MEMS Microelectromechanical Systems NEMS Nanomechanical Systems and NanoDevices

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MEMSMicroelectromechanical SystemsNEMSNanomech
anical Systems and NanoDevices
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Introduction

• MEMS are interdisciplinary in their design,
  fabrication, and operation. They encompass many
  aspects of
• Engineering
• Mechanical (structures and phenomena bending,
  deflecting, oscillations, vibrating fluid
  dynamics)
• Electrical (electrical signals detected,
  generated, processed optoelectronics Integrated
  circuits and devices)
• Chemical and Biochemical (reactions, processes,
  and kinetics of many systems including living
  organisms)
• Science
• Physics and Biophysics (external world vs.
  materials/properties including living organisms
  at macro and nano scale)
• Chemistry, biochemistry, and physical chemistry
  (step more from corresponding engineering
  disciplines towards basic answers)
• Biology (macro and nano effects in plants,
  animals, and humans observed by smart
  transducers)
• Technology
• Macro ex. Fluidics and large mechanical
  structures
• Micro ex. µm scale dimension of transducers, and
• Nano ex.nanodevices CNT, nanoprobes .)

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Integration of Various Scienceand Engineering
Fields
Very powerful performance possible but difficulty
in realization comes due to the interdisciplinary
character of MEMS
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Building Blocks

• Major components in MEMS systems include
• Design
• Much more difficult than IC designs due to the
  interdisciplinary character of MEMS
• Design includes packaging
• Packaging is one of the most challenging step
  both in design and realization
• Transducers must be integrated with electronics
• Integration with ICs is another challenge for
  MEMS due to difficult issues of process
  compatibility
• Fabrication
• Silicon technology is widely used in MEMS with
  new step added
• Dimensions are usually much larger than those in
  ICs even for nano-transducers. To feel NANO you
  do not need to be in the nano-scale size!
• Other materials are included to perform required
  functions of transducers
• MEMS are frequently integrated with fluidics
  (polymers, glass)
• Materials
• Materials that can perform required functions
  (thermo, piezo-, magneto-resististance)
• Interaction with fluidics (half-cell potential,
  corrosion)

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MEMS as a part of CMOS integrated systems
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MEMS as a part of CMOS integrated systems
High complexity of MEMS elements possible
(multi-functional sensing) together with advanced
electronic detection/signal processing. The
trend is to operate sensors in the rf-regime.
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History of MEMS

• Elements of MEMS are almost as old as Integrated
  Circuits (1965???), they originated from ICs but
  found wide acceptance and applications much
  later.
• First MEMS structures evolved from modification
  of Si processes (1970)
• Membranes, cantilevers, nozzles
• and by introducing new materials
• piezoelectric, piezoresistive, now nitrides,
  diamonds ., porous silicon (large active sensing
  area)
• thus producing
• Pressure sensors of high sensitivity also for
  harsh environment operation, chemical capacitive
  sensors.

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Newer History

• Silicon micromachining started in 1980s
• Bulk micromachining, which uses silicon substrate
  (more 3D structures) such as in-jets (also for
  biological molecules
• surface, which uses thin
• silicon films more 2D structures)
• springs, gear trains, rotors..

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MEMS were born.

• Rapid growth of MEMS in 1990s (Japan, Europe,
  then US). Many types of MEMS developed
  mechanical, electrical (wiredwireless), optical,
  chemical .

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Mechanical Structures Were Developed First

• Electromechanical MEMS sensors became very
  popular beams, membranes, hinges .
• Advantages over macroscopic systems sensitivity,
  miniaturization, low noise.
• Applications pressure sensors, accelerometers,
  gyroscopes, micromirrors (digital multimedia)

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Micromechanical Structures

• Micromirrors (gt100k) in a Digital Light Processor
  by Texas Instruments the idea came from etching
  experiments.
• Addressed individually using row-column
  multiplexing (SRAM in CMOS) Digital Micromirrors
  (10x10µm2)
• Advantages bright, high contrast, stability
• Applications image projection, optical
  communication and others maskless lithography,
  DNA microarrays for light assisted synthesis.

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Major MEMS Categories
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Micromechanical Structures

• Mechanical structures as electrical elements

Tunable capacitor tunable inductor
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BioMEMSBiological MEMS

• BioMEMS are used in biology, biophysics,
  biochemistry, medicine, and pharmacy

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Communication from/to/within MEMS

• Traditional electrical signals
• Optical communication microoptoelectromechanical
  systems MOEMS (speed is important)

• Optical signals switched traditionally by
  optical/electrical/optical (OEO) transformation
• Turning optical signals into electrical using
  optical receiver arrays
• Electronics signal processing
• Transforming signals back to optical domain

Includes optical Elements and interconnects
Or directly using optical switches
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Intrinsic Characteristics of MEMS

• Miniaturization dimensions of MEMS structures
  are much larger than in VLSI ICs (µm). Further
  scaling leads to NEMS (nano) that are
  comparable/smaller than ICs (1-100 nm).
• Scaling laws describe how properties/behavior
  change with dimensions
• Scaling of spring constants (ex. behavior of
  cantilevers
• Scaling Law of Area-to-Volume Ratio
• (important in all surface effects forces
  friction, tension, van der Waals etc)
• Microelectronics Integration - the most widely
  used is that with CMOS

E- Young modulus of elasticity l, w, t -
dimensions
Decreasing length of cantilever smaller spring
constant, higher resonance frequency (GHz) and
quality factor (50,000), better sensitivity
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Scaling and DimensionsSpecifically important in
Bio-applications
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Trends in ScalingSi Microeletronics and MEMS
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Devices Sensors and Actuators

• Energy domains
• and Transducers

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Sensors

• Fall into two categories
• Physical force, acceleration, pressure,
  temperaure, magnetic/electric field strength etc.
• Chemical/biological pH, reactions, binding
  between molecules etc.
• Characteristics
• Sensitivity
• Linearity
• Responsivity (large signal-to-noise ratio SNR
  required)
• Johnson noise, a with noise
  , thermal fluctuation, (kBoltzmanns
  constant, Rresistance, Bbandwidth), Gaussian
  distribution
• Shot noise (quantum fluctuation)
• 1/f noise or flicker (pink) noise,(conductance
  fluctuation when currents flow)
• Thermal-mechanical noise floor (mechanical
  motion of elements)
• SNR
• Dynamic range (highest to lowest signals)
• Bandwidth (bandpass)
• Drift (degradation and change of operational
  points)
• Sensor reliability (related to stability of
  operation independently of conditions)
• Cross talk or interference (individually tested
  parameters should not be affected by other
  measurements/signals)
• Development cost and time (vary depending on
  designs and technology, simulations are very
  important in shortening the time-to market)

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Actuators

• Transform energy from/to the mechanical domain
  into/from others electrical (piezoelectricity,
  electrostatic), thermal, magnetic etc.

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Design aspects of actuators

• Torque and force output capacity. Sufficient
  force must be delivered as a response of the
  sensed phenomena.
• Range of motion. Should be adequate to the
  sensed phenomena.
• Dynamic response speed should be fast and
  bandwidth adequate.
• Ease of fabrication and availability of materials
  used for MEMS fabrication.
• Power consumption should be small (portable
  devices) and energy efficiency high.
• Linearity of displacement as a function of
  driving bias.
• Cross-sensitivity and environmental stability.
• Footprinttotal chip area. Arrays frequently
  used for complementary measurements.