An in-plane SiGe differential capacitive accelerometer for above-IC integration

MEMS above-IC monolithic integration can yield a very compact device with good cost-effectiveness. One of the major challenges for this technology is to protect the CMOS from the heat introduced by the MEMS fabrication. In this paper, we present the design and fabrication of a novel lateral capacitive accelerometer, utilizing a low thermal budget SiGe MEMS technology. The accelerometer features a 4 µm SiGe structural layer thickness with a shock protector gap of 500 nm. Benefiting from the low temperature (~450 °C) SiGe MEMS technology, this inertial device demonstrates the achievability of fabricating above-IC mechanical sensors by 3D stacking. In this paper, the accelerometer design will be introduced first, followed by the introduction of the low thermal budget SiGe MEMS fabrication process. The fabricated devices have been characterized with a network/spectrum analyzer. Both a frequency sweep and a dc voltage sweep have been conducted. These electrostatic characterization results will be analyzed and compared with the design model.