Experimental Characterization of Microfabricated Thermoelectric Energy Harvesters for Smart Sensor and Wearable Applications

Microfabricated thermoelectric generators (mu TEGs) are excellent candidates for sustainable power delivery for the next generation of smart sensors and wearable devices through harvesting of waste heat. However, the assembly process and inherently small contact areas for thermal and electrical transport introduce losses which can significantly reduce the effective figure of merit ZT. Further, the form factor of mu TEGs makes these losses extremely challenging to quantify. The relative contributions of the thermoelectric film and interfaces greatly impact the choice of materials, device geometry, and maximum power point operation. A comprehensive study of mu TEG devices including microfabrication, detailed modeling and optimization, and electrical, structural, and thermal characterization of modules and their constituent films is presented. Using a combination of novel infrared microscopy and thin-film characterization techniques, the average thermoelectric material properties and the power output as a function of the true temperature difference across the device are isolated. Power outputs as high as 1 mW for a mu TEG with 13.8 mm(2) footprint and device T of 7.3 K are measured. An order of magnitude reduction in figure of merit for the devices (ZT approximate to 0.03) compared to the constituent thermoelectric films (zT approximate to 0.3), with implications for the selection of maximum power point operation, is demonstrated.