An Improved Analytical Approach for Estimation of Misalignment Error of Sensing Axis in MEMS Accelerometers using Simple Tilt Measurements

A simple experimental method and improved analytical approach based on tilt measurements (output versus angle) is presented to determine the misalignment error in sensing axis direction of single, two or three-axis accelerometer sensors. The approach is advantageous in resolving and measuring the error because the accuracy is enhanced by using identification that is based on differential and reciprocal differential data of the tilt measurements. Furthermore, the method does not require three accelerometers and there is no need for determination of matrix coefficients as is the practice presently followed in the literature. The method is validated on actual prototype sensors fabricated in our laboratory. The experimental results agree well with the theoretical predictions. The estimates obtained from the proposed method compares well with conventional analytical fit method that requires prior knowledge of sensitivity parameter

Determination of Multiple Spring Constants, Gaps and Pull Down Voltages in MEMS CRAB Type Microaccelerometer Using Near Pull Down Capacitance Voltage Measurements

A simple experimental method based on capacitance voltage (CV) measurements is presented to extract the spring constants (k) different actuation voltages and gaps, in crab type capacitive MEMS accelerometer sensors. It is shown that in addition to main spring action provided by the legs of the structure, the additional spring constants related to the interaction of main spring-proof mass joint and corner region of the proof mass also contribute to change in capacitance. The proposed approach is used in resolving and measuring these model parameters simultaneously because all of them can be extracted from the just one CV measurement. It is found that this additional k varies by more than a factor of 10 across the 6-inch wafer. Furthermore, zero bias capacitance C0, zero bias gap g0, main spring constant k and initial pull down voltage Vpd1 vary by factors of 2.4, 2.38, 30 and 3 respectively. The method also allows us to extract different values of pull down and spring constants associated with different regions of crab structure. The experimental results agree well with the theoretical predictions and reported trends in literatures. The method is routinely applied while fabricating the actual prototype sensors fabricated in our laboratory