Shankar Dutta

A corrugated diaphragm based 4H-SiC piezoresistive pressure sensor is designed and investigated for high-temperature pressure-sensing applications. The sensor consists of a square corrugated diaphragm integrated with four piezoresistors arranged in full Wheatstone bridge configuration to enhance stress and pressure sensitivity. Finite element simulations are performed over a pressure range of 0-20MPa & temperature range of 25°C-500°C. The influence of corrugated geometry on mechanical and electrical performance is evaluated, where a five-ring corrugated diaphragm exhibited the highest sensitivity among others. Temperature-dependent analyses reveal that the maximum diaphragm displacement increased from 27.11μm at 25°C to 43.85μm at 500°C, while maximum stress increased from 4001.9MPa to 6181 MPa. The sensor exhibited a linear response of output voltage with pressure at different temperatures. The output voltage and sensitivity decreased with increasing temperature due to reduction in piezoresistive coefficients of 4H SiC. The sensitivity decreases from 857.29μV/MPa at 25°C to 373.4μV/MPa at 500°C. Thermal stability of sensor is also investigated through temperature coefficient of offset (ranging between -147 ppm/°C and -45 ppm/°C), temperature coefficient of sensitivity, and temperature coefficient of resistance (TCR) (lies within 117-172 ppm/°C) analyses. Noise performance also evaluated, showing the sensor maintains output noise voltage below 1.4µV, a signal to noise ratio (SNR) greater than 75dB & a minimum detectable pressure (MDP) of 3.56kPa even at 500°C. The obtained results show that corrugated 4H SiC MEMS pressure sensors offer high sensitivity, good thermal stability and excellent pressure resolution, making them suitable for harsh environment sensing applications.

In this study experimental nanoindentation-derived mechanical properties of a-SiC were directly integrated into finite element simulations to establish the relationship between annealing-induced mechanical evolution and MEMS pressure sensor performance. The a-SiC thin films were deposited on Si substrates by RF sputtering system and later annealed at 10000 C for 1 hour and 2 hours to investigate the effect of thermal treatment on their mechanical properties and MEMS pressure sensor performance. Surface morphology was evaluated by atomic force microscopy, while the nanoindentation technique was used to determine the nanomechanical properties, including hardness, elastic modulus, stiffness, contact depth, and depth recovery ratio. The nanoindentation results revealed a significant reduction in hardness from 37.05 GPa for pristine to 14.82 GPa after 2 hours annealing. Also, a reduction in elastic modulus is also seen from 282.9 GPa for unannealed sample to 156.88 GPa for the 2 hours annealed sample. The increase in contact depth indicates structural relaxation and softening of SiC thin films after annealing. Based on experimentally obtained mechanical properties, SiC-based piezoresistive pressure sensor was designed and simulated over the pressure range of 1-10 MPa. The annealed samples exhibited higher diaphragm displacement, von Mises stress and strain due to reduced hardness, and stiffness. The estimated sensitivity of the sensor structure is 71.47 µV/V/MPa (unannealed), 70.97 µV/V/MPa (1 hour annealed) and 70.47 µV/V/MPa (2 hours annealed), with < 1% (full-scale) non-linearity. The results establish a direct correlation between the mechanical properties and pressure sensor performance induced by annealing.

MEMS based inertial switches have important applications in defense, automobile, and aviation sectors. The materials for these inertial switches are either metals or low-resistivity silicon. This paper discussed about the amalgamation of metal and silicon in the MEMS inertial switch (500 g) structure to achieve high performance and high current handling capability. The switch structure, comprises of four series-parallel beam supported large proof-mass suspended over a gap of 4 µm. The resonant frequency of the switch structure is found to be 4.2 kHz. The dimensions of the switch structure are studied by parametric analysis. The transient response of the gold coated silicon MEMS inertial switch structure showed contact (on-state) duration of 230–380 µs due to the 10% variation in half-sine threshold acceleration value (500 g). The variation in acceleration input pulse width (0.25–1 ms) yielded a large variation in contact duration (2.5–370 µs). In response to two successive half-sine acceleration pulses, variation in contact duration is observed due to the superimposition of residual movement of the proof-mass arising due to first pulse with the response of the second acceleration pulse. The electro-thermal behaviour (under 1A current flow in the switch contact duration) of the gold coated (1.0 µm) switch structure showed a substantial reduction in temperature rise (due to Joule heating) from 413 K to 301 K. Thus, the gold coating on the silicon MEMS inertial switch lowered on-state resistance by one order and improved current handling capability due to less Joule heating issue.

Functional flexible piezo-resonators are of vital interest for designing micro-electrometrical system (MEMS) based high-frequency wearable devices. The magnetoelectric (ME) heterostructure comprising highly magnetostrictive Ni–Mn–In and piezoelectric AlN films was fabricated over flexible substrates to develop the bulk acoustic wave (BAW) resonator. The BAW resonators fabricated over Ni and Kapton substrates show the fundamental resonance at ∼5.535 and 5.400 GHz, respectively. The comparative study of frequency tuning for both resonators has been executed in the presence of a dc magnetic field. A larger frequency shift (ΔfR) of ∼540 MHz was detected at 1200 Oe for a device fabricated over Ni with a sensitivity of ∼5.4 Hz/nT. However, it is 360 MHz in the case of Kapton, with a sensitivity of ∼3.0 Hz/nT. Moreover, the BAW resonator over the magnetostrictive Ni substrate shows a higher tunability of ∼11.4% compared to ∼8.5% for the resonator fabricated over non-magnetostrictive Kapton. The equivalent modified Butterworth–Van Dyke circuit parameters have been extracted by fitting the experimental data with and without an external magnetic field using advanced design system. The effect of an external magnetic field has been thoroughly investigated on device parameters, such as electromechanical coupling coefficient (K2), acoustic velocity, quality factor (Q), and figure of merit. The anisotropic functionality of the fabricated resonator has been studied by measuring the tunability of the resonator in parallel and perpendicular magnetic fields. The present study motivates the incorporation of flexible magnetostrictive substrates for futuristic multifunctional MEMS magnetic field sensor applications.