Electroforming Nanostructured-Based Thermoelectrics

Thermoelectric (TE) materials offer engineering solutions for applications such as cooling without moving parts and conversion of waste heat to electricity. However, devices using existing thermoelectric materials suffer from poor efficiency and high cost. Electrochemical deposition (ECD) has the potential to make the synthesis of thermoelectrics more cost effective and potentially enhance thermoelectric properties. The best thermoelectrics to date are thin film super lattices, fabricated using vapor phase methods [1]. However, these materials have a greatly limited application space due to their limited thickness (~ 10 µm). In this work, ECD techniques are used to nanostructure Bi₂Te₃ based thermoelectric materials over large areas and thicknesses, as well as electroforming it into a mold to enable future batch fabrication. Multiple experiments were performed to better understand scalability of thermoelectric film growth. Large grain boundaries were found to affect density and stoichiometry of the material impacting TE performance.  A 7 liter chemistry make-up and ECD conditions are established targeting wafer scale batch fabrication. The highest Seebeck, 85 µV/K, was found when deposited in small electroformed posts with a resistivity of 5 mΩ cm.

[1] R. Venkatasubramanian, E.S., T. Colpitts, B. O'Quinn,, Nature, 2001. 413: p. 597.