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Carbon Nanotube Based Electrostatic NEMs Devices. Jeffrey Chou March 5, 2008 EE 235. MEMS Based Comb Drive Actuators. As voltage is increased, electrostatic forces bring combs together. Spring is required for restoring force. Rotational Actuators based on Carbon Nanotubes.

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mems based comb drive actuators
MEMS Based Comb Drive Actuators
  • As voltage is increased, electrostatic forces bring combs together.
  • Spring is required for restoring force.
rotational actuators based on carbon nanotubes
Rotational Actuators based on Carbon Nanotubes
  • DC or AC voltages applied to S1, S2, and S3. (~5V)
  • Control position, speed, and direction of rotation

[Fennimore et al. “Rotational Actuators Basd on Carbon Nanotubes”, Nature 2003]

mwnt rotor formation
MWNT Rotor Formation
  • With high voltages, sheer off outer layers of a MWNT to expose a rotating inner layer. (~80V)
  • Utilize the low friction bearing behavior
  • Fabrication
    • E-beam Lithography
    • Deposit Gold/Cr
    • Lift off process
    • Etch oxide substrate
  • Asymmetric rotor plate causes a net torque when there is an applied electric field.
  • Rotational Velocity is theoretically very high, however direct measurements were limited by the video camera framerate

[Bourlon et al. “Carbon Nanotube Based Bearing for Rotational Motions”, Nano Letters 2004]

carbon nanotube based switches
Carbon Nanotube Based Switches
  • Length: 2microns,
  • Width: 70nm
  • After voltages are turned off, 1st and 2nd nanotubes are still stuck together by Van Der Waals forces
    • Good for non-volatile memory
  • Off state can be restored by earth grounding 1st, floating ground 2nd, and 20-25V on 3rd.

[Jang et al. “Nanoelectromechanical Switches with Vertically Aligned Carbon nanotubes”, Applied Physics, 2005]

shorter nanotube switches
Shorter Nanotube Switches
  • When voltages are off, nanotubes return to off state.
  • Length: 1.4 microns
  • Width: 70nm
  • F = 8E*I*d/L^3
  • As nanotubes become shorter, their restoring forces become greater than the attractive Van Der Waals forces.
  • Multi Wall Carbon Nanotubes low interlayer friction provides good rotational motion.
  • High conductivity of carbon nanotubes work well with electrostatic forces.
  • Carbon Nanotubes are key to effective NEMS devices.