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This work presents the in-house design, characterization, and development of an integrated PZT-based piezoelectric MEMS vibration sensor module and its usage in surface roughness prediction of fused silica substrate in a CNC polishing machine. The differential electrical configuration of the MEMS device ensures enhanced acceleration sensitivity to out-of-plane motion, two orders larger than in-plane sensitivity. The Thin-film Piezo on Silicon (TPoS) accelerometer with a PZT layer was fabricated using photolithography, frontal etching, and backside release. A fully integrated module comprising MEMS, amplifiers, and a microcontroller was designed and characterized in a shaker system. The designed module provides a sensitivity of $8.12~mV/{g}$ and a resolution of $5.8~m{g}/\sqrt {Hz}$ . The feed rate, compared to the other polishing parameters, shows the highest correlation with surface roughness. The module’s acceleration-time data were processed by Linear Discriminant Analysis (LDA) and given as input to the neural network together with the feed rate of the polishing spindle. Back Propagation Neural Network (BPNN) algorithm was used to train the machine learning model. The designed module is cost-effective compared to the commercial sensor. The key performance indicators of roughness prediction for the module and the commercial sensor were calculated, showing a Mean Absolute Percentage Error (MAPE) of 6.45% and 5.32%, respectively.

This work reports an exploratory study of novel high quality factor acoustic modes that can be excited using the support transducer topology. The removal of the piezoelectric transducer layer from the high energy confinement mode eliminates the charge cancellation bottleneck. To excite the targeted modes, a frequency match between the thin film piezoelectric on substrate (TPoS) transducer arm and the central Silicon based high quality factor (Q) resonant tank is necessary. The concept of scaling up the frequency without shrinking the device dimensions by exciting higher-order modes has been verified using a third-order Lame mode. The device exhibits a ${Q}$ of 21,632 for a resonant frequency of 58.5MHz. Unexplored modes such as the combination of a square extension mode and a radial contour mode operating in an out-of-phase manner, multiple new higher-order modes, etc. exhibiting very high- ${Q}$ have been realized. The average ${Q}$ values of these new resonator designs range between 15,000 and 50,000, which is exceptional for piezoelectric transduction-based Microelectromechanical resonators. The idea of excitation of degenerate modes using silicon aligned along non- and non- crystalline axes has also been verified. The proof-of-concept of going beyond the traditional approach of resonance excitation scheme will pave the way to the investigation of unexplored modes that hold immense potential across various sectors of MEMS. [2021-0075]

This work shows a differential rotational thermal piezoresistive resonator (DR-TPR) design, fabrication, and characterization. The resonator uses silicon on insulator (SOI) microelectromechanical systems (SOI MEMS) technology. The sensing of carboxyl-polystyrene beads requires estimating the variation in the frequency of the resonator. It can serve as an alternative enabling technology to detect small molecules having wide implementations in clinical and industrial applications. The resonator uses a negative frequency shift to find the change in the mass due to the chemical absorption of the carboxyl-polystyrene beads on the DR-TPR surface. The method of using DR-TPR can attain label-free detection for many future biomarkers. The use of carboxyl-polystyrene beads to showcase the potential of DR-TPR as a mass sensor for future chemical/biosensing applications is the highlight of the paper. It includes the characterization in different concentrations of immobilization on the resonator surface. The work shows the operation of the resonator in an ionic buffer solution which is crucial for its future applications. The Q value of 80 with differential feedthrough cancellation is measured in phosphate-buffered saline (PBS) using DR-TPR.

This letter presents the first nano-gap microelectromechanical systems (MEMS) resonator based on a Metal-Insulator-Metal (MIM) capacitor structure in standard CMOS. We develop an improved mask-less post-CMOS process to chemically remove the thin aluminum copper (AlCu) of the Capacitor-Top-Metal (CTM) with high selectivity to the adjacent materials, yielding a well-defined capacitive transduction gap of only 160 nm. The proof-of-concept resonator is designed in a standard TSMC 180 nm RF CMOS process, with a center frequency of 5.9 MHz, a quality factor of 1,000, and a low motional impedance of 5.7 $\text{k}\Omega $ under a medium dc-bias of 25V. Upon further optimizations, nano-gap CMOS-MEMS resonators based on the proposed CTM-etching technique are promising candidates for fully integrated oscillator applications.

