METHOD OF MANUFACTURING A SEALED THERMOELECTRIC MODULE

Abstract

The present invention relates to a method for manufacturing a thermoelectric module which utilises the concept of solid-liquid interdiffusion bonding for both forming the metallization, interconnection and bonding between the thermoelectric elements and the electric contacts and the forming of a hermetically sealing of the thermoelectric module.

Claims

1. A method manufacturing a thermoelectric module, characterised in that the method comprises: 1) pre-processing a first and second electrically nonconductive cover substrate, each having a first and second surface, for electrical connection and sealing by: i) attaching a stratified layered metallic electric contact element consisting of a first bonding layer of metal A and an optional second bonding layer of metal B onto each location of the first side of the first and the second cover substrate where an electric contact with a thermal element is to be formed, the electric contact element is attached with its first bonding layer facing the first side of the respective cover substrate, and ii) attaching an equally dimensioned stratified layered metallic sealing frame consisting of a first bonding layer of a metal C and an optional second bonding layer of metal D along the periphery of the first side of both the first and the second cover substrate such that the first bonding layer of each metal frame is facing the first side of the respective cover substrate, 2) preparing the formation of the electrical connections between the electrical contact elements and a number of p-doped and a number of n-doped thermoelectric elements, where each p-doped and n-doped thermoelectric element has on a first side and on a second side opposite the first side, a first bonding layer of the metal A and a second bonding layer of the metal B directly onto the first bonding layer, by: j) selecting one of either the first or the second cover substrate: jj) placing a p-doped thermoelectric element with its second bonding layer on its first side facing either the first or the optional second bonding layer of the respective electric contact element on each location where an electrical connection between the p-doped thermoelectric element and the electric contact element is to be formed on the selected cover substrate, and jjj) placing a n-doped thermoelectric element with its second bonding layer on its first side facing either the first or the optional second bonding layer of the respective electric contact element on each location where an electrical connection between the n-doped thermoelectric element and the electric contact element is to be formed on the selected cover substrate, 3) preparing a hermetically sealing of the thermoelectric module by: k) placing a sealing element having on a first side and on a second side opposite the first side a first bonding layer of a metal C and a second bonding layer of a metal D, with its second bonding layer facing either the first or the optional second bonding layer of the sealing frame of the selected cover substrate, and 4) forming both the electrical contacts and the hermetically sealing of the thermoelectric module by: l) placing the non-selected cover substrate such that facing either the first or the optional second bonding layer of its sealing frame and its attached electric contact elements obtains physical contact with the respective second bonding layer of the second side of the sealing element and the respective p- doped and n-doped thermoelectric element placed onto the selected cover substrate, and ll) applying a gentle pressure pressing the first and second cover substrate against each other and annealing to a temperature at which the metal A and metal B and the metal C and D bonds all bonding layers in contact with each other together by solid-liquid interdiffusion, and wherein the melting point of metal A is higher than metal B and the melting point of metal C is higher than metal D, and the metals A and B and metals C and D are chemically reactive towards each other and forms one or more intermetallic compounds by solid-liquid interdiffusion when subject to heating above the melting point of metals B and D.

2. A method according to claim 1, characterised in that it further comprises a pre-processing of the thermoelectric elements, which comprises the following process steps: placing the at number of p-doped and n-doped thermoelectric elements into a deposition chamber, and then: i) depositing a first adhesion layer of a first metal directly onto the first and the second surface of the thermoelectric elements, ii) depositing a diffusion barrier layer of a non-metallic compound of a second metal directly onto the first adhesion layer on the first and second surface of the thermoelectric elements, iii) depositing a second adhesion layer of a third metal directly onto the diffusion barrier layer of the non-metallic compound of the second metal on the first and second surface of the thermoelectric elements, wherein the deposition chamber is either a chemical vapour deposition chamber, a physical vapour deposition chamber, or an atomic deposition chamber, and the deposition of the different layers of steps i) to iii) is obtained by feeding pre-cursor gases with varying chemical composition into the deposition chamber, the non-metallic compound of the second metal is either a nitride or an oxide of the second metal, depositing a first bonding layer of a metal A directly onto the second adhesion layer on the first and second surface of the thermoelectric elements, and depositing a second bonding layer of a metal B directly onto the first bonding layer the on the first and second surface of the thermoelectric elements.

