Showing papers in "IEEE\/ASME Journal of Microelectromechanical Systems in 2020"
TL;DR: In this paper, first-order antisymmetric (A1) mode resonators in 128° Y-cut LiNbO3 thin films with electromechanical coupling coefficients as large as 46.4%, exceeding the state-of-the-art.
Abstract: In this work, we present first-order antisymmetric (A1) mode resonators in 128° Y-cut lithium niobate (LiNbO3) thin films with electromechanical coupling coefficients ( $k^{2}$ ) as large as 46.4%, exceeding the state-of-the-art. The achievable $k^{2}$ of A1 in LiNbO3 substrates of different orientations is first explored, showing X-axis direction in 128° Y-cut LiNbO3 among the optimal combinations. Subsequently, A1 resonators with spurious mode mitigation are designed and fabricated. In addition to the large $k^{2}$ , the implemented devices show a maximum quality factor ( $Q$ ) of 598 at 3.2 GHz. Upon further optimization, the reported platform can potentially deliver a wideband acoustic-only filtering solution in 5G New Radio. [2020–0003]
77 citations
TL;DR: In this article, the authors reported on the first demonstration of the frequency tuning and intrinsic polarization switching of film bulk acoustic resonators (FBARs), based on sputtered AlScN piezoelectric thin films with Sc/(Al + Sc) ratio of approx 30% and showed a coercive electric field at 3 MV/cm.
Abstract: This work reports on the first demonstration of the frequency tuning and intrinsic polarization switching of film bulk acoustic resonators (FBARs), based on sputtered AlScN piezoelectric thin films with Sc/(Al + Sc) ratio of approx 30% A box-like ferroelectric hysteresis behavior of 900 nm-thick Al07Sc03N sputtered films is obtained, showing a coercive electric field at ~3 MV/cm The fundamental thickness-mode resonance of the bulk acoustic wave (BAW) resonator is measured at 317 GHz frequency with an excellent electromechanical coupling coefficient ( $k_{t}^{2}$ ) of 181% The FBAR frequency response is studied, in both (i) the linear tuning regime, upon application of DC electric fields below the coercive field; as well as (ii) the polarization switching regime, upon application of electric fields above the coercive field A large linear tuning range of 215 ppm $\times \,\,\mu \text{m}$ /V is obtained in case (i), resulting from the high scandium content The series resonance frequency of the FBARs is switched ON and OFF in (ii) upon application of 350 V unipolar waveform across the Al07Sc03N thickness This is the first demonstration of the intrinsically switchable AlN-based FBARs with a large tuning range; and record high $k_{t}^{2}$ reported for AlN-based FBARs to date Furthermore, this work paves the way for realization of tunable and switchable wideband acoustic filters operating at super high frequency ranges (SHF) [2020-0203]
67 citations
TL;DR: An overview of microelectromechanical systems (MEMS) resonators for frequency reference and timing applications is presented in this article, where state-of-the-art technologies for improving the overall performance of MEMS resonators, such as quality factor, motional impedance, temperature sensitivity, and initial frequency uniformity, are reviewed in detail.
Abstract: An overview of microelectromechanical systems (MEMS) resonators for frequency reference and timing applications is presented. The progress made in the past few decades in design, modeling, fabrication and packaging of MEMS resonators is summarized. In particular, the state-of-the-art technologies for improving the overall performance of MEMS resonators, such as quality factor ( $Q$ ), motional impedance, temperature sensitivity, and initial frequency uniformity, are reviewed in detail. The challenges and opportunities during the commercialization of MEMS resonators are also stated, and future development trends driven either by technology or market are outlined. This paper intends to provide an outlook for possible research directions of MEMS resonators in frequency reference and timing applications. With outstanding reliability, unique multi-frequency functionality on a single chip, and high accuracy, MEMS resonators show great potential for replacing the quartz crystal resonators which have been dominating the timing market since 1920s. [2020-0106]
60 citations
TL;DR: In this article, a super high frequency (SHF) Lamb and surface acoustic wave resonator based on single-crystal orientation Aluminum Scandium Nitride (AlScN) thin films grown on silicon substrates by molecular beam epitaxy (MBE).
