Design and optimization of a CMOS-MEMS integrated current mirror sensing based MOSFET embedded pressure sensor

Abstract

This paper reports on the design and optimization of a current mirror sensing based MOSFET embedded pressure sensor. A resistive loaded n-channel MOSFET based current mirror circuit integrated with a pressure sensing MOSFET was designed using standard 5 μηι CMOS technology. The piezoresistive effect in MOSFET has been exploited for the calculation of strain induced carrier mobility variation under externally applied pressure. The channel region of the active MOSFET forms a flexible diaphragm of size 100 μm × 100 μm × 2.5 μm which deflects under applied pressure. Finite element method based COMSOL Multiphysics is utilized for the simulation of pressure sensor. T-Spice is employed to evaluate the characteristics of the current mirror pressure sensing circuitry. Simulation results show that the MOSFET embedded pressure sensor has a sensitivity of approx. 10.01 mV/MPa. The pressure sensing structure has been optimized for enhancing the sensor sensitivity to approx. 473 mV/MPa. In addition, the variation in the drain currents of the current mirror MOSFETs due to the (a) mismatch of the active and passive devices, and (b) variations in operating temperature and supply voltage have also been investigated.