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 realworld 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.