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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, 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.

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.

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 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.

Nonlinear physics-based harmonic generators and modulators are critical signal processing technologies for optical and electrical communication. However, most optical modulators lack multi-channel functionality while frequency synthesizers have deficient control of output tones, and they additionally require vacuum, complicated setup, and high-power configurations. Here, we report a piezoelectrically actuated nonlinear Microelectromechanical System (MEMS) based Single-Input-Multiple-Output multi-domain signal processing unit that can simultaneously generate programmable parallel information channels (> 100) in both frequency and spatial domain. This significant number is achieved through the combined electromechanical and material nonlinearity of the Lead Zirconate Titanate thin film while still operating the device in an ambient environment at Complementary-Metal–Oxide–Semiconductor compatible voltages. By electrically detuning the operation point along the nonlinear regime of the resonator, the number of electrical and light-matter interaction signals generated based on higher-order non-Eigen modes can be controlled meticulously. This tunable multichannel generation enabled microdevice is a potential candidate for a wide variety of applications ranging from Radio Frequency communication to quantum photonics with an attractive MEMS-photonics monolithic integration ability.

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 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.

In this work, we explore the generation of higher order harmonics in an electrostatically actuated wide-width beam resonator fabricated by a CMOS-MEMS Titanium Nitride Composite (TiN-C) platform. The explored TiN-C platform can achieve a gap of 400 nm with high transduction efficiency, low motional resistance ( $R_{m}$ ) and enhanced frequency stability. A record-high Radius of Curvature (R.O.C of 11.9 cm) of the fabricated wide-width pseudo free-free beam is achieved among CMOS-MEMS counterparts. The fundamental mode is measured at a resonance frequency of 9.8 MHz. The second and the third higher order harmonics are observed when the resonator is excited at its fundamental flexural mode in the non-linear region. A varying AC voltage drives the resonator from the linear regime into non-linear regime for an applied DC bias of 80 V. The presence of harmonics is confirmed electrically and optically through measurement using the Spectrum Analyzer and the Laser Doppler Vibrometer (LDV) respectively.

An array of short mechanical couplers scheme to realize a support transducer enabled Wine-glass resonator/oscillator exhibiting a quality factor ( $Q$ ) of 17,000 and an oscillator Phase Noise (PN) meeting the GSM spec. at 1 kHz and 1 MHz offsets has been demonstrated in this work. A 20.3-MHz Wine-glass resonator fabricated using the MEMSCAP platform is used to implement the oscillator. The meticulous structural and material engineering aspect of the resonator improves the quality factor of the design from 9,500 to 17,000, making the resonator an ideal candidate for high-end oscillator applications. An attenuator and phase control methodology along with commercially available amplifiers has been used to realize a low phase noise oscillator with a PN of −134.1 dBc/Hz and −152.3 dBc/Hz at 1 kHz and 1 MHz offsets respectively while divided down to GSM's 13 MHz.

In this work, a monolithic tri-axis MEMS gyroscope is realized through a TSMC SOI-MEMS platform and the device is characterized in ambient pressure. To fully make use of the limited chip area, the device is based on a single driving loop to couple the vibrating energy to three axes of sensing loops through Coriolis force. The resonator behavior is first characterized in vacuum, and then the rate measurements are evaluated through the use of spectrum analyzer and Lock-in Amplifier in air. Finally, angle random walks of 24.6 deg/rtsec, 25.4 deg/rt-sec, 9.52 deg/rt-sec, and bias instabilities of 8.78 dps, 11.32 dps, 4.92 dps are measured, respectively.