Abstract: This paper demonstrates super high frequency (SHF) Lamb and surface acoustic wave resonators based on single-crystal orientation Aluminum Scandium Nitride (AlScN) thin films grown on silicon substrates by molecular beam epitaxy (MBE). We report on the experimental frequency response and electromechanical properties of 400 nm-thick crystalline AlScN acoustic resonators with up to 12% Sc/(Sc+Al) ratio. The film thickness is optimized for operation at the SHF range, targeting emerging wireless communication standards, such as 4G LTE/5G. We report on high-performance acoustic devices that take advantage of the crystallinity, and high piezoelectric properties of 400 nm-thick epitaxial AlScN films. Our work presents enhanced effective electromechanical coupling coefficients ( $k_{eff}^{2}$ ) up to 5.3% and unloaded quality factors ( $Q_{m}$ ) of ~192 at 3–10 GHz. However, fabrication challenges due to the high-stress levels of sub-micron AlScN epi-layers grown on Si substrates remain challenging and will be discussed in this paper. [2019-0231]
52 citations
TL;DR: In this paper, the first-order antisymmetric Lamb wave (A1) mode resonator was used for front-end filtering of the 5G wireless communication in the sub-6 GHz frequency range.
Abstract: This paper reports on the demonstrations of first-order antisymmetric Lamb wave (A1) mode resonator as a new platform for front-end filtering of the fifth-generation (5G) wireless communication. The sub-6 GHz resonance in this work is achieved by employing the A1 mode in the micromachined Y-cut Lithium Niobate (LiNbO3) thin films. The spurious modes mitigation is achieved by optimizing the distribution of the electric field. The demonstrated figure-of-merit ( $\text {FoM}=Q\cdot k_{t}^{2}$ ) of 435 marks the first time that a new resonator technology with the FoMs exceeds those of surface acoustic wave (SAW) resonators and thin-film bulk acoustic resonators (FBARs) in the sub-6 GHz (1–6 GHz) frequency range. [2019-0241]
40 citations
TL;DR: In this article, a novel mode-localized resonant accelerometer, which can keep high sensitivity even over a wide range, was proposed to improve the adjustability of sensitivity, a new four degree of freedom (4-DoF) series-parallel resonator array is proposed.
Abstract: This paper reports a novel mode-localized resonant accelerometer, which can keep high sensitivity even over a wide range. To improve the adjustability of sensitivity, a new four degree of freedom (4-DoF) series-parallel resonator array is proposed. Three sensing resonators are mechanically coupled together in series by folding beams and the fourth sensitivity-tuning resonator is electrically coupled in parallel with the sensing system. When the stiffness perturbation caused by acceleration occurs, a change of modal amplitude ratio due to the mode localization phenomenon can be detected. By tuning the voltage on the sensitivity-tuning resonator, the sensitivity of the accelerometer can be altered to keep the amplitude ratio within a reasonable range. The theoretical model of the accelerometer is established and analyzed by numerical method. To confirm the feasibility of the design, a device fabricated by SOI-MEMS technology is tested under open-loop circuit. The measured amplitude ratio sensitivity varies from 1.14/g to 23.37/g with the change of the tuning voltage, and the sensitivity adjustment range reaches 2050%. [2019-0199]
35 citations
TL;DR: The mechanical bracing technique developed in this work involves a novel biodegradable polymer brace that temporarily reduces shank length and consequently, increases its stiffness during implantation, therefore enabling access to deeper brain regions while preserving a low original cross-sectional area of the shanks.
Abstract: A Parylene C polymer neural probe array with 64 electrodes purposefully positioned across 8 individual shanks to anatomically match specific regions of the hippocampus was designed, fabricated, characterized, and implemented in vivo for enabling recording in deep brain regions in freely moving rats Thin film polymer arrays were fabricated using surface micromachining techniques and mechanically braced to prevent buckling during surgical implantation Importantly, the mechanical bracing technique developed in this work involves a novel biodegradable polymer brace that temporarily reduces shank length and consequently, increases its stiffness during implantation, therefore enabling access to deeper brain regions while preserving a low original cross-sectional area of the shanks The resulting mechanical properties of braced shanks were evaluated at the benchtop Arrays were then implemented in vivo in freely moving rats, achieving both acute and chronic recordings from the pyramidal cells in the cornu ammonis (CA) 1 and CA3 regions of the hippocampus which are responsible for memory encoding This work demonstrated the potential for minimally invasive polymer-based neural probe arrays for multi-region recording in deep brain structures [2020-0018]
34 citations
TL;DR: In this paper, a new paradigm for enabling gigahertz higher-order Lamb wave acoustic devices using complementarily oriented piezoelectric (COP) thin films is presented.
