Dynamic Response
Inertial transducers track mechanical displacement through the natural frequency of an oscillating element known in the semiconductor industry as MEMS proof mass resonance. This characteristic frequency depends directly upon the suspended mass dimensions and the stiffness of the supporting micro-machined springs. Manufacturing tolerances govern the nominal value during photolithography steps, but etching variations introduce deviations from the target value.
Environmental conditions shift the output during operation, requiring careful compensation routines in the associated application-specific integrated circuit.
Thermal Drift
Temperature fluctuations alter Young modulus values for silicon structures, changing the mechanical spring constant and shifting the operational baseline. Silicon stiffness decreases as thermal energy rises, causing the natural oscillation frequency to drop predictably across the specified operating range. Calibration curves stored in non-volatile memory correct for this thermal dependence during signal processing phases.
Heating from high electrical drive signals also induces localized thermal gradients, creating mechanical stress across the anchor points of the movable structure.
Damping Control
Gas pressure inside the hermetic cavity dictates the quality factor of the oscillating assembly through viscous squeeze-film resistance. Sealed packaging processes maintain a specific internal atmosphere to balance transient response speed against mechanical noise suppression. Low internal pressure yields high quality factor values, producing sharp frequency peaks that improve resolution during narrow-band measurements.
Excessive gas damping broadens the resonance curve, reducing sensitivity to small inertial inputs while increasing resistance to shock loads.
Measurement Offset
Residual electrostatic forces from nearby electrode plates pull on the movable structure, creating an unwanted electrical spring softening effect. Signal conditioning electronics apply direct current bias voltages to nullify these parasitic forces during initial sensor configuration routines. Electrical aging in the capacitive readout circuitry alters this offset over time, demanding periodic zero-point verification against gravitational references.
Uncorrected offset errors propagate directly into velocity and position calculations, degrading the accuracy of the overall inertial measurement unit.