In this work, we investigate the parametric energy transfer phenomenon in a multi-mode nonlinear piezoelectric resonator over a wide frequency span through a simple, all-electrically interfaced setup. We propose a 4-port PZT-based parametric resonator with two lowest modes around 170 kHz ( $f_{o}$ ) and 340 kHz ( $2 f_{o}$ ) designated for energy receiving and pumping, respectively. The mere $2 f_{o}$ electrical excitation for the energy transfer into other tones is unique and more efficient as compared to the conventional nonlinear operation. By modulating the piezoelectric stress at 340 kHz with actuating signal of CMOS compatible threshold ( $v_{ac} > 500\ \mathrm{mV}$ ), the energy up- and downconversion are recorded in real time by a spectrum analyzer (SA). The wide modulation bandwidths (MBW) of 25 kHz (7.3%) and 30 kHz (8.8%) at $2 f_{o}$ are observed with $v_{ac}$ of 500 mV and 1 V, respectively, where the signal bandwidth of transferred energy at $f_{o}$ is half of the MBW. Furthermore, the mechanical displacements of the resonator and the modes are also verified by a Laser Doppler Vibrometer (LDV) from DC to 800 kHz, showing a displacement amplification factor of 50X at $f_{o}$ as parametric effect is triggered. Compared to the conventional nonlinear harmonics operation under the same input signal (500 mV), the output signal of each mode has been significantly enhanced due to the proposed parametric excitation.

This paper presents CMOS-MEMS fabrication process overview and the use of monolithic integrated devices in the development of frequency control and sensing applications. Post-processing of CMOS wafer can produce oxide-rich resonators that offer high $Q$ and low motional resistance. Frequency stability and transduction efficiency can be further improved by using a TiN-C based process. Both active and passive temperature compensation techniques can be used to fabricate low-power CMOS-MEMS ovenized oscillators that generate highly stable frequency output. Integration of CMOS circuits and MEMS devices can help to realize wide dynamic range pressure sensors, particulate matter (PM 2.5 ) aerosol sensors as well as compact size ultrasound receivers for environmental and biomedical applications.

This paper presents a comprehensive study on the design parameters for MEMS oscillators incorporating nonlinear mechanisms. Three different CMOS amplifier topologies in tandem with double-ended tuning-fork resonators are developed to perform a general study, thus revealing the CMOS circuit design scenarios for low phase noise. The close-to-carrier phase noise cancellation is experimentally demonstrated by either varying the gain and phase of the feedback amplifier or the dc-bias ( $V_{P}$ ) of the resonator for harnessing the optimal bias point at the resonator’s lower bifurcation point. All prototype oscillators in this paper are fabricated by a monolithic 0.35- $\mu \text{m}$ CMOS-MEMS platform with typical open-loop resonator $Q$ -factor of 1500. The best-case close-to-carrier phase noise is obtained from a 1.23-MHz 180- $\mu \text{W}$ integrator-differentiator transimpedance amplifier-based nonlinear oscillator with $V_{P} = 70$ V, exhibiting phase noise of −80 dBc/Hz at 10 Hz, −97 dBc/Hz at 100-Hz, and −112 dBc/Hz at 1-kHz offset (FOM =189.3 dB at 10-Hz offset).

A mechanically coupled array technique to enable a fully differential operation of single-crystal silicon thermal-piezoresistive resonators (TPRs) has been demonstrated to alleviate resistive feedthrough issues often seen in TPRs, therefore, featuring clear resonance behavior with decent signal-to-feedthrough ratio. The proposed thermal-piezoresistive dual-II-BARs exhibits feedthrough reduction of more than 67 dB, and no spurious mode, is found within a wide frequency span. The resonator array together with board-level sustaining circuitry also works as a thermal-piezoresistive oscillator (TPO) and demonstrated its performances for real-time mass sensing. Finally, the proposed TPO mass sensor possesses several key features, including real-time monitoring, fast response time, and most importantly, excellent mass resolution of only 83 fg extracted from the measured TPO’s Allan deviation. [2017-0085]

An extended titanium nitride composite (TiN-C) CMOS-MEMS platform for high-resolution oscillating sensors is presented in this work that attempts to simultaneously validate the (i) vertically-coupled resonator (VCR) pair structure and (ii) embedded piezoresistive (PZR) transduction mechanism in a single chip. With a vertically-coupled design concept, it is beneficial to significantly increase the linearity through the high mechanical stiffness couplers between VCR pair while minimizing the device footprint. On the other hand, the PZR sensing technique is further employed to yield a better signal-to-noise ratio (SNR) with a high gauge factor from non-silicided polysilicon resistor. To accomplish such a design concept in standard CMOS, the enhanced TiN-C platform with "substrate-etching-first" approach is proposed to prevent the tungsten vias (W-VIAs) being etched during the structure release step. As a result, we have successfully demonstrated a 3-array VCR with more than 3x power handling capability in comparison to the conventional planar 9-array counterparts. Moreover, the sub-mW capacitive driving/poly-2 sensing scheme offers a 7x reduction on the background floor than purely capacitive operation based on a single FEOL-embedded VCR with Q > 4,000.

