Dynamic Response Considerations in Typical CMOS-MEMS Accelerometer Structures

This work presents important considerations regarding the dynamic response of a CMOS-MEMS spring-mass-system to step (Heaviside) and ramp (linear input) force stimuli. In the design CMOS-MEMS accelerometers most performance estimations and calculations are based in the steady-state behavior of damped systems, the present report focuses in the transient response and oscillatory error due to external forces actually present in many real-world yet simple applications where vibrations and undesired disturbances might appear. The dynamic model and transfer function of a micro-spring-mass system is obtained according to the technological fabrication parameters of a typical CMOS-MEMS micro-sensor. The displacement and therefore capacitance shift of the microstructure is modeled and simulated primarily while neglecting gravity and the damping phenomena related to air-filled micro gaps inherent to the micro-machining (wet chemical) process needed to release movable metallic structures out of a conventional CMOS integrated circuit. The results are intended to be considered in the design of space applications such as spacecraft instrumentation.