Process-Voltage-Temperature Analysis of a CMOS-MEMS Readout Architecture

Thermal drift is one of the main issues limiting the performance of resonant MEMS sensors. Their impact may be minimized at several levels, such as specific system-level solutions (e.g. differential sensing) or mechanical design (e.g. privileging suspended structures). While solving these issues is essential, one should not overlook the temperature-dependence of the readout and oscillation-sustaining electronics associated to the resonators. Considering monolithic CMOS-MEMS devices, thermal drift of the electronics becomes the main challenge, when off-the-shelf building-blocks are used over a large temperature range (from -40 degrees C to 175 degrees C). In this paper, a process-voltage-temperature analysis of electronics readout is carried out to illustrate this issue. Proposed analysis shows that the phase-difference between the motional signals decreases monotonically with temperature. In extreme voltage-temperature conditions for -3 sigma variability, phase-difference achieves -7.2 degrees at 175 degrees C, VDD = 1.62 V; and 5 degrees at -40 degrees C, VDD = 1.98 V. This result highlights the need of CMOS / MEMS co-design and optimization tools, for improving the thermal stability of resonant sensors in high-end, extreme environments such as automotive applications.