Showing papers in "IEEE\/ASME Journal of Microelectromechanical Systems in 2017"

Review of MEMS Electromagnetic Vibration Energy Harvester

Abstract: This paper mainly introduces the research progress of MEMS electromagnetic vibration energy harvester, hoping to provide valuable guidance and reference for researchers in related fields. In this paper, recent studies are divided into three groups according to their objectives and approaches: reducing the resonant frequency of the harvester to collect low frequency vibration energy from the environment; broadening the bandwidth of the harvester to increase the utilization of the random vibration energy; and developing new process compatible with MEMS for mass production. Besides, maintaining valuable output performances, such as power and power density, is also an important concern in these studies. Limited to the current technology, it is impossible to make a perfect harvester with low resonant frequency, wide frequency band, good compatibility with MEMS, and good output performances at the same time. However, we can focus on one or two characteristics according to the application, to which this paper provides valuable reference. More works on simulation, new process, and detailed design of the components are required in MEMS electromagnetic vibration energy harvesters.

Ultra-Low Resonant Piezoelectric MEMS Energy Harvester With High Power Density

Abstract: We demonstrate a microscale vibration energy harvester exhibiting an ultra-low resonance frequency and high power density. A spiral shaped microelectromechanical system (MEMS) energy harvester was designed to harvest ambient vibrations at a low frequency ( $\mu \text{m}$ -thickness exhibiting remanent polarization of 36.2 $\mu \text{C}$ /cm2 and longitudinal piezoelectric constant of 155 pm/V was synthesized to achieve high efficiency mechanical to electrical conversion. The experimental results demonstrate an ultra-low natural frequency of 48 Hz for MEMS harvester. This is one of the lowest resonance frequency reported for the piezoelectric MEMS energy harvester. Further, the position of the natural frequency was controlled by modulating the number of spiral turns and weight of the proof mass. The vibration mode shape and stress distribution were validated through a finite element analysis. The maximum output power of 23.3 nW was obtained from the five turns spiral MEMS energy harvester excited at 0.25 g acceleration and 68Hz. The normalized area and the volumetric energy density were measured to be $5.04\times 10^{-4}~ \mu \text{W}$ /mm $^{2}~\cdot ~\text{g}^{2}~\cdot$ Hz and $4.92\times 10^{-2} ~ \mu \text{W}$ /mm $^{3}~\cdot ~\text{g}^{2}~\cdot$ Hz, respectively. [2017-0018]

A Review of On-Chip Micro Supercapacitors for Integrated Self-Powering Systems

Abstract: Miniaturized self-powering systems that integrate both energy harvesters and energy storage units as the power sources are essential to realize maintenance-free wireless sensor networks, implantable medical devices, and active radio frequency identification systems. On-chip micro supercapacitors (MSCs) are promising candidates for energy storage in such systems by providing high power densities, fast charge/discharge rates, and long cycle life. Researchers have been improving the performances, especially energy and power densities, of MSCs in recent years. This paper reviews the fundamental working mechanisms and design considerations of on-chip MSCs with special emphasis on the advantages of 3-D configurations. Typical fabrication methods are summarized, and their effects on the device performance and system integration are analyzed. In particular, the power generation of micro energy harvesters and the power consumption of typical wireless micro systems are surveyed, providing the basic and targeting performance requirements of future MSCs that can be integrated with them. [2017-0069]

Thermoresistive Effect for Advanced Thermal Sensors: Fundamentals, Design Considerations, and Applications

Abstract: Microelectromechanical systems sensors have been intensively developed utilizing various physical concepts, such as piezoresistive, piezoelectric, and thermoresistive effects. Among these sensing concepts, the thermoresistive effect is of interest for a wide range of thermal sensors and devices, thanks to its simplicity in implementation and high sensitivity. The effect of temperature on the electrical resistance of some metals and semiconductors has been thoroughly investigated, leading to the significant growth and successful demonstration of thermal-based sensors, such as temperature sensors, convective accelerometers and gyroscopes, and thermal flow sensors. In this paper, we review the fundamentals of the thermoresistive effect in metals and semiconductors. We also discuss the influence of design and fabrication parameters on the thermoresistive sensitivity. This paper includes several desirable features of thermoresistive sensors and recent developments in these sensors are summarized. This review provides insights into how it is affected by various parameters, and useful guidance for industrial designers in terms of high sensitivity and linearity and fast response. [2017-0022]