3. A method according to claim 1, wherein it further comprises a pre-processing of the sealing element, which comprises the following process steps: placing the sealing element into a deposition chamber, and then: a) optionally, depositing a first adhesion layer of a first metal directly onto the first and the second surface of the sealing element, aa) depositing a diffusion barrier layer of a non-metallic compound of a second metal either directly onto the optional first adhesion layer or directly onto the first adhesion layer on the first and second surface of the sealing element, aaa) depositing a second adhesion layer of a third metal directly onto the diffusion barrier layer of the non-metallic compound of the second metal on the first and second surface of the sealing element, wherein the deposition chamber is either a chemical vapour deposition chamber, a physical vapour deposition chamber, or an atomic deposition chamber, and the deposition of the different layers of steps a) to aaa) is obtained by feeding pre-cursor gases with varying chemical composition into the deposition chamber, the non-metallic compound of the second metal is either a nitride or an oxide of the second metal, depositing a first bonding layer of a metal C directly onto the second adhesion layer on the first and second surface of element of the sealing element, and depositing a second bonding layer of a metal D directly onto the first bonding layer the on the first and second surface of the element of the sealing element.

4. A method according to claim 1, wherein it further comprises a pre-processing of the sealing element, which comprises the following process steps in successive order: forming an adhesion layer by depositing a Cu-paste on the first and second side of the sealing element and annealing at a temperature in the range from 600 to 700° C., forming a first bonding layer of a metal C directly onto the adhesion layer on the first and second surface of the sealing element by electroless plating or electroplating, and forming a second bonding layer of a metal D directly onto the first bonding layer the on the first and second surface of the element of the sealing element by electroless plating or electroplating.

5. A method according to claim 1, wherein the attachment of the electric contact elements to the first and second electrically nonconductive cover substrates is obtained by: depositing a patterned layer of a Cu-paste onto the first side of the cover substrates pasta covering the area of the substrates where the sealing frame and the electric contact elements are to be attached and then sintering the Cu-paste by annealing at a temperature in the range from 600-700° C., and depositing a first metal layer of metal A covering the sintered Cu-paste by electroless plating or electroplating, and optionally a second layer—e.g. of metal B onto the first layer of metal A by electroless plating or electroplating.

6. A method according to claim 1, wherein the thermoelectric element comprises a semiconducting thermoelectric conversion material selected from a filled or non-filled CoSb.sub.3-based skutterudite.

7. A method according to claim 2, wherein: the first metal of the first adhesion layer and the second metal of the second adhesion layer is of the same elementary metal, and where the non-metallic compound of the second metal of the diffusion barrier layer is a nitride or an oxide of the same elementary metal as the first and second metal, and the elementary metal of the first metal of the first adhesion layer and the second metal of the second adhesion layer is one of Cr, Cu, Sn, Ta, and Ti, and the non-metallic compound of the second metal of the diffusion barrier layer is a nitride or an oxide of one of Cr, Cu, Sn, Ta, and Ti.

8. A method according to claim 2, wherein the first and second metal is Ti of at least 99.5 weight % purity, the non-metallic compound of the second metal of the diffusion barrier layer is TiN, the metal A of the first bonding layer is Ni and the metal B of the second bonding layer is Sn.

9. A method according to claim 6, wherein the first and second bonding layers of metal A and B, respectively, is deposited by: depositing by vapour deposition the first bonding layer of a metal A directly onto the second adhesion layer on the first and second surface of element of the semiconducting thermoelectric conversion material and the second bonding layer of a metal B directly onto the first bonding layer the on the first and second surface of the element of the semi-conducting thermoelectric conversion material in the same vapour deposition chamber applied for deposition of the first adhesion layer, the diffusion barrier layer and the second adhesion layer structure, or by: depositing the first and second bonding layers by electroplating or by electro-less plating.

