Electrostatic Modification
Physical phenomenon in micro-electromechanical systems arises when an applied electrical potential alters the effective stiffness of a suspended structure. The comb drive comb softening modifies the resonant frequency of a micro-gyroscope by reducing the overall spring constant. It governs the relationship between bias voltage and mechanical behavior but ceases to apply if the driving electrodes do not carry a potential difference.
Frequency Shift
Tuning of micro-machined devices often relies on this electrostatic effect. As voltage increases, the comb drive comb softening reduces the sensor operating frequency. This behavior occurs because the electrostatic force gradient acts in opposition to the mechanical spring force of the flexures.
Engineers utilize this mechanism to align the drive and sense frequencies of resonators.
Voltage Sensitivity
Electrostatic forces are proportional to the square of the applied bias. Thus, the comb drive comb softening displays a non-linear dependence on voltage. Minor fluctuations in power supply stability can lead to unexpected drift in sensor sensitivity, which necessitates highly regulated voltage references.
Stability Limit
Structural failure can occur if the bias voltage exceeds a critical threshold. At this point, the comb drive comb softening forces exceed the mechanical restoring force, causing the fingers to pull together and short-circuit. Designers prevent this outcome by keeping operating voltages well below the pull-in limit.
