Research On Temperature Characteristics And Temperature Compensation Algorithms Of Micro Silicon Resonant Accelerometer Based On The Wafer Package

Silicon resonant accelerometer (SRA) is a MEMS inertial device which senses acceleration by measuring the change in resonant frequency. With small volume, low power consumption and ease to digitize, the SRA potentially replaces the pendulous integrating gyro accelerometer and supports research and development of the next generation navigation system.The temperature error is an important factor restricting the measurement accuracy of SRA. The paper is focused on analysis and experiment of temperature characteristic of accelerometer, measurement method on temperature inside the vacuum chamber of wafer level package (WLP), and temperature compensation algorithm for accelerometer.Firstly, the operational principle, encapsulation technology, and measuring&controlling circuit are introduced. The mechanism of temperature errors is analyzed from three aspects of material characteristics, residual stress and fabricating tolerance. On this basis, theoretical temperature sensitivities of resonant frequency and accelerometer scale factor are calculated as -36 to -12Hz/℃ and 498 to 1570ppm/℃. The temperature measurement error in vacuum chamber of WLP is analyzed according to the temperature transfer model of SRA.Secondly, the fixed-point constant experiments and variable temperature experiments are conducted for accelerometer from-40 to 60 ℃. The temperature curves show that, the temperature sensitivities of resonant natural frequency and accelerometer scale are consistent with the theoretical derivation, respectively as 31.23 to -15.48 Hz/℃ and 703.726 to 1286.632 ppm/℃. In the variable temperature experiments, there is temperature hysteresis between resonant natural frequency and the external platinum resistance, with the maximum hysteresis error 283.75Hz.Thirdly, in the light of temperature difference between the inner and outer of WLP, three temperature measurement methods inside the vacuum chamber are proposed. The methods are measuring temperature using a platinum resistance, through differential resonators and by measuring quality factor of resonator. Comparing the three methods, it is proved that the accuracy of method based on the differential resonators is the highest under dynamic temperature environment.Fourthly, temperature compensation algorithms based on the external platinum resistance and differential resonators for the SRA are studied, and the algorithms have been verified by FPGA in real time. The compensation results show that, the dynamic compensation effect of temperature self-compensation algorithm utilizing differential resonators is better than the algorithm based on a platinum resistance, and the static effect slightly worse. Employing the method of self-compensation, the temperature sensitivities of bias and scale factor can be reduced to 0.75% and 1.21% of the results without temperature compensation.Finally, the temperature-compensated SRA system is tested. The test results show that, the 1σ zero bias stability is 11.54μg, and the temperature sensitivities of bias and scale factor are 0.05 mg/℃ and 9.33 ppm/℃, the performance of which is significantly improved compared to that without compensation.