Thermal fatigue modeling of micromachined gas sensors

The reliability of thin metal films in active parts of microelectromechanical systems (MEMS) is critical for determining their lifetime and has to be accurately analysed specially when periodic changes of temperature induces thermal fatigue. In this paper we present a methodology to estimate the number of cycles to failure in micromachined gas sensors working in pulsed or modulated conditions (thermal cycling) by means of the combination of experimental thin metal elasto-plastic models and coupled thermo-mechanical FEM simulations. The results include thermal fatigue information such as plasticity models, the plastic strain range and the number of cycles to failure of different thin film metallisations, some of them typically used in the standard CMOS technology as the aluminum, other in CMOS compatible technologies, as the nickel, or, in alternative complementary technological procedures, as copper, gold and platinum. (C) 2003 Elsevier B.V All rights reserved.