Papers

AVS2004 Session MN-TuM: MEMS and NEMS: Enabling Tools for Scientific Research

Tuesday, November 16, 2004 8:20 AM in Room 213C

Tuesday Morning

Start	Invited?	Item
8:20 AM		MN-TuM-1 C-MEMS/NEMS: A Novel Technology for Graphite, Ni, and Si Nanoscale Material Formation M. Madou, C. Wang, R. Zaouk, K. Malladi, L. Taherabadi (University of California at Irvine) Carbon microelectromechanical systems (C-MEMS) and carbon nanoelectromechanical system (C-NEMS) have received much attention because of the many potential applications. BioMEMS applications include: DNA arrays, glucose sensors, microbatteries and biofuel cells. Microfabrication of carbon structures using current processing technology, including focused ion beam (FIB) and reactive ion etching (RIE), is time consuming and expensive. Low feature resolution, and poor repeatability of the carbon composition as well as widely varying properties of the resulting devices limits the use of screen printing of commercial carbon inks for C-MEMS. Our newly developed C-MEMS microfabrication technique is based on the pyrolysis of photo patterned resists. Using a suitable catalyst, graphite nanofibers and Ni nanowires were formed. Unlike conventional CVD methods for growing nanotubes in which a gaseous carbon source, such as CH4, is commonly used, we use photoresist as carbon source. Furthermore, Si nanowires were successfully grown without photoresist patterns and a modified solid-liquid-solid (SLS) mechanism was used to explain our results.
9:00 AM		MN-TuM-3 Durability Studies of MEMS/NEMS Materials/Coatings at High Sliding Velocities (upto 10 mm/s) Using a Modified AFM N.S. Tambe, B. Bhushan (The Ohio State University) Most micro/nanoelectromechanical (MEMS/NEMS) devices and components operate at very high sliding velocities (of the order of tens of mm/s to few m/s). Micro/nanoscale tribology and mechanics of these devices is crucial for evaluating reliability and failure issues. Atomic force microscopy (AFM) studies to investigate potential materials/coatings for these devices have been rendered inadequate due to inherent limitations on the highest sliding velocities achievable with commercial AFMs. We have developed a new technique to study nanotribological properties at high sliding velocities (upto 10 mm/s) by modifying the commercial AFM setup with a customized closed loop piezo stage for mounting samples. Durability of various materials/coatings used for MEMS/NEMS applications such as silicon, diamondlike carbon (DLC), polydimethlysiloxane (PDMS), polymethylmethacrylate (PMMA), self assembled monolayer of hexadecanethiol (HDT) and perfluropolyether Z-DOL are studied at various normal loads and sliding velocities ranging between 1 µm/s and 10 mm/s. The effect of different sliding materials on the interface wear is studied by using three different AFM tips, viz. Si, Si₃N₄ and diamond. The tip wear is monitored by measuring the tip radii. The primary wear mechanisms for the different samples at high velocities are deformation of the contacting asperities due to impacts as in the case of single crystal silicon; phase transformation from amorphous to low shear strength graphite as found for DLC; localized melting due to high frictional energy dissipation as found for PDMS and PMMA; and substrate wear as found for HDT and Z-DOL. An analytical model is presented to explain wear mechanisms and different wear regimes at high sliding velocities.
9:20 AM		MN-TuM-4 Chemical Control of Micromechanical Resonators: The Role of Surface Chemistry J.A. Henry, Y. Wang, D. Sengupta, M.A. Hines (Cornell University) The development of high-performance micromechanical resonators would enable advances in many technologies; however, many researchers have noted that the quality factor, or Q, of micromechanical resonators decreases with decreasing resonator size (i.e. increasing resonator frequency.) We have previously shown that the rate of mechanical energy dissipation, which is inversely proportional to Q, in MHz-range micromechanical silicon resonators is strongly affected by the chemical state of the resonator surface. In this presentation, we will present functionalized silicon resonators that have higher performance than the H-terminated resonators -- the previously demonstrated "best termination." Additionally, these functionalized resonators are relatively stable; little degradation is seen after a week in 100% humidity air. The implications of these results on the mechanism of surface-chemistry-induced mechanical energy dissipation will be discussed.
