CMOS-MEMS Integrated MOSFET Embedded Bridge Structure based Pressure Sensor

This paper reports on the design and simulation of current mirror sensing based MOSFET embedded bridge structure for high sensitivity pressure sensing. A current mirror circuit with an output current of 1 mA has been designed using standard 5 mu m CMOS technology. The output transistor of the current mirror forms the active pressure sensing MOSFET which produces a change in its drain current as a result of altered channel mobility under externally applied pressure. The channel region of the pressure sensing MOSFET forms the bridge structure as well as the strain sensing element. The piezoresistive effect in MOSFET has been exploited for the calculation of strain induced carrier mobility variation. COMSOL Multiphysics is utilized for the simulation of pressure sensing bridge structure. T-Spice is employed to evaluate the characteristics of the current mirror pressure sensing circuit. Simulation results show that the MOSFET embedded bridge structure has a pressure sensitivity of 24.08 mV/MPa. An enhanced pressure sensitivity of 1.61 V/MPa is obtained after structure optimization. In addition, the variation in drain current of pressure sensing MOSFET due to the mismatch between the current mirror transistors and load resistances and variations in the supply voltage and operating temperature has also been discussed. These bridge structure based MOSFET embedded pressure sensors are suitable for healthcare and biomedical applications.