In-Situ Sensor-Matrix to Determine Package-Induced Stresses

Nearly all microelectromechanical systems nowadays include bipolar or metal oxide semiconductor (MOS) transistors. Those micro-electro-mechanical systems experience many temperature cycles during their life-time and may fail when the damage accumulation due to mechanical stress becomes critical. In this paper, we present a recently developed method to analyze in-situ the mechanical stress for integrated devices. We use a testchip equipped with stress sensitive on-chip complementary MOS (CMOS) transistors which are arranged in a matrix system without need for an analog multiplexer to improve accuracy. The stress sensitive MOS cells will be calibrated with a beam bending system to obtain the relation between electrical measurement signals and physical stress. A major benefit of our MOS transistor stress cells is that they can be produced in any standard CMOS process. Furthermore, these MOS transistors, in particular their charge carrier mobilities, are much more stress sensitive than resistors. The proposed theoretical explanation is verified by measurements and finite element simulations.