Titanium Disilicide as High-Temperature Contact Material for Thermoelectric Generators

Thermoelectric devices can be used to capture electric power from waste heat in a variety of applications. The theoretical efficiency rises with the temperature difference across the thermoelectric generator (TEG). Therefore, we have investigated contact materials to maximize the thermal stability of a TEG. A promising candidate is titanium disilicide (TiSi₂), which has been well known as a contact material in silicon technology for some time, having low resistivity and thermal stability up to 1150 K. A demonstrator using highly doped silicon as the thermoelectric material has been integrated. A p- and an n-type wafer were oxidized and bonded. After cutting the wafer into pieces, a 200-nm-thick titanium layer was sputtered onto the edges. After a 750°C rapid thermal annealing step, the TEG legs were connected by a highly conductive TiSi₂ layer. A TEG with 12 thermal couples was integrated, and its joint resistance was found to be 4.2 Ω. Hence, we have successfully demonstrated a functional high-temperature contact for TEGs up to at least 900 K. Nevertheless, the actual thermal stability will be even higher. The process could be transfered to other substrates by using amorphous silicon deposited by plasma-enhanced chemical vapor deposition.