Development of a current mirror-integrated pressure sensor using CMOS-MEMS cofabrication techniques

Abstract

Purpose This paper aims to describe the fabrication and characterization of current mirror-integrated microelectromechanical systems (MEMS)-based pressure sensor. Design/methodology/approach The integrated pressure-sensing structure consists of three identical 100-µm long and 500-µm wide n-channel MOSFETs connected in a resistive loaded current mirror configuration. The input transistor of the mirror acts as a constant current source MOSFET and the output transistors are the stress sensing MOSFETs embedded near the fixed edge and at the center of a square silicon diaphragm to sense tensile and compressive stresses, respectively, developed under applied pressure. The current mirror circuit was fabricated using standard polysilicon gate complementary metal oxide semiconductor (CMOS) technology on the front side of the silicon wafer and the flexible pressure sensing square silicon diaphragm, with a length of 1,050 µm and width of 88 µm, was formed by bulk micromachining process using tetramethylammonium hydroxide solution on the backside of the wafer. The pressure is monitored by the acquisition of drain voltages of the pressure sensing MOSFETs placed near the fixed edge and at the center of the diaphragm. Findings The current mirror-integrated pressure sensor was successfully fabricated and tested using in-house developed pressure measurement system. The pressure sensitivity of the tested sensor was found to be approximately 0.3 mV/psi (or 44.6 mV/MPa) for pressure range of 0 to 100 psi. In addition, the pressure sensor was also simulated using Intellisuite MEMS Software and simulated pressure sensitivity of the sensor was found to be approximately 53.6 mV/MPa. The simulated and measured pressure sensitivities of the pressure sensor are in close agreement. Originality/value The work reported in this paper validates the use of MOSFETs connected in current mirror configuration for the measurement of tensile and compressive stresses developed in a silicon diaphragm under applied pressure. This current mirror readout circuitry integrated with MEMS pressure-sensing structure is new and fully compatible to standard CMOS processes and has a promising application in the development CMOS-MEMS-integrated smart sensors.

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

“…Table 2 gives the various piezoresistive coefficients of p-and n-MOSFETs and it is observed that each of the π-coefficients of NMOS is having different magnitude with opposite sign as compared with that of PMOS. From literature [35][36], it has been found that the sign of overall piezoresistive coefficient (π) is negative for PMOS and positive for NMOS. Therefore, the effect of similar stress on the channel resistance and carrier mobility of pressure sensing NMOS and PMOS transistors will be opposite in nature, which is governed by Equation (5).…”

“…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.…”

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

“…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 our earlier work, design, modeling and simulation of n-and p-channel MOSFET-based current mirror-integrated pressure transducer with lesser dimension had been designed and simulated (Kumar et al, 2016). However, the fabrication and testing results of n-channel MOSFET-based current mirrorintegrated pressure transducer had been presented (Kumar et al, 2018). In this work, a resistive loaded p-channel MOSFETbased current mirror-integrated pressure transducer has been fabricated, tested and compared with our earlier reported work.…”

MEMS piezoresistive pressure sensor with patterned thinning of diaphragm

“…Widespread applications of Microelectromechanical systems (MEMS) as sensors (Amiri and Kordrostami, 2018;Hwang et al, 2019;Kumar et al, 2018;Rafiee et al, 2016), switches (Samaali et al, 2015;Kim et al, 2018) and energy harvesters (Kordrostami and Roohizadegan, 2019;Kordrostami and Roohizadegan, 2018;Ghoddus et al, 2019;Ghoddus and Kordrostami, 2018) have revolutionized the technology in terms of the size of the devices (particularly the sensors) and high integration capability with electric circuits (Rafiee et al, 2017;Amiri et al, 2020). Micromachined pressure sensor is the most commonly used MEMS sensors.…”