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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.

For surgical aortic valve replacement, the Society of Thoracic Surgeons score (STSS) is the reference standard for the prediction of operative risk. In transcatheter aortic valve implantation (TAVI) though, where the procedure itself is minimally invasive, the traditional risk assessment is supplemented by CTA. Through a consistent approach to the acquisition of high-quality images and the standardised reporting of annular measurements and adverse root and vascular features, patients at risk of complications can be identified. In turn, this may allow for a personalised procedural approach and treatment strategies devised to potentially reduce or mitigate this risk. This article provides a systematic and standardised approach to pre-procedural work-up with computed tomography angiography (CTA) and explores the current state of evidence and future areas of development in this rapidly developing field.

Atmospheric pressure plasma jets (APPJ) have great potential in wound healing, bacterial disinfection and in cancer therapy. Recent studies pointed out that hydrogels can be used as screens during APPJ treatment, or even be used as reservoirs for reactive oxygen and nitrogen species generated by APPJ in liquids. Thus, novel applications are emerging for hydrogels which deserve fundamental exploration of the possible modifications undergone by the polymers in solution due to the reactivity with plasmas. Here we investigate the possible modifications occurred by APPJ treatment of an amphiphilic poly(ethylene oxide)-based triblock copolymer (tPEO) photo-crosslinkable hydrogel. While APPJ treatments lead to a certain degradation of the self-assembly of the polymeric chains at low concentrations (2 g/L), the polymeric chains are unaffected by APPJ and the hydrogel forming ability is kept. APPJ treatments induced a pre-crosslinking of the network with an increase of the mechanical properties of the hydrogel. Overall, the small modifications induced allow thinking of polymer solutions with hydrogel forming ability a new platform for several applications related to plasma medicine, and thus, with potential in different therapies.

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.

This paper demonstrates, for the first time, a zero-power acoustic wake-up receiver for intrabody links, allowing Implanted Medical Devices (IMDs) to minimize the IDLE power consumption. This architecture is based on Directly Modulated Ultrasonic Transducers (dMUT) made of Lead Zirconate Titanate (PZT) as transmitter (TX), a Piezoelectric Micro Machined Ultrasonic Transducer (pMUT) array as receiver (RX), and a Micro Electro-Mechanical System (MEMS) switch. The role of the dMUTs and the pMUT array is to establish an acoustic link sensitive to signals as low as 50mV pp peak-peak at a distance of 10cm. This low signal triggers the switch which will turn on the IMDs from an IDLE-state to a full power mode.

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.

We introduce a new pentacene-based organic semiconductor, 5,6,7-trithiapentacene-13-one (TTPO). TTPO is a small-molecule organic semiconductor that is simple to synthesize and purify, readily crystallizes, melts in air from 386–388 °C without decomposition, and is indefinitely stable against degradation in acid-free solution. TTPO has a high molar absorptivity, optical and electrochemical HOMO–LUMO gaps of 1.90 and 1.71 eV, respectively, and can be thermally evaporated to produce highly uniform thin films. Its cyclic voltammogram reveals one reversible oxidation and two reversible reductions between +1.5 and −1.5 V. The crystal structure for TTPO has been solved and its unique parallel displaced, and head-to-tail packing arrangement has been examined and explained using high-level density functional theory. High-resolution scanning tunneling microscopy (STM) was used to image individual TTPO molecules upon assembly on a pristine Au(111) surface in ultrahigh vacuum. STM images reveal that vapor-deposited T...

The $��$-$T_3$ model is characterized by a variable Berry phase that changes continuously from $��$ to $0$. We take advantage of this property to highlight the effects of this underlying geometrical phase on a number of physical quantities. The Hall quantization of the two limiting cases is dramatically different - a relativistic series is associated with a Berry phase of $��$ and a non-relativistic series is associated with the other limit. We study the quantization of the Hall plateaux as they continuously evolve from a relativistic to a non-relativistic regime. Additionally, we describe two physical quantities that retain knowledge of the Berry phase, in the absence of a motion-inducing magnetic field. The variable Berry phase of the $��$-$T_3$ model allows us to explicitly describe the Berry phase dependence of the dynamical longitudinal optical conductivity and of the angular scattering probability.

