Tutorial on Micro Electro Mechanical Systems (MEMS)

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1 Tutorial on Micro Electro Mechanical Systems (MEMS) Bruce Kim Department of Electrical, 1

2 ! What is MEMS! Why MEMS! Applications! MEMS Fabrication! MEMS Packaging! Conclusion MEMS 2

3 WHAT IS MEMS! MEMS CONTAINS COMPONENTS OF 1 MICROMETER TO 1 MILLIMETER! CONSTRUCTED TO ACHIEVE A CERTAIN ENGINEERING OR FUNCTIONS BY ELECTROMECHANICAL OR ELECTROCHEMICAL MEANS. 3

4 A MEMS structure 4

5 A gear chain with a mite 5

6 ELEMENTS OF MEMS! TWO PRINCIPLE COMPONENTS! SENSING OR ACTUATING ELEMENT! SIGNAL TRANSDUCTION UNIT 6

7 MEMS AS MICROSENSOR supply Input signal Micro sensing element Trans duction unit Output signal 7

8 Background of MEMS! The first monolithic integrated piezo resistive pressure sensor was in 1971 at CWRU! High volume commercial by National semiconductors in 1974! First capacitive pressure sensor was built in

9 Why MEMS! Small Size! Light Weight! Enhanced permance and reliability! Array Of Devices! Low Cost! High Integration! Added functionality 9

10 SILICON BASED MICRO SENSOR MARKET YEAR UNITS, 1000 REVENUE,mil lion $ Avg unit price,$ Revenue growth Rate,%

11 APPLICATIONS! In automotive Industries! Health care Industry! Aerospace Industry! Telecommunications 11

12 MEMS IN AUTOMOTIVE INDUSTRY! Air Bag deployment! Antilock Braking Systems! Fuel Pump Pressure and Fuel Injection Control! Suspension Systems! Tire Pressure! Engine coolant Temperature and quality 12

13 Accelerometers 13

14 MEMS IN HEALTH CARE! Disposable Blood Pressure! Infusion pump pressure sensors --- to control the flow of intravenous fluids.! Respirators! Kidney dialysis equipment! Lung capacity meters 14

15 A pressure sensor 15

16 MEMS IN AEROSPACE! COCKPIT INSTRUMENTATION PRESSURE SENSORS FOR OIL, FUEL, TRANSMISSION AND HYDRAULIC SYSTEM.! SAFETY DEVICES EJECTION SEAT CONTROLS! MICROGYROSCOPES FOR NAVIGATION AND STABILITY CONTROL! ALTIMETERS! AIRSPEED MEASUREMENT! WIND TUNNEL INSTRUMENTATION! MICROSATELLITES 16

17 Micro needles Biocompatibility Harsh environment Used Today: Space Missions used on shuttle flights RF interrogation JPL looking to add functionality 17

18 MEMS IN COMMUNICATION 18

19 OPTICAL MEMS 19

20 MEMS 20

21 FABRICATION! SURFACE MICROMACHINING! The structural layer has the desired thermal and mechanical properties.! The sacrificial layer supports the structural layer until it is etched Si substrate 21

22 Surface micromachining 22

23 Surface micromachining 23

24 Deposit and pattern oxide oxide 1. Si substrate Sacrificial etch 2. Deposit and pattern poly Poly silicon 3. anchor cantilever Si substrate Si substrate 24

25 Fabrication! LIGA LIthography Galvanomung [Electroplating] Abmung[Injection moulding]! Used to make very high aspect ratio micro moulds that can be used high high volume manufacture Plastic structures 25

26 ! Thermal Forces! Shape-memory alloys! Piezoelectric crystals! Electrostatic ces! Electromagnetic ces Actuation of MEMS 26

27 Actuation- Thermal Forces! Bimetallic strips are actuators! Bonding two materials with distinct thermal expansions! The strip bends when heated or cooled due to difference in thermal expansion. a1 a1>a2 a2 27

28 Shape memory alloys! The alloy tend to turn to their original shape at a preset temperature. SMA (TiNi,Nitinolor) Resistance heating strip Silicon cantilever beam Constraint base 28

29 Piezoelectric crystals! Certain crystals (like quartz) dem with application of electric voltage and vice versa.! Displacement X = dvl/h d=piezo coefficient V= applied voltage L = length H= height of dielectric in between the electrodes electrodes cantilever Constraint base crystal V 29

30 Electrostatic ces! Electrostatic ces are more widely used as the drivers actuators! Coulomb's law ce between two particles F = q 1 q 2 /(4Πεr 2 ) Distance r F q 1 q 2 30

31 Electrostatic ces in parallel plate V F d L F = ε o ε r wlv/(2d) W electrodes A micro gripper 31

32 MEMS FOR HIGH POWER! A HIGH RATING IS OBTAINED BY USING MANY COMPONENTS OF LOW RATINGS.! USING ELECTROMAGNETIC ACTUATION METHOD v SERIES PARALLEL LOAD 32

33 MEMS PACKAGING! MEMS cannot be packaged using conventional IC techniques! Fragile MEMS structure and delicate membranes! Must be packaged immediately to prevent stiction, etc.! A hermetically sealed environment should be present. 33

34 MEMS packaging! At wafer level Release and packaging is done low cost! At Die level they are packaged in ceramic cavity packages. But they are expensive. Singulate and release 34

35 MEMS packaging! Efficient way is to do the release at Wafer Level Packaging(WLP)! Much smaller packages are possible 35

36 packaging! Wafer level MEMS packages used in industries BULK WAFER CAPS 36

37 ! Advantages! Robust! Hermetic! Wafer Level BULK wafer cap Used in accelerometers,gyroscopes,image sensors 37

38 Micro assembled caps ALIGN BOND SEPERATE 38

39 PACKAGING OF EXISTING MEMS 39

40 MEMS market Breakdown 40

41 CONCLUSION! MEMS is a fast growing technology! Success of MEMS is in Design,Process and packaging! Low integration devices! Various packaging techniques present! Wafer level packaging in necessary low cost MEMS 41