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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.

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.

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.

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.

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 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.

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

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. >

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.

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.

Structural and electrical characteristics of silicon field emitter arrays are reported. The authors present a process using anisotropic etching of silicon, and silicon oxidation, to form self-aligned gated field emitter structures. The process uses plasma etching and oxidation to form the field emission tips, and allows control of the aspect ratio of the devices. Processing limits and process latitude are discussed. The authors observed average currents of 0.3 mu A/emitter in 1300-emitter arrays, and the emission is stable at 5*10/sup -8/ torr. The arrays exhibit a soft failure behavior, where individual emission tips fail as the gate voltage is increased, but the array as a whole continues to operate. >

Integrated planar circulator circuits operating at frequencies near 10 GHz have been fabricated using transferred film techniques. A 100 micrometer thick film of single-crystal yttrium iron garnet was transferred onto a metallized silicon die using a bond and lap-back process. The alloy bond layer was formed through a low-temperature solid-liquid interdiffusion process using films of indium and gold. This bond layer proved of sufficient strength to permit removal of the gadolinium gallium garnet substrate through grinding, but chemical analysis of the bond shows that interdiffusion occurs between the bond and metallization layers. These integrated gamet/silicon circulator circuits show good device performance.

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 µm wide, 1 µm thick, and 65 µm long. A voltage applied between the gate and the source closes the switch, connecting the source to the drain. Devices operate for more than 109 cycles in a nitrogen ambient before failure and have an initial contact resistance of less than 50 mΩ. The threshold voltages for these devices are between 30 V and 200 V. Long lifetimes are achieved with a current of 30 mA. The breakdown (stand-off) voltage between the source and the drain is greater than 100 V and the off-impedance exceeds 1012Ω. The modeling of these switches includes a structural model of the beam and a contact resistance model for the electrical contact. Preliminary contact resistance measurements are presented and compared with the modeled contact resistance characteristics.

Using a custom built contact testing system, direct current micro contact damage under hot-switching conditions was explored in ruthenium-on-ruthenium contacts operated at a contact force of approximately 400 µN. For the first time, contact damage on making and breaking contact under bias (leading and trailing edge hot switching) is compared. Trailing-edge hot switching leads to significantly higher adhesion (1.5–4 times higher) than leading-edge hot switching. The high-voltage tests (3.5 V) lead to polarity-dependent material transfer, with material moving in the direction of the electric field. The amount of material transfer does not depend strongly on the current limit from 0.78 to 380 mA. The low voltage (0.71 V) tests result in much less damage, and the material transfer does not have a clear directionality. However, the amount of damage does increase significantly as the current limit is increased from 16 to 78 mA. Also observed for the first time is a new type of high-current, short duration current spike associated with hot switching events at voltages above 1.5 V. The fact that these spikes occur at the higher voltage but not at the lower voltage suggests (but does not prove) that they are associated with the polarity dependent material transfer.

Microelectromechanical system microhotplates fabricated using silicon-on-insulator wafers were designed and fabricated for accelerated lifetime testing of thin films and nanowires. Thin films of Cr∕Ru∕Au, Cr∕Ru, and Ru were examined as well as nanowires of Ru and RuOx. Rapid thermal cycling at a 1kHz pulse frequency was employed for testing the thin films. Nanowires were characterized using 1kHz and 500Hz pulse frequencies. A 40nm layer of sputtered Au deposited on 12nm of sputtered Ru and 8nm of sputtered Cr displayed a sheet resistance of 1.18Ω∕◻ and a lifetime of 267h before failure when cycled with a peak temperature of 692K. Ru thin films with a thickness of 12nm displayed a sheet resistance of 51Ω∕◻ and a lifetime of 10h under the same conditions. Sputtered Ru and RuOx nanowires with thicknesses of 15 and 32nm, respectively, displayed resistivities of 72×10−8 and 320×10−8Ωm. It was found that the cycling frequency did not influence the nanowire lifetimes in air or in N2. Ru nanowires tested in N2 di...

The fabrication and electrical characteristics of 200-nm chromium-gated silicon field emitters are reported. These gated emitters are the smallest yet reported. A turn-on voltage of approximately 35 V represents a sublinear scaling of device operating voltage with device size. Emitter failures appear to be very similar to failures of 2- mu m devices produced using the same process. >

The emerging field of vacuum microelectronics has many promising applications including flat‐panel displays, microwave devices, and ionization sources. The technology is based on arrays of microfabricated micrometer‐scaled gated field emitters. Applications are currently limited by unacceptable reliability due primarily to failures of individual field emitters. The failure of an individual emitter produces a characteristic electrical pulse. A circuit is used to monitor and count these pulses. The technique provides a powerful tool for exploration of stable operating regimes for vacuum microelectronic devices and may be useful in other areas in which vacuum discharges must be monitored.

An emission instability attributed to an oxide layer on a silicon emitter tip surface has been characterized. The instability leads to a current runaway which often results in device failure. When device failure does not occur, the instability is a one time event while the device remains in a vacuum environment. The magnitude of the instability increases with increasing oxide thickness and can be effectively eliminated by etching in buffered HF immediately before testing or device packaging.

Rapid growth of thin SiO2 (

The effects of target voltage and substrate voltage on rf sputtered hydrogenated amorphous silicon are investigated. In the present work, the gas partial pressures and the substrate temperature are held constant, and the deposition rate nearly constant, while the substrate and target potentials are independently varied. Films sputtered at high target voltages exhibit lower photoconductivities which vary less rapidly with substrate bias. Substrate voltages greater than approximately 100 V lead to damaged material. This is evidenced by the appearance of a second conduction path 0.38 eV below the conduction band, and a decrease in photoconductivity.

Rapid growth of SiO2 on silicon is observed following annealing in argon. The enhancement may be reset many times, by annealing, for a growing oxide film. Growth kinetics of the enhancement are different than those of the often discussed initial growth regime enhancement. The anneal time required to produce enhanced growth is a factor of 10 less than that required to reduce interface trap density. Study of the phenomenon at time scales not accessible through furnace processing is made possible by the use of a rapid isothermal processor.

Surface micromachined, electrostatically actuated microswitches have been developed at Northeastern University. Microswitches have an initial contact resistance of 0.5-1 /spl Omega/, and current handling capability of about 20 mA. Typically, contact resistance degrades progressively when the switches are cycled beyond approximately 10/sup 6/ cycles. In this work, the microswitch contact resistance is studied on the basis of a simple, clean metal contact resistance model. Comparison of measured contact resistance (measured as a function of contact force) with the characteristics predicted by the model shows the measured resistance to be higher than the prediction, approximately by an order of magnitude, suggesting that insulating films at the contact interface need to be taken into account. Microswitches with a large number of parallel contacts have also been developed, and measurement data is presented showing that these devices have a current handling capability greater than 150 mA.