2.008 Design & Manufacturing II. Spring 2005 Sang-Gook Kim. MEMS/Nano I spring-2005 S.G. Kim 1. Nano/Micro in ME

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1 2.008 Design & Manufacturing II Spring 2005 Sang-Gook Kim MEMS/Nano I spring-2005 S.G. Kim 1 Nano/Micro in ME My Office: 1-310, sangkim@mit.edu, MEMS/Nanomanufacturing Suggested Reading Microsystem Design by Stephen D. Senturia Massachusetts Institute of Technology Published by Kluwer Academic Publishers, 2001 Fundamentals of Microfabrication BY Marc Madou CRC, 1998 & Small is not small enough? spring-2005 S.G. Kim 2

2 Nano/Micro in ME Fluidics, heat transfer and energy conversion at the microand nanoscale Bio-micro-electromechanical systems (bio-mems) Optical-micro-electromechanical systems (optical-mems) Engineered nanomaterials Nano-Manufacturing Course 2A (Nanotrack) Micro/Nano Group in ME x.html spring-2005 S.G. Kim 3 Moore s Law The number of transistors per chip doubles every 18 months. Moore s Law - Small is not small enough Year of introduction Transistors , , , , , , DX ,180,000 Pentium ,100,000 Pentium II ,500,000 Pentium III ,000,000 Pentium ,000, spring-2005 S.G. Kim 4

3 Why shrink things? Use less materials, energy, power Faster response, better sensitivity, simpler, better accuracy and reliability Performance/$ Minimally invasive spring-2005 S.G. Kim 5 Why shrink things? Shock and impact Scale and form factor Load carrying capability Spider silk v.s. steel spring-2005 S.G. Kim 6

4 Frog, Water Strider, Gecko spring-2005 S.G. Kim 7 K. Autumn, Learn from the nature, but never try to mimic the nature. Biomimetic researches spring-2005 S.G. Kim 8 A. Geim, U. Manchester

5 O O S O O O O O O O O O O O S O S O S O S O O S O O S O S Human hair ~ µm wide Red blood cells with white cell ~ 2-5 µm The Scale of Things -- Nanometers and More Things Natural Dust mite 200 µm Ant ~ 5 mm Fly ash ~ µm ATP synthase The Microworld The Nanoworld 10-2 m 10-3 m 10-4 m 10-5 m 10-6 m 10-7 m 1 cm 10 mm 1,000,000 nanometers = 1 millimeter (mm) 0.1 mm 100 µm 0.01 mm 10 µm 1,000 nanometers = 1 micrometer (µm) 0.1 µm 100 nm Things Manmade MicroElectroMechanical devices µm wide Red blood cells Pollen grain 10-8 m 0.01 µm ~10 nm diameter 10 nm Nanotube electrode Ultraviolet Visible Infrared Microwave Zone plate x-ray lens Outermost ring spacing ~35 nm Head of a pin 1-2 mm Nanotube transistor DOE st Century Challenge Combine nanoscale building blocks to make novel functional devices, e.g., a photosynthetic reaction center with integral semiconductor storage P O O 10-9 m 1 nanometer (nm) DNA ~2-1/2 nm diameter Atoms of silicon spacing ~tenths of nm m Soft x-ray 0.1 nm Quantum corral of 48 iron atoms on copper surface positioned one at a time with an STM tip Corral diameter 14 nm Carbon nanotube ~2 nm diameter Office of Basic Energy Sciences Office of Science, U.S. DOE Version Micro to Nano 20 th Century - Microelectronics and Information Technology Semiconductors, computers, and telecommunication 21 st Century - Limits of Microsystems Technology --- Nanotechnology Moore s law Hard disc drive John Bardeen, Walter Brattain, and William Shockley at Bell Laboratories, First Transistor spring-2005 S.G. Kim 10

6 Limit of Optical Lithography W = k λ/na (Rayleigh Eqn.) In 1975, 405 nm (Hg H-line) at an NA of 0.32, a line width of 10 µm deep-uv (248-nm), 193 nm, 157nm Table 1: Wavelength "Generations" Intel Road Map Nanoimprinting Soft Lithography Dip Pen Lithography SPM-based patterning 193 nm immersion lithography spring-2005 S.G. Kim 11 Year Node Lithography nm i/g-line Steppers nm i/g-line Steppers nm i/g-line Steppers nm i/g-line Steppers nm i/g-line Steppers nm i-line -> DUV nm DUV nm DUV nm DUV nm 193nm nm 193nm -> 157nm nm 157nm -> EUV nm and below EUV Immersion Lithography Exposure UV Light mask photoresist substrate Developing W = k λ/na (Rayleigh Eqn.) NA= n sin a α: acceptance angle Air, n=1 Water, n= nm, sin α ~0.93, resolution factor k~0.25 W in Air? Immersion? spring-2005 S.G. Kim 12