Abstract: In this work, we present a new paradigm for enabling gigahertz higher-order Lamb wave acoustic devices using complementarily oriented piezoelectric (COP) thin films. Acoustic characteristics are first theoretically explored with COP lithium niobate (LiNbO3) thin films, showing their excellent frequency scalability, low loss, and high electromechanical coupling ( $k^{2}$ ). Acoustic resonators and delay lines are then designed and implemented, targeting efficient excitation of higher-order Lamb waves with record-breaking low loss. The fabricated resonator shows a $2^{\mathbf {nd}}$ -order symmetric (S2) resonance at 3.05 GHz with a high quality factor ( $Q$ ) of 657, and a large $k^{2}$ of 21.5% and a $6^{\mathbf {th}}$ -order symmetric (S6) resonance at 9.05 GHz with a high $Q$ of 636 and a $k^{2}$ of 3.71%, both among the highest demonstrated for higher-order Lamb wave devices. The delay lines show an average insertion loss (IL) of 7.5 dB and the lowest reported propagation loss of 0.014 dB/ $\mu \text{m}$ at 4.4 GHz for S2. Notable acoustic passbands up to 15.1 GHz are identified. Upon further optimizations, the proposed COP platform can lead to gigahertz low-loss wideband acoustic components. [2020-0127]
32 citations
TL;DR: In this article, a Lithium Niobate (LN) based shear horizontal (SH0) resonator utilizing suspended and solidly mounted structures for radio frequency (RF) applications is presented.
Abstract: This article reports Lithium Niobate (LN) based shear horizontal (SH0) resonators utilizing suspended and solidly mounted structures for radio frequency (RF) applications. The solidly mounted SH0 structure (also termed guided SH0 structure) is advantageous in obtaining reduced temperature coefficient of frequency (TCF), reduced high frequency overtone spurious responses, and improved power handling. The demonstrated solidly mounted guided SH0 resonators exhibit a mechanical Q as high as 1316 around 950 MHz, and electromechanical coupling factor ( ${k} _{\mathrm {t}}^{\mathrm {2}}$ ) of around 21.8 % - resulting in a figure of merit ( $\mathrm {FoM}=k_{\mathrm {t}}^{\mathrm {2}}\cdot \mathrm {Q}$ ) of 288.
30 citations
TL;DR: In this article, the authors presented a new acoustic MEMS resonator technology, dubbed Aluminum Nitride (AlN) Combined Overtone Resonator (COR), capable of addressing the filter requirements for the 5G high frequency bands in the 6-40GHz range.
Abstract: This work presents a new acoustic MEMS resonator technology, dubbed Aluminum Nitride (AlN) Combined Overtone Resonator (COR), capable of addressing the filter requirements for the 5G high frequency bands in the 6-40GHz range. The COR exploits the multimodal excitation of two higher-order Lamb waves ( $2^{\mathbf {nd}}$ and $3^{\mathbf {rd}}$ order Asymmetrical Lamb Waves) in a suspended thin-film AlN plate to transduce a 2-dimensional vibration mode with high electromechanical coupling coefficient $k_{t}^{2}$ (up to 1.9%) and quality factor $Q>1100 $ at twice the frequency of a fundamental thickness-extensional mode in the same structure. Analytical and finite-element method (FEM) models are developed to describe the working principle of the COR technology and predict the achievable $k_{t}^{2}$ , Q and lithographic frequency tunability. An 8.8 GHz COR prototype was fabricated showing a high $k_{t}^{2}~\sim ~0.3$ % (using a simple top-electrode-only configuration with a 2-mask process) and a groundbreaking $Q\sim {1100}$ which is the highest ever achieved among piezoelectric resonators above 6 GHz. The $f - Q$ product $\sim 1\times 10 ^{\mathbf {13}}$ is the highest among all demonstrated piezoelectric resonators with metallic coverage >50%. Additionally, the capability of the COR technology to deliver contiguous filters with bandwidths between 355 and 592 MHz (aggregated BW >2GHz) in the mmWave spectrum, with relaxed lithographic requirements, is demonstrated by FEM. [2019-0229]
29 citations
TL;DR: In this paper, a compliant mechanical amplifier (mechAMP) was proposed for the sensitivity enhancement in MEMS sensor applications, which can also be applied as mechanical stiffness transformer for the adaption of mechanical signals or as mechanical transformer for MEMS actuators.
Abstract: In this paper, we introduce a compliant mechanical amplifier (mechAMP) suitable for the sensitivity enhancement in MEMS sensor applications. The design, fabrication and characterization of a planar compliant amplifier mechanism is presented with special focus on the kinematic and static system modelling of the displacement and force amplification. We show that the proposed system can also be applied as mechanical stiffness transformer for the adaption of mechanical signals or as mechanical transformer for MEMS actuators. Based on a kinematic model, a compact mechanism with a system size of 930 $\mu \text{m}\,\,\times2080\,\,\mu \text{m}$ and a displacement amplification ratio of 200 with an output displacement in a range of 100 $\mu \text{m}$ was designed. The fabrication of the system was carried out using silicon-on-insulator (SOI) technology. Experimentally, we could verify an amplification ratio of 197.9 for the designed and fabricated system which corresponds to the analytic model by a deviation of about 1%. [2019-0228]
TL;DR: In this paper, the authors focus on various sources of nonlinearities induced by the interaction with the surrounding fluid and by occurrence of geometric large transformations in piezo-micromirrors with large opening angles.