10. A method according to claim 1, wherein: the sealing element is made of either zirconia or aluminium titanate, and metal C is the same as metal A, and metal D is the same as metal B.

11. A thermoelectric module, comprising: a number of thermoelectric elements of semiconducting thermoelectric conversion material doped to n-type conductivity and a number of thermoelectric elements of semiconducting thermoelectric conversion material doped to p-type conductivity, a number electric contact elements comprising a first bonding layer of a metal A, and optionally, a second bonding layer of a metal B deposited directly onto the first bonding layer, a sealing system comprising a first sealing frame, a sealing element, and a second sealing frame, where the first and second sealing frame comprises a first bonding layer of a metal C, and optionally, a second bonding layer of a metal D deposited directly onto the first bonding layer and a first cover substrate in thermal contact with a heat reservoir and second cover substrate in thermal contact with a heat sink, where the thermoelectric elements of n-type conductivity and the thermoelectric elements of p-type conductivity are electrically connected in series by the electric contact elements, each electric contact element is on a first side bonded to at least one thermoelectric element, and on a second side opposite the first side bonded to one of the first and second cover substrate, wherein each thermoelectric element of n-type conductivity and each thermoelectric element of p-type conductivity has on both its first and second surface: i) a first adhesion layer of a first metal deposited directly onto the first and second surfaces, ii) a diffusion barrier layer of a non-metallic compound of a second metal deposited directly onto the first adhesion layer on the first and second surfaces, iii) a second adhesion layer of a third metal deposited directly onto the diffusion barrier layer of the non-metallic compound of the second metal on the first and second surfaces, iv) a first bonding layer of a metal A deposited directly onto the second adhesion layer on the first and second surfaces, and v) a second bonding layer of a metal B deposited directly onto the first bonding layer the on the first and second surfaces, and the sealing element has on a first side and a second side opposite the first side: vi) an adhesion layer of Cu, vii) a first bonding layer of a metal C deposited directly onto the adhesion layer on the first and second sides, and viii) a second bonding layer of a metal D deposited on the first bonding layer, the first sealing frame is at a first side of the first bonding layer attached to the first cover substrate and on the side opposite of the first side bonded to the sealing element by solid liquid interdiffusion bonding, and the second sealing frame is at a first side of the first bonding layer attached to the second cover substrate and on the side opposite the first side bonded to the sealing element by solid liquid interdiffusion bonding, and where the non-metallic compound of the second metal is either a nitride or an oxide of the second metal, the melting point of metal A is higher than metal B and the melting point of metal C is higher than metal D, and the metals A and B and metals C and D are chemically reactive towards each other and forms one or more inter metallic compounds by solid-liquid interdiffusion when subject to heating above the melting point of metal B and D, and the solid liquid interdiffusion bonds are formed by laying the second bonding layer of metal B of the thermoelectric elements and optionally, the electric contact elements, respectively, facing and contacting each other followed by an annealing which causes metal B of the second bonding layer to melt and reacting with metal A of the first bonding layer.

12. A thermoelectric module according to claim 11, wherein the semiconducting thermoelectric conversion material is a filled or non-filled CoSb.sub.3-based skutterudite.

13. A thermoelectric module according to claim 11, wherein the first metal of the first adhesion layer and the second metal of the second adhesion layer is of the same elementary metal, and where the non-metallic compound of the second metal of the diffusion barrier layer is a nitride or an oxide of the same elementary metal as the first and second metal.

14. A thermoelectric module according to claim 13, wherein the elementary metal of the first metal of the first adhesion layer and the second metal of the second adhesion layer is one of Cr, Cu, Sn, Ta, and Ti, and the non-metallic compound of the second metal of the diffusion barrier layer is a nitride or an oxide of one of Cr, Cu, Sn, Ta, and Ti.