7 Aerial density, hard disk Superparamagnetic Effect a point where the data bearing particles are so small that random atomic level vibrations present in all materials at room temperature can cause the bits to spontaneously flip their magnetic orientation, effectively erasing the recorded data spring-2005 S.G. Kim 13 MEMS (Microelectromechanical Systems) Intergrated systems of sensing, actuation, communication, control, power, and computing Tiny, Cheaper, Less power, material.. New functions!!! (chemical, bio, µ- fluidic, optical, ) spring-2005 S.G. Kim 14

8 MEMSMEMS MEMSTechnologies Optical MEMS RF MEMS Data Storage Bio. MEMS Power MEMS MEMS for Consumer Electronics MEMS In Space MEMS for Nano. Materials Processes Systems spring-2005 S.G. Kim 15 Courtesy: Sandia national laboratory History of MEMS Y.C.Tai, Caltech spring-2005 S.G. Kim 16

9 Tiny Products Airbag sensors: Mechanical vs. MEMS DLP (Digital Micromirror Array) DNA chip Optical MEMS spring-2005 S.G. Kim 17 Tiny Products Airbag sensors: Mechanical vs. MEMS spring-2005 S.G. Kim 18

10 Tiny Products DLP (Digital Micromirror TM Array) DLP 10 6 micromirrors, each 16µm 2, ±10 tilt (Hornbeck, Texas Instruments DMD, 1990) spring-2005 S.G. Kim 19 Segway -Tilt -Rotation spring-2005 S.G. Kim 20

11 Vibrating Gyroscope Coriolis Acceleration y z x By Charles Stark Draper Laboratory spring-2005 S.G. Kim 21 Actuation of MEMS devices + insulator - conductive layer conductive substrate Force magnetic layer substrate Force Electrostatic actuation + - EM coil Electromagnetic force + - patterned resistive layer Force + - patterned resistive layer Force substrate substrate Thermal Actuation Piezoelectric Actuation spring-2005 S.G. Kim 22

12 Electrostatic Comb Drive/sensing Paralle Plate Capacitor Capacitance=Q/V=ε A/d d ε Dielectric permittivity of air (8.854x10-12 F/m) Electrostatic Force = ½ ε (A/d 2 ).V 2 Pull-in point: 2/3 d K spring-2005 S.G. Kim 23 Comb Drive C= ε A/d = 2n ε l h/d C = 2n ε l h/d Electrostatic force F el = ½ dc/dx V 2 = n ε h/d V 2 l l V d x spring-2005 S.G. Kim 24

13 Suspension mode failures y x x spring-2005 S.G. Kim 25 Comb Drive Designs linear AC Signal DC Bias AC Signal (180 phase shift) Grating beams Flexures Electrostatic comb-drives rotational spring-2005 S.G. Kim 26

14 ADXL 50 accelerometer Capacitive sensing Comb drive spring-2005 S.G. Kim 27 Swing Analyzer with Tri-axial accelerometer spring-2005 S.G. Kim 28

15 SOI (Silicon on insulator) Begin with a bonded SOI wafer. Grow and etch a thin thermal oxide layer to act as a mask for the silicon etch. oxide mask layer Si device layer, 20 µm thick buried oxide layer Si handle wafer Etch the silicon device layer to expose the buried oxide layer. silicon Thermal oxide Etch the buried oxide layer in buffered HF to release free-standing structures spring-2005 S.G. Kim 29 Microfabrication process flow Single-mask process IC compatible Negligible residual stress Thermal budget spring-2005 S.G. Kim 30

16 Process Flow Wafers Devices Photo resist coating Pattern transfer Photo resist removal Deposition Lithography Etch Oxidation Sputtering Evaporation CVD Sol-gel Epitaxy Wet isotropic Wet anisotropic Plasma RIE DRIE spring-2005 S.G. Kim 31 Micromachining processes Bulk micromachining Surface micromachining Bonding LIGA x-ray lithography, electrodeposition and molding spring-2005 S.G. Kim 32

