Abstract
In this paper we report on a thermoelectric generator (TEG) using thermal isolation provided by a thick porous Si layer locally formed on the Si wafer and thermocouples composed of p-doped polycrystalline Si/Al. The “hot” contacts of the thermocouples lie on the porous Si layer, while the “cold” contacts lie on bulk crystalline Si. A housing was also designed and fabricated in order to transfer any external temperature change on the “hot” contacts of the thermocouples, the “cold” contacts being isolated from the “hot” contacts by a thick resist layer. The fabrication of the sensing element (Si die) is fully compatible with batch Si processing. The output power of the thermoelectric generator depends on the porous Si isolation layer thickness, porosity, structure and morphology. For a mesoporous Si layer of 60% porosity and a macroscopic temperature differential of 10 K, an output power of 0.39 μW/cm2 was measured for a 50 μm thick porous Si layer.
Highlights
Solid state thermoelectric generators (TEGs) are devices that can convert thermal gradients to electrical power through the Seebeck effect [1]
Energy is wasted in the form of heat for a vast variety of everyday situations, ranging from exhaust pipes in cars, to heat generated on a microprocessor to even heat generated by the human body
An effort is so needed in order to increase the output power of any thermoelectric generator
Summary
Solid state thermoelectric generators (TEGs) are devices that can convert thermal gradients to electrical power through the Seebeck effect [1]. Both the thermal conductivity is decreased by nanostructuring and the electrical conductivity is increased by the high doping concentration This result opens new possibilities in the use of polycrystalline Si, a material widely used in Si technology and fully compatible with batch Si processing, in thermoelectrics. Porous Si is a versatile material with tunable properties that depend on its structure and porosity [18,19,20] It shows very low thermal conductivity (more than two orders of magnitude lower than that of bulk crystalline Si at room temperature) [21,22,23] that provides effective thermal isolation from the Si wafer [23], without using any free standing parts. To the best of our knowledge, the use of porous Si thermal isolation in a thermoelectric generator has not been reported before
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