We report an innovative four segmented electrode design of a ring based flexural mode Thin Film Piezo-on-Substrate (TPoS) resonator. It has one of the highest loaded Quality factor (Q l ) among its flexural mode counterparts working in the MHz range. The out-of-plane flexural mode is explored using the differential drive/sense configuration. The unique design of the driving and sensing electrodes along with the 10µm thick Single Crystal Silicon (SCS) in the device layer stack enhances the transduction efficiency and the overall quality factor respectively. The resonator is operated in both air and vacuum to study air damping effects. The device has a resonance frequency (f r ) of 5.25 MHz and features a Q l of 628 in air for a driving power of 0 dBm. An enhancement close to 11 times was achieved when operated in vacuum. The resonator has a Q l of 6,696 and Stop Band Rejection (SBR) of 50 dB in vacuum. Closed-loop measurements using a commercial Phase Locked Loop was carried out. In vacuum, the device exhibits a Phase Noise of -108 dBc/Hz at 1 kHz offset for a 10 kHz loop Bandwidth.

In this work, a quality factor (Q) enhancement technique has been investigated for the fundamental shear-horizontal (SH0) mode lithium niobate resonators. Four supporting tether designs are employed in combination with an optimized release distance to enhance the acoustic isolation and consequently attain a higher Q without introducing spurious modes. The fabricated prototype resonator with tapered tether design at 90 MHz exhibits a Q of 2,600 and an electromechanical coupling ($k_{ t}^{ 2}$) of 17%, resulting in a high figure-of-merit (FoM$= k_{ t}^{ 2} \times Q$) of 442. The Q of 2,600 underlines a 2X Q enhancement from a conventional straight supporting design. The perfectly matched layer (PML) method is adopted to optimize the energy loss with different acoustic boundaries. Results from our comprehensive finite-element analyses (FEA) are also reported to rationalize our design choices and confirm a Q estimation error within 15% of the measured values.

In this work, we report a piezoelectric channel select filter design using a single resonator which utilizes Thin Piezo on Substrate (TPoS) transducer uniquely positioned so as to drive the central bulk Single Crystal Silicon (SCS) into resonance. Here, the support transducers operate in a combined length extension and an in-plane shear mode. A short connector between transducers and central SCS is used to create a frequency split to realize the filter. The device is fabricated using MEMSCAP Inc. AlN-onsilicon platform. A differential drive and single port sense method was employed to realize the narrow bandwidth ($NBW$) filter with a reduced feedthrough level. As a result, we demonstrate a 20.62 MHz TPoS MEMS filter with an extremely flat passband and a tiny bandwidth of 18 kHz (0.087% $BW$), a 4dB Insertion Loss with a 39dB Stop Band Rejection and less than 0.1dB passband ripple.

We propose a novel differential drive and sense double-ended tuning fork (DETF) with wing electrodes to reduce the motional resistance ( $\boldsymbol{R_{m}}$ ) while achieving excellent power handling. The devices are fabricated using back end of line (BEOL) materials of $0.18\boldsymbol{\mu}\mathbf{m}$ 1P6M CMOS process. The wing electrodes are added to the high-velocity region to achieve high transduction efficiency. This increases the device mass ( $\boldsymbol{m_{r}}$ ) which requires increased stiffness ( $\boldsymbol{k_{r}}$ ) to maintain the same resonance frequency. The proposed design has resonance at 1 MHz in vacuum under a dc bias ( $\boldsymbol{V_{P}}$ ) of 30V with $\boldsymbol{R_{m}}$ of $250\ \mathbf{k}\boldsymbol{\Omega}$ for a $\boldsymbol{Q}$ of 2,300. The device can sustain the input power of 438 nW delivered to the resonator, corresponding to −5 dBm of the drive power from the network analyzer (NA), which is around 2000X higher as compared to traditional capacitive MEMS resonator design.

