Thermal Hysteresis Analysis of MEMS Pressure Sensors

摘要

Thermal hysteresis reduction is usually a difficult task to tackle for micromachined pressure sensors especially when shrinking the piezoresistive transducer (PRT) sensing element. Since thermal hysteresis involves the entire thermal cycling history and complicated material properties varied with temperatures, viscoplastic deformation makes the problem very complicated when dealing with high-precision sensor signals. The approach to simplify and quickly resolve the thermal hysteresis problem is the key methodology proposed by this paper. The objective of this project is to optimize the metal layout design on the sensing element and lower down the thermal hysteresis. It is time consuming and cost ineffective to rely purely on the hardware tests to solve the thermal hysteresis problem. ANSYS is used to predict the shear stress at the transducer location and the phenomenological theory of silicon piezoresistance is used to calculate the output voltage and thermal hysteresis. The element-death-and-birth technique is used to simulate the bonding process at various temperature levels for the sensing element packaging. With the aid of the finite element analysis (FEA) tool, the PRT sensing element design was quickly optimized and product development cycle time was reduced.