Isolating Micro-Machined Accelerometer Zero-G Bias Shifts under Static Thermal Cycles
Static thermal zero-g bias shifts in MEMS accelerometers are isolated by enforcing prolonged thermal dwell periods to decouple stress creep from thermal gradients.
Differential Comb Array
Capacitive Architecture
Capacitive sensing architecture consisting of interdigitated finger electrodes. A differential comb array measures changes in capacitance between stationary and moving electrodes. The layout enables high-resolution sensing of sub-micron displacements.
Signal Symmetry
Arrangement of electrodes provides a balanced output that reduces common-mode errors. Because the differential comb array uses opposing electrode pairs, external parasitic capacitance and electromagnetic interference affect both sides of the bridge equally. The resulting signal remains clean even in electrically noisy environments.
Linearity Range
Physical geometry of the fingers determines the relationship between displacement and output voltage. While a single-ended sensor might show non-linear behavior as the gap changes, a differential comb array maintains a proportional response over a wider travel distance. This stability simplifies the back-end signal conditioning circuitry.
Fabrication Precision
Deep reactive ion etching creates the high-aspect-ratio features necessary for these devices. Dimensional tolerances must be held within nanometers to prevent bias errors. If the fingers are misaligned, the differential comb array exhibits an offset that requires electronic nulling during final calibration.
Misalignment often stems from residual stress in the polysilicon layer or thermal expansion during the bonding process, which warps the structural frame and alters the resting gap between fingers.