Transducer Architecture
Micro-machined inertial sensors measure translational acceleration by detecting capacitance changes between movable proof mass comb fingers and stationary substrate electrodes. Specification sheets for the MEMS capacitive accelerometer state full-scale sensing ranges, zero-g bias stability and frequency response bandwidth under controlled laboratory reference conditions. System integrators evaluate these parameters to select suitable motion sensing hardware for automotive safety, industrial tilt monitoring and consumer electronic applications.
Sensing Response
External acceleration forces displace the central silicon proof mass against supporting micromachined flexure springs, altering the distance between interdigitating capacitive sensing plates. Inside a MEMS capacitive accelerometer, differential sense circuits convert this displacement-induced capacitance variation into a proportional output voltage, utilizing high-frequency carrier signals to demodulate low-frequency acceleration signals. Viscous gas damping within the packaged cavity shapes the frequency response, balancing flat passband sensitivity against high-frequency resonance amplification near structural natural frequencies.
Environmental testing subjects packaged units to multi-axis shaker sweeps and thermal shock profiles to characterize bias drift, scale factor temperature coefficients and transverse sensitivity ratios across operating boundaries.
Noise Characterization
Brownian noise generated by residual gas molecules colliding with the proof mass sets the fundamental resolution floor for low-g sensing applications. In a MEMS capacitive accelerometer, reducing gas pressure within the cavity lowers mechanical noise but increases resonant peak Q-factors, requiring active electrostatic damping or precise closed-loop force balance feedback. Sensor designers balance mechanical noise trade-offs against circuit noise contributions from front-end switched-capacitor amplifiers.
Shock Limit
Physical impact forces exceeding mechanical suspension yield strengths cause permanent flexure deformation or proof mass stiction against packaging stops. Beyond specified shock limits, a MEMS capacitive accelerometer exhibits irrecoverable zero-g offset shifts or total structural failure due to beam fracture. Qualification standards require high-g shock survivability verification using drop towers or pneumatic shock hammers prior to flight hardware integration.