Design, Fabrication, and Characterization of Scandium Aluminum Nitride-Based Piezoelectric Micromachined Ultrasonic Transducers

Abstract: This paper presents the design, fabrication, and characterization of piezoelectric micromachined ultrasound transducers (PMUTs) based on scandium aluminum nitride (ScxAl1–xN) thin films (x = 15%). ScAlN thin film was prepared with a dual magnetron system and patterned by a reactive ion etching system utilizing chlorine-based chemistry with an etching rate of 160 nm/min. The film was characterized by X-ray diffraction, which indicated a crystalline structure expansion compared with pure AlN and a well-aligned ScAlN film. ScAlN PMUTs were fabricated by a two-mask process based on cavity SOI wafers. ScAlN PMUTs with 50- and 40- $\mu \text{m}$ diameter had a large dynamic displacement sensitivity measured in air of 25 nm/V at 17 MHz and 10 nm/V at 25 MHz, twice that of AlN PMUTs with the same dimensions. The peak displacement as a function of electrode coverage was characterized, with maximum displacement achieved with an electrode radius equal to 70% of the PMUT radius. Electrical impedance measurements indicated that the ScAlN PMUTs had 36% greater electromechanical coupling coefficient ( $\text{k}_{\mathrm {t}}^{2})$ compared with AlN PMUTs. The output pressure of a $7\times7$ ScAlN PMUT array was 0.7 kPa/V at ~1.7 mm away from the array, which is approximately three times greater that of an $8\times8$ AlN PMUT array with the same element geometry and fill factor measured at the same distance. Acoustic spreading loss and PMUT insertion loss from mechanical transmit to receive were characterized with a 15 $\times $ 15 ScAlN PMUT array via hydrophone and laser Doppler vibrometer. [17509-2017]

A Wireless Passive Pressure and Temperature Sensor via a Dual LC Resonant Circuit in Harsh Environments

Abstract: This paper presents a passive wireless sensor for simultaneously and remotely measuring pressure and temperature under harsh environments. The sensor consists of a dual $LC$ (inductor and capacitor) resonant circuit, one without a cavity and the other with a cavity capacitor for temperature and pressure sensing, respectively. The low-temperature co-fired ceramic technology is used to fabricate the sensor, making it suitable for high-temperature harsh environment operations. Experimental results show the prototype sensor has temperature sensitivity of 8.15 kHz/°C and pressure sensitivity of 1.96 MHz/Bar up to 400°C. [2016-0157]

Single Chip Gas Sensor Array for Air Quality Monitoring

Abstract: This paper describes the fabrication of a four element gas sensor array for monitoring air pollutants, namely CO, CO2, NO2, and SO2. The four micro-heaters share a single suspended SiO2 diaphragm, utilizing thermal proximity to achieve low power consumption (~10 mW for 300 °C). Plasma enhanced chemical vapour deposition SiO2 diaphragm is demonstrated to give higher yield compared with thermally grown SiO2. Sensor array elements are fabricated by customizing each element to sense a specific gas, using different sensing materials. Optimized thin films of ZnO, BaTiO3-CuO doped with 1% Ag, WO3, and V2O5 are used for selective sensing of CO, CO2, NO2, and SO2. Four sensors can be independently controlled to operate at different temperatures to get high selectivity for test gases. The sensor array is packaged on Kovar header, and then characterized for gas sensing. It is demonstrated that the sensors exhibit good sensitivity and selectivity. We report a maximum repeatable response to CO (~78.3% for 4.75 ppm), CO2 (~65% for 900 ppm), NO2 (~1948.8% for 0.9 ppm), and SO2 (~77% for 3 ppm) at operating temperatures of 330 °C, 298 °C, 150 °C, and 405 °C, respectively. [2016-0047]

