We survey progress over the past 25 years in the development of microscale devices for pumping fluids. We attempt to provide both a reference for micropump researchers and a resource for those outside the field who wish to identify the best micropump for a particular application. Reciprocating displacement micropumps have been the subject of extensive research in both academia and the private sector and have been produced with a wide range of actuators, valve configurations and materials. Aperiodic displacement micropumps based on mechanisms such as localized phase change have been shown to be suitable for specialized applications. Electroosmotic micropumps exhibit favorable scaling and are promising for a variety of applications requiring high flow rates and pressures. Dynamic micropumps based on electrohydrodynamic and magnetohydrodynamic effects have also been developed. Much progress has been made, but with micropumps suitable for important applications still not available, this remains a fertile area for future research.

https://microfluidics.stanford.edu/Publications/Micropumps_Cooling/Laser%20Review%20of%20Micropumps%20in%20JMM.pdf

A review of micropumps

An object is to provide a semiconductor device of which a manufacturing process is not complicated and by which cost can be suppressed, by forming a thin film transistor using an oxide semiconductor film typified by zinc oxide, and a manufacturing method thereof. For the semiconductor device, a gate electrode is formed over a substrate; a gate insulating film is formed covering the gate electrode; an oxide semiconductor film is formed over the gate insulating film; and a first conductive film and a second conductive film are formed over the oxide semiconductor film. The oxide semiconductor film has at least a crystallized region in a channel region.

Semiconductor device, and manufacturing method thereof

A Three Dimensional Structure (3DS) Memory (100) allows for physical separation of the memory circuits (103) and the control logic circuit (101) onto different layers (103) such that each layer may be separately optimized. One control logic circuit (101) suffices for several memory circuits (103), reducing cost. Fabrication of 3DS memory (100) involves thinning of the memory circuit (103) to less than 50 microns in thickness and bonding the circuit to a circuit stack while still in wafer substrate form. Fine-grain high density inter-layer vertical bus connections (105) are used. The 3DS memory (100) manufacturing method enables several performance and physical size efficiencies, and is implemented with established semiconductor processing techniques.

