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ABSTRACT: This paper considers the electromechanical response of electrostatic actuators that are driven by both voltage and charge. The model system is an electrostatic actuator in which the suspended electrode is subjected to a driving voltage and the fixed electrode, which is electrostatically floating, is loaded by charge. The response of the system is analyzed using energy methods, and it is shown that the system has two distinct pull-in voltages. It is also shown that the amplitude of charge on the floating electrode is proportional to the average of these two pull-in voltages. Test-actuators were designed, fabricated, and characterized, and their measured response validates the theoretical predictions. A nondisruptive measurement of charge is proposed and demonstrated which enables to monitor charge decay over time.
Journal of Microelectromechanical Systems 03/2011; · 2.10 Impact Factor
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ABSTRACT: This paper reports on the modeling, fabrication, and testing of cantilever- and parallel plate-based laterally actuated platinum-coated polysilicon nanoelectromechanical (NEM) relays. The polysilicon acts as the structural layer, while the platinum serves as a conducting contact material, as well as a local routing layer. The two-part cantilever design utilizes a source made of a compliant beam in series with a stiff bridged perimeter electrode to reduce the secondary pull-in of the source to the gate. The parallel-plate-based relay also uses stiffened electrodes in addition to serpentine structures that reduce the actuation voltage. Overdrive gate voltage in excess of 100% without failure and sharp release of the relay from output are achieved for polysilicon relays with 50nm platinum coating and 500nm actuation gap.
Micro Electro Mechanical Systems (MEMS), 2011 IEEE 24th International Conference on; 02/2011
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ABSTRACT: We demonstrate a temperature sensor consisting of a 2-dimensional, Silicon (Si), Photonic Crystal (PC) attached to the facet of a standard single-mode optical fiber. The 2-D PC sensors are fabricated on standard Si wafers, using a single mask and a combination of isotropic and anisotropic etching, and micro-assembled onto the facets of the optical fibers by Si welding. The temperature of the Si-PC sensor is monitored by measuring its reflectance spectrum in the 1250 nm to 1650 nm wavelength range. The measured reflectivity peak shifts from 100°C to 700°C is 0.1036 nm/°C. The observed spectral shift and temperature sensitivity are significantly higher than other high temperature fiber Bragg grating sensors, and comparable to long-period fiber gratings sensors. The high sensitivity along with the compactness and robustness gives these sensors the strong potential for use in harsh environments.
Sensors, 2010 IEEE; 12/2010
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ABSTRACT: This paper reports the parallel internal electrostatic transduction of a laterally driven Lamé-mode polysilicon resonator. The transducer is fabricated using a manufacturable double nanogap process, where the 50 nm silicon nitride dielectric layers are formed on sidewalls of an optically defined trench by a conformal deposition, which is followed by refilling the trench with a doped polysilicon electrode layer. The transduction electrodes are placed and oriented to maximize electromechanical transduction efficiency for the fundamental Lamé mode. A 128.15 MHz Lamé-mode resonator is driven and sensed differentially, resulting in a motional resistance of 30 kΩ and the quality factor of Q > 12 000 in air.
Journal of Micromechanics and Microengineering 10/2010; 20(11):115036. · 2.11 Impact Factor
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ABSTRACT: This paper presents the characterization of sealed microelectromechanical devices and their packaging fabricated in a polycrystalline 3C silicon carbide (poly-SiC) thin-film encapsulation process. In this fabrication technique, devices are sealed with a nominally 2-??m low-pressure chemical vapor deposition poly-SiC, and the device layer is simultaneously coated with a nominally 0.2- ??m poly-SiC thin film. Device characterization includes measurement of the resonant frequency and the quality factor of double-ended tuning-fork micromechanical resonators, which have a Si-SiC composite beam structure. Experimental results show that the pressure inside the packaging can be controlled from 447 Pa to 15.5 kPa with a 400??C annealing process. The frequency drifts of the encapsulated resonators are less than the frequency noise level (??10.6 ppm) measured over 29 days at 84.6??C ??0.1??C, which suggests that the poly-SiC thin-film packaging technique can offer hermetic packaging for various applications in microelectromechanical systems including inertial sensors. In addition to the packaging performance, the temperature coefficient of Young's modulus for poly-SiC is derived from the resonant-frequency change of resonators with temperature. The reduction of the quality factor due to the poly-SiC coating, predicted in the theoretical model, is confirmed by measurements.