Anchor Loss in Hemispherical Shell Resonators

Abstract: Micromachined hemispherical shell resonators (HSRs) can be used in high accuracy vibratory gyroscopes. These resonators need to have very low energy loss to achieve very high quality factor. Energy might be lost through the anchor, fluid-structure interaction, thermoelastic dissipation, phonon-phonon and phonon-electron interactions, and the resonator surface. This paper investigates energy loss through the anchor of HSRs using a numerical approach. To numerically determine wave radiation from the anchor to the infinite substrate, a perfectly matched layer is used around a finite substrate. Anchor loss investigations in HSRs are classified into four categories. First, the effects of shell properties-material, geometry, and imperfections-are investigated. Second, the relationships between anchor loss and properties of the stem, such as material, geometry, and stemshell misalignments, are studied. Third, the effects of substrate characteristics-substrate material, attachment material between the stem and substrate, and attachment configuration of the substrate and stem-are investigated. Finally, the effects of external motions, such as shock and rotation, are analyzed. It is found that anchor loss in HSRs strongly depends on the shell, stem, and substrate properties. This study also shows that any imperfection in the shell or any misalignment between the shell and stem increases anchor loss by orders of magnitude.

Fabrication of Novel MEMS Microgrippers by Deep Reactive Ion Etching With Metal Hard Mask

Abstract: The fabrication of a novel class of microgrippers is demonstrated by means of bulk microelectromechanical systems (MEMS) technology using silicon on insulator wafer substrates and deep reactive ion etching. Hard masking is implemented to maximize the selectivity of the bulk etching using sputtered aluminum and aluminum–titanium thin films. The micro-roughness problem related to the use of metal mask is addressed by testing different mask combinations and etching parameters. The O2 flow, SF6 pressure, wafer temperature, and bias power are examined, and the effect of each parameter on micro-masking is assessed. Sidewall damage associated with the use of a metal mask is eliminated by interposing a dielectric layer between silicon substrate and metal mask. Dedicated comb-drive anchors are implemented to etch safely both silicon sides down to the buried oxide, and to preserve the wafer integrity until the final wet release of the completed structures. A first set of complete devices is realized and tested under electrical actuation. [2017-0039]

Surface-Micromachined Capacitive RF Switches With Low Actuation Voltage and Steady Contact

Abstract: In this paper, we report fabrication and dynamic characterization of low-actuation-voltage capacitive radio frequency microelectromechanical systems (RF MEMS) switches with improved electromechanical performance. Electromechanical and electromagnetic modeling is used to modify the previously known geometries of switches and the number and size of holes in them to improve their overall dynamic characteristics. The switches are fabricated on a Pyrex glass substrate using a low-complexity four-mask surface micromachining process. These designs of MEMS switches require only 4.8-6.2 V as pull-in voltage. The dynamic behavior of these MEMS switches is investigated experimentally. Measured mechanical resonant frequency and quality factor are found to be in the range of 7.56-10.7 kHz and 1.1 to 1.2, respectively. Measured switching times for all the designs are 33-37 μs at their respective pull-in voltages. These switches show bounce-free switching during contact and fast settling after release. Two of the switch designs have insertion loss of less than 0.25 and 0.7 dB at 20 and 40 GHz, and isolation better than 30 dB. Close agreement between experimentally measured and simulation results demonstrates successful realization of fast-switching capacitive RF MEMS switches at low voltage. [2016-0152].

RF MEMS Inductors and Their Applications--A Review

Abstract: Inductors are primary elements in many radio frequency circuitries and devices. This review gives a comprehensive survey on the developments and performances of fixed and variable RF MEMS inductors. MEMS inductors are the core of this review due to their high-yield performances and the wide choices of possible tuning techniques. First, the factors that constrain high-performance micro coils and the conventional solutions to overcome them are highlighted. Next, this paper systematically reviews varieties of MEMS inductors starting with the fixed inductors and according to inductors' topologies and performance enhancement techniques. In addition, the variable types of inductors are subsequently discussed, mainly from the point of view of their tuning techniques. Many quantitative comparisons are given in terms of the values of quality factor, inductance, self-resonance frequency, and tuning range. This will provide readers with an overall evaluation of different studies and assist them in choosing the inductors' topologies and layouts that best suit their applications. This review also sheds light on different and most common RF MEMS inductors applications, including RF communication devices and wireless sensors and actuators applications. Finally, this paper summarizes the best fabrication and tuning approaches inferred from the reviewed works and discusses some design guidelines to achieve better inductor performance.

