Monolithically integrated thermoelectric energy harvester based on silicon nanowire arrays for powering micro/nanodevices

Abstract

One-dimensional (1D) nanowire structures have been shown to be promising candidates for enhancing the thermoelectric properties of semiconductor materials. This paper goes beyond single nanowire characterization and reports on the implementation of multiple electrically connected dense arrays of well-oriented and size-controlled silicon nanowires (Si NWs) grown by the CVD-VLS mechanism into microfabricated structures to develop thermoelectric microgenerators (μTEGs). Low thermal mass suspended silicon structures have been designed and microfabricated to naturally generate thermal gradients in planar microthermoelements. The hot and cold parts of the device are linked with horizontal arrays of Si NWs growth by a single bottom-up process. In order to improve the performance of the device as energy harvester, the successive linkage of multiple Si NW arrays has been developed to generate larger temperature differences while preserving a good electrical contact that allows keeping small internal thermoelement resistances. The fabricated thermoelements have shown Seebeck voltages up to 60mV and generated power densities up to 1.44mW/cm2 for ΔT=300°C and, working as energy harvesters, a maximum Seebeck voltage of 4.4mV and a generated power density of 9μW/cm2 for ΔT=27°C (across the nanowires) in a single thermoelement. The fabricated microgenerator, taking advantage of the simple planar geometry and compatibility with silicon technology, provides an alternative to the state-of-the-art μTEGs based on non-integrable and scarce V–VI semiconductor materials and a promising energy harvester for advanced micro/nanosystems.