Journal of Microelectromechanical Systems 05/2010; · 2.10 Impact Factor
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ABSTRACT: This paper reports on lateral nanoelectromechanical (NEM) relays based on variations of a two- or three-mask titanium nitride (TiN) sidewall stringer process. Electrically isolated TiN perimeter beams are fabricated from stringers formed on the inside walls of polysilicon trenches, yielding 200 nm wide TiN fins and 200 nm gaps; these dimensions are 3X smaller than the resolution limit of the optical lithography tool (600 nm) utilized. The reduction in the operating voltage is about a factor of 5 compared to 600 nm wide polysilicon beams. Simple scaling could potentially enable sub-1V operation. Five-terminal NEM relays demonstrate successful switching in both directions over 1000 DC-sweep cycles with low drain bias (100 mV).
Micro Electro Mechanical Systems (MEMS), 2010 IEEE 23rd International Conference on; 02/2010
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ABSTRACT: This paper reports internal electrostatic transduction of the 41<sup>st</sup> radial bulk-mode of a ring resonator at 2.75 GHz with a quality factor of 7200 in air. The transducer electrodes are integrated within the vibrating structure in a dense serpentine pattern and strategically placed on the nodal lines to excite the 41<sup>st</sup> order bulk radial mode. The serpentine dielectric transduction results in a low motional resistance of 475 ¿ detected by direct two-port measurements. This resonator is fabricated by a double nanogap process, where 30 nm Si<sub>3</sub>N<sub>4</sub> sidewall layers are formed using a combination of optically defined trenches and deposition of a high-¿ dielectric followed by a doped polysilicon layer.
Micro Electro Mechanical Systems (MEMS), 2010 IEEE 23rd International Conference on; 02/2010
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ABSTRACT: We demonstrate that monolithic 2-dimensional photonic crystals (PCs) confined to the facet, or tip, of single-mode optical fibers can be designed as highly sensitive temperature sensors. Monolithic 2-D photonic-crystals are fabricated on silicon wafers and subsequently released and micro-assembled onto the tip of optical fibers. The PC's reflection spectrum is modulated by the temperature of the sensor and its environment and shows sensitivity comparable to Fiber Bragg Gratings (FBGs). In contrast to FBGs, the compact sensing element is localized at the tip of the fiber and the active sensor element is a disk of 10 mum diameter and 480 nm thickness. The sensor system is made of robust, high-temperature dielectric materials and therefore has the potential to be used for many applications including measurements in harsh environments.
LEOS Annual Meeting Conference Proceedings, 2009. LEOS '09. IEEE; 11/2009
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ABSTRACT: This paper reports the use of internal electrostatic transduction to excite and detect the fifth bulk lateral mode of a 54 mum outer-diameter, 12 mum-wide, and 2.5 mum-thick poly-silicon ring resonator at 1.95 GHz, with a quality factor Q~8000 in room air. The resonator is fabricated on a quartz substrate to reduce electrical feedthrough. The transducer is a sandwich of 500 nm of electrically floating polysilicon between layers of 50 nm of Si<sub>3</sub>N<sub>4</sub>, formed by refill of a trench etched in the structural polysilicon layer. This scalable double-gap internal electrostatic transducer is compatible with conventional optical lithography, since its critical dimensions are defined by deposition.
