Outline

1. MEMS: the state of the art and future challengesPaul RonneyDept. of Aerospace & Mechanical EngineeringUniv. of Southern California, Los Angeles, USAYiguang Ju Department of Engineering MechanicsTsinghua University, Beijing, China

2. Outline • Part 1: Introduction to MEMS • What is MEMS? • Fabrication techniques • Applications • The market for MEMS • Opportunities for the future • What can the government do to help? • Part 2: Power MEMS as an example of MEMS development

3. What is MEMS? • Micro-Electro-Mechanical Systems (MEMS) is a technology that: • Leverages Integrated Circuit fabrication technology by adding additional functions, for example • Mechanical • Chemical • Biological • Optical • Mass-produces ultra-miniaturized components at low cost • Enables radical new micro-system applications, for example • Pressure / acceleration sensors • Power production • Medical devices • Optical switches

4. Advantages of MEMS

5. Microscale fabrication techniques • Bulk Micromachining • Deep reactive ion etching • Surface Micromachining • LIGA • Others • EFAB • Micro EDM • 3-D Lithography • Laser Micromachining

6. Anisotropic Wet Etching of Silicon

7. Deep Reactive Ion Etching

8. Surface Micromachining

9. LIGA process

10. EFAB (Electrochemical FABrication) (NEW) • Analogous to macroscale “rapid prototyping,” “solid freeform fabrication” - enables fabrication of arbitrarily complex 3D structures • Selective electroplating of structural and sacrificial metals • Developed at University of Southern California • Electrochemistry can also be used to deposit other types of materials, e. g. • Thermoelectric • Magnetic • Electrically insulating • Catalytic • Can use existing mechanical design software & modeling tools • No clean room required for device fabrication - much less expensive than silicon-based techniques • Commercialization by MEMGen Inc., Torrance, CA, USA

11. EFAB key technology: “Instant Masking” • Pre-fabricated masks serve as reusable “printing plates” • Polymer mask patterned on anode using conventional photolithography • Lithography for all layers done in parallel,priorto, separate from device fabrication, allowing: • Low-cost, self-contained automated machine • Mask outsourcing - possible collaboration with Chongqing

12. EFAB process flow Selectively deposited material (usually sacrificial) Blanket deposited 2nd material (usually structural) + ( b ) ( c ) ( a ) ( d ) ( e ) ( f )

13. 90m EFAB results • 12-layer chain, ≈ 290 m wide (world’s narrowest?) • Minimum feature size 20 µm • First-generation microcombustor built

14. Applications for MEMS • Pressure transducers • Accelerometers • Gyroscopes • New areas • Optical switches • Gas turbines • Nano-satellite systems • Drug delivery • Power MEMS

15. Switches for fiber-optic networks • Many possible approaches, MEMS and non-MEMS • 3D: much higher density of switches than 2D, MEMS fabrication required

16. Space applications

17. Advanced aircraft applications • “Smart skin” - senses & reduces air drag • Micro-mixing enhancement in engines • Sensing in Gas turbine engine Environment • Flow • Vibration • Temperature • Strain • Pressure Sensors for Stall/Surge Control • Fuel Valve Position Sensors • Chemical Sensors for Emissions Monitoring

18. Microfluidic system for bio-chemical sensing

19. Drug delivery systems • Micromachined needles connected to individual microvalves and supply reservoirs • Each reservoir may contain different type/concentration of drug • May be combined with on-chip biosensor

20. Drug delivery systems (2) (a) Drug delivery chamber (b) Two electrodes (AgCl/Ag electrode and IsOx electrode) for monitoring pH (c) Metal valves

21. MEMS Market (U. S. estimate)

22. Conclusions (MEMS) • Many potential MEMS applications - has been demonstrated in USA • China can become a significant force in MEMS development because of its existing infrastructure and its large yet highly educated workforce • What can the government do to help? • Difference between Japan and USA: USA time from research to market is much shorter - why? • Support and stimulate joint collaborative research between universities and companies • Attract different sources of funding to sustain research - government, workshop registration fees, company staff training • Government provides funds to university for facilities that companies can rent to test new ideas before buying their own facilities • DARPA funds applied research on MEMS but allow universities and companies to retain intellectual property rights for non-government applications

23. Conclusions (MEMS) • Expect 95 of 100 projects to fail (success of other 5 will more than pay for 95 failures) • Balance between “traditional” MEMS areas and “radical” new areas • Traditional Chinese successes in international markets based on production cost advantages, especially lower labor costs • High technology successes in high value-added markets depend on making use of skilled, educated, motivated Chinese workforce • How to judge the future of MEMS technologies? • High value added - unit cost of complete system is high • Enabling technology - can’t work without MEMS devices • Collaboration between industry and universities essential • Inter-disciplinary activity essential

24. Microscale power generation (Power MEMS) • USC effort supported by U. S. Defense Advanced Research Projects Administration (DARPA)