Since two decades piezoelectric MEMS resonator research has been making a headway by leaps and bounds in multiple fronts such as micro/nanofabrication techniques, device and system design, monolithic integration, packaging, material engineering, etc. Piezoelectricity based frequency selective resonant tanks are an integral part of radio frequency communication, inertial sensors, infrared sensors, environmental monitoring modules, energy harvesters, etc. To improve the functionality of the aforementioned modules it is cardinal to understand the underlying concepts of resonator design, material selection, and performance enhancement techniques. Here in this review paper, a comprehensive overview of various piezoelectric thin-film material properties along with different commercial microfabrication platforms with CMOS integration facility is presented. The device characteristics greatly depend on the resonator mode shape and thus suitable modes and thin-film material configurations can be chosen depending on the target frequency, application, and power budget requirements. In addition to device modeling, a synopsis of the several acoustic and material engineering approaches to enhance the figure of merit of the resonator has been presented. The future avenues of piezoelectric MEMS cover a wide spectrum of possibilities such as 5G communication, quantum processing, frequency combs, photonics integration, gesture sensors, etc.

Structural and electrode material engineering methodology to attain quality factor enhancement in a support transducer enabled Wine-glass and Lamé mode resonator has been demonstrated in this work. To boost the quality factor, a series of short mechanical couplers is utilized to link the central resonant structure with the piezoelectric transducer arms. Two different top electrode materials are investigated, and the effect of metal loading on the performance of aluminum nitride (AlN)-on-Si-based resonator is investigated in detail. The new resonator design strategy improves the quality factor of the Wine-glass resonator from 9800 to 16 300 while still being able to maintain a spurious-free spectrum for a 200-MHz span, which is crucial for oscillator applications. An optimized oscillation system is realized using a commercially available low-noise amplifier. Careful positioning of the passive components is utilized to attain an ideal operating point for the resonator in the closed-loop condition. Using this scheme, Wine-glass and Lamé mode resonator-based high-performance oscillators with a low phase noise of -133.6 and -132.7dBc/Hz at 1-kHz offset and -153.7 and -150.4 dBc/Hz at 1-MHz offset, respectively, which satisfy that the Global System for Mobile (GSM) communication requirements are attained when normalized to a 13-MHz carrier frequency.

In this work, we report a novel fully balanced drive and sense thermal-piezoresistive resonator (TPR) in 2P-4M $0.35~\mu \text{m}$ CMOS technology with maskless post-release process. Through the use of the Wheatstone bridge arrangement for both the thermal drive heater resistors and sense piezoresistors, the proposed design greatly simplifies the overall system by removing the need for bias-tee or noisy and power consuming current sink/source. This ensures that the differential terminals of drive and sense ports are at the same DC potential, thus allowing the use of standard differential amplifiers as interface circuits. In addition, this design utilizes bimorph like actuation which enables in-plane motion. An in-plane clamped-clamped beam (CCB) TPR was fabricated, demonstrating a quality factor ( ${Q}{)}$ of 1,600 at 2 MHz with transconductance ( ${g}_{m}{)}$ of $46.8~\mu \text{S}$ for a dc-power of 1.7 mW in a vacuum (1 mTorr). To go one step further, a double-ended tuning fork (DETF) TPR was designed, featuring a transconductance of 62.7 $\mu \text{S}$ with ${Q}$ of 4,400 at 1.9 MHz under the same conditions as CCB. The CCB thermal-piezoresistive oscillator (TPO) implemented using a discrete interface circuit had phase noise of −89 dBc/Hz and −100 dBc/Hz at 1 kHz and 1 MHz respectively while that for DETF TPO was −100 dBc/Hz at 1 kHz and −100 dBc/Hz at 1 MHz in air. Frequency stability was found to be 180 ppb and 125 ppb for CCB and DETF TPOs respectively in air.