This letter presents the design of a low power, low phase noise monolithic oscillator with a back-end-of-line-embedded CMOS-MEMS resonator. The proposed CMOS-MEMS oscillator consists of a double-ended tuning fork resonator and a high gain (>138 dB $\Omega )$ ultra-low input-referred current noise ( $ integrator-differentiator transimpedance amplifier (TIA) with sub-150- $\mu \text{W}$ power consumption. The 1.2-MHz CMOS-MEMS oscillator prototype shows the phase noise better than −120 dBc/Hz at 1-kHz offset and −122 dBc/Hz at 10-kHz offset with moderate dc-bias ( $V_{P} = 22$ V). The proposed oscillator can be operated with reduced MEMS dc bias ( $V_{P} V) and TIA power supply ( $V_{\rm {DD}} V, 65 $\mu \text{W}$ ) while maintaining satisfactory performance. The frequency–power-normalized oscillator phase noise figure-of-merit (will be defined later) of 190 dB is achieved at 1-kHz offset with a resonator $Q$ of 1900, which is comparable with the state-of-the-art using bulk-mode resonators possessing $Q > 100$ k.

A vibrating micromechanical spoke-supported ring resonator employing a central peg-anchor, balanced non-intrusive quarter-wavelength extensional support beams, and notched support attachments attains high $Q$ -factor in vacuum, posting 10 000 at 441 MHz when made of polysilicon structural material and 42 900 at 2.97 GHz when made of microcrystalline diamond. The latter marks the highest $f\cdot Q$ of $1.27\times 10^{14}$ for any acoustic resonator at room temperature, besting even macroscopic bulk-mode devices. Very high $Q$ values like these in a device occupying only 870 $\mu \text{m}^{2}$ pave a path toward on-chip realizations of RF channelizers and ultra-low phase-noise gigahertz oscillators for secure communications. With frequency determined by lithographically defined ring-width rather than radius, a capacitive transducer with a 75-nm gap allows this 2.97-GHz version to achieve a series motional resistance of 81 $\text{k}\Omega $ . Though still higher than desired, this marks a $30\times $ improvement over previous pure polysilicon surface-micromachined solid disk resonators in the gigahertz range, and if predicted performance-scaling holds true, seven such resonators constructed in a mechanically coupled array with 30-nm gap spacing, could lower this to only 300 $\Omega $ . Confidence in a prediction like this stems from the confirmed accuracy of the electrical equivalent circuit described herein that models not only the ring and its transducers, but also its supports. [2015-0132]

An innovative resonance excitation methodology of a two-dimensional array of uniformly patterned structure into extremely high-quality factor (Q) mode using engineered frequency-matched thin piezoelectric film on substrate (TPoS) transducer is demonstrated in this Letter. The passive Q-enhancement can be attained lithographically without adding to the power requirement of the system. A 500 nm thick piezoelectric material facilitates the inter-electrical-mechanical domain coupling, and the displacement generated at the transducer periphery drives the patterned 10 μm thick single crystal silicon plate into various resonant modes. Using this topology, unexplored modes can be generated as well by the forced vibration feature of the interacting resonant tanks. Utilizing a multiport port excitation scheme, multiple modes are explored, while the primary focus is maintained on the Lame mode of the array. In vacuum for an operational frequency of 58.56 MHz, an exceptionally high-quality factor of 58 276 is attained with a motional resistance of 1250 Ω and this is the record-high figure of merit (f × Q = 3.4 × 1012) attained for aluminum nitride-based TPoS based resonators. This successful demonstration of the energy coupling scheme paves a path for the study of existing and investigation of unexplored high-Q modes spanning over a wide range of frequency, making these devices a potential candidate for radio frequency front-end applications. The CMOS compatibility of aluminum nitride makes it an attractive solution for achieving low phase noise monolithically integrated CMOS–microelectromechanical systems oscillators.

A wide-width clamped-clamped beam (CC-beam) resonator and a filter realized using mechanically-coupled resonator tanks have been extensively characterized to attain mixler (i.e., mixer-filter) functionality for a chip-scale frequency translation. Such a resonator has been driven into the nonlinear regime to explore its effect on the mixler operation as well as to obtain the best phase noise performance using the phase-feedback method. The proposed electrostatically transduced mixler operates by utilizing the local oscillator (LO) signal generated from the resonator itself, thus eliminating the need of a function generator or an external quartz crystal oscillator. This technique implemented with all the components on the same silicon substrate shows great potential for miniaturization in wireless communication while achieving 14.4 dB overall mixler loss.

