must have as low a thermal conductivity as possible. In contrast, it is generally desirable for conductor materials to have as high a thermal conductivity value as possible so that heat generated by electrical resistance does not adversely affect the electrical conductivity of the conductor during operation of the device.

In accordance with another aspect of the present invention, there are provided methods for the preparation of invention compositions as described herein, said methods comprising mixing with at least one finely divided low melting point material: (a) one or more finely divided low melting point or high melting point material(s), thereby resulting in a finely divided material mixture,

(b) optionally, dispersing said finely divided material mixture in one or more of :

(i) a solvent, or (ii) a binder system. In preparing invention thermoelectric compositions, the materials powders are weighed and thoroughly mixed to form a precursor powder mixture. This precursor powder mixture can be used alone as thermoelectric composition or dispersed into a solvent or polymer binder system to form a paste. To form thermoelectric composition paste, a solvent or a prepared polymer binder is added and mixed with the precursor powder mixture. Dispersion of the precursor powders into the solvent or polymer binder system can be achieved in a variety of ways, e.g., by using a mechanical stirrer, or the like. The mixed paste can be then deposited and processed to form thermoelectric materials and elements.

As will be understood by those of skill in the art, compositions of the present invention can be employed in a number of different ways. For example, they can be produced as a compressed powder mixture, as a paste if a solvent and/or a binder system are incorporated, and the like. If a powder mixture is used, the powders can be pressed or molded into a desired pattern or mold. Additional methods for depositing the powder form include dispensing, electrostatic transfer, and the like. When a thermoelectric paste is used, the paste can be deposited into desired positions using a variety of techniques known to those of skill in the art, e.g., by pressing, molding, screen printing, stencil printing, pressure filling, dispensing, electrostatic transfer, doctor blading, and the like, into photoimaged or otherwise preformed patterns or molds.

Invention thermoelectric precursor material compositions as described herein are useful as produced, or they may optionally be sintered to form thermoelectric materials. Compositions of the present invention need not, however, be sintered immediately upon manufacture. Rather, invention compositions can be sintered by subsequent users or manufacturers incorporating thermoelectric material precursors and/or unsintered (i.e., precursor) thermoelectric elements formed by invention methods. Therefore the sintering reaction is an optional component of invention methods.

In accordance with another aspect of the present invention, invention compositions are sintered or cured to form thermoelectric elements. During sintering, the low melting point material(s) melt and react with each other, or with the high melting point material(s) to form an electrically conductive composite network with thermoelectric properties. This process is defined here as low temperature reactive- liquid-phase-sintering. To achieve the formation of compounds with thermoelectric properties, the type and amount of the materials mixed in the composition is selected such that once the sintering reaction occurs, a very conductive composite network is formed and compounds having a high Seebeck coefficient are produced as the result of the reaction. As will be understood by those skilled in the art, the conditions required to sinter thermoelectric materials will differ according to the particular thermoelectric material precursors employed. Similarly, the makeup of a particular precursor composition will influence the properties of the cured/sintered thermoelectric material. For example, if used, the polymer binder may be retained in the thermoelectric elements following the low temperature (i.e., less than about 300°C) curing or sintering process. On the other hand, solvents, if used, may be vaporized, however.

Curing or sintering of invention thermoelectric compositions can be achieved in a variety of ways, as can be readily identified by those of skill in the art, e.g., in a convection oven, an inert gas protected oven, a vapor phase condensation oven, or other suitable curing methods known to those skilled in the art. Compositions of the present invention can be cured or sintered at a temperature less than or equal to about 300°C. Upon curing or sintering, invention compositions described herein form thermoelectric materials. The invention will now be described in greater detail by reference to the following, non-limiting examples.

Example 1

In this example, thermoelectric compositions formed by dispersing a mixture of two types of low melting point material powders into an organic binder system are presented. All the materials used in this example are powders with a size range of 5 to 40 μm. After the powders were weighed and mixed thoroughly, the powder mixture was dispersed into an organic binder system to form a paste. The organic binder system had the following composition: epoxy resin - 18.9 wt%, protected curing agent - 54.2 wt%, solvent - 25.2 wt%, and rheological modifier - 1.7 wt%.

