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

The fabrication of thermoelectric generators using standard MOS thin f ilm technology is described. Process sequences are presented for gener ators 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 perfor mance is evaluated and presented for both types of converter in terms of conversion efficiency and voltage and power outputs as a function o f temperature difference. For thermoelements with a carrier concentrat ion of 5 x 10(19) cm-3 the overall Seebeck coefficient for a single th ermocouple is approximately 500 muV K-1 for both silicon on sapphire a nd 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 dimension s 0.5 cm x 1 cm x 0.045 cm. The use of polycrystalline silicon on quar tz as opposed to silicon on sapphire has been shown to offer two major advantages. Firstly, due to the high thermal resistivity of quartz, t he conversion efficiency of the resulting silicon on quartz chip is gr eater than for the silicon on sapphire case. For a substrate of dimens ions 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 polycrystall ine silicon on quartz is adopted, whilst, since the actual processing sequences are similar, manufacturing costs will remain approximately t he same.