Harvesting performance of a planar thermoelectric microgenerator with a compact design

Abstract

In Internet of Things (IoT) systems millions of interconnected devices, each with multiple sensors, demand for sustainable and long term autonomous energy sources. Thermoelectricity offers an alternative to primary batteries for powering sensor nodes with energy harvesting solutions like waste heat recovery. In many of these scenarios, small size and large volume technologies are a request. While standard thermoelectric technologies are not viable for such applications due to their incompatibility with miniaturization and the use of scarce and toxic materials, planar thermoelectric microgenerators offer an advantageous solution. By micromachining and nanostructuring silicon, downsizing thermoelectric microgenerators is possible with an environmentally safe and cost effective approach. In the past, single micro-thermocouples based on mature silicon microfabrication technology combined with the integration of Si or SiGe nanowires as thermoelectric material were fabricated in our group producing power densities of several tens of nW/cm2. In this work, we report a new compact design featuring a high integration density of up to 50 series connected micro-thermocouples in a small footprint chip of 0.5 cm2 to increase the generated power. The devices were characterized mimicking a low-grade waste heat environment under natural and forced convection conditions. For an available heat source at 250 °C, power densities of 316 nW/cm2 under natural convection and up to 4.2 μW/cm2 under forced convection conditions have been achieved.