A Biocompatible and Flexible RF CMOS Technology and the Characterization of the Flexible MOS Transistors under Bending Stresses

To enable medical implants such as artificial retina, smart stent microsensors and other implantable wireless sensors, we developed a biocompatible and flexible RF CMOS technology based on a 0.18 mum CMOS process on 8-inch SOI (silicon on insulator) wafers. The silicon substrate for MOS transistors is 1 mum thick and sandwiched between two parylene layers. Since the potential implantable microsystems are intended to operate under external mechanical stresses, the effects of bending stresses (between -100 MPa to 100 MPa) on the flexible electronic devices are characterized. The piezo-coefficients for the flexible MOS transistors are extracted from measured I-V characteristics. While carrier mobility is linearly related to the stresses in both longitudinal and transverse directions, the threshold voltage is relatively insensitive to stresses. The experiment results can be used for pre-compensations in circuits design based on this technology.