Mechanical Engineering and Applied Mechanics University of Pennsylvania. A glimpse of MEMS. Presented to MEAM 550 (Fall 2001) students

Transcription

1 Mechanical Engineering and Applied Mechanics University of Pennsylvania A glimpse of MEMS Presented to MEAM 550 (Fall 2001) students G. K. Ananthasuresh September 17, 2001

2 What s in a name? Micro-Electro-Mechanical Systems (MEMS) Widely used in Americas. MicroSystems Technology (MST) Popular in Europe. Micromachines Used in Japan. Microscience Some people prefer to call it this way as they begin to explore scientific aspects of MEMS.

3 Outline What are they? How small are they? How are they useful? How do they work? What are they made of? How are they made? How do you design them? What are the modeling and design issues and challenges for us?

4 A MEMS design question What does this mean? 1. MEMS field is somewhat mature because people are asking routine questions about how to design them. 2. There must be something different about designing them. 3. There is a need to learn the basics of the field and be familiar with the jargon of the field. And so we begin

5 What are they? MEMS are systems that integrate sensing actuation computation control communication power They are smaller more functional faster less power-consuming and cheaper!

6 How small are they? Nanotechnology Microsystems Meso Macrosystems 10 nm 1 um 100 um 10 mm 1 m 0 A 1 nm 0.1 um 10 um 1 mm 100 mm 10 m Atoms Molecules DNA Nanostructures Virus Smallest microelectronic features Bacteria Biological cells Dust particles Dia. of human hair MEMS Optical fibers Packaged ICs Packaged MEMS Lab-on-a-chip Plain old machines Humans Animals Plamts Planes, trains, and automobiles Micro-machining Nano-machining Precision machining Macro-machining

7 Why are they small? Micro size is almost incidental. They are small because of the technologies used to make them. And it is economical to make them small when made in large volumes just like microelectronics. Of course, there are some MEMS devices that would not work if they are any bigger.

8 A bit of history There is plenty of room at the bottom - A 1959 lecture by Richard Feynman Pioneered by Professor James Angell at Stanford University, researchers at Westinghouse in late 1960 s into 1970 s Infinitesimal Machinery - A 1983 lecture by Richard Feynman Formal identity ( MEMS ) to the field came in late1980 s

9 What (more) are they? Early on Solid state transducers And later Integrated systems MEMS sensors actuators are batch fabricated are economical have more functionality involve physical, chemical, biochemical phenomena at small scales act upon macro scale too Take leverage of the enormously successful VLSI technology

10 How are they useful Commercial successes Pressure sensors Accelerometers Ink-jet printer heads Projection display with micro mirror array Portable clinical analyzers etc. Movable solids and fluids at microscale made possible lots and lots of sensors and actuators.

11 More applications Inertial measurement devices Accelerometers, gyroscopes Mass data storage Opto-mechanical devices Projection displays, photonics, optics-on-a-chip Flow control Bio-chemical lab-on-a-chip Communication hardware Mechanical filters, RF-switches and relays Chemical microreactors Power MEMS Micro engines, generators

12 A slide from DARPA-MTO website

13 UCLA A slide from DARPA web site MEMS creating large effects an example

14 Bio-flips A slide from DARPA-MTO web site Towards lab-on-a-chip

15 A slide from DARPA-MTO web site Impact on the health-care

16 Outline What are they? How small are they? How are they useful How do they work? Pressure sensor V Capacitive sensing Piezoresistive sensing

17 How do they work? Accelerometer Side view V Top view

18 How do they work? TI s digital light processor torsional beam Tiltable mirror torsional beam actuating electrode 1 actuating electrode 2

19 What lies beneath TI s digital light processor (DLP) and deformable mirror display (DMD) Anatomy of DLP/DMD Ant s leg on the DMD array

20 How do they work Ink-jet printer head paper orifice ejected ink droplet Weight: ng resistive heater drive air bubble Electronics are integrated to trigger the drive bubble

21 How do they work? A mechanical relay Dielectric Signal output V Signal input

22 How do they work? A normally closed fluidic valve Trapped fluid Glass Silicon Glass Flow (Redwood Microsystems)

23 How do they work? A diaphragm pump Diaphragm V Passive inlet valve Passive outlet valve

24 Outline What are they? How small are they? How are they useful How do they work? What are they made of? How are they made?

25 What are they made of? Phase 1: Old materials and old processes Silicon, its oxide, nitride, and some metals IC-chip processing technology Lithography Thin film deposition (e.g., chemical vapor deposition CVD) Etching Doping Phase 2: Old materials and new processes Silicon, its oxide, nitride, glass, polysilicon, and some metals IC-chip processing techniques enhanced as micromachining techniques Sacrificial layer process Dissolved wafer process Wafer bonding LIGA Hexil Deep reactive ion etching Etc.