Three dimensional structure memory

Part I: Background and Fundamentals Introduction, Mohamed Gad-el-Hak, University of Notre Dame Scaling of Micromechanical Devices, William Trimmer, Standard MEMS, Inc., and Robert H. Stroud, Aerospace Corporation Mechanical Properties of MEMS Materials, William N. Sharpe, Jr., Johns Hopkins University Flow Physics, Mohamed Gad-el-Hak, University of Notre Dame Integrated Simulation for MEMS: Coupling Flow-Structure-Thermal-Electrical Domains, Robert M. Kirby and George Em Karniadakis, Brown University, and Oleg Mikulchenko and Kartikeya Mayaram, Oregon State University Liquid Flows in Microchannels, Kendra V. Sharp and Ronald J. Adrian, University of Illinois at Urbana-Champaign, Juan G. Santiago and Joshua I. Molho, Stanford University Burnett Simulations of Flows in Microdevices, Ramesh K. Agarwal and Keon-Young Yun, Wichita State University Molecular-Based Microfluidic Simulation Models, Ali Beskok, Texas A&M University Lubrication in MEMS, Kenneth S. Breuer, Brown University Physics of Thin Liquid Films, Alexander Oron, Technion, Israel Bubble/Drop Transport in Microchannels, Hsueh-Chia Chang, University of Notre Dame Fundamentals of Control Theory, Bill Goodwine, University of Notre Dame Model-Based Flow Control for Distributed Architectures, Thomas R. Bewley, University of California, San Diego Soft Computing in Control, Mihir Sen and Bill Goodwine, University of Notre Dame Part II: Design and Fabrication Materials for Microelectromechanical Systems Christian A. Zorman and Mehran Mehregany, Case Western Reserve University MEMS Fabrication, Marc J. Madou, Nanogen, Inc. LIGA and Other Replication Techniques, Marc J. Madou, Nanogen, Inc. X-Ray-Based Fabrication, Todd Christenson, Sandia National Laboratories Electrochemical Fabrication (EFAB), Adam L. Cohen, MEMGen Corporation Fabrication and Characterization of Single-Crystal Silicon Carbide MEMS, Robert S. Okojie, NASA Glenn Research Center Deep Reactive Ion Etching for Bulk Micromachining of Silicon Carbide, Glenn M. Beheim, NASA Glenn Research Center Microfabricated Chemical Sensors for Aerospace Applications, Gary W. Hunter, NASA Glenn Research Center, Chung-Chiun Liu, Case Western Reserve University, and Darby B. Makel, Makel Engineering, Inc. Packaging of Harsh-Environment MEMS Devices, Liang-Yu Chen and Jih-Fen Lei, NASA Glenn Research Center Part III: Applications of MEMS Inertial Sensors, Paul L. Bergstrom, Michigan Technological University, and Gary G. Li, OMM, Inc. Micromachined Pressure Sensors, Jae-Sung Park, Chester Wilson, and Yogesh B. Gianchandani, University of Wisconsin-Madison Sensors and Actuators for Turbulent Flows. Lennart Loefdahl, Chalmers University of Technology, and Mohamed Gad-el-Hak, University of Notre Dame Surface-Micromachined Mechanisms, Andrew D. Oliver and David W. Plummer, Sandia National Laboratories Microrobotics Thorbjoern Ebefors and Goeran Stemme, Royal Institute of Technology, Sweden Microscale Vacuum Pumps, E. Phillip Muntz, University of Southern California, and Stephen E. Vargo, SiWave, Inc. Microdroplet Generators. Fan-Gang Tseng, National Tsing Hua University, Taiwan Micro Heat Pipes and Micro Heat Spreaders, G. P. "Bud" Peterson, Rensselaer Polytechnic Institute Microchannel Heat Sinks, Yitshak Zohar, Hong Kong University of Science and Technology Flow Control, Mohamed Gad-el-Hak, University of Notre Dame) Part IV: The Future Reactive Control for Skin-Friction Reduction, Haecheon Choi, Seoul National University Towards MEMS Autonomous Control of Free-Shear Flows, Ahmed Naguib, Michigan State University Fabrication Technologies for Nanoelectromechanical Systems, Gary H. Bernstein, Holly V. Goodson, and Gregory L. Snider, University of Notre Dame Index

The MEMS Handbook

An interference modulator (Imod) incorporates anti-reflection coatings and/or micro-fabricated supplemental lighting sources. An efficient drive scheme is provided for matrix addressed arrays of IMods or other micromechanical devices. An improved color scheme provides greater flexibility. Electronic hardware can be field reconfigured to accommodate different display formats and/or application functions. An IMod's electromechanical behavior can be decoupled from its optical behavior. An improved actuation means is provided, some one of which may be hidden from view. An IMod or IMod array is fabricated and used in conjunction with a MEMS switch or switch array. An IMod can be used for optical switching and modulation. Some IMods incorporate 2-D and 3-D photonic structures. A variety of applications for the modulation of light are discussed. A MEMS manufacturing and packaging approach is provided based on a continuous web fed process. IMods can be used as test structures for the evaluation of residual stress in deposited materials.

Photonic mems and structures

Deep X-ray lithography and metal plating when coupled with a sacrificial layer, SLIGA, lends itself to the fabrication of very high aspect ratio metal structures which are mechanically stiff in the substrate direction and can be very flexible in the direction parallel to the substrate. These properties can be exploited by producing a family of new flexure actuators which can produce very significant motion via thermal expansion and magnetic forces. The magnitude of thermal effects and magnetic forces are dependent on actuator geometry. An understanding of each effect allows the design of an actuator which is dominated by one or both effects. The end result is devices intended for large motion actuators in microswitch and positioning applications. They are also useful for material constant measurements of electroplated metals. >

