Pradeep Kumar Rathore

Theoretical and experimental analysis of high Q SAW resonator transient response in a wireless sensor interrogation application

Wireless sensing using SAW resonators calls for an accurate modeling and simulation of the charging and discharging of a resonator, connected to a resonant antenna (monopole/dipole) as a source/load. It is well known that a resonator takes about Q/π time periods of the natural resonant frequency to charge/discharge appreciably. The charging and discharging is critically affected by the static capacitance and the antenna impedance. The present work describes the theoretical modeling and experimental validation of the charging and discharging steps of a high Q SAW resonator in a wireless protocol and loading/unloading transients under variable load conditions are estimated. Furthermore, interrogation range using a monostatic RADAR-like reader (+10 dBm emitted power in the 434 MHz ISM band, -60 dBm detection limit) is estimated in air, dielectric media with or without conducting term, consistent with experimental measurements at 3 m in air when using a monopole antenna, 1! 2 m when using directive Yagi-Uda antenna on the interrogation unit (monopole on the sensor side), 40 cm in tap water, negligible distance in sea water.

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

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.

CMOS-MEMS Based Current Mirror MOSFET Embedded Pressure Sensor for Healthcare and Biomedical Applications

This paper reports on the design and optimization of current mirror MOSFET embedded pressure sensor. A current mirror circuit with an output current of 1 mA integrated with a pressure sensing n-channel MOSFET has been designed using standard 5 µm CMOS technology. The channel region of the pressure sensing MOSFET forms the flexible diaphragm as well as the strain sensing element. The piezoresistive effect in MOSFET has been exploited for the calculation of strain induced carrier mobility variation. 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. COMSOL Multiphysics is utilized for the simulation of pressure sensing structure and Tspice is employed to evaluate the characteristics of the current mirror pressure sensing circuit. Simulation results show that the pressure sensor has a sensitivity of 10.01 mV/MPa. The sensing structure has been optimized through simulation for enhancing the sensor sensitivity to 276.65 mV/MPa. These CMOS-MEMS based pressure sensors integrated with signal processing circuitry on the same chip can be used for healthcare and biomedical applications.

Fabrication of a membrane type double cavity vacuum‐sealed micro sensor for absolute pressure based on front‐side lateral etching technology

Purpose – The purpose of this paper is to describe the fabrication of a miniaturized membrane type double cavity vacuum‐sealed micro sensor for absolute pressure using front‐side lateral etching technology.Design/methodology/approach – Potassium hydroxide‐based anisotropic etching of single crystal silicon is used to realize the cavities under the membrane type diaphragms through channels on the sides. The diaphragms consist of composite layers of plasma‐enhanced chemical vapour deposition (PECVD) of silicon nitride and silicon dioxide. PECVD of silicon dioxide is done for sealing the channels and the cavity in vacuum. Boron thermal diffusion in low‐pressure chemical vapour deposition of polysilicon layer over the membrane is done for realizing resistors. The fabricated device uses Wheatstone half bridge circuit to read the variation of resistance with respect to an applied pressure.Findings – A double cavity vacuum‐sealed absolute pressure micro sensor has been fabricated successfully using front‐side la...

Finite element method based absolute pressure sensitivity optimized membrane type double cavity vacuum sealed piezoresistive sensor

Purpose – The purpose of this paper is to use finite element method for optimizing the membrane type double cavity vacuum sealed structure for the best achievable sensitivity in a piezoresistive absolute pressure sensor and its validation using a standard complementary metal oxide semiconductor (CMOS) process. Design/methodology/approach – A double cavity vacuum sealed piezoresistive absolute pressure sensor has been simulated and optimized for its performance and an analytical model describing the behaviour of the sensor has been described. The 1×1 mm sensor chip has two membrane type 100×30×1.7 μm diaphragms consisting of composite layers of plasma enhanced chemical vapour deposition (PECVD) of silicon nitride (Si3N4) and silicon dioxide (SiO2) each hanging over 21 μm deep rectangular cavity. Potassium hydroxide (KOH) based anisotropic etching of single crystal silicon using front side lateral etching technology is used for the fabrication of the sensor. The electrical readout circuitry uses 318 Ω boron...

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

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-μm CMOS technology. The pressure-sensing structure consists of three identical 10-μm-long and 50-μm-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 × 100 × 2.5 μm. This a...

High sensitivity CMOS pressure sensor using ring channel shaped MOSFET embedded sensing

This paper examines the modeling and simulation of a CMOS-MEMS integrated pressure sensor using ring channel shaped MOSFET embedded sensing technique. A resistive loaded n-channel MOSFET based current mirror pressure sensing readout circuitry has been designed using standard 5 μm CMOS technology. Two structures consisting of a square and a circular ring channel shaped MOSFET embedded on a square and a circular silicon diaphragm, respectively, have been investigated. Piezoresistive effect in MOSFET has been exploited for the calculation of strain induced mobility change under externally applied pressure. Finite element method based COMSOL Multiphysics is utilized for the simulation of pressure sensor. TSpice is employed to evaluate the characteristics of the current mirror pressure sensing circuitry. Simulation results show that the sensitivities of the pressure sensor utilizing the square and the circular diaphragms are approximately 406.88 and 657.91 mV/MPa, respectively. In addition, the non-linearity in the deflection of the square and circular diaphragms as a function of applied pressure has also been investigated. These ring channel shaped MOSFET embedded pressure sensors have a promising application in the design and development of smart sensors for biomedical applications.

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 μm 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.

High sensitivity square ring channel shaped MOSFET embedded pressure sensor integrated with a current mirror readout circuitry

This paper presents the design and simulation of a current mirror sensing based ring channel shaped MOSFET embedded pressure sensor. The pressure sensor is composed of two identical square ring shaped n-channel MOS transistors connected in current mirror configuration with its output transistor integrated on a silicon diaphragm. The diaphragm deflection results in the variation of drain current of embedded MOSFET due to altered channel mobility. Piezoresistive effect in MOSFET has been exploited for the calculation of strain induced carrier mobility variation under applied pressure. COMSOL Multiphysics and T-Spice are used to simulate the structural and electrical behaviour of the pressure sensor. Simulation results show that the pressure sensor has a sensitivity of approximately 407 mV/MPa in the pressure range of 0-1 MPa.