Solid-State Sensors, Actuators and Microsystems Conference, 2009. TRANSDUCERS 2009. International; 07/2009
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ABSTRACT: This work reports a novel wafer-scale packaging method whereby MEMS devices are simultaneously vacuum sealed in a micromachined cavity and clad with a thin polycrystalline silicon carbide (poly-SiC) film. The deposition of poly-SiC is controlled by adjusting the precursor flow rates to yield a uniform film with low residual stress and moderate resistivity to prevent film cracking and device shorting. Functioning poly-SiC clad, silicon-core resonators are tested. Comparison of the resonator quality factor (Q) to a pressure-Q calibration curve determines the pressure within the sealed cavity to be 8 mBar.
Solid-State Sensors, Actuators and Microsystems Conference, 2009. TRANSDUCERS 2009. International; 07/2009
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ABSTRACT: This paper reports the parallel internal electrostatic transduction of a laterally driven Lame-mode polysilicon resonator. This resonator is fabricated using a manufacturable double nanogap process that provides ultrathin high-aspect ratio lateral gaps. The transduction electrodes are optimally placed and oriented to maximize electromechanical transduction efficiency for the fundamental Lame mode. A 128.15 MHz Lame-mode resonator is driven and sensed differentially with a 20 V DC polarization voltage: the motional resistance is about 30 kOmega and the quality factor Q > 12000 in air.
Micro Electro Mechanical Systems, 2009. MEMS 2009. IEEE 22nd International Conference on; 03/2009
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ABSTRACT: This paper shows the first successful combination of dielectrically-transduced 200 MHz resonators with the epi-silicon encapsulation process, and demonstrates a set of important capabilities needed for the construction of CMOS-compatible RF MEMS components. The result shows the resonant frequency of 207 MHz and a quality factor of 6,400. The high fQ (1.2times10<sup>12</sup> Hz) makes this encapsulated resonator an excellent candidate for applications in local oscillators and RF spectrum analyzers.
Micro Electro Mechanical Systems, 2009. MEMS 2009. IEEE 22nd International Conference on; 03/2009
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ABSTRACT: We report on experimental measurements of the optical properties of thin films of poly-crystalline silicon carbide (poly-SiC) deposited by means of low pressure chemical vapor deposition (LPCVD). Measurements in the mid-IR region of the EM spectrum show strong dependence of both far field transmission and surface modes upon the deposition conditions including doping levels, ratio of dichlorosilane (DCS) to 1,3 disilabutane (DSB), and anneals performed on the film. We observe the link between the relative strength of near field phonon polariton resonances, the appearance of a polariton gap, and the achievement of extraordinary optical transmission (EOT).
Optical MEMs and Nanophotonics, 2008 IEEE/LEOS Internationall Conference on; 09/2008
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ABSTRACT: Microfabrication technologies initially developed for integrated electronics have been successfully applied to batch-fabricate a wide variety of micromechanical structures for sensing, actuating, or signal-processing functions such as filters. By appropriately combining the deposition, etching, and lithography steps for microelectromechanical devices with those needed for microelectronic devices, it is possible to fabricate an integrated microsystem in a single process sequence. This paper reviews the strategies for cofabrication, with an emphasis on modular approaches that do not mix the two process sequences. The integrated processes are discussed using examples of physical sensors (infrared imagers and inertial sensors), chemical and biochemical sensors, electrostatic and thermal actuators for displays and optical switching, and nonvolatile memories. By adding new functionality to integrated electronics, the use of microelectromechanical systems is opening new applications in sensing and actuating, as well as enhancing the performance of analog and digital integrated circuits.
Proceedings of the IEEE 03/2008; · 6.81 Impact Factor
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ABSTRACT: This paper describes a microelectromechanical resonator interface to a nanomechanical structure. Our approach to microresonator-nanowire integration employs silicon nanowires as mechanical tuning elements, which perturb the frequency response of the resonator system. Two coupling configurations were designed and tested, the first with a nanowire beam coupled to the maximum displacement points of clamped-clamped microresonators and the second with a coupling beam attached 1.5 mum away from the anchors of the bending mode resonators. A focused-ion-beam (FIB) tool was used to tune the frequency response of the coupled systems. Finally a nanowire coupled bandpass filter with a 3 dB bandwidth about 120 kHz at 17.9 MHz was demonstrated.