Profile Evolution of High Aspect Ratio Silicon Carbide Trenches by Inductive Coupled Plasma Etching

Abstract: Micromachining silicon carbide (SiC) is challenging due to its durable nature. However, plasma and laser etch processes have been utilized to realize deep and high aspect ratio (HAR) features in SiC substrates and films. HAR topologies in SiC can improve SiC-based MEMS transducers (reduced electrostatic gaps) and enable embedded substrate cooling features. Our process used inductive coupled plasma (ICP) etching with sulfur hexafluoride (SF 6 ) and oxygen (O 2 ) and an electroplated Ni hard mask. We examine the formation of SiC trenches by observing aspect-ratio-dependent and time-dependent etch rate and topography in 4H-SiC substrates. In addition, we studied the effect of ICP etch parameters, such as RF bias power (25-100 W), pressure (5-15 mTorr), and O 2 flow fraction (10%-40%), on etch rate and topography. Our process resulted in SiC etch rates between 0.27 and 0.75 μm/min with aspect-ratio-dependent and depth-dependent characteristics. We observed trench profiles that evolve from square (low AR) to “W” (medium AR) and converged “V” (HAR) shapes. Finally, we report the highest aspect ratio (18.5:1) trench achieved to date in 4H-SiC via ICP etching, which supports many SiC-based MEMS applications.

Thermoelastic Dissipation in Micromachined Birdbath Shell Resonators

Abstract: Many MEMS gyroscopes rely on micro mechanical resonators to measure angular rotation. Maximizing their quality factor ( $Q$ ) will help improve accuracy. There are several energy dissipation mechanisms that limit $Q$ . This paper studies the role of thermoelastic dissipation (TED) in micro birdbath shell resonators. Fully coupled thermo-mechanical equations of physical behavior are solved for these shells using a finite-element method. Furthermore, an analytical model is developed to predict TED. The effects of material properties, shell geometry, edge chipping around the shell rim, trimming approaches, thin-film coatings, and operating temperature on thermoelastic $Q$ ( $Q_{{TED}})$ are studied. It is found that the shell material properties and rim thickness have significant impact on $Q_{{TED}}$ . However, edge chipping and most of the shell geometrical parameters do not have large impact. Additionally, this paper shows that some trimming approaches, such as forming grooves along the rim, can improve $Q_{{TED}}$ . A study of the effect of metal coatings on the resonator on $Q$ shows that the coating thickness and material are important factors affecting $Q$ and $Q_{{TED}}$ . The results presented in this paper provide guidelines for the design of other similar high- $Q$ resonators. [2016–0027]

ScAlN MEMS Cantilevers for Vibrational Energy Harvesting Purposes

Abstract: Piezoelectric energy harvesting offers the possibility to make use of ambient vibrations most beneficially to feed low power sensor nodes. This paper demonstrates the fabrication and characterization of piezoelectric cantilevers with AlN and Sc x Al 1-x N (x = 27%) thin films for the evaluations of their energy harvesting performance. The characterization mainly focuses on the measurement of the output power at variable load resistance to achieve maximum power output. Superior properties of ScAlN thin films for energy harvesting compared with AlN films are confirmed. Furthermore, an analytical model is employed to extract material parameters for ScAlN. High piezoelectric coefficients e 31 = 1.6 C/m 2 and d 31 = 6.9 pm/V are determined for ScAlN. Finally, a proof mass is attached to further increase the output power at optimized load resistance.

