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

The results of this paper are pertinent to micromachined integrated chemical sensors, infrared sources and hotplates, among others. We report on the operation and characterization of micromachined complementary metal-oxide semiconductor (CMOS) microstructures with integrated CMOS polysilicon heaters at temperatures up to 1200 K. The new results concern the stability of integrated CMOS polysilicon heaters under such extreme conditions. Two resistance drift phenomena appearing above the polysilicon recrystallization temperature T-cr approximate to 870 K were identified. The first is a reversible resistance relaxation leading to resistance changes of several tens of per cent. Relaxation times are of the order of minutes and point to a thermally activated process. The second drift mechanism leads to slow resistance changes, for example, 3% after six hours above T-cr. Temperature calibration of such devices supported by finite element simulations is proven to be feasible and reliable. Despite the large temperature gradients in the heated microstructures, natural convection in the surrounding gas was found to be ineffective in comparison with heat conduction.