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ObjectivesWe aimed to explore the impact of the COVID-19 pandemic on cardiac diagnostic testing and practice and to assess its impact in different regions in Europe.MethodsThe online survey organised by the International Atomic Energy Agency Division of Human Health collected information on changes in cardiac imaging procedural volumes between March 2019 and March/April 2020. Data were collected from 909 centres in 108 countries.ResultsCentres in Northern and Southern Europe were more likely to cancel all outpatient activities compared with Western and Eastern Europe. There was a greater reduction in total procedure volumes in Europe compared with the rest of the world in March 2020 (45% vs 41%, p=0.003), with a more marked reduction in Southern Europe (58%), but by April 2020 this was similar in Europe and the rest of the world (69% vs 63%, p=0.261). Regional variations were apparent between imaging modalities, but the largest reductions were in Southern Europe for nearly all modalities. In March 2020, location in Southern Europe was the only independent predictor of the reduction in procedure volume. However, in April 2020, lower gross domestic product and higher COVID-19 deaths were the only independent predictors.ConclusionThe first wave of the COVID-19 pandemic had a significant impact on care of patients with cardiac disease, with substantial regional variations in Europe. This has potential long-term implications for patients and plans are required to enable the diagnosis of non-COVID-19 conditions during the ongoing pandemic.

We describe an aluminum nitride (AlN)-based resonant switch for use in a near zero power radio frequency (RF) wake-up receiver. A folded beam structure with a slot compensates for the curvature caused by the stress gradient in the sputtered AlN film and ensures that the released contact gap is approximately equal to the designed contact gap. A 80 kHz resoswitch with a Q of 8600 and an actuation gap of approximately 600 nm turns on when a −4 dBm, 800 MHz signal, square wave modulated at 80 kHz, is applied to the actuator. This AlN electrostatic resonant switch is designed to enable integration with a high gain AlN RF piezoelectric transformer to form a complete ultra-low power RF receiver.

Micromechanical photoswitches (MPs) have shown orders of magnitude lower standby power consumption compared to their solid-state technology-based counterparts. In this paper, we demonstrate that the infrared detection threshold (i.e., the lowest detectable power of incident infrared radiation) of this new type of photoswitch can be effectively decreased by applying a bias voltage across the switch without compromising its key feature of near-zero standby power consumption and low false-alarm rate. We show that by exploiting the electrostatic pull-in effect (using bias voltage of ~7 V), a threshold as low as 76 nW can be achieved, which is the lowest threshold demonstrated to date for MPs. A mathematical model predicting the device threshold under a bias voltage is derived and verified by experiments. Furthermore, the effects of the bias on the device’s stability are carefully studied suggesting the existence of a tradeoff between the detection threshold and the false-alarm rate when the bias is higher than 85% of the pull-in voltage. The source of the instability that causes false alarms is found to originate from charge accumulation over time in the dielectric substrate surrounding the bottom contact, which we believe can be mitigated by an improved contact design. Another effect associated with high bias is the contact stiction after infrared-triggered pull-in. To address this, a microheater is integrated into the switch to reopen the contacts while consuming only $\sim 0.5~\mu \text{J}$ per operation. This paper thus presents an effective solution for post-fabrication threshold adjustment of MPs, which is useful for applications requiring variable thresholds.

Infrared light of specific wavelength triggers a passive microsystem capable of producing a digitized output bit. State-of-the-art sensors use active electronics to detect and discriminate light1,2,3, sound4,5, vibration6,7 and other signals8,9. They consume power constantly, even when there is no relevant data to be detected, which limits their lifetime and results in high costs of deployment and maintenance for unattended sensor networks. Here we propose a device concept that fundamentally breaks this paradigm—the sensors remain dormant with near-zero power consumption until awakened by a specific physical signature associated with an event of interest. In particular, we demonstrate infrared digitizing sensors that consist of plasmonically enhanced micromechanical photoswitches (PMPs) that selectively harvest the impinging electromagnetic energy in design-defined spectral bands of interest, and use it to create mechanically a conducting channel between two electrical contacts, without the need for any additional power source. Our zero-power digitizing sensor prototypes produce a digitized output bit (that is, a large and sharp off-to-on state transition with an on/off conductance ratio >1012 and subthreshold slope >9 dec nW–1) when exposed to infrared radiation in a specific narrow spectral band (∼900 nm bandwidth in the mid-infrared) with the intensity above a power threshold of only ∼500 nW, which is not achievable with any existing photoswitch technologies.