25. The challenge of microcombustion • Hydrocarbon fuels have numerous advantages over batteries • ≈ 100 X higher energy density • Much higher power / weight & power / volume of engine • Inexpensive • Nearly infinite shelf life • More constant voltage, no memory effect, instant recharge • Environmentally superior to disposable batteries • … but converting fuel energy to electricity with a small device has not yet proved practical despite numerous applications • Foot soldiers • Portable electronics - laptop computers, cell phones, … • Micro air and space vehicles

26. The challenge of microcombustion • Most approaches use scaled-down macroscopic combustion engines, but may have problems with • Heat losses - flame quenching, unburned fuel & CO emissions • Heat gains before/during compression • Limited fuel choices – need knock-resistant fuels, etc. • Friction losses • Sealing, tolerances, manufacturing, assembly

27. Smallest existing combustion engine Cox Tee Dee .010 Weight: 0.49 oz.Bore: 0.237” = 6.02 mmStroke: 0.226” = 5.74 mmDisplacement: 0.00997 cu in (0.163 cm3)RPM: 30,000Power ≈ 3 watts

28. Some power MEMS concepts Wankel rotary engine Free-piston engine

29. Some power MEMS concepts Issues • Friction, heat losses • Very tight manufacturing tolerances • High production cost • Very high rotational speed needed to achieve compression (speed of sound doesn’t scale!) • Fuel: may always need to run on hydrogen Micro gas turbine engine (MIT)

30. Some power MEMS concepts Non-IC engine concepts: possible enabling technologies, but don’t address complete system

31. Our approach - microFIRE • Integrated microscale power generation system • Combustion • Heat transfer • Electrical power generation • Fabrication & assembly • “Swiss-roll” heat recirculating burner with toroidal 3-D geometry • Direct thermoelectric conversion of heat to electricity • Monolithic fabrication of the entire device with EFAB • Being developed by MEMGen, Inc. • > $10 million venture capital funding in first year of existence

32. C o m b u s t i o n v o l u m e 1 6 0 0 1 4 0 0 7 0 0 6 0 0 5 0 0 P r o d u c t s R e a c t a n t s 1 6 0 0 1 2 0 0 5 0 0 4 0 0 3 0 0 K microFIRE approach (1) – Combustion • “Swiss roll” heat recirculating burner - minimizes heat losses Toroidal 3-D geometry - further reduces losses - minimizes external temperature on all surfaces One-dimensional counterflow combustor / heat exchanger Two-dimensional “Swiss-roll” burner

33. microFIRE approach (2) - Power generation • Thermoelectric (TE) power generation elements embedded in wall between hot (outgoing product) and cold (incoming reactant) streams

34. 100 mm microFIRE approach (3) - Fabrication • EFAB (Electrochemical Fabrication) • Enables fabrication of arbitrarily complex 3D structures • NASA Jet Propulsion Laboratory proprietary process for electrochemical deposition of Bi2Te3 thermoelectric elements - Process-compatible with EFAB, enabling monolithic fabrication of entire device! • Targets • Weight 500 mg • Volume 0.04 cc • Power 100 mW • Efficiency > 10%

35. microFIRE advantages • Integrated combustor / heat exchanger / power generation • Heat losses / flame quenching problems minimized • External T (IR signature, touch-temperature hazards) minimized • Direct conversion, no moving parts! • No friction losses • No tight manufacturing tolerances • Rugged, reliable, low maintenance • Quiet, stealthy, no vibration • Long life (no wear or fatigue-induced breakage) • Compact • Can use wide variety of conventional hydrocarbon fuels without pre-processing

36. Fabrication of macroscale test devices • Development approach: build macroscale models, test, develop numerical simulation capability, design microscale device • Soligen™ rapid prototyping process for 2-D and 3-D designs in Al2O3 - SiO2 ceramic

37. Mesoscale experiments • Wire-EDM fabrication • Pt igniter wire / catalyst

38. Combustion modes • Combustion usually in “flameless” mode - no visible flame!

39. Quenching limits • Area-averaged V can be 30x stoichiometric burning velocity, even with mixture 33% leaner than conventional lean limit & no insulation • Lower limit can be reduced dramaticallywith catalytic Pt strips …but it can also be increased dramatically

40. Numerical modeling • FLUENT software package, 2D & 3D simulations

41. Numerical modeling High % fuel Low % fuel Reaction rates Temperatures

42. Conclusions (microFIRE) • Combustion in microscale devices feasible even at low temperatures compatible with thermoelectric elements, but will probably require heat recirculation & catalytic assistance • Combustion behavior under such conditions quite different from conventional flames • Expect similar findings in most other microscale systems - performance cannot be predicted based only on macroscale results

43. Challenges for Power MEMS • microFIRE-specific • Developing & calibrating gas-phase & surface chemistry sub-models • Modelling electrochemical processes - rely less on empirical testing • Catalyst preparation, degradation & restoration • Challenges for all micro-chemical/thermal/fluid systems • Auxiliary components - valves, pumps, fuel tanks • System integration and packaging

44. Thanks to • Chongqing Science & Technology Commission • Chongqing University • … and especially U. S. Defense Advanced Research Projects Administration (DARPA) Microsystems Technology Office !!!