Lecture 1 Introductions of NanoMicro ElectroMechanical System - PowerPoint PPT Presentation

Title: Lecture 1 Introductions of NanoMicro ElectroMechanical System


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Lecture 1Introductions of Nano/Micro
Electro-Mechanical System
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Feynmans Vision

• There is plenty of room at the bottom (1959)
• To print Encyclopedia Britannica on a pin head of
  diameter of 1.6 mm? shrink 25,000 times in linear
  scale, i.e., a dot will be 8 nm in size
• If we can store 24 million books (1015 bits) in a
  1/200 inch crystal, each dot is stored with 5x5x5
  atoms
• DNA molecules use approximately 50 atoms to store
  one bit of information
• Manipulating and controlling things on a small
  (atomic?) scale

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William McLellans Micro Electric Motor
The motor is 3.81 mm wide. The huge object above
it is the head of a pin.
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What are MEMS/NEMS?

• MEMS/NEMS is a batch-fabricated integrated nano-
  and microscale system performing sensing,
  computing and actuating functions
• MEMS/NEMS is a way of making things -
  fabrication technology
• MEMS/NEMS is a methodology operation, design
  and analysis of nano- and microsystems

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What are MEMS?

• MEMS are systems that integrate
• sensing, actuation, computation, control,
  communication and power subsystems
• Functional block-diagram of MEMS

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Benefits from Micro-systems

• Miniaturization save materials, save power,
  faster time response, better performance
• Integration integrated with IC and other
  systems, reduce system size and cost save
  adapters and interconnections.
• Batch fabrication cheap, disposable (most
  important driving force)

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How are NEMS/MEMS made?

• NEMS/MEMS are not just assembly of very small
  components. System integration is achieved
  through the monolithic process similar to IC
  fabrication (in design and manufacture)
• NEMS/MEMS fabrication shares a lot of tools and
  process techniques developed for IC industry,
  such as photolithography, etching, etc.
• There are some novel techniques specifically
  developed for NEMS/MEMS micro-fabrication
  purpose, such as LIGA, Micro-molding, etc.

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CMOS based processing techniques

• Photolithography
• Oxidation
• Diffusion
• Ion Implantation
• Thin film Deposition
• Etching
• Metallization

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IC process technology
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Novel micromachining techniques

• Bulk Micro-machining
• Surface Micro-machining
• LIGA (Lithographic, Galvanoformung,
  Abformtechnik) process
• Novel processing techniques
• Self-assembly techniques

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Surface and Bulk Micromachining
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LIGA Examples

• 200mm deep structures
• Coat with thick resist
• Pattern with X-rays
• Electroplate exposed area with Ni
• Machine to /- 5mm
• Use titanium and Cu as sacrificial layers

MCNC
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Focused Ion Beam Milling

• Apply ion beam directly onto substrate through a
  mask
• No resist layer
• Anisotropic
• Be able to make thick microstructure (about 100mm)

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Laser-assisted Chemical Deposition

• Chemical deposition from vapor phase by
  laser-assisting
• Laser Nd-YAG (neodymium yttrium aluminum garnet)
  or Ar
• Substrates
• - silicon
• - carbon
• - boron
• - oxides
• - nitrides
• - carbides
• - borides
• - metals

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SAM (Self-Assembled Monolayers)
The two different thiols are injected into glass
filters. They diffuse slowly and attach to the
gold substrate.
alkanethiolate SAM preparation on gold substrates
in the (111) preferred direction
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What are NEMS/MEMS made of?

• Si, SiO2 and Si3N4 are most popular materials
  used in NEMS/MEMS.
• - IC process compatible (mature process
  techniques)
• Si is brittle, strong, good thermal, hydrophilic,
  stable to chemicals, bio-friendly, and can be
  very pure with best known impurity control
• SiO2 is a good insulator, very stable solid form
  (not easily dissolved or etched), not permeable
  to most molecules except alkali ions (in
  particular sodium and potassium), hydrophobic,
  residual charge have known way to control
• Si3N4 is also a good insulator, very rigid, very
  stable and not permeable to most molecules,
  serious residual charging

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Popular Metals in MEMS

• Al has low melting point, is easy to fabricate,
  noncorrosive, may cause spikes in Si (but good
  bonding), usually doped with 2 Si for better
  properties
• Au, Ti, W and silicides are also popular
  alternatives.
• For better conductivity Ag, Cu, Au and Al (in
  order)
• For better resistance to electromigration use
  doping or metals with higher atomic weight.
• Metal bi-layers to solve adhesion (Cr, Ti, Ni,
  Pt)
• Transparent contact ITO (indium-tin-oxide), but
  notice its high resistivity

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Comparison of Si MEMS properties
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Transducer

• Transducer a device that converts one form of
  energy to another
• Energy forms as input and output
• thermal temperature, heat, heat flow,...
• mechanical position, velocity, acceleration,
  force,
• pressure, ...
• chemical concentration, composition, reaction
  rate
• optical intensity, wavelength, phase,
  polarization
• magnetic field intensity, flux,
  magnetization, etc.
• electrical voltage, current, charge,

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Sensor and Actuator

• Sensor and actuator are kinds of transducers
• Sensors
• magnify/demagnify an environmental perturbation
  (signal/noise) and transform into an observable
  energy form
• Actuators
• use small controlled energy to cause an
  observable (or controllable) perturbation
  (movement/energy radiation) to the environment

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Transducing Materials Piezoresistivity

• Piezoresistivity pressure (or stress) to change
  in resistivity
• Si is the most popular piezoresistive material.
• Crystalline Si larger sensitivity, poly or
  amorphous less temperature perturbation
• Piezoresistivity is usually a strong function of
  the carrier type and the crystal orientation

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Transducing Materials Piezoelectricity

• Piezoelectricity pressure (or stress) to charge
  or fields
• Piezoelectricity only exists in materials with
  ionic bonds and non-cubic lattice structures
  (based on charge polarization asymmetry)
• Popular piezoelectric materials PZT (lead
  zirconate titanate, a ceramic), ZnO, BaTiO3, PVDF
  (polyvinylidenefluoride), Quartz, GaN and SiC.