Residual stress gradients often negatively affect the performance of MEMS devices, causing film curvature and changing the designed gaps of released structures. In this work, we built folded beams designed to compensate for the film curvature and keep the actuator gaps of sensitive resonant switches constant. While the average stress gradient is cancelled by our designs, we find that random variations in the stress gradient (rather than random variations in device dimensions) cause the majority of the observed variation in actuator gap. To our knowledge, this has not previously been reported, and represents an important limitation on MEMS designs using sputtered films. The standard deviation of the 400 nm contact gap for a folded beam of total length 152 µm and width 108 µm was measured to be about 134 nm. Using parameters measured from test cantilevers, our simulations predict that about 98% of the variation in contact gap is due to stress gradient variation, rather than variations in device geometry.

Zero-power infrared (IR) sensors based on Plasmonically-enhanced Micromechanical Photoswitches (PMPs) have recently been demonstrated, showing the capability to detect IR signatures with near-zero standby power consumption. However, current prototypes fail to discriminate between a targeted IR source (e.g. a flame) and a spurious one (e.g. an exhaust plume) having overlapping IR emission wavelengths, potentially getting triggered ON in the presence of strong interference and creating false alarms. This paper reports on the first experimental demonstration of a PMP augmented with an integrated passive false-alarm prevention mechanism to effectively desensitize it to spurious IR sources while maintaining a small footprint and near-zero standby power consumption. By incorporating two different narrowband plasmonic absorbers on a PMP - one tuned to the targeted IR wavelength and the other to a spurious wavelength - we show that the electrical contacts close in response to IR radiation at the targeted wavelength and remain open in the presence of spurious wavelengths, thereby preventing false alarms. Such an enhanced PMP prototype targeting flame detection with a threshold ~600 nW (minimum detectable IR power) is demonstrated showing zero false alarm to interfering IR sources. The increased reliability enabled by this technique makes PMP technology an ideal candidate for the implementation of large-scale maintenance-free wireless sensor networks with unlimited battery lifetimes.

Since the mid-1990s, political polarization has been on the rise in the U.S. as Democratic and Republican parties have become increasingly dichotomized ideological structures, where loyalists are either for or against a particular issue. While claims of differences may be more media hyperbole than realistic, affective polarization, where there is increased animosity between parties, is on the rise (Abramowitz & Webster, 2016; Iyengar, Sood, & Lelkes, 2012; Iyengar & Westwood 2015; Mason, 2015). Drawing from theories in the fields of social psychology, political science, and network science, we investigate the extent to which community-building is possible on social media platforms, where partisanship has forced Americans to choose sides on politically charged issues. Analyzing 81,316 tweets circulated on the day of and following the Day of Action for Net Neutrality on July 12, 2017, we test whether social media platforms can assuage the often heated offline tensions on politically charged topics and present brokers that can help online users work through their differences, or toward compromise. In support of research that suggests that social media platforms are mere “echo chambers” for existing groups, we also conclude that this will not change unless the construction of human social networks are considered, alongside the existing technical architecture of social media platforms that maintains the dominance of like-minded associations. Tempering the online influence of political leaders, particularly legislators and organizations may also foster more productive conversations. Thus, we conclude with suggestions for how social media companies can work towards the goal of community building by connecting users with brokers, individuals who span the divide between politically disconnected communities.

This paper reports on the first demonstration of an infrared (IR) wireless sensor node (WSN) with near-zero standby power consumption. The prototype presented here employs a plasmonically-enhanced micromechanical photoswitch (PMP) that exploits the energy contained in the impinging IR spectral band of interest itself, to perform passive sensing and digitizing functions. The palm-sized IR WSN demonstrated in this work comprises a vacuum-packaged PMP (IR power threshold ∼284 nW, lithographically-defined IR absorptance: ∼89% at 4.6 μm, 0.75 μm bandwidth) connected to a CMOS load-switch which wakes up a coin battery-powered sub 1-GHz wireless microcontroller to transmit data when the IR signal of interest is detected. The standby power consumption for the IR WSN was measured to be just ∼2.6 nW: a >1900X improvement over state-of-the-art pyroelectric IR WSNs, while offering integrated spectral-selectivity. This work represents the first demonstration of an OFF-but-alert WSN that awakens only in the presence of a signal of interest, resulting in near-unlimited battery-life when deployed to detect infrequent but time-critical events.