A novel mechanism to drive pure single crystal silicon (SCS) micromechanical structure into resonance using piezoelectric transducer uniquely positioned at its support/anchor location is being reported for the first time with exceptional performance. The resonator was fabricated using MEMSCAP's PiezoMUMPs platform. This innovative method makes use of the excellent piezoelectric property of the Aluminum Nitride (AlN) thin film along with low crystal defect property of SCS, thus ensuring a very low motional impedance and high-quality factor (Q) performance. A differential drive/sense method was employed to reduce the feedthrough and eliminate spurious modes close to wine-glass (desired) mode of the SCS resonator. As a result, the designed wine-glass mode resonator operating at 21 MHz is successfully demonstrated with a motional resistance (R m ) of 1.8 kΩ and a loaded Q of 8,054 in air at 0 dBm driving power. Connecting the resonator to a lock-in amplifier with phase locked loop (PLL), a phase noise of −106 dBc/Hz at 100 Hz offset and −125 dBc/Hz at 1 kHz offset for a carrier frequency of 20.936 MHz was recorded.

A gated (on/off operation PM2.5 (aerosol) sensor utilizing CMOS-MEMS thermal-piezoresistive oscillator (TPO) calibrated by a commercial optical aerosol sensor (OAS) has been demonstrated in this work. The thermophoresis effect often seen in the thermal-drive devices to hinder the landing of aerosol (incense) onto the sensor proof-mass is resolved by the gated operation to ensure the functionality of the proposed sensor. In this improved scheme, the impactor used for particle guidance was designed meticulously to enhance the landing probability of the small (∼0.6μm) size aerosol on the proof-mass of the CMOS-MEMS resonator. As compared to the regular particle sensors, this improved setup can detect particles with diameter 5 times smaller. This is of epitome importance as pollutant aerosol particles found in the environment are less than m. 1μm. The enhanced sensitivity of the proposed sensor system enables this technique to be potentially utilized in pollutant monitoring systems implemented by the health regulatory boards across the world. With the OAS calibration, the CMOS-MEMS thermal-piezoresistive oscillator can detect aerosol concentration within a range of 50 μg/m3 to 200 μg/m3.

This work reports a 40-MHz lithium niobate-on-oxide (LN/S1O2) micromechanical resonator which simultaneously features a compensated temperature coefficient of frequency (TCf f of −13 ppm/°C and a record high Q > 3,900 in vacuum (Q > 1,600 in air) for low phase noise oscillators. A high-quality 0.7 μm X-cut LN thin film atop a 2 μm SiO 2 compensation layer was used to form the body of the proposed resonator based on a quasi-fundamental shear horizontal (Q-SH0) plate wave with acoustic propagation in 170° rotated from the Y-axis. The proposed LN-SiO 2 resonator is suspended through 5-μm narrow-width supporting beams to mitigate the acoustic energy loss to the substrate, thus exhibiting a best-case Q of 3,900 in vacuum with k eff 2 > 3.8% (FOM = k eff 2 ×Q > 148). The closed-loop oscillator was demonstrated with a commercial phase-locked loop (Zurich HF2LI PLL) under a loop bandwidth of 90 kHz. Measured phase noise for the 40-MHz LN-S1O 2 Q-SH 0 wave oscillator at 1 kHz and 10 kHz offsets is −110 dBc/Hz and −123 dBc/Hz, respectively, with a minimal bias instability of only 6.2 ppb.

CMOS-MEMS resonators, which are promising building blocks for achieving monolithic integration of MEMS structure, can be used for timing and filtering applications, and control circuitry. SiO2 has been used to make MEMS resonators with quality factor Q > 104, but temperature instability remains a major challenge. In this paper, a design that uses an embedded metal block for temperature compensation is proposed and shows sub-ppm temperature stability (−0.21 ppm/K). A comprehensive analytical model is derived and applied to analyze and optimize the temperature coefficient of frequency (TCF) of the CMOS-MEMS composite material resonator. Comparison with finite element method simulation demonstrates good accuracy. The model can also be applied to predict and analyze the TCF of MEMS resonators with arbitrary mode shape, and its integration with simulation packages enables interactive and efficient design process.

