Design and fabrication of MEMS thermoelectric generators with high temperature efficiency

Abstract

For MEMS devices with power consumption in the range of micro-watts, thermal energy harvesting becomes a viable candidate for power supply. This paper describes a multipurpose platform to fabricate thermoelectric generators in a combined surface and bulk micromachining process. The thermocouples are deposited by thin-film processes with high integration density on the wafer surface. To provide a large thermal contact area, the heat flow path is perpendicular to the chip surface (cross-plane) and guided by thermal connectors. One thermocouple junction is thermally connected via electroplated metal stripes to the heat source and thermally insulated to the heat sink by a cavity in the wafer substrate. Simulations show that approximately 95% of the entire temperature difference over the device is located between the two thermocouple junctions. Power factors of 3.63 × 10⁻³ μW mm⁻² K⁻² and 8.14 × 10⁻³ μW mm⁻² K⁻² can be achieved with thermopiles made of Al and n-poly-Si or p-Bi_0.5Sb_1.5Te₃ and n-Bi_0.87Sb_0.13, respectively. Measurements of fabricated devices show a linear output voltage of 76.08 μV K⁻¹ per thermocouple and prove the feasibility of the concept.