Silicon-Based Monolithic Planar Micro Thermoelectric Generator Using Bonding Technology

Abstract: A technology of planar micro thermoelectric generators (μTEGs) with double thermal deflections is presented in this letter. We focus on the development of an original technic of bonding pillars etched on a first silicon wafer onto the fragile membranes of a second silicon wafer. The monolithic devices realized are able to convert waste heat into electrical power. The maximum output power for a live-membranes-based μ TEG is 12.3 μ W/cm 2 , for an input power of 2 W/cm 2 . This kind of μ TEG has a high thermal resistance. It is deduced to be 44.3 K/W, which allows a heat adaptation to any environment with a high thermal resistance.

Stress Effects and Compensation of Bias Drift in a MEMS Vibratory-Rate Gyroscope

Abstract: Long-term gyroscope drift can be effectively removed by employing simultaneous on-chip stress and temperature compensation. Stress effects are significant and their inclusion augments the commonly applied temperature compensation. A silicon-on-insulator matched-mode z-axis vibratory-rate gyroscope, as a prototype testbed to study these effects, includes released silicon resistors connected in a Wheatstone bridge as on-chip stress sensors. The gyroscope is ovenized within 300 K ± 20 mK using an external heater and an on-chip temperature sensor to suppress the temperature effects. The gyroscope is in-house vacuum packaged and operated at matched closed-loop drive and sense modes. Stress compensation significantly suppresses long-term drift resulting in 9°/h/√Hz angle random walk and 1°/h bias instability at 10000 s (around 3 h) averaging time, which is seven times improvement over the uncompensated gyroscope output. The sensitivity of zero-rate offset to stress is -0.22°/day/Pa and -0.045°/day/Pa for the tests with and without externally applied stress, respectively.

A Review on Development and Optimization of Microheaters for High-Temperature In Situ Studies

Abstract: Microelectromechanical systems (MEMS)-based sample carriers became a breakthrough for in situ inspection techniques, especially in transmission electron microscopy where the sample carrier functions as a microsized laboratory and enables dynamic studies on samples, such as nanoparticles, nanowires, lamellas, and 2-D materials. Microheaters allow for in situ manipulation of samples by applying heat stimuli such that sample properties and interactions can be studied in real time at elevated temperatures. However, currently developed microheaters still suffer from undesired effects such as mechanical deflection and limitations in temperature range, accuracy, and homogeneity. This review discusses advancements in the technological development of microheaters. Methods and results found in the literature are categorized to provide an overview of optimization methods for thermoelectromechanical design aspects. The knowledge from various application fields, including a critical reflection on mesoscopic material properties, is combined into a series of design guidelines. These compose instructions for developing and optimizing microheater characteristics, such as mechanical and thermal stress, temperature accuracy and homogeneity, power consumption, response time, and sample drift. Although this review and guide are applicable to many application fields that require a microheater, an emphasis is laid on aspects most relevant to the microheater as a high-temperature sample carrier for in situ experiments. [2017–0149]

Experimental Observation of Noise Reduction in Weakly Coupled Nonlinear MEMS Resonators

Abstract: In this paper, we present the strongly nonlinear behavior of a 2-degree-of-freedom weakly coupled microelectromechanical systems (MEMS) resonator system in a mixed nonlinear regime, using a closed-loop phase feedback oscillator approach. Three out of four nonlinear bifurcation points within a strongly nonlinear coupled resonator system, with both electrical and mechanical nonlinearities, were revealed. Furthermore, we are able to study the amplitude and frequency stabilities of the resulting system when biased at the bifurcation points. Specifically, we discover that, as compared with the linear case, orders of magnitude improvement in amplitude and frequency signal resolution can be observed at the nonlinear bifurcation points, demonstrating that coupled nonlinear MEMS resonators can be useful for enhancing the amplitude and frequency stability for relevant applications. [2017-0092]