17 LIGA (lithographie galvanoformung abformtechnik) X-ray on PMMA, electroplating metal and molding polymer High aspect ratio >100:1, up to 1000 µm x-rays Mask PMMA Wafer Ni electroplating Molded Polymer spring-2005 S.G. Kim 33 LIGA parts Sandia National Laboratory spring-2005 S.G. Kim 34

18 Bonding Silicon Direct Bonding (Silicon Fusion Bonding) Anodic Bonding(Electrostatic Bonding, Field Assisted Thermal Bonding) Intermediate Layer Bonding MIT Microturbine Project Epstein, Schmidt, et al, MIT spring-2005 S.G. Kim 35 Bulk, Surface, DRIE Bulk micromachining involves removal of the silicon wafer itself Typically wet etched Inexpensive equipments IC compatibility is not good. Surface micromachining leaves the wafer untouched, but adds/removes additional thin film layers above the wafer surface. Typically dry etched Expensive equipments IC compatibility, conditionally. Polysilicon p-si Anti-stiction bump spring-2005 S.G. Kim 36

19 Bulk machining Square nozzle Pumping ink? spring-2005 S.G. Kim Piezoelectric ink jet 37 Ink jet printer A quasi-mems case Thermal jet by HP Superheat ink 250oC Peak pressure 1.4 MPa Refills in 50µs spring-2005 S.G. Kim 38

20 Thermal ink jet spring-2005 S.G. Kim 39 Pressure sensor spring-2005 S.G. Kim 40

21 Surface Micromachining Deposit sacrificial layer Si PSG By HF Poly by XeF2 Pattern anchors Deposit/pattern structural layer Etch sacrificial layer spring-2005 S.G. Kim 41 Surface micromachining Structure sacrificial etchant Polysilicon Silicon dioxide HF SiNx PSG HF Silicon dioxide polysilicon XeF2 SiNx polysilicon XeF2 Aluminum photoresist oxygen plasma spring-2005 S.G. Kim 42

22 Residual stress gradients More tensile on top Less tensile on top Just right! spring-2005 S.G. Kim 43 Micromirror Arrays XGA 1024 X ,432 pixels VGA 640 X ,200 pixels Human Hair 50 µm spring-2005 S.G. Kim 44

23 Materials Metals Al, Au, ITO, W, Ni, Ti, TiNi, Insulators SiO 2 - thermally grown above 800 o C or vapor deposited (CVD), sputtered. Large intrinsic stress Si x N y insulator, barrier for ion diffusion, high E, stress controllable Polymers: PR, SU-8, PDMS Glass, quartz Silicon stronger than steel, lighter than aluminum single crystal, polycrystalline, or amorphous spring-2005 S.G. Kim 45 Silicon Atomic mass average: Boiling point: 2628K Coefficient of linear thermal expansion: / C Density: 2.33g/cc Young s modulus: 47 GPa Hardness scale: Mohs 6.5 Melting point: 1683K Specific heat: 0.71 J/gK Electronic grade silicon % purity spring-2005 S.G. Kim 46

24 Materials Single crystal silicon Anisotropic crystal Semiconductor, great heat conductor Polycrystalline silicon polysilicon Mostly isotropic material Semiconductor Semiconductor Electrical conductivity varies over ~8 orders of magnitude depending on impurity concentration (from ppb to ~1%) N-type and P-type dopants both give linear conduction. Two different types of doping Electrons (negative, N-type) --phosphorus Holes (positive, P-type) --boron spring-2005 S.G. Kim 47 Silicon Ingot Czochralski (CZ) method Float Zone (FZ) method. 1 to 12 diameter spring-2005 S.G. Kim 48

25 2.008-spring-2005 S.G. Kim 49 Miller indices [abc] in a cubic crystal is just a directional vector (abc) is any plane perpendicular to the [abc] vector ( )/[ ] indicate a specific plane/direction { }/< > indicate equivalent set of planes/directions [001] [abc] [010] b c a [100] spring-2005 S.G. Kim 50

26 Crystallographic planes [001] {100} (001) [010] [100] (100) (010) spring-2005 S.G. Kim 51 Crystallographic planes [001] [100] (110) [010] (111) (001) o spring-2005 S.G. Kim 52

27 Wafers of different cuts (111) (100) (110) (111) (100) (111) o Bulk Si spring-2005 S.G. Kim 53 Anisotropic wet etching When a (100) wafer with mask features Oriented to <110> direction is placed in an anisotropic etchant. A square <110> oriented mask feature results in a pyramidal pit spring-2005 S.G. Kim 54

28 Pressure sensor spring-2005 S.G. Kim 55