In this work, a real-time PM2.5 sensor module with high mass resolution and wide detection range is successfully demonstrated while the module consists of a two-stage aerosol impactor, a Thin-film Piezoelectric-on-Silicon (TPoS) MEMS oscillator, and a micro-pump. The aerosol impactor’s collection efficiency of 51% for $2.54~\mu \text{m}$ and 50% for $1.03~\mu \text{m}$ is verified for stage 1 and stage 2, respectively. A length-extensional mode TPoS MEMS resonator is implemented, featuring a resonant frequency of 4.05 MHz and a quality factor ( ${Q}$ ) of 438 in air. To achieve a portable sensor module, a board-level sustaining circuit, which includes a transimpedance amplifier (TIA), a phase shifter, a band-pass filter, and a buffer circuit are integrated to fulfill the condition of Barkhausen criteria for oscillation. Phase noise of −111.92 dBc/Hz at 1 kHz offset was recorded under ambient pressure and room temperature for a carrier frequency of 4.05 MHz. The mass resolution for the PM2.5 sensor implemented in this work is 0.71 pg. Finally, an incense was used to produce the liquid type particles continuously for the aerosol measurement. The coefficient of determination ( ${R} ^{2}$ ) of 0.81 between the frequency slope of the proposed sensor and the aerosol concentration of the commercial optical aerosol sensor within a range of $10~\mu $ g/m3 to $1000~\mu $ g/m3. This work successfully integrated MEMS, circuit, and air flow technologies to realize a complete mass sensing module, and has the potential to be implemented in the particulate matter concentration monitoring applications of air.

In this study, a Thin-film Piezoelectric-on-Silicon (TPoS) MEMS oscillator is successfully demonstrated that uses lead zirconate titanate (PZT) thin-film piezoelectric layer deposited on a single-crystal silicon substrate to realize a length-extensional mode resonator, having a resonant frequency of 5.12 MHz and a quality factor ( ${Q}$ ) of 311. For closed-loop implementation, a commercial Lock-in amplifier with a Phase Locked Loop (PLL) facility was used to fulfill the Barkhausen criteria for oscillation. The mass resolution and sensitivity of the proposed mass sensor are 0.54 pg and 4.96 Hz/pg, respectively. Finally, a board-level sustaining circuit, which includes a transimpedance amplifier (TIA) and an attenuator is integrated with the TPoS MEMS resonator for oscillation to achieve a portable sensor. Phase noise of −104.11 dBc/Hz at 1 kHz offset was recorded under ambient pressure and room temperature for a carrier frequency of 5.12 MHz. The mass resolution for the board-level mass sensor implemented in this work is 0.15 pg.

We present a thermally driven piezoresistively sensed resonator primarily consisting of backend of line (BEOL) CMOS material for mass sensing applications. A detailed analysis of the operation mechanism has been performed to develop a mathematical and an electrical equivalent model. The thermal-piezoresistive resonator (TPR) is composed predominantly of low loss materials like silicon dioxide (SiO2) and polysilicon for drive and sense. A differential configuration with drive and sense isolation was employed to significantly reduce the feedthrough level. Theoretical and simulated values are validated with experimental data. The proposed design has a resonance frequency of 5.13 MHz with a transconductance ( ${g}_{m}$ ) of 7.8 $\mu \text{S}$ in the vacuum ( ${g}_{m}$ of ${5}~\mu \text{S}$ in the atmospheric pressure for 2.7-mW bias power at 5.09 MHz. One of the highest reported quality factors ( ${Q}$ ) of 2600 for CMOS-MEMS was achieved in air, while the same in the vacuum was >10 000. The thermal-piezoresistive oscillator (TPO) has Allan Deviation of 80 ppb and 20 ppm in ambient pressure using a lock-in amplifier with a phase-locked loop (PLL) and interface circuit using commercial amplifiers on printed circuit board (PCB), respectively. Using silver nanoparticles, the mass sensitivity of 24.96 kHz/ng was measured. The extracted mass resolution in air was 16.3 fg, thus having great potential to serve as an aerosol sensor.

