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.
Zero-Rate Gyro Drift
Bias Variation
Slow variation in the output signal of an angular rate sensor when no rotational input is applied is a primary metric of inertial measurement quality. For micromachined gyroscopes, zero-rate gyro drift defines the slow accumulation of angle error over time due to sensor bias fluctuations. This drift determines the long-term accuracy and the positioning reliability of the navigation system.
Temperature Effect
Fluctuating ambient temperatures and localized self-heating of the drive electronics can cause major shifts in the sensor bias. These temperature changes alter the physical dimensions and resonance properties of the sensor’s vibrating structure, which in turn causes the zero-rate gyro drift to vary. This variation requires specialized temperature compensation algorithms to maintain accurate readings.
Calibration Compensation
Compensating for this drift requires the use of mathematical models that relate the bias variation to measured temperature and elapsed time. The calibration parameters are stored in the sensor’s non-volatile memory and are applied to the raw output during operation. This compensation reduces the zero-rate gyro drift by an order of magnitude, enabling the sensor to be used in precise tactical-grade navigation tasks.
Performance Evaluation
Characterizing this error involves tracking the gyroscope’s output over several hours while the sensor is held completely stationary on a stable reference platform. High-precision test tables isolated from seismic and building vibrations are used to ensure that no rotational inputs affect the measurement. The collected data are analyzed using Allan variance methods to identify the different noise components that contribute to the zero-rate gyro drift.
This analysis allows engineers to verify that the sensor meets the requirements for guidance and control systems before it is integrated into the final hardware.