Polymer Die Attach Selection Criteria for Low Drift Inertial Measurement Units
Polymer die attach selection governs MEMS IMU bias drift by balancing storage modulus, glass transition temperature, and long-term viscoelastic stress relaxation.
Comb Drive Gap Displacement
Electrostatic Actuation
Silicon-based microstructures utilize electrical potentials across interdigitated fingers to generate mechanical force and controlled motion in miniature systems. In these devices, comb drive gap displacement describes the lateral or longitudinal variation in the spacing between fixed and movable capacitive fingers. This physical shift determines the capacitance change per unit of mechanical stroke.
Actuator Motion
High-aspect-ratio silicon etching defines the micro-scale suspension that supports the movable electrode structure. When an operating voltage is applied, the electrostatic force pulls the suspended electrode, altering the comb drive gap displacement until the mechanical restoring force of the supporting springs balances the electrostatic pull. This equilibrium state governs the dynamic range of the micro-actuator.
Drift Effect
Mechanical stress in the anchor points or thermal gradients across the silicon substrate can cause unintended offsets in the zero-voltage state. This variation alters the nominal comb drive gap displacement and degrades the repeatability of the actuator positioning. Such structural offsets are typically mitigated by incorporating symmetric spring geometries that compensate for uniform thermal expansion.
Transduction Calibration
Calibration protocols establish the relationship between the applied voltage and the resulting stroke by measuring the capacitive feedback of the system under controlled conditions. High-resolution optical interferometers track the comb drive gap displacement directly to verify the electrical transduction coefficients against analytical electrostatic models. This verification is essential for ensuring linearity across the full operating range of the sensor.
The optical measurement runs in a vacuum chamber to eliminate air damping effects during the characterization process.