Microelectromechanical Systems (MEMS) An introduction What are MEMS 3-D Micromachined Structures 3-D Micromachined Structures Applications: Passive Structures

Microelectromechanical Systems (MEMS) An introduction What are MEMS 3-D Micromachined Structures 3-D Micromachined Structures Applications: Passive Structures www.phwiki.com

Microelectromechanical Systems (MEMS) An introduction What are MEMS 3-D Micromachined Structures 3-D Micromachined Structures Applications: Passive Structures

McClune, Christine, Executive Producer and Traffic Reporter has reference to this Academic Journal, PHwiki organized this Journal Microelectromechanical Systems (MEMS) An introduction Jr-Lung (Eddie) Lin Department of Mechanical in addition to Automation Engineering, I-Shuo University Email: ljl@isu.edu.tw Outline Introduction Applications Passive structures Sensors Actuators Future Applications MEMS micromachining technology Bulk micromachining Surface micromachining LIGA Wafer bonding Thin film MEMS Motivation Microresonators MEMS resources Conclusions What are MEMS (Micro-electromechanical Systems) Fabricated using micromachining technology Used as long as sensing, actuation or are passive micro-structures Usually integrated with electronic circuitry as long as control in addition to /or in as long as mation processing

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3-D Micromachined Structures Linear Rack Gear Reduction Drive Triple-Piston Microsteam Engine Photos from S in addition to ia National Lab. Website: http://mems.s in addition to ia.gov 3-D Micromachined Structures Movies from S in addition to ia National Lab. Website: http://mems.s in addition to ia.gov 2 dust mites on an optical shutter Deflection of laser light using a hinged mirror Applications: Passive Structures Inkjet Printer Nozzle

Applications: Sensors Pressure sensor: Piezoresistive sensing Capacitive sensing Resonant sensing Application examples: Manifold absolute pressure (MAP) sensor Disposable blood pressure sensor (Novasensor) Piezoresistive Pressure Sensors Piezoresistive Pressure Sensors Wheatstone Bridge configuration Illustration from “An Introduction to MEMS Engineering”, N. Maluf

Applications: Sensors Acceleration Air bag crash sensing Seat belt tension Automobile suspension control Human activity as long as pacemaker control Vibration Engine management Security devices Monitoring of seismic activity Angle of inclination Vehicle stability in addition to roll Inertial sensors Accelerometers Accelerometers Accelerometer parameters acceleration range (G) (1G=9.81 m/s2) sensitivity (V/G) resolution (G) b in addition to width (Hz) cross axis sensitivity

Capacitive Accelerometers Stationary Polysilicon fingers Based on ADXL accelerometers, Analog Devices, Inc. Spring Inertial Mass Anchor to substrate Displacement Applications: Actuators Texas Instruments Digital Micromirror DeviceTM Array of up to 1.3 million mirrors Invented by Texas Instruments in 1986 For an animated demo of this device, go to http://www.dlp.com/dlp-technology/ Each mirror is 16 mm on a side with a pitch of 17 mm Resolutions: 800×600 pixels (SVGA) in addition to 1280×1024 pixels (SXGA) Digital Micromirror Device From “An Introduction to Microelectromechanical Systems Engineering” by Nadim Maluf

Digital Micromirror Device From “An Introduction to Microelectromechanical Systems Engineering” by Nadim Maluf => Acheive grey scale by adjusting the duration of pulse Switching time: 16 µs (about 1000 times faster than the response time of the eye) Mirror is moved by electrostatic actuation (24 V applied to bias electrode) Projection system consists of the DMD, electronics, light source in addition to projection optics Placing a filter wheel with the primary colors between light source in addition to the micromirrors => Achieve full color by timing the reflected light to pass the wheel at the right color Some future applications Biological applications: Microfluidics Lab-on-a-Chip Micropumps Resonant microbalances Micro Total Analysis systems Mobile communications: Micromechanical resonator as long as resonant circuits in addition to filters Optical communications: Optical switching Microfluidics / DNA Analysis