The pastes prepared as described above were then deposited on an epoxy-glass composite substrate using doctor blading to form 2 cm x 0.2 cm x 0.003 cm depositions. The paste depositions were then dried at 120°C for 15 minutes in a convection oven and cured at 215°C for 15 minutes in a vapor phase condensation oven. The conductivity and Seebeck coefficient of these materials were then tested. The test results are presented in Table 1. Table 1

Composition Organic Se BiSn PbBiSn Seebeck Resistivity

No. binder (wt%) (wt%) (wt%) (wt%) Coefficient (Ω.cm) (μV/°K)

1A 16 28 56 ~ +20 0.15

IB 19 18 63 ~ -65 0.002

Thus, it can be seen that varying the components of invention compositions impacts on whether, upon sintering, the final material is an N or P-type thermoelectric material and also effects the resistivity thereof. Example 2

In this example, both low melting point material powder and high melting material powder were incorporated into an organic binder system to form thermoelectric materials. The powders of low melting point materials and high melting point materials were weighed and mixed to form a powder mixture. The powder mixture was then dispersed into an organic binder system using mechanical stirring to form a thermoelectric composition. The organic binder system contains: epoxy resin - 18.9 wt%, protected curing agent - 54.2 wt%, solvent - 25.2 wt%, and rheological modifier - 1.7 wt%.

The compositions were applied on an epoxy-glass substrate using doctor blading to form 2 cm x 0.2 cm x 0.003 cm depositions and subsequently cured. For composition 2 A, the curing profile was: drying at 120°C for 15 minutes in a convection oven, and curing at 150°C for 15 minutes in a convection oven. For compositions 2B, 2C and 2D, the curing profile was: drying at 120°C for 15 minutes in a convection oven, and curing at 215°C for 15 minutes in a vapor phase condensation oven. The conductivity and Seebeck coefficient of the cured compositions were then tested. The test results are listed in Table 2.

Table 2

Composition No. 2A 2B 2C 2D

Organic binder 19 18 20 19 (wt%)

BiSn 29 51 low (wt%)

S 27 melting (wt%)

PbSnBi 31 material (wt%)

Se 29 25 10

(wt%)

As 7 4

(wt%)

High Te 17 30 melting (wt%) material Cu 54

(wt%)

Ni 10 (wt%)

Resistivity (Ω.cm) at 0.002 0.02 1.2

20°C

Seebeck Coefficient ~ + 20 + 130 + 60 65

(μV/°K) at 20°C

Thus, by selectively varying components and by adding different high melting point materials to invention compositions, thermoelectric materials with wide ranging resistivities and very good thermoelectric power ratings can be obtained upon curing.

While the invention has been described in detail with reference to certain embodiments thereof, it will be understood that modifications and variations are within the spirit and scope of that which is described and claimed.

Claims

That which is claimed is:

1. A composition useful for the preparation of thermoelectric materials and thermoelectric elements, said composition comprising:

(a) two or more different finely divided materials, wherein at least one of said materials is a low melting point material having a melting point of < 300┬░C,

(b) optionally, a binder system, and

(c) optionally, a dopant, wherein said combination produces P- or N-type thermoelectric materials upon curing.

2. A composition according to claim 1, wherein said low melting point material is one or more of P, S, Bi, In, Pb, Sn, Se, Ga, Cd, and/or Zn.

3. A composition according to claim 1, wherein at least one of said finely divided materials is a high melting point material having a melting point of > 300 ┬░C.

4. A composition according to claim 3, wherein said high melting point material is one or more of Ag, As, Au, Al, Cu, Sb, Si, Te, Ni, Zn, Fe, Ge, Mo, Mn,

Co, Mg, Ti, W, CuS, Cu₂S, Bi₂Te₃, Bi₂Se₃, and/or PbTe.

5. A composition according to claim 1, wherein said finely divided materials comprise particles with a size in the range of about 1 ╬╝m up to about 1 mm.

6. A composition according to claim 1, wherein said binder system comprises one or more of a solvent, a fluxing agent, or a polymer resin system.