15. A thermoelectric module according to claim 11, wherein the metal A of the first bonding layer is one of the following elementary metals; Au, Ag, Cu, Ni, Ni—V alloy with from 6.5 to 7.5 atom % V, and the metal B of the second bonding layer is one of the following elementary metals; In or Sn.

16. A thermoelectric module according to claim 11, wherein the first and second metal is Ti of at least 99.5 weight % purity, the non-metallic compound of the second metal of the diffusion barrier layer is TiN, the metal A of the first bonding layer is Ni and the metal B of the second bonding layer is Sn.

17. A thermoelectric module according to claim 11, wherein: the thickness of the first adhesion layer (2) is in one of the following ranges; from 20 nm to 2 μm, from 50 nm to 1.5 μm, from 100 nm to 1.5 μm, from 200 nm to 1.5 μm, or from 500 nm to 1.5 μm, the thickness of the diffusion barrier layer (3) is in one of the following ranges: from, 50 to 5000 nm, from 75 to 3000 nm, from 100 to 2000 nm, from 150 to 1000 nm, from 150 to 750 nm, from 200 to 500 nm, from 200 to 400 nm or from 200 to 300 nm, the thickness of the second adhesion layer (4) is in one of the following ranges; from 20 nm to 1000 nm, from 30 nm to 750 nm, from 40 nm to 500 nm, from 100 nm to 400 nm, or from 150 nm to 300 nm, the thickness of the first bonding layer (5) of metal A is in one of the following ranges; from 1 μm to 1 cm, from 1 μm to 0.5 cm, from 1 μm to 0.1 cm, from 2 μm to 500 μm, from 2 μm to 100 μm, from 2 μm to 50 μm, or from 3 μm to 10 μm, and the thickness of the second bonding layer (6) of metal B is in one of the following ranges; from 300 nm to 0.75 cm, 300 nm to 0.3 cm, 300 nm to 750 μm, from 200 nm to 400 μm, from 200 nm to 75 μm, from 200 nm to 30 μm, or from 300 nm to 3 μm.

18. A thermoelectric module according to claim 11, wherein the method further comprises depositing a 10 to 50 nm thick layer of Au directly onto one of the first adhesion layer, the second adhesion layer, or the first bonding layer, or two or more of these.

19. A thermoelectric module according to claim 11, wherein: the sealing element is made of either zirconia or aluminium titanate, and metal C is the same as metal A, and metal D is the same as metal B.

Description

LIST OF FIGURES

[0103] FIG. 1 is a facsimile of FIG. 1 of U.S. Pat. No. 6,660,926 showing a schematic representation of the crystal structure of the mineral skutterudite.

[0104] FIG. 2a) is a schematic side view illustrating the structure of a thermoelectric device involving one P-doped and one N-doped element of thermoelectric conversion material.

[0105] FIG. 2b) is a copy of FIG. 18 of U.S. Pat. No. 6,660,926 (without text on the figure) showing a similar TE-module as shown in FIG. 2a) involving several P-doped and one N-doped elements of thermoelectric conversion materials electrically connected in series.

[0106] FIGS. 3a) and 3b) is a schematic view of the sealing frame when attached to the cover substrates as seen from the side and from above, respectively.

[0107] FIG. 4a) and b) is a schematic view as seen from above of the first and second cover substrates after deposition and attachment of the sealing frame and the electric contact elements according to one example embodiment.

[0108] FIG. 5 is a schematic side view illustrating the ADA/SLID-structure on TE-elements employed by the invention.

[0109] FIGS. 6a) to 6c) are schematic side views illustrating the principle of forming a SLID-bond.

[0110] FIG. 7 is a schematic side view illustrating the assembly of one P-doped and on N-doped TE-element having the ADA/SLID-structure according to the invention for interconnecting them is series by SLID-bonding to three electric contact elements.