Abstract: In this work, we address the modelling of piezo-micromirrors with large opening angles. We focus on various sources of nonlinearites induced by the interaction with the surrounding fluid and by occurrence of geometric large transformations. Specific attention is also devoted to the piezoelectric coupling coefficient. Piezoelectric thin films have gained attention as key materials for the actuation of micro devices since they provide high drive forces, enabling devices with higher performances compared to electrostatic actuation. However they also induce material nonlinearities that cannot be neglected. The model is validated using experimental data obtained for various excitation levels. [2020-0229]
TL;DR: The miniature EHT platforms described in this paper represent a proper microenvironment for culturing and studying EHTs and reduce the cost of cell cultures and increases assay throughput.
Abstract: We present a wafer-scale fabricated, PDMS-based platform for culturing miniaturized engineered heart tissues (EHTs) which allows highly accurate measurements of the contractile properties of these tissues. The design of the platform is an anisometrically downscaled version of the Heart-Dyno system, consisting of two elastic micropillars inside an elliptic microwell with volume ranging from 3 down to $1\mu \text{L}$ which supports EHT formation. Size downscaling facilitates fabrication of the platform and makes it compatible with accurate and highly reproducible batch wafer-scale processing; furthermore, downscaling reduces the cost of cell cultures and increases assay throughput. After fabrication, the devices were characterized by nanoindentation to assess the mechanical properties of the pillars and transferred to 96-well plates for cell seeding. Regardless the size of the platform, cell seeding resulted in successful formation of EHTs and all tissues were functionally active ( i.e. showed cyclic contractions). The precise characterization of the stiffness of the micropillars enabled accurate measurements of the contractile forces exerted by the cardiac tissues through optical tracking of micropillar displacement. The miniature EHT platforms described in this paper represent a proper microenvironment for culturing and studying EHTs. [2020-0130]
TL;DR: The neuromorphic MEMS accelerometer was able to accurately emulate non-linear autoregressive moving average models and compute the parity of random bit streams in a test system with a non-trivial transfer function, showing a robustness that is well-suited to anticipated applications.
Abstract: This study presents the design, fabrication, and test of a micro accelerometer with intrinsic processing capabilities, that integrates the functions of sensing and computing in the same MEMS. The device consists of an inertial mass electrostatically coupled to an oscillating beam through a gap of 8 $\mu \text{m}$ . The motion of the inertial mass modulates an AC electrostatic field that drives the beam in its non-linear regime. This non-linearity is used to implement machine learning in the mechanical domain, using reservoir computing with delayed feedback to process the acceleration information provided by the inertial mass. The device is microfabricated on a silicon-on-insulator substrate using conventional MEMS processes. Dynamic characterization showed good accelerometer functionalities, with an inertial mass sensitivity on the order of 100 mV/g from 250 to 1300 Hz and a natural frequency of 1.7 kHz. In order to test the device computing capabilities, two different machine learning benchmarks were implemented, with the inputs fed to the device as accelerations. The neuromorphic MEMS accelerometer was able to accurately emulate non-linear autoregressive moving average models and compute the parity of random bit streams. These results were obtained in a test system with a non-trivial transfer function, showing a robustness that is well-suited to anticipated applications. [2019-0238]
TL;DR: This paper presents the design, fabrication, and characterization results of a paper-based, low-cost, easy-to-use, comfortable and wearable tactile sensor array for human health monitoring applications and demonstrates its capability of detecting atrial fibrillation from BP pulse waveform measured from an AFib patient.
Abstract: This paper presents the design, fabrication, and characterization results of a paper-based, low-cost, easy-to-use, comfortable and wearable tactile sensor array for human health monitoring applications. Paper substrate and spray-deposited metallic electrodes and traces are employed to achieve a low fabrication cost. Capacitive sensing scheme employing a deformable triangular PDMS sensing membrane is chosen due to its high sensitivity and zero DC power dissipation. Trade-offs among different sensor array designs are investigated to achieve an optimal design, which consists of a $1\times 5$ sensor array occupying an area of 10 mm $\times10$ mm. Each sensor in the array achieves a nominal capacitance value and sensitivity of approximately 1 pF and 30 fF/mmHg, respectively. Fabricated sensor array can be comfortably attached to an individual’s temporal region and ankle area to monitor real-time blood pressure (BP) pulse waveform with high fidelity, from which heart rate and heart rate variability information can be accurately obtained. In addition, the prototype sensor array demonstrates its capability of detecting atrial fibrillation (AFib) from BP pulse waveform measured from an AFib patient. [2020-0179]
TL;DR: The design, fabrication, and characterization of a compact pMUT array of piezoelectric micromachined ultrasonic transducer array and its application to photoacoustic imaging is presented.