Basic microfabrication technologies Deposition Chemical vapor deposition (CVD/PECVD/LPCVD) Epitaxy Oxidation Evaporation Sputtering Spin-on methods Etching Wet chemical etching Istropic Anisotropic Dry etching Plasma etch Reactive Ion etch (RIE, DRIE) Patterning Photolithography X-ray lithography Bulk micromachining Anisotropic etching of silicon Bulk micromachining Anisotropic etch of {100} Si 54.74º a 0.707a

Bulk micromachining: Pressure sensors Piezoresistive elements SiO2 p+ Si <100> Si Surface Micromachining substrate Important issues: selectivity of structural, sacrificial in addition to substrate materials stress of structural material stiction Surface Micromachining Most commonly used materials as long as surface micromachining: substrate: silicon sacrificial material: SiO2 or phosphosilicate glass (PSG) structural material: polysilicon Alternative materials

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Surface Micromachining Polysilicon deposited by LPCVD (T~600 ºC) usually has large stress High T anneal (600-1000 ºC) as long as more than 2 hours relaxes the strain Photo from R.T. Howe, Univ. of Calif, Berkeley, 1988 Low temperature, thin film materials has much less intrinsic stress Stress Surface Micromachining Surface tension of liquid during evaporation results in capillary as long as ces that causes the structures to stick to the substrate if the structures are not stiff enough. Stiction To avoid this problem make the structures stiffer (ie, shorter, thicker or higher Young’s modulus) use super-critical drying in CO2 (liquid supercritical fluid gas) roughen substrate to reduce contact area with structure coat structures with a hydrophobic passivation layer LIGA – X-ray Lithography, Electroplating (Galvano as long as mung), Molding (Ab as long as mung) Deposit plating base Deposit photoresist Expose in addition to develop photoresist Immerse in chemical bath in addition to electroplate the metal Remove mold

LIGA Photos from MCNC – MEMS group Wafer bonding- Anodic bring sodium contating glass (Pyrex) in addition to silicon together heat to high temperature (200-500 ºC) in vacuum, air or inert ambient apply high electric field between the 2 materials (V~1000V) causing mobile + ions to migrate to the cathode leaving behind fixed negative charge at glass/silicon interface bonding is complete when current vanishes glass in addition to silicon held together by electrostatic attraction between – charge in glass in addition to + charges in silicon Piezoresistive pressure sensor Summary: MEMS fabrication MEMS technology is based on silicon microelectronics technology Main MEMS techniques Bulk micromachining Surface micromachining LIGA in addition to variations Wafer bonding

A laser beam is focused on the structure in addition to the reflected light is collected with an intensity (or quadrant) detector. The deviation of the beam is proportional to the deflection Optical detection Optical detection of electrical actuation Resonance is inversely proportional to square of the length 20 MHz resonances measured with 10 m-long a-Si:H bridges (Q~100 in air; Q up to 5000 in vacuum) Resonance frequency MEMS Resources Reference Books Nadim Maluf, An Introduction to Microelectromechanical Engineering (Artech House, Boston,2000) M. Elewenspoek in addition to R. Wiegerink, Mechanical Microsensors (Springer-Verlag, 2001) Héctor J. De Los Santos, Introduction to Microelectromechanical (MEM) Microwave Systems (Artech House, Boston, 1999) Websites S in addition to ia National Lab: http://mems.s in addition to ia.gov Berkeley Sensors in addition to Actuators Center: http://www-bsac.eecs.berkeley.edu MEMS Clearinghouse: http://www.memsnet.org/ Some companies with MEMS products Accelerometers – Analog Devices: http://www.analog.com/technology/mems/index.html Digital Light Processing Projector- Texas Instruments: http://www.dlp.com Micro-electrophoresis chip – Caliper Technologies: http://www.calipertech.com

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