The discovery of a superconducting phase in sulfur hydride under high pressure with a critical temperature above 200 K has provided a new impetus to the search for even higher $T_c$. Theory predicted and experiment confirmed that the phase involved is H$_3$S with Im-3m crystal structure. The observation of a sharp drop in resistance to zero at $T_c$, its downward shift with magnetic field and a Meissner effect confirm superconductivity but the mechanism involved remains to be determined. Here, we provide a first optical spectroscopy study of this new superconductor. Experimental results for the optical reflectivity of H$_3$S, under high pressure of 150 GPa, for several temperatures and over the range 60 to 600 meV of photon energies, are compared with theoretical calculations based on Eliashberg theory using DFT results for the electron-phonon spectral density $\alpha^2$F($\Omega$). Two significant features stand out: some remarkably strong infrared active phonons at $\approx$ 160 meV and a band with a depressed reflectance in the superconducting state in the region from 450 meV to 600 meV. In this energy range, as predicted by theory, H$_3$S is found to become a better reflector with increasing temperature. This temperature evolution is traced to superconductivity originating from the electron-phonon interaction. The shape, magnitude, and energy dependence of this band at 150 K agrees with our calculations. This provides strong evidence of a conventional mechanism. However, the unusually strong optical phonon suggests a contribution of electronic degrees of freedom., Comment: 10 pages, 8 figures. Main manuscript and supplementary information

The $��$-$T_3$ model extrapolates between the pseudospin $S=1/2$ honeycomb lattice of graphene and the pseudospin $S=1$ dice lattice via parameter $��$. We present calculations of the magnetic properties of this hybrid pseudospin model, namely the absorptive magneto-optical conductivity and the Hofstadter butterfly spectra. In the magneto-optics curves, signatures of the hybrid system corollary a doublet structure present in the peaks, resulting from differing Landau level energies in the $K$ and $K^{\prime}$ valleys. In the Hofstadter spectra, we detail the evolution of the Hofstadter butterfly as it changes its periodicity by a factor of three as we vary between the two limiting cases of the $��$-$T_3$ model., 12 pages, 11 figures, submitted to Phys. Rev. B on May 30, 2016

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.

A combined molecular dynamics and finite element model and simulation of contact and adhesion between a rough sphere and a flat surface has been developed. This model uses the results of molecular dynamics (MD) simulations, obtained using an embedded atom potential, of a nanoscale Ru-Ru asperity contact. A continuum finite element model of an elastic–plastic microscale Ru-Ru contact bump is then created. In this model, the surface roughness is represented by a system of nanoscale asperities, each of which is represented by a nonlinear hysteretic force vs. distance relationship. The nonlinear hysteretic character of these relations is determined from curve-fits of the MD results. Load vs. interference and contact area vs. interference are determined using this two-scale model for loading and unloading. Comparisons with a single-scale continuum model show that the effect of the nanoscale asperities is to reduce both the adhesion and the real area of contact. The choice of Ru as the material for this work is...

Due to fundamental scaling laws, the effect of surface forces becomes relatively large for microscale structures, such as MEMS. The operation of an ohmic MEMS microswitch relies on repeated make-and-break contacts, typically between each of two metal tips and a metal drain. Large contact forces are desirable for low contact resistance, but the resulting plastic deformation at this small scale, as well as the breaking through of contaminant films, further increases the adhesion force which can then exceed the restoring force of the actuator. This stuck-closed failure, also known as stiction, is a major hindrance to switch reliability and to the ultimate commercialization of these devices. In this article we review the experimental and modeling efforts which have been directed to achieving an improved understanding of adhesion in an ohmic MEMS microswitch.

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.

An elastic-plastic microcontact with adhesion was studied using a finite element model. This model differs from the existing models, in that it includes the effect of adhesion on the deformation and stresses field, making it applicable to a wide range of material properties. It shows two distinct separation modes, brittle separation and ductile separation. To the best of our knowledge this is the first time that a finite element model has predicted ductile separation in an adhesive contact. Three key parameters affecting the contact and separation modes are also discussed. Further work is expected to fully reveal the effect of these parameters on the separation modes.

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.

Finite-element simulations have been used to predict intermodulation distortion in a gold-on-gold contact-type microelectromechanical systems microswitch. The simulations are used to find the variation in switch resistance with input power that is a result of temperature-dependent electrical resistivity and thermal conductivity. This resistance variation leads to intermodulation distortion. In a similar way, a closed-form expression is found for the variation of resistance with contact force. It is found that this also produces a variation in resistance due to the input voltage variation at high frequencies, which also leads to intermodulation distortion. The sideband power due to thermal effects was found to be -103dBc for a 1-W input signal leading to a third-order intermodulation intercept point of +81.3dBm. The sideband power due to contact force effects was found to be less than -140dBc for a 1-W signal. The methods for prediction of intermodulation distortion used in this paper are applied to measured data for the variation of resistance with switch current and gate voltage, leading to predictions of intermodulation levels based on real switch parameters. The effect of contact force on intermodulation can become significant if the difference frequency of the excitation is near the natural frequency of the device.

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.

The interfacial shear stress between gold and dielectrophoretically assembled single-walled carbon nanotubes can be increased by annealing in N2, by e-beam irradiation, or by e-beam deposition of carbon. For the first time this increase has been measured, using a technique developed by this group that is based on NEMS cantilever measurements combined with modeling. Annealing increases the shear stress by more than a factor of 3 over its value of 87 MPa for untreated gold surfaces, while e-beam irradiation increases the shear stress by more than a factor of 2 and carbon deposition increases the shear stress by a smaller amount.