This paper reports on the first experimental demonstration of threshold scaling of near-zero standby power micromechanical photoswitches with bias voltage. By leveraging electrostatic actuation, we show that the infrared (IR) power detection threshold of a plasmonically-enhanced micromechanical photoswitch (PMP) can be improved by over one order of magnitude (from ∼1.3 μW to ∼76 nW) while maintaining near-zero power consumption in standby. Such an improvement of threshold directly translates to an over 4 times increased detection range when the PMP is used for standoff detection of hot exhaust plume. Furthermore, the demonstrated technique also enables postfabrication trimming of the device contact gap for achieving desired threshold, which is particularly useful for adapting the device to detect changing IR radiation. The unprecedented combination of near-zero standby power consumption and ultralow threshold of our PMP technology paves the way for the development of unattended IR sensor nodes with dramatically extended lifetime and detection range.

This paper reports the first experimental demonstration of a near-zero power (

Resonant switches (resoswitches) using a novel design and fabrication process are reported. A folded beam structure compensates for the stress-gradient-induced bending in the sputtered AlN material and ensures that the free end of the center actuated beam is in plane with the anchor beams. A 21.14 kHz resoswitch with a Q of over 2000 and an actuation gap of 1.3 μm is turned on at the resonant frequency with a 0.5dBm 800MHz carrier that is square wave modulated at 21.14 kHz. This demonstration shows the feasibility of monolithically integrating a high gain RF piezoelectric transformer with a high-Q electrostatic resoswitch for a zero stand-by power RF wake-up receiver.

This paper reports on the first demonstration of a passive light-actuated micromechanical relay (LMR). Differently from any existing switching element, the proposed LMR relies on a plasmonically-enhanced thermomechanical coupling to selectively harvest the impinging electromagnetic energy, in a specific spectral band of interest, and use it to mechanically create a conducting channel between the device terminals without the need of any additional power source, which directly translates into a near-zero standby power consumption. The first of a kind prototype presented here is selectively activated by an ultra-narrow band radiation in the mid-wavelength infrared (IR) spectral region (−5.5 μm). The strong and spectrally selective absorptivity (−95% at 5.5 μm with a full width at half maximum of ∼1.1 μm) and the high thermomechanical coupling of the fabricated structure result in the first experimental demonstration of a LMR with an ultra-low actuation threshold of only 950 nW suitable for the realization of a new class of zero-power IR digitizers capable of producing a quantized output bit in the presence of a unique IR spectral signature of interest.

Nearly two-thirds of Americans use smartphones to access the Internet. Among these users, 10 percent of Americans who own a smartphone do not have any other form of high-speed Internet access at home beyond their basic data plan, while others have no data plan at all. According to recent data from Pew Research Center, vulnerable populations that include low-income and less literate populations are more likely to be smartphone-dependent when compared to others that are less reliant on their mobile devices. Further, these same populations also tend to be unbanked, uninsured, transient, or those living with other family members and friends.Given these life circumstances and how certain populations are accessing the Internet, it is imperative that regulatory policies encourage consumer access to critical information that include employment, education, health-related resources, and government services. While reforms to make the cost of broadband affordable are significant in supporting vulnerable groups, programs that offer free or low-cost online content to these groups should be equally encouraged.In 2015, the Federal Communications Commission’s (FCC) Open Internet, or net neutrality rules, prescribed standards around consumers’ accessibility to online content. In particular, these rules, primarily directed to certain network operators or Information Service Providers (ISPs), prohibit the blocking of online content, services, applications, and devices; and discouraged the unreasonable degradation of certain online traffic. The Open Internet rules also ban the throttling and prioritizing of traffic, and institute “common carriage,” or a Title II framework that applies to both wireline and wireless services. While many scholars concluded that the 2015 Open Internet rules delivered the essential elements requested by the net neutrality advocates, the FCC also permitted under the net neutrality framework zero-rated services that, if viewed as pernicious, could be subjected to the “general conduct standard” that prohibits unreasonable conduct by ISPs, particularly when there are perceived consumer harms or anti-competitive behaviors. By definition, zero rating is the practice of offering online content at no cost, or free, to consumers. The content can direct consumers to certain online content, or a series of web sites, again for free, in a manner that doesn’t count against consumers’ data caps or, in some cases, can be accessed without an existing data plan. In some business arrangements between network operators and content providers, zero-rated services do not have an exchange of funds between the distributor and the content creator, while in other instances, the foregone costs are reimbursed to operators through a practice referred to as “sponsored data.” Given this definition, this paper will argue that zero rating, online content has a direct public and consumer benefit in buffering the economic vulnerabilities associated with unmanaged online data use that usually results in fees and surcharges due to consumer overages. This paper will also discuss that this practice also provides the incentive to consumers and carriers to access the more socially beneficial aspects of the Internet, simply because they have the data. This paper will dive into the arguments that present these practices as net neutrality violations and share case studies on companies that are deploying zero-rated services. Finally, this paper will assert that any blanket ban of this practice by the FCC runs counter to the agency’s Open Internet bright line rules and has the potential to choke the experimentation of services that could potentially accelerate broadband access.

