A novel CMOS-MEMS integrated pressure sensing structure based on current mirror sensing technique

Abstract

Purpose -The present paper aims to propose a basic current mirror-sensing circuit as an alternative to the traditional Wheatstone bridge circuit for the design and development of high-sensitivity complementary metal oxide semiconductor (CMOS)-microelectromechanical systems (MEMS)-integrated pressure sensors. Design/methodology/approach -This paper investigates a novel current mirror-sensing-based CMOS-MEMS-integrated pressure-sensing structure based on the piezoresistive effect in metal oxide field effect transistor (MOSFET). A resistive loaded n-channel MOSFET-based current mirror pressure-sensing circuitry has been designed using 5-m CMOS technology. The pressure-sensing structure consists of three identical 10-m-long and 50-m-wide n-channel MOSFETs connected in current mirror configuration, with its input transistor as a reference MOSFET and output transistors are the pressure-sensing MOSFETs embedded at the centre and near the fixed edge of a silicon diaphragm measuring 100 ϫ 100 ϫ 2.5 m. This arrangement of MOSFETs enables the sensor to sense tensile and compressive stresses, developed in the diaphragm under externally applied pressure, with respect to the input reference transistor of the mirror circuit. An analytical model describing the complete behaviour of the integrated pressure sensor has been described. The simulation results of the pressure sensor show high pressure sensitivity and a good agreement with the theoretical model has been observed. A five mask level process flow for the fabrication of the current mirror-sensing-based pressure sensor has also been described. An n-channel MOSFET with aluminium gate was fabricated to verify the fabrication process and obtain its electrical characteristics using process and device simulation software. In addition, an aluminium gate metal-oxide semiconductor (MOS) capacitor was fabricated on a two-inch p-type silicon wafer and its CV characteristic curve was also measured experimentally. Finally, the paper presents a comparative study between the current mirror pressure-sensing circuit with the traditional Wheatstone bridge. Findings -The simulated sensitivities of the pressure-sensing MOSFETs of the current mirror-integrated pressure sensor have been found to be approximately 375 and 410 mV/MPa with respect to the reference transistor, and approximately 785 mV/MPa with respect to each other. The highest pressure sensitivities of a quarter, half and full Wheatstone bridge circuits were found to be approximately 183, 366 and 738 mV/MPa, respectively. These results clearly show that the current mirror pressure-sensing circuit is comparable and better than the traditional Wheatstone bridge circuits. Originality/value -The concept of using a basic current mirror circuit for sensing tensile and compressive stresses developed in micro-mechanical structures is new, fully compatible to standard CMOS processes and has a promising application in the development of miniaturized integrated micro-sensors and sensor arrays for automobile, medical and industrial application...

Fabrication and testing of PMOS current mirror-integrated MEMS pressure transducer

“…The deviation in the performance of n-and ptype sensors are mainly due to the difference in piezoresistive coefficients of n-and p-channel MOSFETs and variation in the diaphragm thickness of the two devices. The PMOS current mirror-integrated MEMS pressure sensor is again simulated using the dimensions of the fabricated sensor and parameters extracted from the tested results, as listed in Table II (Rathore et al, 2015). MEMS and AC/DC modules of COMSOL Multiphysics software have been used for the structural analysis of the diaphragm and piezoresistive behavior of p-channel MOSFET-equivalent piezoresistors under applied pressure.…”

“…Under externally applied pressure, carrier mobility of transistors M2 and M3 changes due to the piezoresistive effect in MOSFETs (Bradley et al, 2001). The variation in carrier mobility of pressure-sensing MOSFETs M2 and M3 results in the variation of their drain currents and voltages (Rathore et al, 2015;Kumar et al, 2018). An output voltage V out corresponding to the input applied pressure is obtained across the drain terminals of pressure-sensing MOSFETs M2 and M3 as shown in Figure 1 and is given by the following equation:…”

“…In particular, various types of field-effect transistor-based (FET-based) pressure transducers have been studied, designed and fabricated recently (Svensson et al, 1996;Hynes et al, 1999;Dai et al, 2007;Rathore et al, 2015;Kim et al, 2015). The monolithic integration of CMOS-MEMS can improve the sensor performance remarkably by reducing the device assembly that results in high quality factor, low response time, compact size, easy mass production and low cost (Witvrouw et al, 2004;Eswaran and Malarvizhi, 2013).…”

Design and simulation of a novel dual current mirror based CMOS‐MEMS integrated pressure sensor

“…In another approach, piezo-MOS sensing, that is piezoresistive effect in MOSFET, has also found a promising application in the monolithic integration of CMOS and MEMS [19][20][21]. Piezo-MOSFETs integrated with microstructures have attracted significant interest among the researchers all over the world [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36]. In particular, various types of MOSFET based pressure transducers have been studied, designed and developed.…”

MEMS piezoresistive pressure sensor with patterned thinning of diaphragm

“…Micromachined pressure sensor is the most commonly used MEMS sensors. It is also one of the best-known commercialized MEMS sensors due to its wide horizon of applications and the possibility of co-integration with electronic integrated circuits (Tran et al, 2018;Rathore et al, 2015). In MEMS pressure sensors, the pressure variations are transformed into deflection of a diaphragm which is in turn measured by using the changes of the capacitance or the resistance (Pekarek et al, 2015).…”