7. A composition according to claim 6, wherein said solvent is one or more of a ketone, an alcohol, a glycol, an aromatic, an ester or an ether.

8. A composition according to claim 6, wherein said polymer resin is an epoxy, a phenolic, a novolac, a polyurethane, a polyimide, a bismaleimide, a maleimide, a cyanate ester, a polyester, a polyvinyl alcohol, or a polyurea.

9. A composition according to claim 1, wherein said dopant is Ag₂S, or Sbl

10. A composition according to claim 1, wherein said dopant is in powder form having a particle size in the range of about 1 ╬╝m up to about 100 ╬╝m.

11. A composition for the preparation of thermoelectric materials and thermoelectric elements, said composition comprising:

(a) two or more different finely divided materials, wherein said finely divided materials comprise: (i) in the range of about 15 up to about 100 wt% of at least one finely divided low melting point material having a melting point of < 300┬░C, and

(ii) in the range of about 0 up to about 85 wt% of a finely divided high melting point material having a melting point of > 300┬░C,

(b) in the range of 0 up to about 85 wt% of a binder system, and

(c) in the range of 0 up to about 10 wt % of a dopant, wherein said combination produces thermoelectric materials upon curing.

12. A composition for the preparation of thermoelectric materials and thermoelectric elements, said composition comprising:

(a) in the range of about 30 up to about 85 wt% of at least one finely divided low melting point material having a melting point of < 300┬░C, (b) in the range of about 5 up to about 45 wt% of at least one finely divided high melting point material having a melting point of > 300┬░C,

(c) in the range of about 15 up to about 40 wt% of a binder system, and

13. A thermoelectric element produced by curing a composition according to claim 1.

14. A thermoelectric element produced by curing a composition according to claim 11.

15. A thermoelectric element produced by curing a composition according to claim 12.

16. A method for producing thermoelectric elements, said method comprising:

(a) applying a composition according to claim 1 to a substrate, and subsequently

(b) heating said composition to a temperature sufficient to effect a curing or sintering thereof.

17. A method according to claim 16, wherein said composition is applied to said substrate by pressing, molding, screen printing, stencil printing, pressure filling, dispensing, electrostatic transfer, or doctor blading into photoimaged or otherwise preformed patterns or molds.

18. A method for creating thermoelectric elements or precursor thereof, said method comprising:

(a) selectively imparting a pattern to a pattemable insulator layer, thereby forming pattern holes therethrough,

(b) selectively depositing P- and N-type thermoelectric materials into portions of said pattern holes, and

(c) optionally, curing and/or sintering said P- and N-type thermoelectric pastes,

wherein said pattern holes into which said P-type thermoelectric paste is deposited are not the same as the pattern holes into which said N-type thermoelectric paste has been deposited, such that a layer of thermoelectric elements is formed containing one or more thermoelectric couples.

19. A method according to claim 18, wherein said thermoelectric paste is a polymer thick film thermoelectric paste or a ceramic thick film thermoelectric paste.

20. A method according to claim 19, wherein said ceramic thick film thermoelectric paste comprises: a) ceramic thermoelectric materials or precursors thereof, b) a suitable solvent, c) optionally, an organic binder, and d) optionally, glass frit.

21. A method according to claim 19, wherein said polymer thick film thermoelectric paste comprises:

a) thermoelectric materials or precursors thereof, b) a polymer binder, and c) optionally, a suitable solvent.

22. A method according to claim 18, wherein said pattemable insulator is selected from the group consisting of photopattemable epoxies, epoxy-acrylates, polyimide-based resins, epoxy based resins, thermoplastics, methacrylates, cyclic hydrocarbons and phenolic based resins.

23. A method according to claim 18, wherein said pattemable insulator layer is patterned by photoimaging and subsequent development, plasma etching, sand blasting, laser drilling, chemical etching or mechanical drilling.

24. A method according to claim 18, wherein said pattemable insulator is applied by laminating, screen printing, curtain coating, doctor blading, spraying, spin coating, roller coating, extrusion, or stencil printing.