This work investigates the performance enhancement of piezoelectric bulk mode mode-matched gyroscopes based on a secondary phase feedback loop. An independent phase feedback loop realized by a lock-in amplifier is applied on a 10 MHz multiple ports piezoelectric device to harness its effective stiffness and damping factor for better gyroscope performance. The multiple ports device is designed based on support transducer topology with eight transducer arms, some of which drive the central resonant tank into a secondary elliptical mode. Open-loop measurement with varied phase delay is adopted to carry out the best working condition (i.e. higher Q-factor, smaller frequency split). Therefore, the measured scale factor results in a 1.56 times improvement through boosting the Q-factor of the driving mode. The minimum frequency split compensated by the phase feedback could reach 13.4 ppm with a tuning phase of 60° and tuning voltage of 0.1 V. The bias instability of the proposed gyro through the help of phase feedback loop could be reduced by 2.13 times. The achievement in this work has shown that the phase feedback mechanism could indeed help to improve the performance of the resonant transducers.

This letter reports a CMOS-microelectromechanical system (MEMS) pressure sensor comprising a double-ended tuning fork capacitive resonant transducer and a Pirani gauge thermal transducer in a single device configuration, which demonstrates a wide-range pressure sensing capability, small form factor, and sensor fusion. The device integrated with an interfaced circuit was fabricated through a 0.35- μ m CMOS foundry process, together with an in-house release process. Thanks to the resonant transducer which is sensitive to pressure due to squeezed-film damping effect, the high pressure sensing range is achieved by measuring resonant frequency shift, whereas the medium pressure region is sensed by quality factor ( Q ) change of the resonator. As a result, a full-scale range of 10–760 torr is realized by the proposed CMOS-MEMS pressure sensor using its resonant transducer. To further extend the measurement range to the lower pressure range, an embedded thermal transducer of the device is used to serve as Pirani gauge that is capable of detecting pressure from 0.02 to 10 torr by the use of thermal resistance $(R_{{\rm{th}}})$ change. Through a simple algorithm combining variations of Q , resonant frequency $f_{o}$ , and thermal resistance $R_{{\rm{th}}}$ , the proposed resonant Pirani gauge pressure sensor features a very wide-range pressure sensing capability from 0.02 to 760 torr.

This paper introduces the comprehensive design concepts, procedure, and post-process flow of a robust manufacturing platform for complementary metal-oxide- semiconductor microelectromechanical systems (CMOS-MEMS) resonant transducers with enhanced frequency stability and capacitive-transduction efficiency. Thanks to a sandwich-stacking configuration of the interconnection metal line (TiN/AlCu/TiN) existing in standard CMOS technology, a deep-submicron TiN-to- TiN gap is successfully demonstrated by removing the central AlCu alloy layer through the proposed post-fabrication platform, thus realizing a novel titanium nitride composite (TiN-C) structure. Compared with the traditional release approaches utilized in the general post-CMOS fabrication, the proposed TiN composite transducer with TiN-to-TiN gap can simultaneously attain (i) a 400nm air gap for effective electrostatic transduction, (ii) adequate material selection and arrangement for near-zero frequencytemperature coefficient, and (iii) conductive electrodes to overcome frequency drift induced by dielectric charging during capacitive operation. In Part I of this study, the design guideline, layout rules, and detailed post-fabrication flow are addressed. The fabrication results of each post-process step are also exhibited. Numerical analysis, experiment results, and further discussions in terms of frequency stability for resonant transducers will be covered in Part II. [2018-0230]

The Part II of this paper presents the numerical model and experimental validations of the CMOS-MEMS resonant transducers fabricated by a reliable TiN-composite (TiN-C) platform. To characterize the frequency behavior of the proposed resonator, an analytical model based on average displacement is used to determine the equivalent lumped parameters of the proposed devices. Considering the free-free beam (FFB) design elaborated in Part I, the oxide fin provides a very strong boundary restriction, which forces the vibration like a short clamped-clamped beam (CCB) combined with two additional tip cantilevers. This segmented analytical model shows a good agreement with our measurement results. In addition, the implementation of TiN-to-TiN transduction gap and oxide-rich composite structure has enabled a deep sub-micron ( $TC_{f}$ ) is achievable by taking temperature coefficient of Young’s modulus ( $TC_{E}$ ), the coefficient of thermal expansion (CTE), and residual stress of standard BEOL into consideration. As a result, the proposed TiN-C pseudo free-free beam (PFFB) resonator shows the lowest passively compensated $TC_{f}$ of 0.6 ppm/K in CMOS-MEMS technology to date, revealing the excellent frequency stability over temperature and time for practical applications in the future.

