AVS1996 Session MM-WeP: Micro-Electro-Mechanical Poster Session

Wednesday, October 16, 1996 5:00 PM in Ballroom A

Wednesday Afternoon

Time Period WeP Sessions | Topic MM Sessions | Time Periods | Topics | AVS1996 Schedule

MM-WeP-1 Microengineered Mass Spectrometer with Novel Electron Source
C. Sun, W. Carr, K. Farmer (New Jersey Institute of Technology)
A microengineered mass spectrometer device has been designed, simulated, and fabricated. MEMS process techniques are used to scale down the dimension of an existing mass spectrometer. This miniature device uses a field emission microtip array as an electron source to ionize the unknown input gas molecules. The ions are extracted by an electric field and follow a curved trajectory that is determined by the ion mass, charge state and the crossed combination of static electric and magnetic fields. The separated ions are then collected at different locations on parallel planar electrodes. This device uses two processed silicon substrates approximately 1cm\super 2\, where one is a cathode electron source and the other is the ion collector. This microsystem has the potential to be integrated with small current amplifier circuits for increasing sensitivity. Our target application is portable measurement of airborne contaminants.
MM-WeP-2 MEMS-based Flow Controller
A. Johnson (TiNi Alloy Company)
The next generation of analytical instruments will require mass flow controllers which are smaller, more versatile, and less expensive than existing systems. MEMS technology may revolutionize sensing and control functions in mass flow controllers by enabling manufacture of miniature valves and sensors. We have combined micromachined valves and flow sensors with digital control in prototype mass flow controllers and pressure regulators. The size of the systems is dramatically reduced in size, and the advantages of programmable control are realized. The first generation of these systems are assembled from discrete components bonded to a common substrate. The valve (8 mm by 5 mm by 2 mm) embodies a TiNi thin-film shape-memory alloy actuator, and the flow sensor is an unpackaged commercial thermal sensor. A second generation mass flos controller is planned in which the valve actuator and flow/pressure sensor are microfabricated as an integrated MEMS device.
MM-WeP-3 Acoustooptic and Thermooptic All-fiber Devices Based on Sputter Deposited Piezoelectric and Resistive Coatings
G. Fox, C. Muller, C. Wuthrich, N. Setter, N. Ky, H. Limberger (Ecole Polytechnique F\aa e\d\aa e\rale de Lausanne, Switzerland)
Sputter deposition has been used to produce piezoelectric and resistive coatings on standard telecommunication optical fibers. The fiber coatings are used to actuate the optical properties of the glass fiber, providing the capability of producing novel active all-fiber optical devices. Piezoelectric coatings are used to provide strain induced changes in the optical properties of the fiber, while joule heating of the resistive coatings provides temperature induced changes in the optical properties. Two types of active all-fiber devices, phase modulators and tunable filters, have been fabricated and characterized. Phase modulator devices use the strain or temperature induced changes in the fiber refractive index and path length to modulate the phase of the optical signal passing through the fiber. Wavelength tunable filters were prepared by depositing the actuator coating onto a fiber that contained an intra-core Bragg-grating, which acts as a wavelength specific reflection filter. A description of the fabrication and characterization of these acoustooptic and thermooptic all-fiber devices will be presented.
MM-WeP-4 Investigation of Tunneling Noise for the Application in Microgravity Accelerometers
J. Wang, P. Zavracky (Northeastern University); B. Dolgin (Jet Propulsion Laboratory)
Electron tunneling through a vacuum barrier between a tip electrode and a plane electrode has been widely used in Scanning Tunneling Microscope(STM) to achieve real space images on an atomic scale. In recent years, with the development of micromachining, electron tunneling has also found applications in semiconductor sensors as a supersensitive position transducer. Tunneling accelerometers have already demonstrated sensitivity of 10-4A per square root Hz at 10khz. However, it has been found that tunneling tips suffer from low frequency noise, which may limit their usefulness for high sensitivity low frequency measurements. The purpose of paper is to investigate the electron tunneling noise in tunneling tip accelerometers. A special test structure with a flat tip is designed and fabricated using silicon micromachining technology. The advantages of using a flat tip are that the tip height is easily controlled during processing and it may have the potential to reduce the noise due to the possible multiple tip tunneling. The tunneling distance is controlled by an electrostatic force applied between the proof mass and tip electrodes. A closed-loop control circuit is implemented for the tunneling device to obtain a stable operation in vacuum. Analysis based on theoretical calculations and measurements shows that the flicker noise level is much higher than that of other tunneling process related noise sources including shot noise and Johnson-Nyquist noise for the frequencies below 100 Hz. Noise spectrum is obtained for different ambient and vacuum pressures. The results show that the tunneling noise level is much lower in vacuum than that when operating in air especially for low frequency region. It is believed that the surface condition of tunneling electrodes plays an important role in the noise performance. The random movement of ambient molecules, surface diffusion of adsorbed molecules and the surface adsorption and desorption process are the main reasons for 1/f noise.
