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This work introduces a capacitive micromachined ultrasonic transducer (CMUT) with a reduced-gap architecture implemented in the PolyMUMPs technology. The proposed structure enables the realization of high-frequency CMUTs, for the first time in a commercial surface micromachined technology, suitable for in-air ranging applications, as well as immersion applications such as non-destructive testing (NDT). Moreover, the elements were operated at 70 V DC biasing and driven with a 5 V narrow pulse provided through a USB connection, making the CMUTs suitable for portable devices. The proposed reduced-gap architecture lowers the needed operating voltage for the CMUT elements resonating at high frequencies. This is illustrated here through an analysis of the CMUT operating principle. Finite element simulations show that the proposed reduced-gap design provides a ∼4× bias voltage supply reduction over the traditional architecture to achieve the required vibration, leading to a sufficient acoustic pressure. Acoustic measurements of the proposed CMUT in-air show a 3.33 MHz resonance frequency with a ranging distance up to 27 mm. The CMUT element was sealed using a Parylene-C coating under-vacuum for immersion-applications. In an underwater pulse-echo setup, the backplate-echo of a 3 mm thick aluminum plate was detected. Moreover, the Parylene-C coating served as a method for increasing the fractional bandwidth (BW) by more than 100% at the expense of shifting the CMUT resonance to a higher frequency up to 4.55 MHz. Such immersed operation is promising for non-destructive testing (NDT) applications.

This work presents a Lame mode resonator featuring a novel gap closing mechanism, which employs electrostatic force to reduce the capacitive transduction gaps to submicrometer values in order to overcome fabrication technology critical spacing limitations. This leads to significant resonator loss and motional resistance reduction while maintaining high $Q$ -factor even in air. Prototypes were fabricated in two commercial silicon-on-insulator processes. Upon the application of a dc voltage of 55 V between the resonator structure and the electrodes, the gaps sizes are reduced to as low as 200 nm. A resonance frequency of 18 MHz with $Q$ -factors as high as 866 000 was observed under 1 mtorr vacuum and as high as 32 000 at atmospheric pressure. A loss of 33 dB was measured at 55 V, which corresponds to an equivalent resistance of 4.4 $\text{k}{\Omega }$ , more than 60 times lower than that of a similar design without a gap closing mechanism at the same voltage. This significantly reduces the complexity of the oscillation sustaining circuitry. The frequency tuning range is also increased significantly as a result of the gap reduction, which can be useful for overcoming ambient conditions and fabrication variations.

This article presents a 6.89 MHz MEMS oscillator based on an ultra-low-power, low-noise, tunable gain/duty-cycle transimpedance amplifier (TIA) and a bulk Lamé-mode MEMS resonator that has a quality factor (Q) of 3.24 × 106. Self-cascoding and current-starving techniques are used in the TIA design to minimize the power consumption and tune the duty-cycle of the output signal. The TIA was designed and fabricated in TSMC 65 nm CMOS process technology. Its open-loop performance has been measured separately. It achieves a tunable gain between 107.9 dBΩ and 118.1 dBΩ while dissipating only 143 nW from a 1 V supply. The duty-cycle of the output waveform can be tuned from 23.25% to 79.03%. The TIA has been interfaced and wire bonded in a series-resonant oscillator configuration with the MEMS resonator and mounted in a small cavity standard package. The closed-loop performance of the whole oscillator has been experimentally measured. It exhibits a phase noise of −128.1 dBc/Hz and −133.7 dBc/Hz at 1 kHz and 1 MHz offsets, respectively.

This paper presents a bulk-mode disk resonator utilizing a transverse piezoelectric actuation technique to drive the single crystalline silicon disk structure in its wine-glass bulk mode of resonance. The device is fabricated by post-processing dies from a commercial microelectromechanical systems process and combines high quality factor and relatively low motional resistance. Post-process fabrication steps are used to reduce the width of the anchor beam supports, and consequently reduce the anchor losses. This results in a factor of 3 increase in the quality factor. Post-processed resonators were measured to have resonance frequencies of 23 MHz and quality factors of 13000 in atmospheric pressure, increasing to 31000 in 1 mTorr vacuum. The devices also demonstrate motional resistances of 21 kQ in atmospheric pressure, reducing to 8.8 kQ in 1 mTorr vacuum without requiring any dc voltage for operation.