In this paper, we present a silicon on insulator (SOI)-based MEMS oscillator that comprises a ring-shaped rotational mode resonator incorporating fully differential design for operation in aquatic environment using the thermal drive piezoresistive sense transduction. The differential scheme used in the resonator design enables high feedthrough cancellation, thus leading to floor value close to −62 dB with sufficient signal to feedthrough ratio (SFR) and allowing a later oscillator implementation. The proposed differential ring-shaped thermal piezoresistive resonator (DR-TPR) when made to operate in the rotational mode exhibits the special feature of minimizing the effect of viscous damping in liquid environment, attaining a quality factor value as high as 537 with a stopband rejection of 8.5 dB. The closed-loop measurement using the HF2LI lock-in amplifier with PLL from Zurich Instruments helps us to realize the differential ring-shaped thermal piezoresistive oscillator (DR-TPO) showing phase noise of −77.6 dBc/Hz at 1-kHz offset and −89.54 dBc/Hz at 10-kHz offset. The proposed DR-TPO in liquid environment can provide a frequency resolution of 6.95 Hz extracted from the measured Allan deviation, which corresponds to a minimum detectable mass of 4.11 pg, thus paving a way to both physical and biomedical detection in liquid.

An innovative topology to realize high-performance bulk mode devices made up of low-defect material by driving them into resonance using piezoelectric thin-film transduction is proposed and implemented in this paper. Here, the piezoelectric transducer is uniquely positioned at the bulk mode’s support location. To realize the resonators, MEMSCAP Inc.’s PiezoMUMPS platform was utilized. Wine-glass and Lame bulk mode devices are demonstrated to establish the feasibility of the support transducer drive/sense mechanism. Several drive/sense combinations of the balanced–unbalanced setup were measured. For the differential-in differential-out configuration, reduced feedthrough and enhanced stop-band rejection was observed. As a result, the Wine-glass and Lame mode resonators having a resonance frequency ( $f_{r}$ ) of 20.943 and 21.15 MHz with a motional resistance ( $R_{m}$ ) of 1.68 and 3.88 $\text{k}\Omega $ and a loaded quality factor ( $Q_{l}$ ) of 9940 and 6840, respectively, operating in vacuum at 0-dBm driving power are demonstrated. Temperature Coefficient of Frequency of −26.4 and −25 ppm/K is recorded for Wine-glass and Lame mode resonators, respectively. To characterize the closed-loop response of the devices, they were connected to a lock-in amplifier with phase-locked loop, and a phase noise of −122 and −118 dBc/Hz at 1-kHz offset were measured for Wine-glass and Lame mode resonators, respectively. [2018-0092]

This work reports the successful excitation of a novel bulk acoustic mode whose actuation and sensing are facilitated by the support transducer topology (STT). The design methodology concurrently supports low motional impedance and high energy confinement features which are crucial for frequency reference components in Radio Frequency communication. A conventional bulk mode operating in the width extension (WE) mode is deployed to efficiently excite the higher-order radial mode using the STT design feature of resonant frequency matching. The thin-film piezoelectric on substrate support transducers excited in a WE mode is mechanically coupled to the bulk silicon allowing the acoustic energy of the MEMS resonator to be stored maximally in the high-quality factor (Q) resonant tank, thereby alleviating the overall losses due to low-Q of the piezoelectric thin film and electrode material. The resonator exhibits a Q of 19 728 at 63.56 MHz resonant frequency with a motional resistance (R m) of 368 Ω when measured in vacuum at a power level of 0 dBm. Under cryogenic measurement conditions, the device recorded a Q of 24 153 at 15 K. A standalone WE resonator is studied to put a spotlight on the quality factor enhancement technique using the STT. The STT enabled novel bulk mode enhances the overall Q by 320% and halves the R m. When implemented as an oscillator, its performance exceeds the Global System for Mobile communication standards phase noise (PN) requirements. PN of −136.95 dBc Hz−1 and −161.52 dBc Hz−1 at 1 kHz and 1 MHz offset, respectively, were recorded when normalized to a carrier frequency of 13 MHz.