A fully monolithic complimentary metal–oxide– semiconductor-microelectormechanical systems (CMOS-MEMS) oscillator comprised of an ovenized double-ended tuning fork resonator to enable ultra-low heater power operation of only 0.47 mW over entire temperature span (–40 °C to 85 °C) and a low noise sustaining circuit to achieve low phase noise has been demonstrated in a Taiwan Semiconductor Manufacturing Company (TSMC) 0.35- $\mu $ m CMOS process. The combination of low thermal conductivity material and high thermal isolation design is the key to attaining ultra-low-power heater operation in a sub-mW level. Passive temperature compensation scheme is also conducted in the proposed CMOS-MEMS resonator by an oxide-metal composite structure, showing a low temperature coefficient of frequency (TC $_{f}$ ) of only +5.1 ppm/°C, which is suited for the use in ovenized oscillator systems. By implementing a constant-resistance temperature control scheme, the frequency drift of the resonator smaller than 120 ppm from −40 °C to 85 °C is demonstrated in this paper, indicating an equivalent TC $_{f}$ smaller than 1 ppm/°C, a record-low value against its CMOS-MEMS counterparts. The CMOS-MEMS oscillator operating at 1.2 MHz demonstrates a phase noise of −112 dBc/Hz at 1-kHz offset and −120 dBc/Hz at 1-MHz offset while drawing less than 1.3 mW. The entire power consumption of the ovenized oscillator system is confirmed to be less than 1.8 mW (oscillator + micro-oven), verifying the great potential of low power oven-controlled MEMS oscillators realized in CMOS-MEMS technology. [2014-0068]

We propose an apodization technique-based composite thin-film bulk acoustic wave resonator (c-FBAR) design to enable the displacement and strain energy confinement at the central section of the resonator while in operation at the resonance mode. Sinc-shaped AlN on Silicon on Insulator apodized c-FBARs is designed to attain close to 90% energy localization. In this paper, a single crystal silicon as the mechanical layer and an AlN piezoelectric material as the transducer layer of the resonator implemented by InvenSense Inc.’s AlN MEMS-CMOS platform renders an asymmetric feature to the traditional FBAR resonator. The nature of composite thin-film piezoelectric on substrate FBAR resonators in the super high-frequency (SHF) range is studied in detail. Furthermore, a complete deembedding procedure to extract the resonator parameters from the CMOS + MEMS measured data is also explained meticulously. A complete equivalent circuit modeling for c-FBAR operating in the SHF is provided. Measurement data statistics show that sinc c-FBAR features superior electromechanical coupling coefficient ( $k_{\mathrm {\mathbf {teff}}}^{\mathrm {\mathbf {2}}}$ ) than that of pentagon c-FBAR. As a result, we successfully demonstrate a sinc c-FBAR resonator operating at 3.264 GHz with an electromechanical coupling coefficient of 2.12%, a loaded quality factor ( $Q$ ) of 790 and an unloaded $Q$ of 2507.

An apodization method is illustrated in this work to enable displacement and strain energy confinement at the central section of the composite thin Film Bulk Acoustic wave Resonator (c-FBAR) while in operation at the resonance mode. The device is excited at a higher order thickness extensional mode. The proposed resonator is designed in sinc shape to attain high degree of energy localization. Here, the thin film piezoelectric on substrate (TPoS) configuration implemented by the Aluminum Nitride (AlN) MEMS-CMOS InvenSense Inc. platform is used to realize the resonators. The c-FBAR performance parameters are extracted through de-embedding the CMOS+MEMS measured data. An equivalent electrical modeling for c-FBAR operating in the Super High Frequency (SHF) is demonstrated. We successfully report a sinc c-FBAR resonator operating at 3.264 GHz with an electromechanical coupling coefficient >2.12%, an unloaded Q >2,500, and Figure of Merit of 53.