Magnetic Tuning of Nonlinear MEMS Electromagnetic Vibration Energy Harvester

Abstract: Ambient mechanical vibrations are an untapped yet attractive energy source for powering wireless sensor nodes in the upcoming Internet-of-Things. Here we demonstrate the magnetically induced frequency tuning effect in a MEMS electromagnetic vibrational energy harvester. Spiral-shaped springs and double-layer copper micro-coils are fabricated on silicon substrate using MEMS fabrication processes. Numerical simulations and finite-element analysis exhibit substantial transformation in the potential energy and stiffness profiles due to controlled changes in the magnetic repulsion force between the transducing and tuning magnets, which effectively modifies the frequency response profile. Specifically, by increasing the repulsive interaction between the transducing and tuning magnets, both the linear and nonlinear frequency response profiles can be shifted toward higher frequencies. This experimentally validated magnetic tuning mechanism can potentially be implemented in MEMS vibrational energy harvesters with other transduction mechanisms and in other micro-mechanical oscillators for broader frequency response tunability.

On-Chip Dynamic Mode Atomic Force Microscopy: A Silicon-on-Insulator MEMS Approach

Abstract: The atomic force microscope (AFM) is an invaluable scientific tool; however, its conventional implementation as a relatively costly macroscale system is a barrier to its more widespread use. A microelectromechanical systems (MEMS) approach to AFM design has the potential to significantly reduce the cost and complexity of the AFM, expanding its utility beyond current applications. This paper presents an on-chip AFM based on a silicon-on-insulator MEMS fabrication process. The device features integrated xy electrostatic actuators and electrothermal sensors as well as an AlN piezoelectric layer for out-of-plane actuation and integrated deflection sensing of a microcantilever. The three-degree-of-freedom design allows the probe scanner to obtain topographic tapping-mode AFM images with an imaging range of up to 8μm × 8μm in closed loop.

MEMS for Nanopositioning: Design and Applications

Abstract: Nanopositioners are high-precision mechatronic devices that are capable of generating mechanical motion with nanometer or sub-nanometer resolution. With this motion typically being available over mechanical bandwidths of several kilohertz or greater, nanopositioners have become important tools for many areas of nanotechnology. A major development in nanopositioning has been the use of microelectromechanical systems (MEMS) fabrication processes to produce microscale nanopositioners. These MEMS-based devices are conceptually similar to their macroscale counterparts, typically comprising an end effector, actuators, sensors, and suspension structures. However, MEMS nanopositioners potentially offer additional significant advantages as a result of their microfabricated nature, including a much smaller footprint, higher bandwidth, batch manufacturability, and potential for integration with electronic circuits. This paper reviews key concepts regarding the design, actuation, and sensing of MEMS nanopositioners, and explores how they have been implemented in state-of-the-art devices within a range of nanotechnology applications.

Design, Optimization, and Realization of a High-Performance MOEMS Accelerometer From a Double-Device-Layer SOI Wafer

Abstract: An ultrasensitive single-axis out-of-plane micro optical electro mechanical system (MOEMS) accelerometer with a relatively low cross-axis sensitivity based on a designated micromachined sensing structure and grating interferometry cavity is proposed. While seeking to achieve high performances, we investigated and optimized the design of the mechanical structure, with tensile stress in the flexure close to the ultimate yield strength of monocrystalline silicon. Expressions for acceleration-displacement sensitivity are given and compared with the results of finite-element-method simulations. The highly symmetric accelerometer was fabricated through a particular fabrication process on a specific double-device-layer silicon-on-insulate wafer. The acceleration-displacement sensitivity of the optimal sensing structure, as obtained from static acceleration measurement, was $158.20~\mu \text{m}$ /g and outperforms its previously reported counterparts. Experimental results revealed that the MOEMS accelerometer with an optimal design achieved an acceleration sensitivity of 2485 V/g with a resonant frequency of 34.5 Hz and a noise level of 185.8 ng/(Hz) $^{0.5}$ , corresponding to a resolution of $1~\mu \text{g}$ , as well as a cross-axis sensitivity of 3.48%/0.1 g, which is one order smaller than the conventional one. The proposed design may pave the way for the applications that require extremely high sensitivity, low cross-axis sensitivity, and comparatively low-frequency response, such as seismology and microgravity detection. [2017-0034]

Parametric Noise Reduction in a High-Order Nonlinear MEMS Resonator Utilizing Its Bifurcation Points