This research presents a mass sensor based on a piezoelectric thin-film MEMS oscillator with high mass resolution, real-time detection, and extremely linear behavior for gas sensing. A length-extension (LE) mode aluminum nitride (AlN) resonator with a designed frequency of 5.17 MHz has a quality factor (Q) of 747 in air, which is twice the LE mode lead zirconate titanate (PZT) resonator design. To achieve a miniaturized sensor module, a board-level piezoelectric oscillator consists of an AlN MEMS resonator, a commercial amplifier, an all-pass filter, a band-pass filter, and buffer circuits to fulfill the oscillation conditions. A carrier frequency of 5.17 MHz and a phase noise of-115 dBc/Hz at 1 kHz offset in air were observed. A mass resolution of 0.38 pg for the demonstrated mass sensor is implemented in this research. Finally, the gaseous acetone measurement results present the coefficient of determination (R2) of 0.98 between the frequency shifts and the gas volume of 0.5 ml to 5.0 ml, showing the potential to be used as a real-time monitor for gas sensing applications in ambient.

This work presents an in-house design, fabrication, and characterization of a resonant piezoelectric MEMS device using the Thin-film Piezoelectric-on-Silicon (TPoS) process of AlN to realize a Lorentz force-based magnetic sensor. The magnetometer is designed by employing the flapping-mode of the rectangular resonator fixed at the center of the two opposite edges. The resonator is characterized by Laser Doppler Vibrometer and electrical measurements which show a resonance frequency of 356 kHz with $Q$ of 767 in air. The output voltage of the magnetometer shows a linear increase with magnetic field strength indicating sensitivity and responsivity of 79.28 mV/T and 2128 ppm/T respectively. The frequency response of the device also shows a phase inversion upon reversing the direction of the magnetic field. The measured instability in the magnetic field was 0.283 µT extracted from Allan deviation, to the best our knowledge the lowest value among state-of-the-art A1N MEMS magnetometers.

This work demonstrates an integrated thermally actuated piezoresistive micromechanical oscillator realized using TSMC $0.35\ \mu \mathrm{m}$ CMOS-MEMS platform. The oscillation in ambient condition was verified with a frequency output of 1 MHz and Allan Deviation of 1.7 ppm, which corresponds to a frequency resolution of 1.7 Hz. Here we also present the application of the oscillator as a pressure sensor, showing the possibility of using this thermal piezoresistive oscillator (TPO) to sense the pressure variation in the surroundings. After a series of pressure measurements, it was confirmed that this system has the potential to become a sensor for real-time monitoring of environmental pressure, with a sensing range from 40 mTorr to 760 Torr. The linear output frequency change in this logarithmic sensing range is about 2.5 kHz. The TPO has Allan Deviation of 0.5 ppm in the low pressure regime corresponding to a frequency resolution of 0.5 Hz. The proposed TPO can potentially be integrated with other sensors, such as temperature, humidity, and aerosol sensors, in the same substrate using our mature CMOS-MEMS fabrication platform to form a fully integrated environmental sensor hub.

