All-Silicon Micro-Thermoelectric Generator for IoT Applications

In the next decade, a new digital revolution will be held over the expansion of the Internet of Things (IoT), involving the deployment of trillions of nodes in multiple locations. The exponential growth of these kind of wireless devices represents a major challenge in terms of their energy supply [1]. Among the available environmental sources, heat can be harvested by means of thermoelectric devices [2]. This work presents a new generation of densely packaged all-silicon microthermoelectric generators (μTEGs) with planar architecture.<br/><br/>Optimized p-doped silicon nanowires with 80 ± 30 nm in diameter are epitaxially integrated as dense arrays into these generators for an improved performance [3]. A procedure to reliably place a heat sink on top of the devices, boosting the fraction of external thermal gradient captured by the thermoelectrically active nanowires, is described. These improvements boosts the generated voltage up to six times with respect to that of a bare μTEG, leading to output powers well within the range of IoT needs (10-100 μW/cm²). Specifically, the μTEG on top of a heat source above 200°C and under still air convection conditions generates more than 10 μW/cm². When exposed to the same temperatures and to an airflow of 1.3 m/s (equivalent to a light breeze) the power density increases above 80 μW/cm².<br/><br/>Moreover, a long-term stability study running the device in load matching conditions for a period of 1000 h does not show degradation below 200°C. Finally, the suitability of connecting the μTEG with the current state of the art DC-DC converters is discussed, showing how eventual transients in real operation conditions could allow the device to reach the required cold start-up voltages.<br/><br/>Overall, the results shown here demonstrate the readiness of the presented μTEG as a valid power source for IoT applications at the microscale.<br/><br/>[1] E. Hittinger, P. Jaramillo, "Internet of things: Energy boon or bane?" Science 364(6438), 326–328 (2019).<br/>[2] E. Bell, "Cooling, Heating, Generating Power, and Recovering Waste Heat with Thermoelectric Systems." Science 321(5895), 1457–1461 (2008).<br/>[3] J.M. Sojo-Gordillo, et al., "Tuning the thermoelectric properties of boron-doped silicon nanowires integrated into a micro-harvester." Advanced Materials Technologies 7(2101715) (2022).