In this paper we present a 3D nonlinear dynamic model which describes the transient mechanical analysis of an ohmic contact RF MEMS switch, using finite element analysis in combination with the finite difference method. The model includes real switch geometry, electrostatic actuation, the two-dimensional non-uniform squeeze-film damping effect, the adherence force, and a nonlinear spring to model the interaction between the contact tip and the drain. The ambient gas in the package is assumed to act as an ideal and isothermal fluid which is modeled using the Reynolds squeeze-film equation which includes compressibility and slip flow. A nonlinear contact model has been used for modeling contact between the microswitch tip and the drain electrode during loading. The Johnson–Kendall–Roberts (JKR) contact model is utilized to calculate the adherence force during unloading. The developed model has been used to simulate the overall dynamic behavior of the MEMS switches including the switching speed, impact force and contact bounce as influenced by actuation voltage, damping, materials properties and geometry. Meanwhile, based on a simple undamped spring–mass system, a dual voltage-pulse actuation scheme, consisting of actuation voltage (Va), actuation time (ta), holding voltage (Vh) and turn-on time (ton), has been developed to improve the dynamic response of the microswitch. It is shown that the bouncing of the switch after initial contact can be eliminated and the impact force during contact can be minimized while maintaining a fast close time by using this open-loop control approach. It is also found that the dynamics of the switch are sensitive to the variations of the shape of the dual pulse scheme. This result suggests that this method may not be as effective as expected if the switch parameters such as threshold voltage, fundamental frequencies, etc. deviate too much from the design parameters. However, it is shown that the dynamic performance may be improved by increasing the damping force. The simulation results obtained from this dynamic model are confirmed by experimental measurement of the RF MEMS switches which were developed at the Northeastern University. It is anticipated that the simulation method can serve as a design tool for dynamic optimization of the microswitch. In addition, the approach of tailoring actuation voltage and the utilization of squeeze-film damping may provide further improvements in the operation of RF MEMS switches.

We have designed and characterized a MEMS-based Fabry–Perot device (MFPD) to measure vibration at high temperatures. The MFPD consists of a micromachined cavity formed between a substrate and a top thin film structure in the form of a cantilever beam. When affixed to a vibrating surface, the amplitude and frequency of vibration are determined by illuminating the MFPD top mirror with a monochromatic light source and analyzing the back-reflected light to determine the deflection of the beam with respect to the substrate. Given the device geometry, a mechanical transfer function is calculated to permit the substrate motion to be determined from the relative motion of the beam with respect to the substrate. Because the thin film cantilever beam and the substrate are approximately parallel, this two-mirror cavity arrangement does not require alignment or sophisticated stabilization techniques. The uncooled high-temperature operational capability of the MFPD provides a viable low-cost alternative to sensors that require environmentally controlled packages to operate at high temperature. The small size of the MFPD (85–175 µm) and the choice of materials in which it can be manufactured (silicon nitride and silicon carbide) make it ideal for high-temperature applications. Relative displacements in the sub-nanometer range have been measured and close agreement was found between the measured sensor frequency response and the theoretical predictions based on analytical models.