This paper presents Lame bulk mode square resonators fabricated in a novel silicon-on-insulator technology, MicraGEM-Si. Structures are formed by patterning two wafers with several etched depths and wafer bonding them to create the released movable resonator structures. Two distinct anchoring architectures are studied: one with suspension beams at the nodal corner points, and the other with a central anchoring support. The center support architecture can be suitable for realizing high-performance gyroscopes. Resonators with different support sizes are fabricated and characterized. Fabricated devices were measured to operate at a resonance frequency of ~18 MHz and quality factors as high as ~42000 in atmospheric pressure, which to the best of our knowledge is the highest reported to date at such an ambient pressure, and ~871000 in 100-mtorr vacuum, corresponding to a f·Q product of ~1.6×10 13 .

With increasing air pollution levels across the globe, there has been a significant increase in the global health crisis. But the problem remains unchecked in various parts of the world, due to the lack of low-cost and high accuracy air quality sensors. This paper proposes a new technique based on piezoelectric micro-electro-mechanical systems (MEMS) to measure the amount of particulate matter (PM) suspended in the air. Commercially available PM sensors suffer from many disadvantages - namely size, cost, and accuracy. Previous attempts at using MEMS to measure PM have failed to make a significant impact due to the lack of a mechanism to sort the suspended particles based on their sizes and clear the sensing area from the particles after each measurement. The sensor proposed here, consisting of i) a piezoelectric resonating membrane, ii) a virtual impactor, and iii) a thermophoretic plate attempts to address the issues faced by other sensors, while achieving a very compact size and a significantly lower cost. On exposing the sensor to suspended particles in a container, a significant shift in the resonant frequency is observed, once the particles settle on the resonating membrane. The gradual shift in the resonant frequency supports the application of the proposed sensing solution to measure the mass of the PM in the air.

This paper reports on the design and fabrication of metal-oxide gas sensors, utilizing aerosol jet printing, combined with microhotplates fabricated through a process based on the industrial PolyMUMPs technology. Fabrication is complemented with in-house post-processing steps that do not require additional alignment or dry etching equipment, which greatly reduces the fabrication complexity. Aerosol jet printing is used to deposit thin homogeneous metal-oxide films, with micron thickness. A heating temperature over 300 °C is achieved by the microhotplates, at ~24 mW of power consumption. Measurement results demonstrate that the fabricated sensors exhibit good sensitivity and feature ultra-fast response times - as low as 1.2 seconds.

This paper presents a microelectromechanical system (MEMS)-based oscillator based on a Lam&eacute, mode capacitive micromachined resonator and a fully differential high-gain transimpedance amplifier (TIA). The proposed TIA is designed using TSMC 65 nm CMOS technology and consumes only 0.9 mA from a 1-V supply. The measured mid-band transimpedance gain is 98 dB &Omega, and the TIA features an adjustable bandwidth with a maximum bandwidth of 142 MHz for a parasitic capacitance C P of 4 pF. The measured input-referred current noise of the TIA at mid-band is below 15 pA/ Hz . The TIA is connected to a Lam&eacute, mode resonator, and the oscillator performance in terms of phase noise and frequency stability is presented. The measured phase noise under vacuum is &minus, 120 dBc/Hz at a 1-kHz offset, while the phase noise floor reaches &minus, 127 dBc/Hz. The measured short-term stability of the MEMS-based oscillator is &plusmn, 0.25 ppm.

This paper presents a novel operation mechanism for ultrasonic testing in-water. The mechanism employs the surface-tension forces between the water and ultrasonic probe surfaces to cause an elongation (meniscus) of the water column and thus focuses the ultrasonic beam. The proposed meniscus-mode operation mechanism exploits this phenomenon to amplify the ultrasonic signal in comparison to the traditional fully-immersed setup. The visualization of the proposed mechanism is presented with the aid of finite-element simulations. In addition, the ultrasonic signal amplification due to operation in meniscus-mode is demonstrated experimentally using a capacitive micromachined ultrasonic transducer (CMUT) fabricated in PolyMUMPs technology. A factor of ∼2.24× improvement in the ultrasonic signal strength is measured.

