3D structures with piezoresistive sensors in standard CMOS

Aluminum hinges and polysilicon piezoresistors have been fabricated in a standard commercial CMOS process with one maskless post-processing step. The hinges and piezoresistors are formed using the metal interconnect and transistor gate layers in the CMOS process. Xenon difluoride is shown to be a simple and effective alternative to standard bulk etchants for this process, because of its extreme selectivity and gentle gas phase etch. Preliminary results from a piezoresistive accelerometer are given.