9:40 AM		MN-TuM-5 Tribological and Wear Studies of ALD and SILAR Coatings for MEMS Devices C. Nistorica, J.-F. Liu, I. Gory, G.D. Skidmore (Zyvex Corporation); F.M. Mantiziba, B.E. Gnade (University of Texas at Dallas); J. Kim (Kookmin University, Korea) This paper describes a study of the static friction and wear of coated microelectromechanical systems (MEMS) using thermally actuated friction micro-devices. In order to characterize static friction and wear, a tribological deep reactive ion etched (DRIE) silicon test microstructure is developed. Reproducibility of the data is proved by testing multiple devices in parallel. Conformal coatings consisting of 10 nm thick atomic layer deposited (ALD) TiO₂ or ZrO₂ and successive ionic layer adsorption and reaction (SILAR) deposited MoS₂ or ZrO₂ films are applied on the MEMS silicon test devices. The effect of film roughness, velocity as well as the effect of humidity on friction and wear is studied by exposing the coated MEMS devices to a relative humidity varying between 5% and 100%. The coatings were found to behave differently, ZrO₂ and MoS₂ decreasing the coefficient of friction by 40% compared to uncoated devices, while TiO₂ presented a decrease in the coefficient of friction only at higher humidity. The wear data for the ALD coated devices, quantified from the point of view of debris creation and stability of the friction coefficient, indicate much improvement over native oxide coated silicon devices, while the SILAR coatings showed high wear.
10:00 AM		MN-TuM-6 MEMS-based Force-Detected Nuclear Magnetic Resonance Spectrometer T. George, K. Son, C. Lee, N.V. Myung, E.R. Urgiles (Jet Propulsion Laboratory); L.A. Madsen, G.M. Leskowitz, R.A. Elgammal, D.P. Weitekamp (California Institute of Technology) NMR Spectroscopy is the premier spectroscopic method used for identification of chemical compounds. A miniaturized portable NMR spectrometer is highly desirable for field investigation of materials and in-situ planetary exploration. We are developing a novel microfabricated force-detected nuclear magnetic resonance (FDNMR) spectrometer with predicted sensitivity superior to conventional NMR at micron scales. This higher sensitivity arises from the signal-to-noise ratio scaling as d^0.5 for the force detection technique, and as d² for conventional NMR (d: sample diameter). Other force detection approaches suffer from broadening of the NMR lines and losses in sensitivity due to the magnetic field gradient imposed on the sample. We overcome this problem by producing a homogenous magnetic field across the sample using a symmetric magnet assembly. Our FDNMR detector consists of a harmonic oscillator comprised of a detector magnet mounted on a microfabricated Si beam. The detector magnet sits within an annular magnet and thus provides a uniform magnetic field over the entire sample volume. Rf pulses applied to the sample modulate the dipole-dipole interaction between the nuclear magnetic moment of the sample and the detector magnet at the mechanical resonance frequency of the oscillator. We detect the resulting motion of the mechanical oscillator at the Brownian-motion limit using a fiber-optic interferometer. In this paper, we present the microfabricated detector assembly of the MEMS-based force-detected nuclear magnetic resonance (FDNMR) spectrometer.
10:20 AM		MN-TuM-7 Frequency-Tuning for Control of Parametrically-Resonant Mass Sensors W. Zhang, K. Turner (University of California, Santa Barbara) Parametric-resonance based mass sensing leads to increased sensitivity over other resonant methods¹. In this work, we present a frequency-tuning approach to measuring mass change in an ultra-sensitive mass sensor. This scheme drives the oscillator using an electrical signal with fixed frequency and tunes the natural frequency to match the driving frequency by feeding back a DC offset to the sensor. Instead of monitoring frequency shift of oscillation in a micro-oscillator, mass change in the sensor can be detected by measuring the DC offset shift, making the sensor amenable to closed-loop control. Different from conventional harmonic resonance based mass sensor, this mass sensor detects mass change in a micro-oscillator based on parametric resonance phenomenon¹. In a prototype mass sensor with natural frequency of 83k Hz, less than 1 Hz of frequency shift has been measured at air pressure, which is equivalent to 0.0012% of the mass of the micro-oscillator (less than 1 pg mass change in this prototype mass sensor). Due to the configuration of the micro-oscillator, which is driven by a pair of non-interdigitated electrodes, the natural frequency can be tuned by changing the DC offset in driving electrical AC signal. Since the frequency of parametric resonance at the stability boundary is related to natural frequency (doubled), the parametric resonance frequency can be tuned by DC offset feedback as well. By matching the fixed frequency of driving electrical signal with parametric resonance frequency using DC offset, the actual natural frequency change, and the mass change, can be found from monitoring shifts in the DC offset. This scheme and the prototype mass sensor has been built and tested. Potential applications include water quality monitoring, gas leakage sensing, and bio sensing, such as DNA, protein, and virus assay. ¹W. Zhang et al, Sens. Actuators A, Phys., 102/1-2 (2002).