Many countries have an increasingly aging population. In recent years, mobile technologies have had a massive impact on social and working lives. As the size of the older user population rises, many people will want to continue professional, social and lifestyle usage of mobiles into 70s and beyond. Mobile technologies can lead to increased community involvement and personal independence. While mobile technologies can provide many opportunities, the aging process can interfere with their use. This workshop brings together researchers who are re-imagining common mobile interfaces so that they are more suited to use by older adults.

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.

Lobsters use their antennae to navigate among obstacles along the ocean floor. Effective ambulation requires that the lobster, or a biomimetic lobster robot whose behavior is patterned after a real lobster, must distinguish between antenna bending due to contact and bending due to flow. The analysis presented here shows that the key feature appears to be the taper of the antennae. The curvature of a tapered antenna due to an end-load is nearly constant whereas the curvature distribution due to flow is nearly a quadratic function of the arc-length measured from the tip of the antenna.

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.

Microfabricated multiple-channel glass chips were successfully interfaced to an electrospray ionization mass spectrometer (ESI-MS). The microchip device was fabricated by standard photolithographic, wet chemical etching, and thermal bonding procedures. A high voltage was applied individually from each buffer reservoir for spraying sample sequentially from each channel. With the sampling orifice of the MS grounded, it was found that a liquid flow of 100-200 nL/min was necessary to maintain a stable electrospray. The detection limit of the microchip MS experiment for myoglobin was found to be lower than 6 x 10(-8) M. Samples in 75% methanol were successfully analyzed with good sensitivity, as were aqueous samples. The parallel mutliple-channel microchip system allowed ESI-MS analysis of different samples of standard peptides and proteins in one chip.

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.

A novel and effective technique is developed to make the first determination of shear stress between dielectrophoretically assembled single-walled carbon nanotubes (SWNTs) and surfaces. The results demonstrate that we can vary the shear stress by a factor of 20 by functionalizing a gold surface with different alkanethiols. The interfacial shear stress between a small bundle of SWNTs and a gold surface with and without self-assembled monolayers of alkanethiol (2-phenylethanethiol or 2-aminoethanethiol) is determined. The measurements are based on simple NEMS cantilever beams, a nanomanipulator, and a scanning electron microscope (SEM). It is emphasized that the measured quantity is the slack in the nanotube (not the shear stress) induced by the nanomanipulation. The shear stress is determined from the slack through a mechanics model. An average shear stress of 87 MPa between SWNTs and gold surfaces is obtained. For the tests on the self-assembled 2-aminoethanethiol surface, an average shear stress of 142 MPa is obtained. For the self-assembled 2-phenylethanethiol surface, the shear stress is determined to be around 7.2 MPa with an estimated work of adhesion of 0.5 J/m(2).

This paper presents a finite element approach for modeling a thermal-electrical-mechanical coupled-field contact comprised of an elastic hemisphere pressed against an elastic half-space. The goal of this investigation is to develop a fundamental understanding of the behavior of this multiphysics contact, with a particular interest on the contact area through which current flows. The results from the model illustrate a distinct difference in contact behavior between force control and displacement control in the presence of an applied electrical potential/current. It is shown that, while Hertz contact theory can be used to accurately predict the behavior of the contact under force control, a new relationship is established to accurately predict the behavior of the contact under displacement control.

A finite element model of a layered hemisphere contacting a rigid flat, which includes the effect of adhesion, is developed. In this analysis elastic-plastic material properties were used for each of the materials comprising the layered hemisphere. The inclusion of the effect of adhesion, which was accomplished with the Lennard-Jones potential, required a special procedure. This configuration is of general theoretical interest in the understanding of adhesion. It has also been suggested as a possible design for a microswitch contact because, with an appropriate choice of metals, it has the potential to achieve low adhesion, low contact resistance, and high durability. The effect of the layer thickness on the adhesive contact was investigated. In particular the influences of layer thickness on the pull-off force, maximum contact radius, and contact resistance were determined. The results are presented as load versus interference and contact radius versus interference for loading and unloading from different values of the maximum interference.

This paper presents a novel and easily controllable method for measurement of the interaction of single-wall carbon nanotubes (SWNTs) with surfaces using simple cantilever beams, a nanomanipulator, and a scanning electron microscope (SEM). A small SWNT bundle is assembled across two cantilevers by dielectrophoresis, with one cantilever much more flexible than the other. The flexible cantilever is then pushed away from the stiffer cantilever in order to produce slip between the SWNTs and the cantilever surface. When the cantilever returns to its initial position, axial slack is observed in the SWNTs. A theoretical model has been developed to calculate the shear stress between the SWNT bundle and the cantilever surface, based on the measured axial slack. For a gold cantilever surface, an average interfacial shear stress of 113 MPa was obtained.

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