Poly-SiGe-Based MEMS Thin-Film Encapsulation

This paper presents an attractive poly-SiGe thin-film packaging and MEM (microelectromechanical) platform technology for the generic integration of various packaged MEM devices above standard CMOS. Hermetic packages with sizes up to 1 mm2 and different sealed-in pressures ( ~ 100 kPa and ~ 2 kPa) are demonstrated. The use of a porous cover on top of the release holes avoids deposition inside the cavity during sealing, but leads to a sealed-in pressure of approximately 100 kPa, i.e. atmospheric pressure. Vacuum ( ~ 2 kPa) sealing has been achieved by direct deposition of a sealing material on the SiGe capping layer. Packaged functional accelerometers sealed at around 100 kPa have an equivalent performance in measuring accelerations of about 1 g compared to a piezoelectric commercial reference device. Vacuum-sealed beam resonators survive a 1000 h 85°C/85%RH highly accelerated storage test and 1000 thermal cycles between -40°C and 150°C.