A 3-D mechanically-coupled resonator array has been demonstrated for the first time using CMOS-MEMS technology. A high-performance vertically-coupled (VC) CMOS-MEMS resonator pair was utilized to extend the array topology into 3-D configuration with an on-chip interfaced circuit through a TSMC 0.35 μm 2P4M CMOS-MEMS platform. An array design of 9 VC pairs (N = 18 where N is the number of constituent resonators of an array) was fabricated and characterized with resonance frequency of 5.64 MHz and 0-factor of 1,092. As compared to a single VC pair (N = 2), the Saddle (SA) mode (undesired mode) was eliminated in the array design by the use of electrode phasing at the cost of weak spurious modes around the desired resonance. The 3-D array oscillator was also realized by using an instrumental Lock-in + PLL system. Under same dc biasing, the proposed 3-D array achieves better power handling and phase noise performance over the single VC pair. This technology is expected to bring more functionalities towards medium-scale integrated (MSI) micromechanical circuits.

In this work, a high-performance mass sensor utilizing CMOS-MEMS thermal-piezoresistive resonator (TPR) sustained by an instrumental Lock-in and PLL circuit for oscillation is demonstrated. Under a low dc power consumption of the device with only 1.75 mW, the motional transconductance (gm) of the proposed TPR reaches record-high values both in vacuum (118.4 μA/V) and air (16.96 μA/V) among all reported CMOS-MEMS TPRs [1] and even on par with single crystal silicon (SCS) TPRs [2]. The unique design of a butterfly-shaped TPR with its low thermal capacitance (C th ) actuator beams is the key to improve the transduction efficiency and sensor sensitivity. The mass resolution of the proposed thermal-piezoresistive oscillator (TPO) attains 29.8 fg, which is extracted from the measured Allan deviation of 89 ppb. To verify the mass sensing capability, a pico-liter ink jet printing setup was used to demonstrate the real time response and frequency shifts corresponding to a number of droplets printed onto the proof-masses of the TPO with a high sensitivity of 1.946 Hz/pg, well suited for future aerosol detection.

This letter presents the design of a micromechanical oscillator based on a vertically coupled (VC) CMOS-microelectromechanical systems (MEMS) resonator pair for phase noise reduction. The prototyped resonator pair consists of two vibrating plates coupled with each other, thus providing enhanced power handling while keeping compact footprint. The proof-of-concept oscillator based on a 6.5-MHz, VC mode resonator achieves a phase noise of −97 dBc/Hz at 1-kHz offset and −118 dBc/Hz at 1-MHz offset from carrier with a resonator size of $30\times 30\mu \text{m}^{\mathrm {\mathbf {2}}}$ . Compared with its nonresonance-coupled saddle mode counterpart, the VC-mode-based oscillator features 10-dB phase noise reduction using the same oscillator circuit setup. The design concept of this letter can be extended to three dimensional (3-D) mechanically coupled resonator designs in the future. [2015-0053]

We report a thermally driven and piezoresistively sensed CMOS-microelectromechanical systems (MEMS) resonator with quality factor $Q >10$ 000 and stopband rejection of 15 dB under CMOS-compatible bias voltage. The bias voltage requirement of this letter is two orders of magnitude lower than that of the previous CMOS-MEMS capacitively transduced resonators. In addition, the combination of the bulk-mode resonator design and high- $Q$ SiO2/polysilicon structural material leads to resonator $Q >10$ 000, a key index for low-phase-noise oscillators and low-insertion-loss filters. The resonator with a center frequency at 5.1 MHz was fabricated using a standard 0.35 $\mu $ m 2-poly-4-metal CMOS process, featuring low cost, batch production, fast turnaround time, easy prototyping, and MEMS/IC integration. To resolve the feedthrough issue often seen in conventional thermal-piezoresistive resonators: 1) separation of the heater and piezoresistor is first adopted because of the routing flexibility of the structural configuration offered by CMOS back-end-of-line materials and 2) fully differential measurement scheme is then applied to the proposed device, both of which enable a low-feedthrough level with 65-dB improvement as compared with its single-ended counterpart.

A foundry-oriented capacitively driven CMOS-MEMS resonator using differentially piezoresistive sensing is successfully demonstrated to enable effective feedthrough cancellation with more than 20-dB feedthrough floor reduction as compared to its capacitive readout. The resonator is mainly formed by high-Q SiO2 structure utilizing metal wet etching and XeF2 release processes, while the polysilicon layer (originally CMOS gate poly material) embedded inside the resonator structure serves as a piezoresistor for vibratory detection. In addition, such a composite structure enabling electrical isolation realizes decoupling of the capacitive and piezoresistive transductions, allowing the selection (or switching) of the preferred readout scheme using the same resonator device. The proposed resonator consists of only one single capacitor for driving and a simple beam structure for both vibration and detection, therefore greatly simplifying the device design and facilitating future CMOS-MEMS implementation. This paper achieves resonator , more than 28-dB signal-to-feedthrough ratio, and two-times smaller motional impedance than that of the single-ended piezoresistive detection using the same device and driving condition. Furthermore, the piezoresistive operation offers a simple temperature compensation scheme for CMOS-MEMS resonators via the adjustment of the dc current through the piezoresistor, therefore showing 1.4-times improvement on thermal stability as compared to their capacitive readout.