25. A method according to claim 18, wherein said thermoelectric pastes are deposited by screen printing, pressure filling, doctor blading, automatic dispensing, or stencil printing.

26. A layer of thermoelectric elements produced by the method of claim 18.

27. An article of manufacture incorporating one or more thermoelectric elements according to claim 26.

28. A method for forming a thermoelectric module or precursor thereof, said method comprising:

(a) fabricating conductive traces on a first insulating plane, thereby forming a first trace-containing layer,

(b) forming on said first trace-containing layer a layer of thermoelectric elements according to claim 26, (c) optionally:

(i) forming an intermediate trace-containing layer by applying conductive traces on first and second sides of an insulating plane, (ii) affixing said first side of said intermediate trace-containing layer to said layer of thermoelectric elements,

(iii) affixing to said second side of said intermediate trace- containing layer a next layer of thermoelectric elements, and (iv) optionally repeating steps (i) - (iii),

(d) fabricating conductive traces on the layer of thermoelectric elements formed during step (b) or affixed during the last iteration of step (iii), if carried out, thereby forming a second layer of conductive traces, and

(e) affixing a second insulating plane to said second layer of conductive traces, thereby forming a second trace-containing layer, wherein said thermoelectric element(s) is electrically connected to said conductive traces on said first, second and any intermediate insulating planes such that a thermoelectric module is formed.

29. A method according to claim 28, wherein said insulating planes comprise an electrically insulating material selected from the group consisting of polymers, polymer-based composites, insulated metals, metal matrix composites and ceramics.

30. A method according to claim 28, wherein said conductive traces are fabricated by etching metal laminates, vapor deposition of metals, or depositing conductive pastes.

31. An article of manufacture incorporating one or more thermoelectric modules manufactured according to the method of claim 28.

32. A method for forming a thermoelectric module or precursor thereof, said method comprising:

(a) fabricating conductive traces on a first and a second insulating plane, thereby forming first and second trace-containing layers,

(b) applying a pattemable insulating layer to said first trace-containing layer,

(c) forming on said pattemable insulating layer a layer of thermoelectric elements according to claim 26,

(d) optionally, (i) forming an intermediate trace-containing layer by applying conductive traces on first and second sides of an insulating plane,

(ii) affixing a first side of said intermediate trace-containing layer to said layer of thermoelectric elements, (iii) forming on said pattemable insulating layer a layer of thermoelectric elements according to step (c), and (iv) optionally, repeating steps i-iii

(e) laminating the second trace-containing layer to said layer of thermoelectric elements, and (f) optionally heating said laminate under conditions suitable to sinter the thermoelectric pastes, thereby forming a thermoelectric module.

33. A method for forming a thermoelectric module or precursor thereof, said method comprising:

(b) forming a layer of thermoelectric elements according to claim 26,

(c) optionally, (i) forming one or more intermediate trace-containing layers by applying conductive traces on first and second sides of an insulating plane,

(ii) forming one or more layers of thermoelectric elements according to step (b),

(d) laminating said layer of thermoelectric elements, and any optional trace- containing layers alternating with any optional layers of thermoelectric elements, between said first and second trace-containing layers, and

(e) optionally heating said laminate under conditions suitable to sinter the thermoelectric pastes, thereby forming a thermoelectric module.

34. A method for the preparation of compositions according to claim 1, said method comprising mixing with a least one finely divided low melting point material:

(a) one or more finely divided low melting point or high melting point material(s), thereby resulting in a finely divided material mixture, and

(i) a solvent, or (ii) a binder system.

35. A method according to claim 18, wherein said thermoelectric paste comprises:

(a) two or more different finely divided materials, wherein at least one of said materials is a low melting point material having a melting point of < 300┬░C, (b) optionally, a binder system, and

36. A method according to claim 28, wherein said thermoelectric paste comprises:

37. A method according to claim 32, wherein said thermoelectric paste comprises:

(b) optionally, a binder system, and (c) optionally, a dopant, wherein said combination produces P- or N-type thermoelectric materials upon curing.

38. A method according to claim 33, wherein said thermoelectric paste comprises:

(b) optionally, a binder system, and