Fabrication of Miniature Thermoelectric Generators Using Bulk Materials

Abstract

Miniature thermoelectric modules (TEMs) are required for micro power generation as well as local cooling, and they should have small size and high performance. However, conventional bulk TEMs generally have in-plane dimensions of a few centimeters, and empty space between the legs for electrical isolation makes efficient miniaturization difficult. In this study, a miniature TEM with footprint of about 0.35 cm² and leg height of 0.97 mm was fabricated by reducing the dimensions of the legs and attaching them together to form a closely packed assembly, without using microelectromechanical processes. First, Bi_0.4Sb_1.6Te₃ (BST) and Bi₂Te_2.7Se_0.3 (BTS) ingots were made by ball milling and spark plasma sintering, and the ingots were cut into thin plates. These BST and BTS plates were then attached alternately using polyimide tapes, and the attached plates were sliced vertically to produce thin sheets. This process was repeated once again to make chessboard-like assemblies having 20 p–n pairs in an area of 0.35 cm², and electrical contacts were formed by Ni sputtering and Ag paste coating. Finally, thermally conductive silicone pads (~500 μm) were attached on both sides of the assembly using electrically insulating interface thermal tapes (∼180 μm). The maximum output power (P _max) from the miniature module was about 28 μW and 2.0 mW for temperature difference (ΔT) of 5.6°C and 50.5°C, respectively. Reducing the contact resistance was considered to be the key to increase the output power.