Integrated CMOS-MEMS clamped-clamped beam resonators using metal wet etching technique are demonstrated with passive temperature compensation through the use of SiO2 and large stopband rejection via circuit integration. Such performance is enabled by the high- Q structural material (i.e., SiO2) and embedded electrodes (i.e., metal) for capacitive transduction without the need of complex post-CMOS processes. In virtue of exceptional selectivity of metal wet etchant to SiO2 among CMOS layers, the use of release holes needed for most of isotropic etching processes could be eliminated, hence substantially preserving the integrity of resonator structures. In this paper, CMOS-MEMS clamped-clamped beams with SiO2-rich structural design are fabricated and tested in vacuum under a two-port measurement configuration, exhibiting the lowest temperature coefficient of frequency (TCf) in CMOS-MEMS-based resonators with a turnover point at room temperature. Such a resonator monolithically integrated with readout circuitry using a standard CMOS 0.35 μm 2P4M process is tested with significantly enhanced performance, showing resonator Q's up to 6100, stopband rejection ~60 dB, and low noise floor at center frequency ~8 MHz, therefore benefiting future timing references and RF-MEMS building blocks for next-generation wireless communication applications.

A 1 MHz 4 ppm temperature-stable micro-oven μOven) controlled monolithic CMOS-MEMS oscillator has been demonstrated in this work, exhibiting heating power in sub-mW across the 100°C temperature span. The proposed novel isothermal μOven platform consists of dual heaters, one of which stabilizes the resonator temperature while the other of which serves as built-in self-test (BIST) to mimic ambient temperature, and a resistive temperature detector (RTD) for local resonator temperature monitoring. By adapting the constant-resistance (CR) feedback temperature control scheme, the integrated 1 MHz CMOS-MEMS oscillator shows a maximum frequency inaccuracy of only 4 ppm during a fast temperature ramp across the 94°C testing span (i.e., < 43 ppb/°C). The oscillator circuit shows a worst-case bias instability of 60 ppb and phase noise (PN) of −105 dBc/Hz at 1-kHz offset (Q = 1,700).

This work presents the design and characterization for composite Aluminum Nitride on Silicon based thin Film Bulk Acoustic Wave Resonators (c-FBAR) fabricated using a proprietary InvenSense AlN-MEMS + CMOS process. High performance pentagon shaped resonators are fabricated and operated under a high-order thickness-extensional mode with an electromechanical coupling coefficient of 2.21% and an unloaded quality factor of ∼1,933 at 3.26 GHz. Detailed de-embedding is performed to remove the parasitic elements which would degrade the resonator performance in the GHz operational frequency range. After de-embedding, motional resistance of 1.5 Ω is recorded. Such an InvenSense platform allows us to realize MEMS + CMOS integrated systems where an inverter based Pierce oscillator with power consumption of 0.5 mW at 1.1V bias is designed. However, insufficient performance of the MEMS resonator impedes the oscillator implementation. The circuit has an active area of 55×85 μm2 and overall CMOS-MEMS integrated area is about 300×250 μm2.

In this work, a 1.2-MHz CMOS-MEMS DETF (double-ended tuning fork) resonator with its on-chip tunable transimpedance amplifier (TIA) is designed to measure the ring-down response of the resonator circuit for pressure sensing applications. From the time-domain ring-down waveform, the frequency and quality factor of the resonator circuit can be extracted corresponding to its environmental pressure. Due to the effect of the squeezed-film damping caused by environmental pressure, the quality factor would change accordingly, thus affecting the waveform of the ring-down characteristic. By measuring the ring-down response under various pressure levels, the designed resonator circuit features a wide pressure sensing range from 0.8 Torr to 220 Torr.