Development of interconnection materials for Bi₂Te₃ and PbTe thermoelectric module by using SLID technique

In this study, low-temperature Bi₂Te₃ and mid-temperature PbTe thermoelectric modules are assembled by the technique of Solid Liquid Interdiffusion (SLID). Scanning electron microscope is carried out for issues relating to factors limiting the reliability, growth of intermetallic compounds, and thermal stability. For low-temperature thermoelectric module, N-type Bi₂Te₃ is bonded to alumina substrates by using a Ni/Sn/Ag system. During bonding and subsequent aging reaction at 200 °C, Sn reacts with Ag to form Ag₃Sn, and Ni reacts with Sn to form Ni₃Sn₄. This reaction process takes less than 72 h to exhaust the entire Sn layer to produce a bonding that can withstand temperature as high as 480 °C. The interfacial reaction, Ni penetration depth, and IMC kinetics between Ni and Bi₂Te₃ at 200, 250, and 300 °C are also investigated in detail. For mid-temperature thermoelectric module, N-type PbTe is bonded to alumina substrates by using a Ag/In/Ag system. During assembly at 190 °C, all Ag/In/Ag joint are transformed into Ag₂In, which has the melting temperature above 670 °C, in less than 2 minutes. Furthermore, this Ag-In joint has passed high temperature storage test at 400 °C for 1000 h. The success of solid liquid interdiffusion technique and related contact materials provide a cost effective way to assemble thermoelectric modules for power generating or cooling applications which require long term operations at high temperatures.