Analysis of thermal hysteresis on micromachined accelerometers

One of the most critical parameters on any transducer device is the offset in a static g-field. The offset must be repeatable as one cycles the temperature of the device. A variance in offset after a temperature cycle is defined as thermal hysteresis. This phenomenon is non-linear and is extremely difficult to compensate for with an ASIC. This paper discusses the methodology used to analyze, model, and correct a prototype accelerometer design that had significant thermal hysteresis. It steps through the experiments which demonstrate that the major cause of the hysteresis was an aluminum thin film on the transducer die, the Finite Element Analysis (FEA) modeling used to simulate this phenomenon and the final experimental data. The final solution for this transducer was to decrease the metal thickness by 50%, which reduced the magnitude of the hysteresis to a level that would allow the product to operate within the specifications of 2.25 V to 2.75 V (with a 5.0 V power supply) with an acceptable process capability.