This paper presents a wine-glass bulk mode disk resonator based on a novel transverse piezoelectric actuation technique to achieve bulk mode resonance of the single crystalline silicon disk structure. The device is fabricated in a commercial microelectromechnical systems (MEMS) process, and combines reasonable quality factor and superior motional resistance in a low-cost technology. External capacitive electrodes are used for electrostatic tuning of the resonance frequency, relying on the electrostatic spring softening effect. The resonator was measured to have a resonance frequency of $\sim 15$ MHz and a quality factor of $\sim 2000$ in atmospheric pressure, increasing to $\sim 5000$ in 100-mtorr vacuum. The temperature co-efficient for the frequency of the device was also measured to be about −40 ppm/°C. The resonator requires no dc voltage for operation, but its resonance frequency can be tuned by varying the applied dc voltage on the capacitive electrodes with a factor of 1 ppb/ $\text{V}^{\mathrm {\mathbf {2}}}$ . [2015–0202]

This work presents a Lamé mode resonator featuring a novel gap closing mechanism, which employs electrostatic force to reduce the capacitive transduction gaps to submicrometer values in order to overcome fabrication technology critical spacing limitations. This leads to significant resonator loss and motional resistance reduction while maintaining high Q -factor even in air. Prototypes were fabricated in two commercial silicon-on-insulator processes. Upon the application of a dc voltage of 55 V between the resonator structure and the electrodes, the gaps sizes are reduced to as low as 200 nm. A resonance frequency of 18 MHz with Q -factors as high as 866 000 was observed under 1 mtorr vacuum and as high as 32 000 at atmospheric pressure. A loss of 33 dB was measured at 55 V, which corresponds to an equivalent resistance of 4.4 [Formula: see text], more than 60 times lower than that of a similar design without a gap closing mechanism at the same voltage. This significantly reduces the complexity of the oscillation sustaining circuitry. The frequency tuning range is also increased significantly as a result of the gap reduction, which can be useful for overcoming ambient conditions and fabrication variations.

This paper presents a combined magnetometer/accelerometer sharing a single surface micromachined structure. The device utilizes electrical current switching between two perpendicular directions on the structure to achieve a 2-D in-plane magnetic field measurement based on the Lorentz force. The device can concurrently serve as a 1-D accelerometer for out-of-plane acceleration, when the current is switched off. Accordingly, the proposed design is capable of separating magnetic and inertial force measurements, achieving higher accuracy through a single compact device. The sensor supports static operation at atmospheric pressure, precluding the need for complex vacuum packaging. It can alternatively operate at resonance under vacuum for enhanced sensitivity. The device is fabricated using a low-temperature surface micromachining technology, which is fully adapted for above-IC integration on standard CMOS substrates. The resonance frequency of one of the fabricated structures is measured to be 6.53 kHz with a quality factor of $\sim 30$ at a 10-mTorr ambient vacuum level. The magnetic field and acceleration sensitivities of the device are measured using discrete electronics to be 1.57 pF/T and 1.02 fF/g, respectively, under static operation. [2014-0171]

In this paper, two high-voltage charge pumps (CPs) are introduced. In order to minimize the area of the pumping capacitors, which dominates the overall area of the CP, high-density capacitors have been utilized. Nonetheless, these high-density capacitors suffer from low breakdown voltage, which is not compatible with the targeted high-voltage application. To circumvent the breakdown limitation, a special clocking scheme is used to limit the maximum voltage across any pumping capacitor. The two CP circuits were fabricated in a 0.6- μm CMOS technology with poly0-poly1 capacitors. The output voltage of the two CPs reached 42.8 and 51 V, whereas the voltage across any capacitor did not exceed the value of the input voltage. Compared with other designs reported in the literature, the proposed CP provides the highest output voltage, which makes it more suitable for tuning MEMS devices.

We demonstrate the first optical switch based on a rotating microelectromechanical device integrated with silicon nitride waveguides. This prototype has less than 15 dB of total insertion loss and requires actuation voltages below 120 V.

Recent work to create components for the miniaturization of optical coherence tomography (OCT) systems is presented. The proposed approach relies on the micro-fabrication of microelectromechanical systems (MEMS) electrostatic actuators with integrated optical components onto the same die. This can enable very compact and cost effective components that have the potential of reducing the cost and form-factor of OCT systems. In this paper, the progress on two integrated OCT subsystems is presented: a continuously-variable optical delay line and a wavelength-swept filter. These components are suitable to implement time-domain or frequency-domain OCT, respectively. The integrated rapidly tunable optical delay line is based on a laterally rotating MEMS micro-mirror, while the swept filter is based on a rotating MEMS micro-motor.

This article reports on the development of thin films of p- and n-type bismuth telluride compounds which are suitable for microelectromechanical systems (MEMS) thermoelectric energy harvesters. Films were prepared by the pulsed laser deposition technique. It is shown that the thin films of binary Bi-Te alloys outperformed considerably their ternary counterparts. Furthermore, the highest thermoelectric figure of merit (ZT) was found to be 0.39 for the p-type Bi 32 Te 68 alloy, whereas the optimal n-type alloy was Bi 25 Te 75 , which was characterized by a relatively low stress gradient.

