Micro-fabrication and characterization of highly doped silicon-germanium based thermoelectric generators

Over the last decades of research on sustainable energy, thermoelectric generation has been identified as a potential energy harvesting solution for a wide range of applications. Nowadays, the commercial thermoelectric technology is almost entirely based on tellurium alloys, it mainly addresses room temperature applications and it is not compatible with MEMS and CMOS processing. In this work, silicon-germanium based micro-devices have been designed, developed and characterized with the aim of addressing the heat recovery needs of the automotive industry. The micro-scale of the fabricated devices, together with the full compatibility with silicon micro-processing, also profiles an interesting potential for application in the autonomous sensor field. Most importantly, the configuration and the fabrication processes of such silicon-based generators constitute a platform to transfer the results of decades of promising material investigations and engineering into practical micro-scaled thermoelectric generators. The room temperature characterization of the manufactured micro-generators revealed power factors up to 13.9x10-3 µW/(cm2K2) and maximum output power density up to 24.7 µW/cm2. In such temperature range, the micro-devices manufactured in this work are still not as performing as the state-of-the-art bismuth-telluride based technology. However, at around 300 C, the developed micro-modules are predicted to produce a maximum power output of 1.2-1.5mW under 10 C temperature gradient, which corresponds to 35-45% of the room temperature performance of the only commercial bismuth telluride based micro-devices. The results show that silicon-germanium micro-modules could potentially compete with the state-of-the-art commercial micro-devices, being better performing at higher temperature, but also offering the advantage of being a sustainable MEMS and CMOS compatible option for autonomous sensors integration