THE DESIGN AND FABRICATION OF A MINIATURE THERMOELECTRIC GENERATOR USING MOS PROCESSING TECHNIQUES

The fabrication of thermoelectric generators using standard MOS thin film technology is described. Process sequences are presented for generators based on both silicon on sapphire and polycrystalline silicon on quartz substrates; the active elements being formed in both cases by ion implantation of alternate n-type and p-type regions. Device performance is evaluated and presented for both types of converter in terms of conversion efficiency and voltage and power outputs as a function of temperature difference. For thermoelements with a carrier concentration of 5 x 10(19) cm-3 the overall Seebeck coefficient for a single thermocouple is approximately 500 muV K-1 for both silicon on sapphire and silicon on quartz. Extrapolation of results indicates that voltage and current levels suitable for powering a microelectronic circuit (i.e. greater than 1 muA at 1 V) can be obtained from a chip of dimensions 0.5 cm x 1 cm x 0.045 cm. The use of polycrystalline silicon on quartz as opposed to silicon on sapphire has been shown to offer two major advantages. Firstly, due to the high thermal resistivity of quartz, the conversion efficiency of the resulting silicon on quartz chip is greater than for the silicon on sapphire case. For a substrate of dimensions 0.5 cm x 1 cm x 0.045 cm the improvement in device efficiency is almost 50 fold. Secondly, material costs are reduced when polycrystalline silicon on quartz is adopted, whilst, since the actual processing sequences are similar, manufacturing costs will remain approximately the same.