This work introduces a novel dodecagon bulk mode gyroscope structure with parallel plate comb drives. A major contribution, compared to prior art, is that adding combs connected to the central disk structure, at the points of maximum vibration amplitudes, increases the drive strength and results in significant improvement in sensitivity. This can enable the fabrication of high performance bulk-mode gyroscopes in standard commercial MEMS technologies. Prototypes were measured to operate at frequencies of ~1.5 MHz, with quality factors of ~33,000, at a 10 mTorr vacuum level. Preliminary measurements using discrete electronics show a rate sensitivity of 0.31 μV/°/sec, corresponding to a capacitance sensitivity of 0.43 aF/°/sec/electrode.

This work presents a novel die-level post-processing technique for dies including released movable structures. The procedure was applied to microelectromechanical systems (MEMS) chips that were fabricated in a commercial process, SOIMUMPs from MEMSCAP. It allows the performance of a clean DRIE etch of sidewalls on the diced chips enabling the optical testing of the pre-released MEMS mirrors through the chip edges. The etched patterns are defined by photolithography using photoresist spray coating. The photoresist thickness is tuned to create photoresist bridges over the pre-released gaps, protecting the released structures during subsequent wet processing steps. Then, the chips are subject to a sequence of wet and dry etching steps prior to dry photoresist removal in O2 plasma. Processed micromirrors were tested and found to rotate similarly to devices without processing, demonstrating that the post-processing procedure does not affect the mechanical performance of the devices significantly.

This paper reports on the design and suggested fabrication steps of a bulk mode dodecagon disk gyroscope. A major contribution of this work, compared to prior art, is that it enables the fabrication of this important class of gyroscopes in commercially available and low-cost SOI technologies — e.g. MEMSCAP's SOIMUMPs. The structure was simulated using COMSOL, operates at 8.14 MHz, and exhibits a competitive rate sensitivity of ∼2.3 pA/°/s, a high dynamic range of 2000°/s, and a mechanical noise of 1°/√hr, for a quality factor of 10,000.

A MEMS bulk micromachined vibratory gyroscope is designed and fabricated in a commercial and low-cost SOI technology — MEMSCAP SOIMUMPs. The device was carefully designed to mitigate micro-fabrication limitations, while achieving high performance. Theoretical analysis of the drive and sense modes was performed in order to reduce the crosstalk between them, while still using a simple gyro structure. The device was simulated using COMSOL taking into account the anisotropic elastic properties of the ‘100’ single-crystalline silicon device layer for added accuracy. The gyroscope operates at 35 kHz with a 5 V DC bias voltage. The relatively low bias voltage leads to significant simplifications in the design of the biasing circuitry, and results in lower power consumption and electrical noise, while ensuring compatibility with standard integrated circuits technologies. The device exhibits a simulated rate sensitivity of ∼ 3 aF/°/s, and its theoretical mechanical noise is calculated to be 0.6 °/√hr. Measurements show a resonance frequency of 27.5 kHz and a quality factor of 120,000 at a 10 mTorr level of vacuum.

A CMOS variable gain driving circuit with output signal amplitude control for gyroscopes with wide range of quality factors is presented. The driving circuit can be used for gyroscopes with Q values higher than 500. The circuit uses a current-commutating switching mixer to control the gyroscope driving signal level. Conventional driving circuits use automatic gain control (AGC) which suffers from limited linear range and the need for an off-chip capacitor for the peak detector and loop filter. Two stage variable gain amplifier is used in the proposed design to ensure enough gain for oscillation for such a wide range of quality factors. Analog and digital amplitude control methods are used to cover wide range of driving signal amplitude with enough accuracy to hit the maximum driving signal level without sacrificing gyroscope linearity. Due to the high DC gain of the amplifier chain, DC offset resulting from mismatches might saturate the amplifier output. DC offset correction is employed using a secondary negative feedback loop. The proposed driving circuit is being fabricated in 0.6µm CMOS technology.

In this work, a complete single-ended readout circuit for capacitive MEMS gyroscope using chopper stabilization technique is presented. A novel noise cancellation technique is used to get rid of the bias noise. The circuit offers superior performance over state of the art readout circuits in terms of cost, gain, and noise for the given area and power consumption. The full circuit exhibits a gain of 58dB, a power dissipation of 1.3mW and an input referred noise of 12nV/√Hz. This would significantly improve the overall sensitivity of the gyroscope. The full circuit has been fabricated in 0.6µm CMOS technology and it occupies an area of 0.4mm × 1mm.