Electrostatic Coupling
Micro-electromechanical systems utilize interdigitated metallic structures to convert physical displacement into measurable electrical signals. The comb finger capacitance arises from the overlapping regions of stationary and movable electrode fingers in a MEMS accelerometer or gyroscope. This structure creates a highly sensitive capacitive network that changes with the motion of proof masses.
It is the primary mechanism for detecting sub-nanometer movements in consumer and industrial sensors.
Displacement Sensitivity
Finger spacing and overlap area determine the electrical output of the sensor. As the proof mass moves, the distance between opposing fingers changes, modifying the capacitance according to electrostatics. This modification causes a proportional shift in the sensor electrical characteristics.
The displacement sensitivity depends directly on how many finger pairs are integrated into the design.
Parasitic Influence
Fringe fields and substrate interactions introduce unwanted offset currents. These parasitic effects limit the resolution of the sensor by contributing a fixed capacitance that does not vary with movement.
Metrological Evaluation
Precision capacitance bridges and high-frequency lock-in amplifiers evaluate the electrical characteristics during manufacture. The testing system applies a known excitation voltage to the device terminals and detects the minuscule currents flowing through the interdigitated structure. This process is carried out at wafer level to filter out defective dies before packaging.
Calibration runs establish the nominal value and verify that the variation lies within strict limits set by the manufacturer.