Abstract: In this paper, we present the design, fabrication, and characterization of a compact $4\times 4$ piezoelectric micromachined ultrasonic transducer (pMUT) array and its application to photoacoustic imaging. The uniqueness of this pMUT array is the integration of a $4~\mu \text{m}$ -thick ceramic PZT, having significantly higher piezoelectric coefficient and lower stress than sol-gel or sputtered PZT. The fabricated pMUT array has a small chip size of only $1.8\times1.6$ mm2 with each pMUT element having a diameter of $210~\mu \text{m}$ . The fabricated device was characterized with electrical impedance measurement and acoustic sensing test. Photoacoustic imaging has also been successfully demonstrated on an agar phantom with a pencil lead embedded using the fabricated pMUT array. [2020-0087]
TL;DR: In this paper, a two-step fabrication method combining 3D printing with two-photon polymerization (TPP) and aluminum sputtering is demonstrated, and a thermal actuator was printed with a mechanism in three-dimensional space without additional assembly steps.
Abstract: The fabrication and integration of microactuators with 3D micromechanisms are necessary to develop microrobots with higher capability and complexity. In this work, a two-step fabrication method combining 3D printing with two-photon polymerization (TPP) and aluminum sputtering is demonstrated. Actuators using two different transduction mechanisms (thermal and electrostatic) were fabricated in this process, and a thermal actuator was printed with a mechanism in three-dimensional space without additional assembly steps. This work also provides parameterized characterizations which can be used as design guidelines for building actuators and mechanisms. A design approach to electrically isolate the actuators from the substrate is introduced so that the device can be functional after two fabrication steps without patterning the metal layer. Metal coverage on the sidewalls of trenches are characterized, which provides a design space for deciding electrode gaps and heights in electrostatic actuators. Using these guidelines, 500 $\mu \text{m}$ long thermal actuators showed a maximum displacement of 18.0 $\mu \text{m}$ at 8.31mW and reliably actuated up to 8,500 cycles. An interdigitated electrostatic comb-drive actuator was also successfully demonstrated, displacing 12.7 $\mu \text{m}$ when 160V was applied. Finally, a 3D actuated mechanism was designed by incorporating a thermal actuator with 3D compliant mechanisms to flap 250 $\mu \text{m}$ long wings. Flapping motion was successfully demonstrated. [2020-0010]
TL;DR: In this article, the relationship between frequency asymmetry and circularity error is discussed, which can be used to predict the resonator performance and a simplified model is built to analyze the effect of gap deviation on the capacitance variation.
Abstract: Micro glassblowing can be utilized in the fabrication of high-precision micro shell resonator due to its acceptable cost and promising performance. Geometric imperfection characterization and electrode assembly are important but challenging tasks for manufacturing high-quality resonators. This paper characterizes the geometric imperfection of the micro shell resonator and proposes a novel precise assembly process for micro shell resonators with out-of-plane electrodes. The crucial geometric imperfections including thickness imperfection, circularity error and anchor non-planarity of the glassblowing structures are experimentally characterized. The sample resonator exhibits a circularity error below 0.2 % and an anchor non-planarity of 300 nm. The relationship between frequency asymmetry and circularity error is discussed, which can be used to predict the resonator performance. A simplified model is built to analyze the effect of gap deviation on the capacitance variation of the resonator. Finally, a sacrificial layer-free electrode assembly method is proposed, which achieves small ( $ ) capacitance gaps with relatively low tolerance. [2019-0235]
TL;DR: In this paper, the authors demonstrate a fabrication technology to realize intelligent, transdermal, minimally invasive microneedle array by crosslinking a hydrogel, Polyethylene Glycol Diacrylate (PEGDA) by photo-polymerization using Digital Light Processing (DLP) based 3D printing.