Materials with large piezoelctricity usually have
very large permittivity too (the degree of
polarization)
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Perovskite Structure

• Perovskite is a cubic unit cell with Ti at the
  corners, O at the midpoints of the edges, and Ca
  in the center
• Stress induces uneven displacement of anions and
  cations (electric dipole)

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Transducing Materials Thermoelectricity

• Thermoelectricity conversion between heat
  (temperature) and electricity
• Two thermoelectric effect Seebeck effect and
  Peltier effect
• Applications thermal sensors, refrigerators and
  generators
• Popular thermoelectric materials SiGe, Bi2Te3,
  PbTe, Alumel, Cromel, Nicrosil,

Seebeck effect
Peltier effect
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Design of NEMS/MEMS

• Micro- and Nano-scale operation principles
• - Microscale Classical Mechanics and
  Electromagnetics
• - Nanoscale Quantum effects, Nanoelectromechanic
  s
• Feasible fabrication process flow
• - Manufacturable
• - Cost effective
• Analysis and modeling of devices and systems
• - Gather learning (many micro- and nanoscale
  phenomena
• are against intuitions)
• - Saving development time and cost

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Micro- and Nano-scale operation principles

• Micro- and Nano-scale physics may behave
  differently in macro-scale world, e.g. Sticking
  effect, surface tension, quantum tunneling effect
• Surface effects are playing more important roles
  in the operational physics of micro- and
  nano-structures and devices
• - What is the ratio of surface atoms/all atoms
  for a cube of size 1 cm3, 1 mm3 and 1 nm3 ?
• - Assume atomic size 0.25nm,
• 1 nm3 (64-8)/640.875
• 1 mm3 (6x40002)/(4000)30.0015
• 1 cm3 (6x(4x107)2)/(4x107)31.5x10-7

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Scaling analysis

• Most physical quantities (force, mass, volume,
  etc.) scale differently with dimension L
• Example weight-lifting of human being. Assume
  the muscle stress is the same for different human
  body size,
• Body weight L3
• Weight-lifted
• (muscle stress) x (area)
• constant x L2
• (Body weight)2/3

World weight-lifting record Vs. Body weight
Log weight-lifted
Log body weight
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Challenges and Opportunities

• Proportional scaling only applied to objects in
  limited size range
• New phenomena and operation principles are
  associated with nano-scale structures and systems
  
• More fundamental research activities, engineering
  practices and leading-edge fabrication
  technologies are required for the deployment of
  MEMS/NEMS

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Design strategy

• System integration systematically analyzes the
  system and its components for every detail to
  make best resource management and scheduling on
  manufacturing, design, functions, cost,
  marketability, and reliability
• Design integration build model hierarchy through
  reduction and abstraction for reasonable design
  space in each layer and division (divide,
  conquer...., and integrate)

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Design process
Standard MEMS design process
Standard IC design process
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Examples of MEMS Applications

• Mechanical transducers
• Strain gages, Accelerometers, Gyroscopes,
  Pressure sensors, Microphones, Electrostatic
  motor, Shape Memory Alloy, Piezoelectric,
  Mechanical resonators, Mechanical Relays and RF
  switches
• Optical transducers
• Photo conductive sensors, Junction-based photo
  detectors, Capacitive photo sensors, Thermal
  Optical detector, Light Emitters, Reflective and
  Transmissive Micromechanical light Modulators,
  Fiber optic couplers, Reflective components
  (mirror), Transmissive components (Wave guide,
  lenses), Filters, Integrated Optical systems
• Magnetic transducers
• Hall effect sensor, Flux gate, Tunneling,
  Motors, Eddy current detector, Magnetic
  read/write head, Micro-Inductors

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Examples of MEMS Applications

• Thermal transducers
• Thermal Resistive, Thermal Couple, Junction
  based Thermal sensors, Thermal Gas pressure
  sensor, Flow sensor, Humidity sensor and Peltier
  effect heat pumps
• Chemical and Biological transducers
• Passive Chemical Sensors, Electrochemical
  Transducers, Biosensors, Biological Chemical
  Sensors (taste Odor), Thin Film Batteries,
  Penetrating Neural Probes
• Fluid devices
• Flow Channel, Mixer, Pumps, Valve, Separator,
  Droplet generators, Filters, Interconnects, Flow
  sensors, Viscosity/Density Sensors, Ink-Jet
  printer heads

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Sandias micro mechanical lock
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Micro-Motor and Micro-Mirror
Electrostatic Micro Motor fabricated from Si
(Texas Instruments)
Micro Mirror (Lucent Technologies)
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Piezoresistive Pressure Sensor
Thickness of diaphragm lt 1 mil. (25 mm)
Die size 105 mil. x 105 mil. (2.67 mm x 2.67 mm)
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Magnetic Transducer
Magnetic Read/Write head
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Thermoelectric Modules
Laser cooling modules
Fiber optics cooling modules
Telcom cooling module
Infrared sensor
Power generator
Multi-stage module
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Bio-chemical transducer
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Penetrating Neural Probe
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Biological chip (lab-on-a-chip)
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Smart Pill (drug delivery system)