10:40 AM		MN-TuM-8 Field Emission from a Tungsten MEMS Structure D. Cruz (UCLA/Sandia National Laboratories); J.P. Chang (University of California, Los Angeles); M.G. Blain (Sandia National Laboratories) We have investigated the field emission properties of free-hanging tungsten MEMS structures. The structures act as electrodes for a Paul ion trap. The ion trap consists of two end cap electrodes, a ring electrode, and a detector, fabricated in seven layers of tungsten molded about SiO2 and then released to realize a free-hung structure. In this work, different ion trap sizes (inner ring electrode radius of 1 and 1.5um) and three different sized arrays (1e4, 1e5 and 1e6 traps) were fabricated and tested for field emission. To test whether field emission may be a problem during the operation of the ion trap, voltage was applied between the outer edge of one of the end caps and the inner edge of the ring electrode. Since electrode separations are on the order of 0.5um and electrode edges are sharp, field emission may occur if a suitably large potential difference is applied. The arrays were tested at atmospheric pressure and under vacuum, 1e-6 torr. The atmospheric tests showed turn-on voltages of 150V for the 1 and 1.5um traps. Currents of 3uA were achieved for the 1um trap 1e6 array at 300V. The vacuum tests showed turn-on voltages of 200V, and lower currents at 300V for the 1um trap array. The current-voltage responses were fitted well to the Fowler-Nordheim characteristics, confirming the field emission from the devices. The difference in current between the test conditions, however, suggests a breakdown discharge at atmosphere pressures. A stable emission was obtained at 300V for 5 min. in vacuum for the 1um trap 1e6 array. The measurements show that field emission will not be an issue for operation of the traps at the required rf amplitudes; however, the results suggest an interesting alternative application for such structures as field emission devices. *Sandia is a Multiprogram Laboratory Operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000
11:00 AM		MN-TuM-9 Suspended Waveguide-Based Tunable Integrated Optical Filters on Indium Phosphide MEMS Platform M. Datta, M.W. Pruessner, D.P. Kelly, R. Ghodssi (University of Maryland, College Park) We propose widely-tunable planar-waveguide-based integrated optical filters on a monolithic InP platform with on-chip parallel-plate capacitive MEMS actuation as the tuning mechanism. These compact (2 mm x 1 mm), fiber-coupled, batch-fabricated filters are perfectly suited for low-cost wavelength division multiplexing optical networks. Each device consists of a moving input waveguide, a fixed output waveguide, deep-etched (>5 micron) Distributed Bragg Reflector (DBR) input and output mirrors integrated with the waveguides, an orthogonal suspension-beam, and a pair of fixed electrodes. All the components are processed monolithically using projection photolithography and methane/hydrogen reactive ion etching, followed by a sacrificial etching step in order to render the input waveguide movable as well as to prevent optical losses due to substrate-leakage (the suspended waveguide approach). InP is etched in multiple cycles, periodically removing the polymer by-products with oxygen plasma to ensure vertical sidewalls with acceptable roughness (<50 nm). By moving the input mirrors electrostatically, we realize a variable-length Fabry-Perot tunable cavity. The filters are designed to demonstrate an wavelength tuning range of 340 nm (1270-1610 nm) with the applied voltage below 10 V. The novel micromachined semiconductor/air-gap DBR mirrors provide a broad high-reflectivity spectrum. Single-stage filters with structurally-stable higher-order DBR mirrors exhibit a full-width-half-maximum (FWHM) of 60 nm. Filter Q-factor can be improved by expanding the input beam or cascading multiple filters. We will present preliminary results for design and fabrication of these devices.
11:40 AM		MN-TuM-11 Use of Plasma Polymerisation Process for Fabrication of Micro Electromechanical System (MEMS) for Micro-Fluidic Devices M. Dhayal, H.G. Hyung (Dongshin University, South Korea); H.J. Lee (Chonnam National University, South Korea); J.S. Choi (Dongshin University, South Korea) In recent years the need for nano electromechanical system (NEMS) and micro electromechanical system (MEMS) devises in chemistry, biology and medical field has increased the interest of researcher to improve and develop new fabrication techniques to capable of building 3D structures with materials othe than silicon or with silicon. In our research we are developing a well-controlled plasma polymerisation process reator to fabricate NEMS and MEMS devises. A comparison of performance of MEMS fabricated using conventional techniques such as photolithography and reactive ion etching in our study has been also investigated. These devises are planed to use for fabrication of micro pumps for micro-fluidic devices.