MM-WeP-6 Numerical Simulation of Microstructure Hydrodynamics
A. Lopez, C. Wong, M. Stevens, S. Plimpton (Sandia National Laboratories)
Recent advances in microsciences and technology, like Micro- ElectroMechanical Systems (MEMS), have generated a group of unique liquid flow problems that involve characteristic length scales of a micron. Currently, there is difficulty in using the traditional approach to analyze microscale transport phenomena. This problem may be due to the continuum or equilibrium assumption not being valid for liquid flows in microscale geometries or under high stress. Also, in manufacturing processes such as coatings, current continuum models are unable to predict wetting/de-wetting phenomena for non-equilibrium systems. It is suspected that in these systems, molecular-level processes can control the interfacial energy and viscoelastic properties at the liquid/solid boundary. Sandia has developed a massively parallel molecular dynamics (MD) code to address this new class of non-equilibrium, transport problems for microscale structures. The goal is to better understand microscale transport mechanisms, fluid-structure interactions, and scale effects in order to develop models for MEMS design. Specifically, the MD code has been used to analyze liquid channel flow problems for a variety of channel widths, e.g. 0.005-0.5 microns. We will present results from MD simulations of Poiseuille flow and Couette flow problems and address both scaling and modeling issues. For Poiseuille flow, the numerical predictions will be compared with experimental data to investigate the variation of the friction factor with channel width. For Couette flow, the numerical predictions will be used to determine the degree of slip at the liquid/solid boundary.
MM-WeP-7 Toward Nanometer Scale Actuators
P. Hartwell, F. Bertsch, N. MacDonald (Cornell University)
Nanoactuators composed of single crystal silicon (SCS) beams, 200 nm wide, have been fabricated using a modified SCREAM [1,2] process. The integrated procss is an extension of the SCREAM process and is compatible with all current SCREAM device designs, including devices with integrated 20nm diameter tips. It incorporates a new electrical and thermal isolation scheme to create complex, electrostatically driven nanoactuators and nanomechanical structures. The process shows promise of scaling further to a minimum feature size (MFS) below 100 nm. By scaling the MFS, larger forces are generated and larger capacitance changes and displacements are achieved. Electron beam lithography is used for pattern definition. Our beams are fabricated using a deep RIE etch, a sidewall passivation layer, and an isotropic RIE release etch. A new planar, thermal oxide isolation scheme was developed to electrically and thermally isolate released structures from the substrate. The planarity of the process makes it compatible with high resolution electron beam lithography. Completed beams are SCS with a minimal aluminum metallization on the top surface. The process produces released, low stress, isolated, SCS beams with features approximating the lithographic linewidth. [1] K.A. Shaw, Z.L. Zhang, and N.C. MacDonald, Sensors and Acuators A, 40, 63 70 (1994). [2] N.C. MacDonald, "SCREAM MicroElectroMechanical Systems," (Invited Paper) Special Issue of the Journal of Microelectronic Engineering on Nanotechnology, to be published July, 1996.
MM-WeP-8 Self-aligned Microlens(SAM) Fabricated by using Silicon Micromachining Technology for Microcolumn Electron Beam
Y. Lee, K. Chun, Y. Kuk (Seoul National University, Korea)
Recently, there have been more promising research results on microcolumn electron beam and microlens is one of the most important elements affecting the performance of it. In this paper, we propose a microlens with new structure named Self-Aligned Microlens(SAM). While conventional lenses are fabricated by bonding different materials such as silicon and glass, SAM has two electrodes for extracting, accelerating and focusing of electrons in one silicon wafer. The electrodes consist of two symmetrical and doubly clamped polysilicon bridges with holes on both sides. Between two bridges, cavity is formed by anisotropic etching of silicon in order that electrons can pass through it. Therefore, SAM eliminates extra bonding process and alignment errors. Both surface- and bulk- micromachining technology were used for fabricating SAM. Its structure was realized by removing sacrificial polysilicon layer and bulk silicon simultaneously in EDP solution while remaining polysilicon bridge passivated with thermally grown oxide. The advantages of this device are 1) The alignment accuracy of microlens can be controlled within a few micrometers because alignment error is determined by that of double side mask aligner, 2) The productivity of microlens can be remarkably increased because time-consuming and imprecise anodic bonding processes can be reduced. In addition to these advantages, we can also state that SAM laid the foundation for the integration of microcolumn toward multi-column array which enables to perform high-throughput electron beam lithography. We are now carrying out energy analysis in microcolumn electron beam system.
Time Period WeP Sessions | Topic MM Sessions | Time Periods | Topics | AVS1996 Schedule