As an essential part of an optical imager project, there was the need for a very high aspect ratio MEMS optical scanning mirror (5 mm ? 150 ?m clear aperture), capable of a ?2? sweep at 1 kHz with an applied voltage less than 200 V. This paper reports on the design, fabrication, modeling and testing of such an electrostatically actuated MEMS mirror. Fabrication involves using a 1?0?0 n-type double side polished silicon wafer, along with surface and bulk micromachining techniques, to produce a mirror with nickel torsion springs and nickel electrostatic actuators. There were 8 masks and 20 processing steps required. The performance of these devices was measured and found to be within the required specifications. Analysis involved developing models to predict the dynamic behavior of these MEMS micromirrors. A basic parallel plate capacitor model was adjusted with finite element analysis to account for fringing fields. Young's modulus of the electroplated nickel was determined to be 110 GPa from a comparison of the model with the results of dynamic testing, and the residual strain test structures led to a value of 0.0029 for the residual strain. Each of these values is within the rather wide range of published values. Once these values were determined, the model agreed very well with the measurements of the dynamic angular response of the mirror.

A technique for performing nanomechanical testing of free-standing structures using contact scanning mode atomic force microscopy (AFM) has been developed and implemented. The technique consists of performing a contact mode scan of an area of a cantilever test structure as well as of an area that does not deform. The use of two different values of the force during the scan allows the effect of the topography of the test structure to be eliminated. Also note that in this constant force scan, the bending moment in the test cantilever changes continuously with the position of the applied force, allowing both the stress and strain to change even though the force remains constant. With the dimensions of the structure known, material properties (i.e. the elastic modulus) can be determined from the relationship between the applied force and the structural deflection. This method is not susceptible to nonlinearities in the AFM photodetector and allows for piezo drift during testing to be quantified and corrected. 50 nm thick chromium cantilever structures were fabricated for testing using electron-beam lithography. The determination of the elastic modulus gave consistent results as the AFM tip was scanned along the cantilever. As is the case with AFM fixed position force–displacement measurements, the accuracy of the results is affected by uncertainties in the measured AFM cantilever stiffness and by uncertainties in the test structure dimensions. This testing method can be performed by any AFM capable of scanning in the contact mode without requiring specialized software. Fabrication of the cantilevers requires only a single-mask process.

Microelectromechanical devices are increasingly being integrated into electronic circuitry. One of these types of devices is the microswitch, which acts much like a three-terminal field-effect transistor (FET). While various microswitches are currently being developed, their dynamic behavior is not well understood. Upon closing, switches bounce several times before making permanent contact with the drain. In this paper, a time-transient finite difference analysis is used to model the dynamic behavior of two different electrostatically actuated microswitch configurations. The model uses dynamic Euler-Bernoulli beam theory for cantilevered beams, includes the electrostatic force from the gate, takes into account the squeeze-film damping between the switch and substrate, and includes a simple spring model of the contact tips. The model and simulation can be used as design tools to improve switch performance and reduce switch bounce in future designs.

Surface micromachined, electrostatically actuated microswitches have been developed at Northeastern University. Microswitches with gold contacts typically have an initial contact resistance of the order of 0.1 Ω over the first 10 5 cycles of lifetime while cold-switching 4 mA, and have a current handling capability of about 20 mA. In general, the contact resistance decreases over the first few thousand switch cycles, and degrades progressively when the switches are cycled beyond approximately 10 6 cycles. In this work, the microswitch contact resistance is studied on the basis of a clean metal contact resistance model. Comparison of the measured contact resistance (measured as a function of contact force) with the characteristics predicted by the model shows approximate agreement. The discrepancies between the model characteristics and measurements are discussed briefly.

Single-crystal scandium-substituted barium hexaferrite crystals have been characterized and used in the fabrication of miniature monolithic circulators on silicon-glass wafers. The single crystal has an anisotropy field of 8700 Oe, saturation magnetization of 3900 G, and ferromagnetic resonance linewidth of 100 Oe. Microstrip impedance transformers were fabricated on the surrounding glass substrate to facilitate the testing and make fabrication compatible with semiconductor processing. Through-reflect-line (TRL) was used to calibrate the insertion loss and reflection due to the exponentially tapered microstrip transformer. The insertion losses are reasonably low for both unsaturated and saturated bias magnetic field conditions. Operation of the circulator has been measured at Ka-band frequencies both above and below the ferromagnetic resonance frequency.