Abstract: An electrostatically actuated non-linear microelectromechanical systems (MEMS) resonator can describe double hysteresis behavior in the measured frequency response due to the interplay between electrical and mechanical non-linearities in the system. This paper provides the first experimental mapping of the stable and unstable branches of the frequency response of a MEMS resonator describing a double hysteretic frequency response using a closed-loop phase feedback oscillator. Furthermore, the frequency stability of the oscillator is compared for varying amplitude and phase feedback conditions, and it is experimentally demonstrated that parametric noise up-conversion can be suppressed in such a system by suitably biasing the resonator at one of the four bifurcation points in such a system. This result is qualitatively consistent with theoretical prediction and demonstrates that improved frequency stability in a non-linear MEMS oscillator is possible by suitably biasing the resonator using simultaneous amplitude and phase feedback.

Lithium Niobate MEMS Chirp Compressors for Near Zero Power Wake-Up Radios

Abstract: This paper presents the first demonstration of chirp compressors based on laterally vibrating modes in suspended lithium niobate thin films. Both shear-horizontal and length-extensional modes have been explored and demonstrated with the electromechanical coupling coefficients of 30% and 39%, respectively, in a double-dispersive delay line structure. The high electromechanical coupling, along with the low propagation loss in the suspended thin film, produces a low insertion loss of 10 dB over a large fractional bandwidth of 50%. The best fabricated device demonstrates a delay-bandwidth product of 100, and provides a voltage gain of 5 to the corresponding chirp signals. Moreover, significant signal-to-noise ratio enhancements (>100), collectively enabled by the processing gain and filtering characteristics of the chirp compressors, have been demonstrated. The measured devices, in this paper, greatly outperform state-of-the-art chirp compressors based on surface acoustic waves in insertion loss for a comparable TB . As a result, signal-to-noise ratio enhancement and voltage gain have been simultaneously demonstrated for the first time in a passive device and the analog domain. The high performance can be harnessed to greatly enhance the sensitivity of near zero power wake-up radio receivers and enable low-power wireless connectivity for Internet of Things applications. [2017–0126]

DRIE Trenches and Full-Bridges for Improving Sensitivity of 2-D Micromachined Silicon Thermal Wind Sensor

Abstract: This paper presents the design, fabrication, and performance of a micromachined silicon thermal wind sensor with improved sensitivity. Deep reactive ion etching (DRIE) trenches are fabricated between the heater and the thermistors to suppress the lateral heat conduction in the chip. In addition, eight thermistors symmetrically arranged in four directions around the heater form two Wheatstone full-bridges, resulting in about 50% increase of the sensitivity with respect to four thermistors. Based on these two methods, the sensitivity of the micromachined silicon thermal wind sensor is improved remarkably, which is verified by the experiment. The results show that the measurement wind speed range is up to 33 m/s in constant voltage (CV) mode with the initial heating power of 256 mW. The sensitivity is measured to be 29.37 mV/ms−1 at the wind speed 3.3 m/s, achieving improvement of about 226%, compared with that of the traditional wind sensor. Wind direction measurement results show that airflow direction over the full range of 360° is determined with an accuracy of ±5°. [2017-0052]

High Figure of Merit Nonlinear Microelectromagnetic Energy Harvesters for Wideband Applications

Abstract: We report a new approach for designing high-performance microelectromechanical system (MEMS) electromagnetic energy harvesting devices, which can operate at low frequency (<;1 kHz) over the ultrawide bandwidth of 60-80 Hz. The output power from the devices is increased significantly at a low optimized load and this overall enhancement in performances is benchmarked using a "power integral (Pf)" figure-of-merit. The experimental results show that the efficient nonlinear designs produce large Pf values, giving rise to one of the highest normalized Pf densities among the reported MEMS scale nonlinear energy harvesting devices. This improvement is achieved by suitably designing the nonlinear spring architectures, where the nonlinearity arises from the stretching strain of the specifically designed fixed-fixed configured spring arms under large deflections and gives rise to wideband output response. Different fundamental modes of the mechanical structures are brought relatively close, which further widens the power-frequency response by topologically varying the spring architectures and by realizing the same using the thin silicon-on-insulator substrate using MEMS processing technology. In addition, we have used the magnet as proof mass to increase the output power in contrary to conventional approach of using the coil as the proof mass in micro-electromagnetic energy harvesters. The high performance obtained from the MEMS energy harvesters with integrated double layer micro-coil is compared with the same using wire wound copper coil. The experimentally obtained results are qualitatively explained by using a finite-element analysis of the designed structures.

