@. Nano-Electro-Mechanical Switches. David Elata On sabbatical leave from Faculty of Mechanical Engineering Technion - Israel Institute of Technology Visiting at Stanford University Professor Roger T. Howe. #.
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International Technology Roadmap for Semiconductor Evaluation of Emerging Research Devicesfor "Beyond CMOS" information processing.
Two types of devices considered:NEM relayandNEM-FET
power management and
static and non-volatile memory
Intel paper: Ma et al. "Metal contact reliability of RF MEMS switches", SPIE 6463, 646305, 2007.
Zero off-state current
Zero sub-threshold swing (naturally digital)
Theoretical prediction 1~10ns
due to mechanical motion [2,3]
K. Akarvardar et al. "Design Considerations for Complementary Nanoelectromechanical Logic Gates", IEDM 2007, 299-303, 2008.
K. Akarvardar et al. "Energy-Reversible Complementary NEM Logic Gates", 66th DRC, 2008.
●Structures must be compensated for residual and thermal stress (average and gradient) - no cantilevers or membranes, symmetric structures preferable.
●Deformable structures must be made from amorphous or single crystalline(avoid grain-size effects ).
The unwarranted impact bouncing and release vibrations may be alleviated by using the energy-reversible operation scheme .
Fabrication of laterally actuated devices facilitates symmetric design which enable energy-reversible operation.
S. Givli et al., Int. J. Solids and Struct., 40, 6703-6722, 2003.
All demonstrated nano-switches to date (NEM cantilever beam, CNT, nanowire) required voltages higher than CMOS (3~10V).
The energy-reversible scheme has the potential for lower operation voltage, but is yet to be demonstrated.
Fast operation requires low contact resistance but too little resistance leads to failure  (Three-terminal device currently characterized):
W. W. Jang et al. "Fabrication and characterization of a nanoelectromechanical switch with 15-nm-thick suspension air gap", App. Phys. Lett., 92, 103110, 2008.
Contact conduction (cont'd):
Conduction at the nano-scale must be better understood to improve design. In macroscopic relays, where free particles have no effect, the dynamic electrode 'scratches' the static electrode. Abrasive contact in NEMS is not an option.
In test devices, switches are loaded through pads that have huge parasitic capacitance, therefore switches drain uncontrolled current upon contact. In actual devices this capacitance will be lower.
RF ohmic switches that were tested in air (even with N2 purge), failed due to polymerization of organic molecules on the contacting electrodes . This failure mechanism turns ohmic switches into capacitive switches.
Hermetic packaging of test devices seems to be crucial.
Casimir and van der Waals surface interaction forces must be better modeled, and characterized with test structures 2<g<15nm. (calibrate the effects of finite conductivity and surface roughness).
Surface interaction forces may be used to increase contact force, and latch the switch in contact (turning switch into non-volatile memory).
U. Mohideen et al. "Precision Measurement of the Casimir Force from 0.1 to 0.9 um", Phys. Lett. Rev., 81, 4549 - 4552, 1998.
●Coveted: high stiffness, high strength, low density, low resistance, chemical and mechanical stability.
Aligned CNT structural layers micromachined by masking/plasma etching .
Y. Hayamizu et al. "Integrated three-dimensional microelectromechanical devices from processable carbon nanotube wafers", Nature Nanotechnology, 3, 289-294, 2008.
Dynamic threshold voltage
low sub-threshold leakage with high on-state current
Low sub-threshold swing (2mV/decade).
Conduction through channel in semiconductor - no ohmic contact required.
Driving voltage:mV range + fast switching, while retaining high Con/Coff. Is it possible at the nano-scale?
Nano switch + capacitive RF-MEMS
40nm gate oxide,12V pull-in  3 MV/cm - Frenkel-Pool leakage
Fixed (injected) charge in dielectric isolation layer can be used to achieve non-volatile memory.
Can dielectric charging be controlled?
Capacitive switches are adversely affected not only by the net (average) fixed charge but also by its spatial distribution (variance) .
Possible remedy: Raytheon Schottky switch with recombination of injected charge .
N. Abele et al., "Suspended-gate MOSFET: bringing new MEMS functionality into solid-state MOS transistor", IEDM 2005, 479-481, 2005.
X. Rottenberg et al. "Analytical model of the DC actuation of electrostatic MEMS devices with distributed dielectric charging and nonplanar electrodes", JMEMS, 16, 1243-1253, 2007.
B. Pillans et al. "Schottky barrier contact-based RF MEMS switch", MEMS 2007, 167-170, 2007.
Thermal dependence of dielectric charging.
Charging in logic NEM-FET, discharging in NEM-FET non-volatile memory.
Hermetic sealing important as in RF-MEMS
Beyond CMOS - more than Moore:
NEM-FET nano resonator 
Resonant Suspended Gate MOSFET
C. Durand et al. "In-Plane Silicon-On-Nothing Nanometer-Scale Resonant Suspended Gate MOSFET for In-IC Integration Perspectives", Electron Device Letters, 29, 494-496, 2008.
Out-of-plane nano switch 2008, KAIST
Lateral E-R nano switch
2008, EPFL + IEMN
Thank you for your attention