Micro Electro Mechanical Systems, 2008. MEMS 2008. IEEE 21st International Conference on; 02/2008
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ABSTRACT: An analytical model for the suspended-gate field-effect transistor (SGFET), dedicated to the dc analysis of SGFET logic circuits, is developed. The model is based on the depletion approximation and expresses the pull-in voltage, the pull-out voltage, and the stable travel range as a function of the structural parameters. Gate position is explicitly expressed as a function of the gate voltage, thus enabling the convenient integration of the analytical SGFET relationships into the standard MOSFET models. Starting from the new SGFET model, the influence of the mechanical hysteresis on the circuit steady-state behavior is discussed, the potential of using the SGFET as an ultra-low power switch is demonstrated, and the operation of the complementary SGFET inverter is analyzed.
IEEE Transactions on Electron Devices 02/2008; · 2.32 Impact Factor
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ABSTRACT: The operation and performance of complementary nanoelectromechanical (CNEM) logic gates are investigated. NEMS structures featuring dimensions 2 to 3 orders of magnitude smaller than the present MEMS relays are considered. Various metals are benchmarked to silicon as the cantilever beam material. We show that the CNEM inverters featuring laterally actuated beams, 10 nm gap and low density materials such as Si or Al can achieve nanosecond pull-in delay and sub-0.1 fJ switching energy at V<sub>DD</sub> = 1.5 V while occupying an area as small as 0.03 mum<sup>2</sup>.
Electron Devices Meeting, 2007. IEDM 2007. IEEE International; 01/2008
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ABSTRACT: This paper demonstrates an electrostatic transducer for lateral contour-mode resonators in which the transduction gaps are filled with a liquid dielectric (water) having much higher permittivity than air ( kappa<sub>water</sub> = 80.1). Aqueous transduction is more efficient than air-gap transduction (lower motional impedance) and has a higher frequency tuning range compared than solid-dielectric transduction. We have demonstrated a 42 MHz poly-SiGe disk resonator with de-ionized (Dl) water confined to the electrode gaps. The resonator has a measured quality factor (Q) of 3,800, motional impedance (Rx) of 3.9 kOmega and 3% series frequency tuning range.
Solid-State Sensors, Actuators and Microsystems Conference, 2007. TRANSDUCERS 2007. International; 07/2007
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ABSTRACT: In this work, we investigate the characteristics of a MOSFET with a hybrid solid/liquid gate-dielectric structure, which can be used for fluidic sensor applications. This "WetFET" device is made using a standard MOSFET fabrication process with additional steps to selectively remove portions of the gate dielectric and to subsequently refill the resultant gaps with liquid. Characteristics of the first prototype WetFET device are presented and analyzed with the aid of device simulations. It is concluded that as transistor performance is highly sensitive to the gate dielectric properties, this structure is promising for creating new, efficient sensors.
VLSI Technology, Systems and Applications, 2007. VLSI-TSA 2007. International Symposium on; 05/2007
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ABSTRACT: The authors present modeling approaches to describe the coupling of modes in a resonant vibratory rate gyroscope. Modal coupling due to off-diagonal stiffness and damping terms is considered. Three analytical modeling approaches are presented in the context of a z-axis micromechanical vibratory rate gyroscope fabricated in an integrated polysilicon surface-micromachining process. The first approach is based on frequency-response analysis of the gyroscope output. The second approach takes the route of state-space-based system identification to identify the modal-coupling parameters. A third approach based on measured vibration data identifies the coupling parameters due to stiffness and damping. These three methods are then applied to predict the extent of displacement and force coupling between the drive and the sense axes of an existing device as a function of varying degrees of matching between the resonant frequencies associated with the drive and the sense modes. Experimental data show that as the resonant frequencies of the drive and sense modes are brought closer together, an improvement in overall resolution and scale factor of the device is obtained at the expense of an enhanced coupling of forces to displacements between the two axes and the onset of instability for an open-loop sensing implementation
IEEE Sensors Journal 11/2006; · 1.52 Impact Factor
