Operation and short-term drift of polysilicon-heated CMOS microstructuresat temperatures up to 1200 K

Abstract

The results of this paper are pertinent to micromachinedintegrated chemical sensors, infrared sources and hotplates, among others.We report on the operation and characterization of micromachinedcomplementary metal-oxide semiconductor (CMOS) microstructures withintegrated CMOS polysilicon heaters at temperatures up to 1200 K. The newresults concern the stability of integrated CMOS polysilicon heaters undersuch extreme conditions. Two resistance drift phenomena appearing abovethe polysilicon recrystallization temperature Tcr≈870 Kwere identified. The first is a reversible resistance relaxation leadingto resistance changes of several tens of per cent. Relaxation times are ofthe order of minutes and point to a thermally activated process. Thesecond drift mechanism leads to slow resistance changes, for example, 3%after six hours above Tcr.Temperature calibration of such devices supported by finite elementsimulations is proven to be feasible and reliable. Despite the largetemperature gradients in the heated microstructures, natural convection inthe surrounding gas was found to be ineffective in comparison with heatconduction.