Abstract: We demonstrate a new fabrication technology to realize “intelligent”, transdermal, minimally invasive microneedle array ( i $\mu $ NA) by crosslinking a hydrogel, Polyethylene Glycol Diacrylate (PEGDA) by photo-polymerization using Digital Light Processing (DLP) based 3D printing The photo-polymerization conditions have been optimized so that the mutually exclusive requirements of excellent mechanical strength while retaining hydrogel properties of PEGDA are met which would allow swelling/delivery of therapeutic cargo of diclofenac sodium via diffusion An array having 100 microneedles arranged in a $10\times 10$ array was successfully 3D printed which efficiently penetrated human skin during ex vivo characterization In vitro drug release studies demonstrated that the PEGDA based i $\mu $ NA behaves as a stimuli responsive device showing distinct release characteristics from external stimuli such as temperature and pH [2020-0133]
TL;DR: Based on photolithography, it is demonstrated how to build heterogenous systems that are scalable as well as biologically stable– the MOTEs can function in saline water for more than six months, and in a mouse brain for two months (and counting).
Abstract: In vivo, chronic neural recording is critical to understand the nervous system, while a tetherless, miniaturized recording unit can render such recording minimally invasive. We present a tetherless, injectable micro-scale opto-electronically transduced electrode (MOTE) that is $\sim 60~\mu \text{m}\,\,\times 30~\mu \text{m}\,\,\times 330~\mu \text{m}$ , the smallest neural recording unit to date. The MOTE consists of an AlGaAs micro-scale light emitting diode ( $\mu $ LED) heterogeneously integrated on top of conventional 180nm complementary metal-oxide-semiconductor (CMOS) circuit. The MOTE combines the merits of optics (AlGaAs $\mu $ LED for power and data uplink), and of electronics (CMOS for signal amplification and encoding). The optical powering and communication enable the extreme scaling while the electrical circuits provide a high temporal resolution ( $ ). This paper elaborates on the heterogeneous integration in MOTEs, a topic that has been touted without much demonstration on feasibility or scalability. Based on photolithography, we demonstrate how to build heterogenous systems that are scalable as well as biologically stable– the MOTEs can function in saline water for more than six months, and in a mouse brain for two months (and counting). We also present handling/insertion techniques for users (i.e. biologists) to deploy MOTEs with little or no extra training. [2020-0080]
TL;DR: In this paper, the authors proposed a quasi-zero-stiffness mechanism that is compatible with MEMS technologies together with a micromaching approach for adjusting the stiffness precisely.
Abstract: High-precision microelectromechanical inertial sensors based on spring-mass structures are of great interests for a wide range of applications, including inertial navigation, disaster warning and resource exploration. Lowering the resonant frequency is essential to further improve the sensitivity of the sensors. However, conventional approaches are facing insurmountable difficulties from size reduction to machining precision. This paper proposed a novel quasi-zero-stiffness mechanism that is compatible with MEMS technologies together with a micromaching approach for adjusting the stiffness precisely. By improving the compliance of a typical spring with a negative-stiffness compensation mechanism induced by axial force, the resonant frequency of the micro spring-mass structure is lowered to 0.7 Hz, which is at least 3 times lower than current state-of-the-art micro structures. Based on this ultra-sensitive micro structure base on the quasi-zero-stiffness mechanism, the micro inertial sensor, with a chip size of a postage stamp, has shown a low self-noise of 0.6 nrad/ $\surd $ Hz at 0.04 Hz and a high long-term stability that are comparable to traditional pendulum inertial sensors. It is the first micro device, to our knowledge, that can successfully measure the tidal tilt signal. [2020-0048]
TL;DR: In this paper, the dynamic response of two different types of double-ended tuning fork MEMS resonators is studied both in the linear and nonlinear regimes, and a one degree of freedom (1 dof) model able to predict the frequency response of the device is proposed.
Abstract: Numerical modelling of MicroElectroMechanical Systems (MEMS) resonators is still attracting increasing interest from the sensors community especially when the nonlinear regime is activated. Here, the dynamic response of two different types of double-ended tuning fork MEMS resonators is studied both in the linear and nonlinear regimes. A one Degree Of Freedom (1 dof) model able to predict the frequency response of the device is proposed. Geometric and electrostatic nonlinearities are simulated through Finite Elements and Integral Equations, respectively. The total dissipation of the resonator is computed by taking into account both the thermoelastic and the nonlinear fluid contributions. Experimental measurements performed on resonators fabricated in polysilicon and single crystal silicon validate the proposed model showing a very good agreement with theoretical predictions. [2020-0240]
TL;DR: In this paper, a vacuum-sealed 2D transducer array is constructed on an SGW3 glass substrate with copper through-glass interconnects, and the fabrication process is described in detail.
