Development of a thermoelectric energy harvester with thermal isolation cavity by standard CMOS process

A micro thermoelectric generator that combines the conventional in-plane and cross-plane designs is developed to harvest effectively the thermal gradient, where heat flux from the top to bottom surface is confined passing through the in-plane thermocouples. A thermal isolation cavity is created underneath the thermocouples to prevent heat loss, maintain temperature gradient, and improve output power. Analysis shows that, with 10 μm cavity depth, the thermocouple's temperature gradient is above 99% of the hot/cold side temperature difference. By comparison, it is only 14% for those without the isolation cavity. Simulation results show that the optimal thermocouple of 71 μm × 4 μm × 0.275/0.18 μm (length × width × thickness for P-/N-thermolegs) has matching electrical/thermal resistance and can achieve the maximum power factor 0.0473 μW/cm2 K2 and voltage factor 2.788 V/cm2 K. The design is validated by standard CMOS process, where the isolation cavity is realized by dry etching post-process. Design verification by TSMC 0.35 μm 2P4M (2-poly and 4-metal) CMOS process shows that the thermocouple 60 μm × 4 μm can provide the power factor 0.0417 μW/cm2 K2 and voltage factor 2.417 V/cm2 K.