This study reports on a miniaturized PM2.5 sensor module utilizing a thin-film piezoelectric-on-silicon (TPoS) MEMS oscillator with real-time detection and high mass resolution. An aerosol impactor is used to serve as a particle size-selective sampler. A TPoS MEMS resonator utilizes a length-extensional mode with a quality factor (Q) of 1109 and a resonant frequency of 5.79 MHz in air. A transimpedance amplifier (TIA) interface circuit using UMC 0.18 μm CMOS technology is implemented, having an impedance gain of 81.64 dB. To demonstrate a miniaturized mass sensor module, a board-level oscillator is integrated by a TPoS resonator, an in-house designed TIA IC interface circuit, an all-pass filter based phase shifter, buffer circuits, and a band-pass filter to fulfill Barkhausen criteria. For a carrier frequency of 5.79 MHz, a phase noise of -102.54 dBc/Hz at 1 kHz offset in air is recorded while the mass resolution of 0.21 pg for the PM2.5 sensor is demonstrated in this study. Finally, the aerosol measurement results within the concentration of 10 μg/m3 to 1000 μg/m3 show the coefficient of determination (R2) of 0.84 between the frequency slope and the environment concentration of aerosol.

This work demonstrates an ultra-compact low power oscillating micromechanical active pixel array based on a 0.35 µm back-end of line (BEOL)-embedded CMOS-MEMS technology. Each pixel consists of a 3-MHz clamped-clamped beam (CCB) MEMS resonator and a power scalable transimpedance amplifier (TIA) that occupies a small area of 70 × 60 µm2 and draws only 85 µW/pixel. The MEMS resonator is placed next to the TIA with less than 10 µm spacing thanks to the well-defined etch stops in the titanium nitride composite (TiN-C) CMOS-MEMS platform. A multiplexing phase-locked loop (PLL)-driven oscillator is employed to demonstrate the chip functionality. In particular, a nonlinear operation of the resonator tank is used to optimize the phase noise (PN) performance and Allan deviation (ADEV) behavior. The ADEV of 420 ppb averaged over best 3-pixels is exhibited based on such a nonlinear vibration operation.

This work reports a novel design for high-frequency piezoelectric gyroscopes using support transducer which enables an efficient energy coupling from a length-extensional mode into a degenerate secondary elliptical mode (n = 3). The gyroscope structure is made by a single crystalline silicon (SCS) disk supported by eight-transducer arms. Large drive mode displacement is excited through piezoelectric AlN thin films on transducer arms. The simulation of the proposed gyroscope shows a high scale factor of 12.24 nA/°/s at resonator Q of 10,000 in a mode-matched condition. The device was fabricated using the PiezoMUMPs process with 10 μm thick silicon structural layer. The fabricated gyroscope shows that the frequency split between drive and sense mode is only 600 Hz at the mean resonant frequency of about 9.976 MHz in air (equivalent to 60 ppm), verifying our design efficacy. The measured scale factor of the proposed gyroscope is around 54.01 μV/°/s before demodulation.

In this work, a piezoelectric MEMS based vibration sensor with a unique gimbal shaped guard ring in differential electrical configuration has been designed for enhanced acceleration sensitivity in out-of-plane direction and reduced in-plane crosstalk. The Thin-film Piezo on Silicon (TPoS) accelerometer was fabricated using a GlobalMEMS Inc. PZT platform. This method makes use of the excellent piezoelectric property of the Lead Zirconate Titanate (PZT) thin-film along with low crystal defect property of single crystal silicon, thus ensuring a good combination of sensitivity, resolution, bandwidth, reliability, and lifetime. A system-level approach was adopted to integrate the MEMS device with a charge amplifier and a microcontroller. The device performance was compared with the standard reference accelerometer for 1-g load. The developed MEMS sensor module was further implemented for surface roughness prediction in a quartz polishing system using machine learning algorithm incorporating both the acceleration-time data and the feed rate of the polishing spindle.

In this paper, for the first time, the phenomenon of mode localization has been investigated for a 3-DOF thermal piezoresistive MEMS coupled-resonator attaining a decent quality factor value of 1,367 in ambient condition. The differential scheme enables effective feedthrough cancellation leading to enhanced signal to noise ratio (SNR). The proposed mechanically coupled differential ring-shaped thermal piezoresistive resonator (DR-TPR) is made to operate in rotational mode to minimize the effect of viscous damping caused by the surrounding medium. The utilization of mode localization in coupled TPR introduces the inherent enhancement of sensitivity and common-mode rejection compared to the frequency shift counterparts to open doors for the realization of different sensors working in ambient conditions.