High Accuracy Resonant Pressure Sensor With Balanced-Mass DETF Resonator and Twinborn Diaphragms

Abstract: The design and fabrication of a resonant pressure sensor based on balanced-mass double-ended tuning fork resonator with twinborn diaphragms are described. It is shown that the thermal stress and the out-of-plane displacement of the vibrating beams of the resonator could be significantly reduced by adopting some appended structures. The simulation results of the frequency versus pressure relationship of the sensor also match the theoretical analysis over the full scale very well. The sensor is fabricated by dry/wet etching and silicon bonding technology with 4' silicon structure layer and 7740 glass cap. System in packaging is performed with cuboid glass tube to isolate thermal stress. The vacuum packaged sensor is electrostatically excited to vibration, which yields a high Q-factor of 22795. To compensate and calibrate the sensor under temperature influence, the polynomial algorithm is used. Under self-excited oscillation via an automatic gain control circuit, the sensor is characterized of an experimental maximum error of 0.021%FS over the range 20-185 kPa. Measurements also show a pressure sensitivity larger than 20 Hz/kPa and a zero-load resonant frequency of about 34 kHz. As such, the resonant pressure sensor can be applied in high accuracy pressure measurements.

Scaling and Performance Analysis of MEMS Piezoelectric Energy Harvesters

Abstract: Vibrational energy harvesters have been phenomenally adopted to absorb energy from mechanical vibrations and convert them into electrical energy. Power developed by such harvesters depends significantly on material properties and harvester geometry. Moreover, the power generated by micro-scale harvesters scales down rapidly. Hence, it is important to find scaling rules that ensure maximum power generation irrespective of the harvester size. In this paper, we derive an expression for the power generated by a piezoelectric harvester of a unimorph topology and show how this expression can be decomposed into five multiplicative factors representing size scaling, composition, inertia, material, and power factor (SCIMP). We present explicit expressions for each factor and show how these factors can be used for optimizing the performance of a harvester. The proposed factors provide an intuitive and insightful method for exploring an unwieldy multidimensional design space along five vectors that are particularly amenable to constraint-based choices a harvester designer has to make. The proposed method of analysis results in unique performance indices, enabling the comparison of harvester performance across different designs. We compute and compare the power developed by several MEMS harvesters reported in the literature using our method and show how this method can be used effectively for designing MEMS scale harvesters.

A Closed-Loop Readout Configuration for Mode-Localized Resonant MEMS Sensors

Abstract: This letter presents the first experimental results on the closed-loop characterization of a mode-localized microelectromechanical resonator system. Comparisons between the closed-loop oscillator approach and the open-loop frequency sweep approach show good agreement of output metrics including the amplitude ratios and mode frequencies. This new approach enables real-time measurements using emerging mode-localized resonant sensors and represents an important step toward realizing sensors based on this measurement principle.

The Design and Analysis of Piezoresistive Shuriken-Structured Diaphragm Micro-Pressure Sensors

Abstract: This paper presented a novel 0-3 kPa piezoresistive pressure sensor with high sensitivity and linearity. A shuriken-structured diaphragm (SSD) is designed for the first time to solve the conflict between the sensitivity and linearity for piezoresistive pressure sensors. A trade-off between the stress on the diaphragm edge and the deflection of the diaphragm was achieved by this SSD design according to the numerical simulation. The effects of the glass substrate and the passivation films on the sensing performance were also studied numerically and experimentally. The experimental results indicated the present pressure sensor had a sensitivity of 4.72 mV/kPa/V and a linearity of 0.18 %FSO (full scale output) in the pressure range of 0-3 kPa, which were 28.3% and 50% better than the previous works.