Evaluation of MOS devices as mechanical stress sensors

The influence of mechanical stress on metal-oxide-semiconductor (MOS) devices has been studied and analyzed for their applicability as in-situ sensors that are capable of measuring packaging induced and/or externally applied stress. Experimental results indicate that either compressive or tensile stress would alter the electrical characteristics of MOS devices in a regular pattern and that can be explained by substrate piezoresistivity. The regularity of electrical parameter variation of MOSFETs and the high sensitivity in correspondence with mechanical stress have made them very attractive as stress sensors since they may provide accurate and localized stress-state measurements. Through careful analysis, appropriate MOSFET-based sensors may be designed for proper on-site stress measurement in packaging and other stress detection applications. In addition, the mechanical stress also cause MOS devices to exhibit shorter lifetime that can be attributed to the occurrence of stress-induced charge-trapping sites in gate oxide. For MOSFETs utilized as stress sensors, the reliability issue related to mechanical stress has to be accounted and certain modification of stress-state extraction procedure will be needed to maintain valid stress measurement.