In this paper, we discuss our work on surface micromachined microswitches and microrelays that are based on electroplated materials. We have successfully fabricated devices with lifetimes exceeding 107 cycles cold switched at current levels exceeding 10 ma. Contact resistance is consistently below one ohm for a single contact. Multiple contact devices have much lower effective contact resistance. ©1999 John Wiley & Sons, Inc. Int J RF and Microwave CAE 9: 338–347, 1999.

We have analytically formulated the problem that a ferrite circulator junction is biased by a nonuniform magnetic field. Interport impedances of the junction can, therefore, be solved numerically. Nonuniform-bias field will reduce the transmission bandwidth, and the circulation condition is apt to be altered if the bias field shows nonuniformity near the center of the junction. Our calculation compares very well with measurements.

We have calculated the S-parameters and losses in ferrite-film-junction circulators using a new effective-field theory assuming TEM-like propagation. Conductivity loss dominates the dielectric and magnetic losses in Y-junction circulators fabricated on ferrite films with thicknesses less than 200 /spl mu/m. It is plausible to fabricate Y-junction thin-film circulator at X-band with insertion loss less than 0.5 dB if the film thickness is larger than 100 /spl mu/m. The quality of the conductor plane is important in reducing the overall insertion loss of the thin-film-junction circulator.

Micromechanical switches and relays realized by a simple surface micromachining process are presented. The devices use a nickel cantilever beam and gold-to-gold electrical contact, and are electrostatically actuated. They have lifetimes exceeding 109 cycles, and a current handling capability of 150 mA.

Micromechanical switches have been fabricated in electroplated nickel using a four-level surface micromachining process. The simplest devices are configured with three terminals, a source, a drain, and a gate and are 30 /spl mu/m wide, 1 /spl mu/m thick, and 65 /spl mu/m long. A voltage applied between the gate and source closes the switch, connecting the source to the drain. Devices switch more than 10/sup 9/ cycles before failure and exhibit long-lifetime hot switching currents up to 5 mA. The initial contact resistance is less than 50 m/spl Omega/. The breakdown (stand-off) voltage between the source and the drain is greater than 100 V and the off-current is less than 20 fA at 100 V.

Although metal-to-metal direct contact MEMS switches are a promising alternative to solid state switches in RF communication systems, the reliability of their electrical contacts has proven to be a barrier to entry to the market. Hot switching is known to have the most damaging effect on the contacts although an understanding of all the mechanisms leading to this damage is a work-in-progress. In this investigation, a customized Atomic Force Microscope was used to study the electrical contacts. The contacts were cycled at approach rates of 115 μm/s, 440 μm/s and 4400 μm/s and at different polarities. While material transfer is confirmed to be the primary source of contact damage, the results suggest that two different mechanisms could be at play at the leading and trailing edge of a hot switched cycle. A polarity driven mechanism and a contact separation rate dependent mechanism were observed. Low-level transient currents up to a few μA that may or may not be related to the material transfer, were observed at the leading edge of the switching cycle.

This paper describes the hot switching damage in a MEMS switch contact. Under hot switched conditions, material transfer leading to contact erosion causes the performance of RF MEMS switches to degrade over their lifetime. Hot switching performance of RF MEMS switches is one of the major reliability issues and is presently affecting the marketability of these devices despite their proven advantages over solid state switches which are currently used in RF systems. The phenomena leading to such damage both at the leading and trailing edge of a switching cycle are investigated in this paper.

This paper presents a finite element method approach for modeling a thermal-electrical-mechanical coupled-field contact comprised of an elastic hemisphere and an elastic half space. The goal of this model is to develop a fundamental understanding of the behavior of a multi-physics contact with a particular interest in the contact area. The results from the model illustrate a clear difference in contact behavior between force control and displacement control in the presence of an applied electrical potential. It is shown that, while Hertzian contact theory can be used to accurately predict the behavior of the contact under force control, a new relationship must be established to accurately predict the behavior of the contact under displacement control. This relationship can be applied to RF MEMS switch contact bumps as well as macro scale electrical contacts.Copyright © 2011 by ASME

Planar microstrip Y-junction circulators have been fabricated from metallized 130-/spl mu/m-thick self-biased strontium hexaferrite ceramic die, and then bonded onto silicon die to yield integrated circulator circuits. The impedance matching networks needed to transform the low-impedance circulator outputs were deployed on low-loss alumina or glass dielectrics to minimize circuit losses. These magnetically self-biased circulators show a normalized isolation and insertion loss of 33 and 2.8 dB, respectively, and a 1% bandwidth for an isolation of 20 dB. Application of small (H

