A comparative study on p- and n-channel MOSFET embedded pressure sensing structures integrated with current mirror readout circuitry

Abstract

This paper presents a comparative study on p- and n-channel MOSFET embedded current mirror integrated pressure sensing structures. The pressure sensing structure consists of three MOSFETs connected in a resistive loaded current mirror configuration. The input constant current source MOSFET of the current mirror acts as a reference transistor and the output MOSFETs are the strain sensing elements. The pressure sensing MOSFETs are embedded on a flexible silicon diaphragm for sensing the tensile and compressive stresses developed in the diaphragm under applied pressure. Current mirror pressure sensing circuits employing n- and p-channel MOSFETs were designed for an output current of 1 mA using standard 5 µm CMOS technology. The piezoresistive effect in both n- and p-channel MOSFETs have been exploited for the calculation of strain induced carrier mobility variation under applied pressure. Simulation results show that under tensile stresses both n- and p-channel MOSFETs have high sensitivities of approximately 373 and 590 mV/MPa, respectively. However, the pressure sensitivity of the n-channel device is found to be much higher than that of p-channel MOSFET under compressive stresses and their sensitivities are found to be approximately 408 and 42 mV/MPa, respectively. The overall pressure sensitivities of n- and p-channel MOSFET based current mirror pressure sensing circuits have been found to be approximately 782 and 633 mV/MPa, respectively.