26 What are they made of (contd.) Phase 3: New materials and old processes Polymers More metals Ceramics Silicon carbide Piezoelectric films Ferroelectric films Shape-memory materials, etc. e.g., PDMS George Whitesides at Harvard Phase 4: New materials and new processes Processes unconventional to the microelectronic field Processes that re-define the size of MEMS micro to meso or nano Deposition and etching for the new materials

27 How are they made? Surface micromachining Deposition of thin films (mainly polysilicon) Etching using masks Layered construction Bulk-micromachining Carving features into bulk wafers by etching Wafer bonding Patterning individual wafers Wafer-to-wafer bonding LIGA HEXIL

28 Micromachining is not precision machining! Precision machining Relative tolerance (feature to part size) is better than For micromachinig, it is 10-2 to Roughly what we have for building houses. With micromachining, You can make it small, but not precisely. (at least not yet. Wait for nanotechnology )

29 Surface micromachining Deposit or grow silicon dioxide Silicon wafer Pattern the oxide using a mask Deposit polysilicon Pattern polysilicon Sacrifice oxide layer by dissolving The sacrificial layer process to make released structures (Berkeley)

30 Isotropic etching Types of etching With agitation Without agitation Anisotropic etching (111) plane (111) (100) silicon (110) silicon Slanted surfaces

31 Bulk micromachining Etch using a mask Boron doping using a mask Silicon wafer Flip and bond to a glass Glass Dissolve undoped silicon Boron doped dissolved wafer process (Michigan)

32 Wafer bonding Etch a cavity in a wafer Bond another wafer Thin down / polish and etch Released cantilever using MIT s wafer bonding process

33 Making an electrostatic micromotor using surface micromachining Side view Top view After sacrificing oxide layers Rotor Stator poles Cronos MUMPs (formerly MCNC MUMPs)

34 Making a micromotor Deposit poly0 Etch poly0 Deposit oxide1 Dimples in oxide1 Etch oxide1 Deposit poly1

35 Making a micromotor (contd.) Etch poly1 Deposit oxide2 Cross-section up to this point Cronos MUMPs (formerly MCNC MUMPs)

36 Making the micromotor (contd.) Etch oxide2 Deposit poly2 Etch poly2 Deposit and etch metal Cronos MUMPs (formerly MCNC MUMPs) Cross-section before sacrificing oxide layers

37 Finished micromotor

38 Micromotor after release Cronos MUMPs (formerly MCNC MUMPs)

39 How much should we know about u-fab?

40 Visualize device from a verbal description of the process Being able to draw the process flow diagrams from a description. Shallow pits were etched into n-type substrates, and p-type deflection electrodes were diffused in the above pits, followed by fusion bonding of a second wafer above the first. The top wafer was then ground and polished down to a thickness of 6 um. A passivation layer was then formed on the top wafer and sensing piezoesistors were formed using ion implantation, after which contact holes for metallization to connect to he diffused deflection electrodes were etched. Bond pads and interconnect metallization were then deposited and patterned, followed by etching of the diaphragm from the back of the wafer. Finally, two slots were etched next to the beam to release it over the buried cavity. (Petersen et al., 1991) See

41 Visualize the process steps from a device cross section Visualizing a process from a cross-section. How was this made? See

42 MEMS Foundries You don t have to make them if you don t want to or can t. Cronos MUMPs (formerly MCNC s MUMPs) Now, owned and operated by Uniphase.

43 Making elements of mechanisms A surface micromachined hinge (Kris Pister, Berkeley) Substrate hinge

44 Floating hinges Mask layout

45 Electrostatic comb drive Misaligned comb capacitors align creating actuation. Folded-beam suspension Moving combs Shuttle mass anchor Fixed combs

46 Sandia s micro mechanical lock Pin in a maze

47 Close-up of Sandia s micro lock

48 Merry go-around for mites See Sandia s web site for animation

49 Sandia s SUMMiT process revolute joint Rotor Pin Substrate

50 Deep etching Deep RIE (reactive ion etching) to get vertical sidewalls over large depths of several hundred microns. E.g., SCREAM (Cornell) bulk-micromachining

51 SCREAM process Noel MacDonald, Cornell university Deposit and pattern mask oxide Etch bottom sidewall oxide Deep RIE silicon etch Second deep RIE silicon etch Deposit sidewall oxide Isotropic silicon etch

52 Packaging! Packaging access to and protection from the external macro world Packaging is a big problem with MEMS. Sometimes, it may be better not integrate sensor/actuator and electronics. Packaging serves Signal redistribution Mechanical support Power distribution Thermal management Fluidic fittings Etc. Some techniques Ball and wire bonding Flip-chip Sandia s process Research continues

53 Outline What are they? How small are they? How are they useful How do they work? What are they made of? How are they made? How do you design them? What are the modeling and design issues and challenges for us?

54 Modeling and design of MEMS What is different? Integration of sensor, actuator, mechanism, processor, power, and communication makes system level tasks challenging -- common representation for multiple energy domains Device level too has multiple energy domains -- macromodels Component level -- coupled energy domain equations Mask level -- geometric modeling

55 Modeling and design of MEMS System Representing as block diagrams of multi-domain subsystems Device Reduced order macro models of the components Component (physical) Multiple, coupled energy behavioral simulations Artwork of masks and process Defining mask geometry for the process steps Each level involves design There is analysis (forward) problem and synthesis (inverse) problem.

56 The future of MEMS? The proverb: Forecasting is difficult, especially the future. (from Chinese fortune cookies) In any case, MEMS will impact the following industries: Automotive Aerospace Biomedical/bio-tech Health-care Telecommunication Information technology

57 Books Further reading Principles of microfabrication Marc Madou Micromachined transducers: A source book Greg Kovacs Microsystem Design Steve Senturia MEMS: Advanced materials and fabrication methods National Research Council (NRC) committee report, 1997 An Introduction to Microelectromechanical Systems Engineering N. Maluf Microsensors J. W. Gardner Sensor Technology and Devices L. Ristic Transducers, Sensors, and Detectors R. G. Seippel Microactuators: Electrical, Magnetic, Thermal, Optical, Mechanical, Chemical, and Smart Structures M. Tabib-Azar Nano- and Microelectromechanical Systems: Fundamentals of Nano- and Microengineering S. E. Lyshevski