Intrinsic failures of gated field emitters have been studied. The gate-emitter voltage drops from typical values of 140 V to 10-70 V in less than 10 ns at the onset of a failure. Measurements with an electrostatic probe indicate that plumes of ions and electrons are ejected into vacuum. The measured ion current to the probe is typically 10% of the electron current. The voltage during the event and the ion-to-electron current ratio measured at the probe are characteristic of a cathodic vacuum arc plasma. For series resistors less than 1 k Omega , the arc is continuous, while the series resistors greater than 10 k Omega , the arc is intermittent. Initiation of the failure based on ion-space charge enhancement of the emitter electric field is modeled with the plasma simulation code PDS1. These structures provide a controlled geometry for studying arcs of micron size dimension. >

The current through the buried oxides of single- and multiple-implant SIMOX and bond and etchback silicon-on-insulator (BESOI) wafers was measured as a function of radiation dose. From these measurements, conductivity and static capacitances are derived. High-frequency capacitances were also measured. Leakage current through the buried oxide of multiple-implant SIMOX is considerably less than that of single-implant SIMOX (more than an order of magnitude). High-frequency and static capacitances, as a function of total dose, were used to study the buried-oxide-top-silicon interface and the buried-oxide-bottom-silicon interface. Multiple implant had fewer interface traps than single implant at prerad and after irradiation. >

A multifunctional optical MEMS sensor system that can be used for the simultaneous measurement of displacement, temperature, and pressure has been fabricated. The system is based on an array of micromachined Fabry-Perot devices suitable for high temperature and pressure operations. The central concept of the sensor system is that airflow force around the moving structure (air viscous damping) strongly affects the oscillating height of the microcavity and hence, the mechanical performance of the device. The major effect that the viscosity and the density of the air have on the damping provides the mechanism for the simultaneous detection of pressure and temperature in addition to displacement. Since the air is trapped by the viscous damping effects there is no need for a sealed cavity. In addition, the very simple configuration in the optical interferometric system can be considered for the integration in the sensor system package. A model to accurately predict the frequency response of the Fabry-Perot structure subjected to a mechanical excitation on the substrate at different pressures and temperatures is presented. The model shows that shifts of the order of 10.5°C and 7.46psi can be detected for temperatures and pressures around 536°C and 446psi respectively using 90μm long microcantilever beams vibrating at a frequency of 97.4 kHz. To the best of our knowledge, this sensor array is one of the few, if not the only MOEMS device in the literature capable of simultaneous measurement of displacement, temperature, and pressure in high temperature environments.

Three key parameters describing contacts with adhesion were identified in previous investigations. Here a series of finite element simulations of a single load/unload cycle of a contact are performed to study the impact of each of these parameters. The results show that one parameter (S) is most important in determining the separation mode, i.e. brittle or ductile separation. Smaller S leads to brittle separation while larger S gives ductile separation. The transition between the two separation modes occurs at about S = 1.2 which corresponds to the theoretical stress being somewhat greater than the hardness.Copyright © 2007 by ASME

In this paper, we present some current research issues in contact failures in ohmic RF MEMS microswitches. Such experimental and modeling research encompasses contact mechanics (including elastic, plastic, and adhesive contacts) and the related phenomena of brittle and ductile separation. Furthermore the contact interface is not static, but rather is known to evolve over the lifetime of the switch. Also discussed are contamination failures.Copyright © 2007 by ASME

This paper presents the design, fabrication and testing results of a Fabry-Perot Micro-Opto-Mechanical Device (FPMOD) used as a vibration sensor. The un-cooled high-temperature operational capability of the FPMOD provides a viable low-cost alternative to sensors that require environmentally controlled packages to operate at high temperature. The FPMOD is a passive MEMS device that consists of a micromachined cavity formed between a substrate and a top thin film structure in the form of a cantilever beam. When affixed to a vibrating surface, the amplitude and frequency of vibration are determined by illuminating the FPMOD with a monochromatic light source and analyzing the back reflected light to determine the deflection of the beam with respect to the substrate. Given the Fabry-Perot geometry, a mechanical transfer function is calculated to permit the substrate motion to be determined from the relative motion of the beam with respect to the substrate. Because the thin film cantilever beam and the substrate are approximately parallel, this convenient two-mirror cavity arrangement needs no alignment, no reference arm, and no sophisticated stabilization techniques. The small size of the FPMOD (85-175μm), the choice of materials in which it can be manufactured (Silicon Nitride and Silicon Carbide), and its simple construction make it ideal for harsh high-temperature applications. Relative displacements in the sub-nanometer range have been measured and close agreement was found between the measured sensor frequency response and the theoretical predictions based on analytical models.

