Electrical Contact Fabrication and Measurements of Metals and Alloys to Thermoelectric Materials
- PDF / 600,224 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 57 Downloads / 201 Views
1044-U10-10
Electrical Contact Fabrication and Measurements of Metals and Alloys to Thermoelectric Materials Jonathan James D'Angelo1, Edward J Timm2, Fei Ren3, Bradley D Hall3, Eldon Case3, Harold Schock2, Mercouri Kanatzidis4, Duck Young Chung5, and Timothy P Hogan6 1 Electrical and Computer Engineering, Michigan State University, 2120 Engineering Building, East Lansing, MI, 48823 2 Mechanical Engineering, Michigan State University, East Lansing, MI, 48823 3 Chemical Engineering and Material Science, Michigan State University, East Lansing, MI, 48823 4 Chemistry, Northwestern University, Evanston, IL, 60208 5 Material Science Division, Argonne Nation Laboratory, Argonne, IL, 60439 6 Electrical and Computer Engineering, Michigan State University, East Lansing, MI, 48823 ABSTRACT Low electrical contact resistance is essential for the fabrication of high efficiency thermoelectric generators in order to convert heat to electricity. These contacts must be stable to high temperatures and through thermal cycling. A ratio of the contact resistance to the leg resistance below 0.1 is the goal for fabrication of a high efficiency thermoelectric power generation device. Here we present the fabrication procedures and characterization of contacts of metal alloys to Pb-Sb-Ag-Te (LAST) and Pb-Sb-Ag-Sn-Te (LASTT) compounds[1,2]. Contacts were fabricated and measured for both ingot and hot pressed materials. Stainless steel 316 has shown a low resistance contact to these thermoelectric materials when the proper bonding conditions are used. Different time-temperature-pressure conditions for bonding to ntype and to p-type legs are presented. Contact resistances below 10µΩcm2 have been measured. In addition, break tests have shown bond strengths exceeding the semiconductor fracture strength. One of the considerations used in selecting iron alloys for electrical interconnects is the similarity in the coefficient of thermal expansion to the LAST and LASTT materials which is 18-20 ppm/ºC and relatively temperature insensitive. Contacts to the thermoelectric materials were accomplished by diffusion bonding in a furnace developed in our lab at Michigan State University. The furnace is capable of reaching temperatures of up to 1000ºC with a controlled atmosphere of a reducing gas. Fabrication procedures and contact data are presented in this paper. INTRODUCTION Contact resistance can significantly degrade the overall efficiency of a thermoelectric power generation device [3]. In order to guarantee applicable module efficiency a ratio of the contact resistance to the leg resistance below 0.1 is needed.
0.3
δ = 0.0 δ = 0.1
0.25 δ=
η
0.2
R
δ = 0.5
c
R
0.15 0.1 0.05 0
0
0.5
1
1.5
2
2.5
3
ZT
avg
Figure 1 Efficiency degradation due to contact resistance [3]
Here we present the progress of making electrical contacts that have a low contact resistance and are mechanically strong. Many different contact materials have been tested, and some discoveries of materials that show a δ < 0.1 have been made. The development of both hot