[0111] FIG. 8 is a schematic view illustrating of a vertical cross-section cut taken along the line marked A′-A″ in FIGS. 4a) and 4b), showing the structure of the TE-module according to the invention after assembly and SLID-bonding.

EXAMPLE EMBODIMENT OF THE INVENTION

[0112] The invention is described in more detail by way of an example embodiment of a thermoelectric module with a similar construction as illustrated in FIGS. 4a) to 8.

[0113] The example embodiment utilises a filled or non-filled CoSb.sub.3-based skutterudite as the semiconducting thermoelectric conversion material intended to operate at high temperatures, i.e. at temperatures in the range from about 0° C. up to about 800° C. The semiconducting thermoelectric conversion material of the TE-element is thus a filled or non-filled CoSb.sub.3-based skutterudite. Each TE-element is provided with the ADA-structure, where the first and second adhesion layer is made of one of Cr, Ta or Ti, and especially preferred of Ti of at least 99.5 weight % pure Ti. The diffusion barrier layer is a nitride of the same metal as employed in the adhesion layers. Thus, the especially preferred ADA-structure comprises a first adhesion layer of Ti of at least 99.5 weight % pure Ti, a diffusion barrier layer of TiN, and a second adhesion layer of Ti of at least 99.5 weight % pure Ti. The first bonding layer of metal A is made of one of; Au, Ag, Cu, Ni, a Ni—V alloy with from 6.5 to 7.5 atomic% V, or a Ni—P alloy with from 5 to 12 weight% P, and metal B is one of; In or Sn. In an especially preferred embodiment the metal A of the first bonding layer of both the TE-element and the electric contact element is Ni or Ni-V alloy with from 6.5 to 7.5 atomic % V, and the metal B of the second bonding layer of both the TE-element and the electric contact element is Sn. The thicknesses of the layers of the example embodiment may be:

[0114] the thickness of the first adhesion layer is in one of the following ranges; from 20 nm to 2 μm, from 50 nm to 1.5 μm, from 100 nm to 1.5 μm, from 200 nm to 1.5 μm, or from 500 nm to 1.5 μm,

[0115] the thickness of the diffusion barrier layer is in one of the following ranges: from, 50 to 5000 nm, from 75 to 3000 nm, from 100 to 2000 nm, from 150 to 1000 nm, from 150 to 750 nm, from 200 to 500 nm, from 200 to 400 nm or from 200 to 300 nm,

[0116] the thickness of the second adhesion layer is in one of the following ranges; from 20 nm to 1000 nm, from 30 nm to 750 nm, from 40 nm to 500 nm, from 100 nm to 400 nm, or from 150 nm to 300 nm,

[0117] the thickness of the first bonding layer of metal A is in one of the following ranges; from 1 μm to 1 cm, from 1 μm to 0.5 cm, from 1 μm to 0.1 cm, from 2 μm to 500 μm, from 2 μm to 100 μm, from 2 μm to 50 μm, or from 3 μm to 10 μm, and

[0118] the thickness of the second bonding layer of metal B is in one of the following ranges; from 300 nm to 0.75 cm, 300 nm to 0.3 cm, 300 nm to 750 μm, from 200 nm to 400 μm, from 200 nm to 75 μm, from 200 nm to 30 μm, or from 300 nm to 3 μm.

[0119] The combination of employing an adhesion layer of pure Ti having a more than 99.5% purity based on the total weight of the Ti-phase, a diffusion barrier layer of TiN and a contact layer of Ni has proven to provide an especially robust metallisation exhibiting excellent electric and thermal conductivities of CoSb.sub.3-based skutterudite thermoelectric conversion materials, which may easily and securely be bonded to the electrodes of the thermoelectric device by use of the SLID-technology. That is, the electrode may be bonded to the CoSb.sub.3-based skutterudite thermoelectric conversion material by depositing a contact layer of Ni and then a bonding layer of Sn on the electrode, and then bonding them together by pressing the bonding layers of Sn together and heating them until the Sn reacts with the Ni and forms one or more of the following intermetallic compounds; Ni.sub.3Sn, Ni.sub.3Sn.sub.2, or Ni.sub.3Sn.sub.4.