A finite element model was built to study the contact of a micro hemisphere in elastic-plastic contact with a rigid flat. The effect of adhesion on the deformation and stress fields is included, using the Lennard-Jones potential, which makes this model applicable to a wide range of the Tabor parameter. Both loading and unloading are considered. In the case of Ruthenium (Ru), the results demonstrate reasonable agreement with a previous model applicable to the DMT region. However for a Gold (Au) contact, which is in the JKR region, the results differ significantly.Copyright © 2006 by ASME

Production of truly monolithic microwave integrated circuits that incorporate ferrite passive control elements has been hindered by the material property mismatches between ferrites and semiconductors. In this work, monolithic Y-junction circulators were fabricated by bonding 100-/spl mu/m-thick single-crystal yttrium iron garnet films to silicon at 195/spl deg/C, and then removing the gadolinium gallium garnet substrate. S-parameter measurements on the circulator and matching microstrip circuit yield an isolation of 20 dB over a 1 GHz bandwidth at 9 GHz, with a minimum insertion loss near 1 dB. Improvements in circuit design and fabrication techniques may yield monolithic circulators that are fully compatible with large-scale semiconductor manufacturing methods.

This paper presents a method for predicting the size of intermodulation products due to contact heating in a contact type MEMS microswitch. The primary origin of intermodulation distortion in the microswitch is the variation of the switch resistance at the difference frequency due to the temperature dependence of the resistivity and thermal conductivity of materials in the switch. This varying resistance modulates the high frequency signals, resulting in intermodulation products. The resistance of the switch was modeled using a finite element simulation that predicted resistance variations at a variety of frequencies and power levels. This procedure leads to IIP3 predictions on the order of +64.8 dBm for this switch. This result corresponds to a sideband power of -73.3 dBc for a 1 W input.

This paper reports the measurement and theoretical analysis of noise in surface micromachined tunneling tip devices. The devices are fabricated using the surface micromachining technology. The bending beams and proof masses are formed by electroplating of nickel and gold. The tips are made by plating metal on the partially etched sacrificial layer. Noise spectra are obtained and compared for different electrode materials and different operating pressures. The results show that 1/f noise dominates in the low frequency region and the 1/f noise level in the vacuum is lower than that in air ambient. A mathematical model is established to simulate the 1/f noise related to surface adsorption-desorption process.

A monolithic circulator junction has been fabricated on a single-crystal Sc-doped Ba-hexaferrite film transferred onto a silicon substrate. Operation of the circulator has been measured at Ka-band for both above and below ferromagnetic resonance (FMR). The circulator junction is operational even when the ferrite substrate is partially magnetized.

Using an AFM-based test setup, experiments were performed on Ru microcontacts under a variety of leading and trailing edge hot switching conditions, including different voltages, different currents, different polarities (including bipolar and ac up to 20?MHz), and different approach and separation rates. It was found that hot switching damage is a complex phenomenon for microcontacts. It consists of a number of different mechanisms occurring simultaneously to different degrees depending on the hot switching conditions. It was determined through a combination of experiments and models that the mechanisms leading to contact erosion operate when the electrodes are separated by less than a few ? or are barely touching. For leading edge hot switching, i.e. hot switching when the contacts are closing, the main damage mechanism was found to be associated with currents less than 0.15?mA. Pre-contact currents were observed on uncleaned contacts and were not found to contribute to contact damage. Despite the damage caused by hot switching, it was found that unless the contact material is almost or completely eroded, hot switching does not lead to high contact resistance or high adhesion on Ru contacts. Under bipolar hot switching conditions, microcontacts with a 400??N contact force maintained a contact resistance of less than 1?? and a pull-off force less than 60??N for more than 100 million cycles.