Structural Deflection
Mechanical displacement within micro-electromechanical interdigital arrays alters the nominal spacing between rigid fixed fingers and flexible movable fingers under external mechanical load. When acceleration or packaging stress forces the movable mass sideways, capacitive comb gap deformation occurs along the sensitive axis. This physical narrowing or widening of the air gap modifies the baseline capacitance of the transducer.
The phenomenon governs the differential readout in MEMS accelerometers, setting the physical boundary where linear mechanical compliance transitions into uncompensated geometric distortion.
Electrostatic Pull
Voltage differences applied across adjacent finger pairs generate electrostatic forces that pull the flexible structures toward the stationary electrodes. As the potential increases, capacitive comb gap deformation intensifies through a positive feedback mechanism known as electrostatic softening. The attractive force varies inversely with the square of the gap distance, creating non-linear mechanical behavior at high drive voltages.
Operational stability requires keeping bias potentials below the critical pull-in voltage where opposing fingers make contact and cause electrical shorting.
Transduction Shift
Distortion of the physical gap geometry introduces systemic scale factor errors into the sensor output signal. Because capacitive comb gap deformation alters the nominal parallel-plate approximation, calculated sensitivity deviates from ideal linear equations across the full operational range. Temperature variations worsen the mechanical distortion by inducing thermal expansion differences between the silicon substrate and the ceramic package.
Calibration algorithms correct second-order non-linearities, but unmodeled gap variations directly degrade zero-point repeatability and harmonic distortion performance.
Verification Limit
Verification of comb finger geometry occurs during wafer-level probing using optical interferometry and high-frequency capacitance meters. Factory qualification protocols establish maximum acceptable gap variations across ambient temperature ranges. Standard testing procedures reject dies where capacitive comb gap deformation exceeds two percent of nominal spacing under maximum operating voltage.
