Planar-type SiGe thermoelectric generator with double cavity structure

Abstract

Thermoelectric power generation is a promising technology that can directly convert thermal energy into electrical energy and is expected to be applied as power supplies for low-power electronic devices, such as sensors. In particular, planar-type devices fabricated based on lithography processes not only enable significant device miniaturization and lower cost but also take advantage of materials with smaller dimensions, such as thin films and nanowires, which have attracted much attention in recent years. Silicon germanium (SiGe) is a promising thermoelectric material due to its relatively high power factor, low thermal conductivity, and compatibility with standard top-down fabrication process. We design and fabricate a planar-type thermoelectric generator with a double cavity structure using a 240 nm thick Si0.8Ge0.2 thin film and report its performance improvement. When the temperature difference is applied to the device, the measured power density of 100 μWcm−2 was achieved at ΔT = 15 K, namely, the performance normalized by the applied temperature was 0.43 μWcm−2K−2. Finally, the dependence of the device performance on the SiGe film thickness is discussed. The results from our simulation show that a maximum performance of 1.75 μWcm−2K−2 can be achieved by the current device structure, indicating the potential for future applications as thermoelectric energy harvesters.