Abstract: A critical component in a three-dimensional (3D) ultrasound imaging system is a two-dimensional (2D) transducer array. A 2D transducer array is also essential for the implementation of a compact form factor focused ultrasound system for therapeutic applications. Considering the difficulty associated with developing 2D transducer arrays using piezoelectric technology, capacitive micromachined ultrasonic transducer (CMUT) technology with the inherent advantages has emerged as a candidate to develop these devices. Previously, we demonstrated that 2D CMUT arrays can be fabricated with through-glass-via interconnects on borosilicate substrates using anodic bonding. In this paper, we present a fabrication process for implementing $16\times 16$ -element 2D CMUT arrays on an alkali-free glass substrate using the sacrificial release method. The vacuum-sealed $16\times 16$ -element 2D CMUT array is built on an SGW3 glass substrate with copper through-glass interconnects. The fabrication process developed for the 2D CMUT array is described in detail. Across the 256 elements of the 2D CMUT array, the mean resonant frequency is measured as 4.76 MHz with a standard deviation of 46.6 kHz. Also, the mean device capacitance across the array is measured as 1.17 pF with a standard deviation of 0.12 pF, and these results agree with the finite-element analysis. This study shows an alternative method to fabricate 2D CMUT arrays on glass substrates with metal interconnects, especially when the substrate is not suitable for anodic bonding. In addition to improved reliability and reduction in parasitic interconnect capacitance and resistance, this fabrication method benefits from the flexibility of developing 2D CMUT arrays on any type of insulating substrate, and still attain optimum uniformity in both yield and functionality of the fabricated devices. [2019-0246]
TL;DR: In this article, the authors reported the approach to boost the acoustic performances of PMUTs including vibrational amplitude, acoustic pressure and electromechanical coupling by using the pinning boundary structure.
Abstract: This paper reports the approach to boost the acoustic performances of PMUTs (Piezoelectric Micromachined Ultrasonic Transducers) including vibrational amplitude, acoustic pressure and electromechanical coupling by using the pinning boundary structure An analytical model is developed based on an assumed mode shape and is validated with matching results from numerical simulations Prototyped devices are fabricated and tested with a measured 25X improvement in displacement and 35X higher pressure output per volt at resonance as compared to those of PMUTs with clamped boundary As a demonstration example, a PMUT-based ultrasonic tilt sensor is investigated with measured result using the receiving PMUT’s pressure amplitude for a tilting range of ±8 degrees and an error of ±07 degrees [2020-0152]
TL;DR: In this paper, a high heat flux sensor based on structure-enhanced micromachined thermopile is designed and fabricated, which exhibits excellent repeatability in more than 200 laser pulses at 0.12 to 1.10 MW/m2.
Abstract: Transient heat flux sensors are widely used in unsteady thermal analyses. Commercial sensors currently available for high heat flux, however, have relatively low sensitivity. Micromachined thermopile based sensors with advantages of high sensitivity and small size, have been used for the measurement of heat flux produced by black body (usually in the level of W/m2), but not been tried to measure a heat flux on the order of MW/m2. In this paper, a high heat flux sensor based on structure-enhanced micromachined thermopile is careful designed and fabricated. Experiments using a powerful laser were conducted at ambient temperature to study the general performance, as well as the limit heat flux, of the sensor. The results show that the output signals have a linear characteristic with heat flux from 0.12 to 1.10 MW/m2. The sensitivity and response time of the sensor are $1.50\times 10^{-6}$ Vm2/W and 14 ms at 0.12 MW/m2, respectively. The sensor exhibits excellent repeatability in more than 200 laser pulses at 0.44 MW/m2. Limit check reveals that the sensor remains a good repeatability at 0.77 MW/m2 and can survive at 1.10 MW/m2. The designed sensor shows a high performance and will provide a new effective path for measuring high heat flux fast and sensitively. [2019-0160]
TL;DR: In this article, dual-mode ovenized MEMS resonators are demonstrated with an in-chip device layer micro-oven that utilizes less than 30mW for resonator temperature control over variations in external temperature from −40°C to +60°C.
Abstract: We demonstrate two novel dual-mode ovenized MEMS resonators, each with an in-chip device layer micro-oven that utilizes less than 30mW for resonator temperature control over variations in external temperature from −40°C to +60°C. The device layer micro-oven enables correction for ambient temperature variations and achieves a 1-week frequency stability for the output mode over temperature near 1.5 ppb for the Lame-mode resonator. The devices were built in the Epi-Seal fabrication process and take advantage of the exceptional long-term stability of MEMS resonators built in that process. These results exceed all prior reports for frequency stability over time and temperature for MEMS resonators and have the potential to impact the development of miniature, low-power time references. [2019-0054]
TL;DR: In this paper, a microfluidic capacitor is printed as two separate halves to enable facile support material removal, and then fasten the parts together via designed integration features.