Thermo-magnetic metal flexure actuators

Polysilicon resonant microbeams can be used as strain-sensitive elements to replace conventional silicon piezoresistors in precision sensor applications, such as pressure sensors and accelerometers. These elements are combined with conventional silicon diaphragms or flexures with a proof mass to convert pressure or acceleration directly into a frequency output. Vacuum-enclosed resonant microbeam elements 200 or 400 μm long, 45 μm wide and 1.8 μm thick have been fabricated using LPCVD mechanical-grade polysilicon at the University of Wisconsin. Q-values determined using gain/phase analysis are typically over 25 000. Lower Q-values are primarily the result of residual gas in the cavity. Closed-loop operation from −60 to 180°C using piezoresistive sensor and electrostatic drive has been achieved with automatic gain control (AGC) to prevent overdrive. The characteristic resonance frequencies of the beams have been measured, with 550 kHz, 1.2, 2.2 and 5.2 MHz being typical of the frequencies of the one-dimensional bending modes for the 200 μm length. These measurements of the multiple resonance frequencies of a single beam provide a means of testing mathematical models of the dynamic behavior as well as determining the residual beam stress. The one-dimensional (1D) differential equation of motion of a doubly clamped single-span beam with an axial load can be solved analytically for lateral natural frequencies and mode shapes. These 1D solutions have been verified by 3D finite-element methods. In addition, the finite-element models are used to identify both lateral and torsional modes. The closed-form solutions agree closely with the numerical results and the experimental data.

Characteristics of polysilicon resonant microbeams

Fabrication of micromechanical devices from polysilicon films with smooth surfaces

Typical IC processing is fundamentally two dimensional; sensors are three-dimensional structures. In surface micromachining, two-dimensional IC processing is extended to sensor structures by the addition of one or more sacrificial layers which are removed by lateral etching. The resulting sensor structures involve the substrate and one or more deposited films which form the intended micromechanical component. The concepts of this type of sensor manufacturing are readily demonstrated by considering absolute pressure transducers in some detail. Absolute pressure transducers involve a vacuum-sealed cavity and a deformation sensing technique. The cavity is formed from the substrate and a low-pressure chemical vapor deposited polycrystalline silicon film. The mechanical properties of this film must be controlled well enough to allow the device to be designed. This implies morphological control during processing. Optimized films which do exhibit controlled compressive or tensile strains exclude oxygen or nitrogen and are therefore not modified by extended hydrofluoric acid etches. Their mechanical behavior is monitored by micromechanical test structures which measure Euler buckling and thereby determine the value of the built-in strain. The cavity vacuum is established by reactive sealing. Long-term vacuum integrity is achieved by a low-stress silicon nitride barrier which also acts as a dielectric isolation barrier. Sensing is accomplished via deposited polysilicon resistors. These devices behave like metal resistors in terms of their temperature coefficient of resistance and noise figure. Their piezoresistive behavior is larger than that of typical metal film structures and smaller than that of single-crystal resistors. Pressure sensors with four diaphragms, two active and two inactive, have been constructed and optimized towards manufacturability. The measured performance is excellent and agrees with the predictions of the design algorithm.

Surface micromachined pressure transducers

Resonant force sensors are devices which convert axially applied forces to changes in resonant frequency. These structures are fundamentally wires or beams or more complicated structures which are in a vacuum envelope. They become interesting and useful if they can be miniaturized, can be fabricated from a single material in a cost effective manner and can be excited and read via simple techniques. The devices which are reported here satisfy most of the above criteria. The construction material involves a silicon substrate, tensile strain polysilicon films and strain-compensated silicon nitride deposits. Clamped-clamped beams of polysilicon, typically 400,μm long, 40,μm wide and 2μm thick are fabricated with an isoplanar process over an oxide filled tub. Low-pressure chemical-vapor-deposited (LPCVD) nitride is used as a second sacrificial layer which also serves to support a second polysilicon layer which is part of the vacuum envelope. Internal surface adhesion problems are avoided by freeze-sublimation procedures which remove surface tension-induced beam deflections. Passivation and sealing is accomplished via LPCVD nitride and reactive sealing. Excitation and sensing is accomplished via ion implanted resistors. Experimental results always produce quality factors, Q , above 35 000. Resonant frequencies to 750 kHz have been achieved. It is estimated that these devices can measure axially applied forces below 0.1 dyne with standard electronic interfaces.

Henry Guckel

Papers

Thermo-magnetic metal flexure actuators

Characteristics of polysilicon resonant microbeams

Fabrication of micromechanical devices from polysilicon films with smooth surfaces

Surface micromachined pressure transducers

The application of fine-grained, tensile polysilicon to mechanicaly resonant transducers