Network of thermoelectric nanogenerators for low power energy harvesting

We report the design, elaboration and measurements of an innovative planar thermoelectric (TE) devices made of a large array of small mechanically suspended nanogenerators (nanoTEG). The miniaturized TE generators based on SiN membranes are arranged in series and/or in parallel depending on the expected final resistance adapted to the one of the load. The microstructuration allows, at the same time, a high thermal insulation of the membrane from the silicon frame and high thermal coupling to its environment (surrounding air, radiations). We show a ratio of 45% between the measured effective temperature of the membrane, (and hence of the TE junctions), and the available temperature of the heat source. The temperature difference generated across the TE junction reaches a value as high as 60 K per mm. Energy harvesting with this planar TE module is demonstrated through the collected voltage on the TE junctions when a thermal gradient is applied, showing a harvested power of 0.06 mu Watt for a 0.5 cm(2) chip for an effective temperature difference of 6.8 K. The optimization of nanoTEGs performances will increase the power harvested significantly and permit to send a signal by a regular communication protocol and feed basic functions like temperature measurement or airflow sensing.