Ibrahim Bel-Hadj's thesis
"Design of planar thermoelectric micro-generators integrating a 2.5D thermopile topology".

Defence on Friday 18 March, at 10.30 a.m.
Amphitheater of the IEMN - Central Laboratory - Villeneuve d'Ascq

Jury :

- Sylvie BÉGOT, Senior Lecturer HDR, University of Franche-Comté, FEMTO-ST, Rapporteur
- Étienne GAVIOT, University Professor, Le Mans University, Rapporteur
- Jean-Pierre VILCOT, CNRS Research Director, IEMN, Examiner
- Dimitri TAINOFF, Senior Lecturer, Grenoble Alpes University, Examiner
- Katir ZIOUCHE, University Professor, University of Lille, Thesis supervisor
- Zahia BOUGRIOUA, CNRS Research Fellow, IEMN, Thesis co-supervisor
- Didier LECLERCQ, University Professor, University of Lille, Guest speaker

Summary:

The considerable growth in applications linked to recent advances in the Internet of Things (IoT) means that new solutions need to be developed for harvesting the energy around us to power microsystems. The abundance of heat in our environment means that thermal energy recovery devices could be one of the solutions. In this work, we have developed a family of planar thermoelectric micro-generators (µTEGs), incorporating an original 2.5D thermopile topology periodically folded and distributed on a multi-membrane, capable of directly converting heat into useful electrical energy. This thermopile, with its high integration density, uses thermocouples based on metallic thermoelectric materials (Chromel and Constantan), associated electrically either in series or in parallel, enabling the internal electrical resistance of these µTEGs to be drastically reduced (down to around a hundred Ohms).
To obtain maximum output power from these modules, 3D numerical modelling using COMSOL Multiphysics® at thermal level was used to optimise their dimensions. The devices were manufactured using low-cost CMOS-compatible processes, using non-polluting, abundant and environmentally-friendly materials. It used the DRIE deep-etching technique on Silicon wafers to release membranes of adjustable lengths, enabling the thermal resistance of the µTEGs to be adapted to their environment. The devices produced in the technology centre were characterised using specific measurement benches developed for this purpose. By recovering one Watt of heat, thermogenerated electrical power of a few hundred microwatts can be achieved. This places these new 2.5D µTEGs among the best state-of-the-art µ-modules using metallic thermoelectric materials.

Abstract:

The tremendous growth of applications related to recent advances in the Internet of Things (IoT) requires the development of new solutions for harvesting/scavenging the environmental energy to power microsystems. The abundance of heat in our environment allows thermal energy harvesting devices to be one of the solutions. In this work, we have developed a family of planar micro-thermoelectric generators (µTEG), integrating a novel 2.5D thermopile topology periodically folded and distributed on multi-membrane, capable of converting heat directly into useful electrical energy. This thermopile, with high integration density, uses thermocouples based on metallic thermoelectric materials (Chromel and Constantan), electrically associated either in series or in parallel, allowing to drastically reduce the internal electrical resistance of these µTEGs (down to a hundred Ohms).
A 3D thermal modelling in COMSOL Multiphysics® was used to design the optimal dimensions of the modules so they would deliver the maximum output power. The fabrication of these devices is made by low-cost CMOS-compatible processes, using non-polluting, abundant and environmentally friendly materials. Deep reactive ionic etching (DRIE) of Silicon wafers is used to release membranes with adjustable lengths allowing to adapt the thermal resistance of these µTEGs to their environment. The devices realized in IEMN clean room, have been characterized using specific measurement benches developed for this purpose. The harvesting of one Watt of heat leads to thermo-generated electrical powers of a few hundred microwatts. This ranks these new 2.5D µTEGs among the best state-of-the-art µ-modules using metallic thermoelectrics.