[0120] The deposition of the ADA-structure and the first and second bonding layers may advantageously be obtained by the following process steps:

[0121] employing at least one element of a n-type or p-type doped semiconducting thermoelectric conversion material of a filled or non-filled CoSb.sub.3-based skutterudite having a first and second surface on opposite sides,

[0122] placing the at least one element of semiconducting thermoelectric conversion material into a deposition chamber, and then: [0123] i) depositing a first adhesion layer of a first metal directly onto the first and the second surface of the element of the semiconducting thermoelectric conversion material, [0124] ii) depositing a diffusion barrier layer of a non-metallic compound of a second metal directly onto the first adhesion layer on the first and second surface of the semiconducting thermoelectric conversion material element, [0125] iii) depositing a second adhesion layer of a third metal directly onto the diffusion barrier layer of the non-metallic compound of the second metal on the first and second surface of the element of the semiconducting thermoelectric conversion material, [0126] iv) depositing a first bonding layer of a metal A directly onto the second adhesion layer on the first and second surface of element of the semi-conducting thermoelectric conversion material, and [0127] v) depositing a second bonding layer of a metal B directly onto the first bonding layer the on the first and second surface of the element of the semiconducting thermoelectric conversion material,
wherein

[0128] the deposition chamber is either a chemical vapour deposition chamber, a physical deposition chamber, or an atomic deposition chamber, and the deposition of the different layers of steps i) to v) is obtained by feeding pre-cursor gases with varying chemical composition into the deposition chamber,

[0129] the non-metallic compound of the second metal is either a nitride or an oxide of the second metal, and

[0130] the melting point of metal A is higher than metal B and metal B is chemically reactive towards metal A at their common interface when subject to heating above the melting point of metal B forming an intermetallic compound by solid-liquid interdiffusion.

[0131] The sealing element of the example embodiment is a frame made of zirconia equipped with a single adhesion layer instead of the ADA-structure, followed by a first and second bonding layers as described above for the TE-elements of the example embodiment. The deposition of the adhesion layer and the first and second bonding layers may advantageously be obtained simultaneously by the same method as described above for the TE-elements by simply placing the sealing frame in the same deposition chamber.

[0132] The inventor has discovered that the bonding strength and the electric and thermal conductivity of the layers forming the metallisation structure may be significantly improved by practically avoiding any oxidation of the metal phases (Ti, Ni or Sn) during and after deposition. That is, the deposition process should advantageously be performed in a protected atmosphere practically void of oxygen (i.e. having less than 50 ppm oxygen) or made under a vacuum (i.e. at a pressure of less than 1000 Pa). Alternatively, if the handling of the thermoelectric material after formation of the metallisation involves exposure to air/oxygen, the metallic surfaces deposition proves may include depositing 10 to 50 nm of Au on top of the metal layer as an oxidation resistance layer. The oxidation resistance layer may be applied onto either the Ti layer (the adhesion layer), the contact layer (Ni) or the bonding layer (Sn), or one two or more of these.

[0133] The pre-processing of the first and second electrically nonconductive cover substrates is obtained by depositing a patterned layer of a metal pasta of i.e. Cu onto the first side of the cover substrates, pressing the first bonding layer of each electric contact element that is to be attached to the cover substrates against the deposited metal pasta and then annealing at a temperature which sinters the metal pasta with the cover substrates and the metal of the first bonding layer of the electric contact elements. In the case of using Cu-paste, the annealing is performed at 600-700° C. in an inert atmosphere of i.e. argon gas. Similarly, the attachment of the sealing frame may be obtained by including the peripheral region of the cover substrates when depositing the patterned layer of metal pasta followed by pressing the first bonding layer of the sealing frame against the deposited metal pasta and then annealing at a temperature which sinters the metal pasta with the cover substrate and the metal of the first bonding layer of the sealing frame.