Abstract: PolyJet-based additive manufacturing (or “three-dimensional (3D) printing”) techniques allow for micro-to-mesoscale fluidic systems to be produced with multiple, fully integrated materials and unparalleled geometric versatility (due to the use of sacrificial support materials). Although the PolyJet 3D printing process is autonomous and fast, the post-processing methods required to remove the sacrificial materials can be exceedingly time-intensive for systems with enclosed channels, often resulting in device degradation. To bypass such issues, here we present a novel “additive assembly” strategy for realizing PolyJet-printed multi-material microfluidic components. In this work, we print a microfluidic capacitor as two separate halves to enable facile support material removal, and then fasten the parts together via designed integration features. Fabrication results revealed a significant reduction in post-processing time by approximately 98% compared to enclosed control designs. Experimental results for burst-pressure testing– a measure of component integrity– revealed that the additively assembled microfluidic capacitors retained a maximum internal pressure in excess of 189 kPa before failure. The results suggest that the presented additive assembly strategy holds promise for greatly extending the utility of PolyJet 3D printing for micro- and millifluidic applications. [2020-0111]
TL;DR: The design, fabrication, and preliminary bench-top characterization of a high-density, polymer-based penetrating microelectrode array, developed for chronic, large-scale recording in the cortices and hippocampi of behaving rats, are presented.
Abstract: We present for the first time the design, fabrication, and preliminary bench-top characterization of a high-density, polymer-based penetrating microelectrode array, developed for chronic, large-scale recording in the cortices and hippocampi of behaving rats. We present two architectures for these targeted brain regions, both featuring 512 Pt recording electrodes patterned front-and-back on micromachined eight-shank arrays of thin-film Parylene C. These devices represent an order of magnitude improvement in both number and density of recording electrodes compared with prior work on polymer-based microelectrode arrays. We present enabling advances in polymer micro-machining related to lithographic resolution and a new method for back-side patterning of electrodes. In vitro electrochemical data verifies suitable electrode function and surface properties. Finally, we describe next steps toward the implementation of these arrays in chronic, large-scale recording studies in free-moving animal models. [2020-0109]
TL;DR: In this article, the authors investigated the phase sensitivity of magnetoelastic sensors for the detection of low-frequency and low-amplitude magnetic fields and showed that the fundamental LOD is limited by additive phase noise due to thermal-mechanical noise of the resonator, i.e. by thermally induced random vibrations of the cantilever, and by thermal-electrical noise of piezoelectric material.
Abstract: Magnetoelastic sensors for the detection of low-frequency and low-amplitude magnetic fields are in the focus of research for more than 30 years. In order to minimize the limit of detection (LOD) of such sensor systems, it is of high importance to understand and to be able to quantify the relevant noise sources. In this contribution, cantilever-type electromechanical and magnetoelastic resonators, respectively, are comprehensively investigated and mathematically described not only with regard to their phase sensitivity but especially to the extent of the sensor-intrinsic phase noise. Both measurements and calculations reveal that the fundamental LOD is limited by additive phase noise due to thermal-mechanical noise of the resonator, i.e. by thermally induced random vibrations of the cantilever, and by thermal-electrical noise of the piezoelectric material. However, due to losses in the magnetic material parametric flicker phase noise arises, limiting the overall performance. In particular, it is shown that the LOD is virtually independent of the magnetic sensitivity but is solely determined by the magnetic losses. Instead of the sensitivity, the magnetic losses, represented by the material’s effective complex permeability, should be considered as the most important parameter for the further improvement of such sensors in the future. This implication is not only valid for magnetoelastic cantilevers but also applies to any type of magnetoelastic resonator. [2020-0219]
TL;DR: In this paper, a wideband SH0 mode lithium niobate acoustic delay line (ADL) based RF oscillator has been demonstrated using the classical linear time-invariant (LTI) phase noise model.
Abstract: An RF oscillator has been demonstrated using a wideband SH0 mode lithium niobate acoustic delay line (ADL). The design space of the ADL-based oscillators is theoretically investigated using the classical linear time-invariant (LTI) phase noise model. The analysis reveals that the key to low phase noise is low insertion loss (IL), large delay ( ${\tau }_{\mathbf {G}}$ ), and high carrier frequency ( $\mathbf {f}_{\mathbf {o}}$ ). Two SH0 ADL oscillators based on a single SH0 ADL ( $\mathbf {f}_{\mathbf {o}}= 157$ MHz, IL = 3.2 dB, ${\tau }_{\mathbf {G}} = 270$ ns) but with different loop amplifiers have been measured, showing low phase noise of −114 dBc/Hz and −127 dBc/Hz at 10-kHz offset with a carrier power level of −8 dBm and 0.5 dBm, respectively. These oscillators not only have surpassed other Lamb wave delay oscillators but also compete favorably with surface acoustic wave (SAW) delay line oscillators in performance. [2019-0223]