Bound Mobile Lubricants QCM Experiments

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Bound Mobile Lubricants QCM Experiments

• Brendan Miller
• Worakarn Neeyakorn
• Sang Min Lee
• Adam Hook
• Chris Brown
• Jacqueline Krim
• Physics Department
• NCSU

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Progress ReportThrust III MEMS

• Perform Quartz Crystal Microweighing (QCM)
  mobility studies of bound plus mobile phases to
  document nanodynamical behavior of candidate
  lubricants that directly overlap with the
  modeling efforts.

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MEMS (Micro Electro-Mechanical systems)
Adhesion of micromachined structures to the
underlying substrate after the final sacrificial
layer etch
?

• This release related stiction problem is largely
  remedied by SAMs such as OTS (Octadecyltrichloros
  ilane).
• SAMs have limitations however for friction
  reduction,
• Its also difficult to apply them uniformly to
  obtain 100 coverage of the silicon surfaces.

Vapor Phase Lubricant
Alternative approach?
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Vapor Phase Lubricants in extreme environments

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Quartz Crystal Microbalance (QCM)

• Thin crystal disk oscillates in a shear mode
• Adsorbed material lowers the resonant frequency
  
• fads
  (4fres2/Zq)(m/A)

• If the shear stress is below about 103 N/m2, it
  will slip
• enough to be detected by the QCM
• The slip time (?) is deduced from Q and f

(Krim and Widom, PRB, v. 38, n.17, 1988)
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Experimental Setup
Figure shows a diagram of experimental setup (top
view). An experimental crystal is placed in the
middle.
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TCP and TBPP uptakes results
We have performed a quartz crystal microbalance
(QCM) study of the nanotribological properties of
organo-phosphate (TCP and TBPP) layers adsorbed
from the vapor phase onto silicon (amorphous
silicon and MEMS-like polysilicon), and OTS
treated silicon. The latter systems have been
studied in order to explore whether
organophosphates and OTS in combination might
prove synergistic from a tribological point of
view. The below table shows the results of 3-5
monolayers of adsorbed film.
Table 1 Summary of experimental results from
TBPP and TCP uptake on Si, Clean Si
and OTS surfaces. The film thickness is listed
in units of monolayers.
(W. Neeyakorn, M. Varma, C. Jaye, C. Grant, J.
Krim, submitted to Tribology Letters)
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QCM study on Amorphous and Crystalline Silicon

• Perform the QCM experiments on the MEMS-like
  silicon surfaces and compare with results of
  amorphous Silicon.
• Si is deposited onto Ti layers to a thickness
  of 1000A? by solid source Si-Ge MBE (375oC, RMS
  14.43nm).

Figure 4 Raman Spectroscopy of a-Si and Poly-Si
samples. The presence of crystalline silicon is
confirmed by the intense peak feature located at
520 Rcm -1. ( Sang Min Lee, James Burnett,
Robert Nemanich, NCSU)
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The Morphology of Si-film on QCM Measured by AFM
poly-Si (375oC), RMS14.43nm
Amorphous Si (commercial), RMS6.31nm
amorphous-Si (350oC), RMS9.65nm
poly-Si (400oC), RMS18.42nm
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Auger Analysis

• Auger surface scan of the vapor phase lubricant
  exposed/OTS-coated silicon surfaces after 1 hour
  run.

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Current Project Status

• We have now completed the project where we
  performed a QCM
• study of the nanotriobological properties of
  organophosphate (TCP and
• TBPP) layers adsorbed from the vapor phase onto
  both silicon, and
• OTS treated silicon.
• The QCM experiments on the MEMS-like
  Polysilicon surfaces
• were carried out. However, coating the
  polysilicon surface with OTS
• Became challenging since the solution delaminated
  the deposited
• silicon layer.
• The preliminary studies of the
  sensitivity of film layer to the
• environmental gases (Ar and CO2) were also
  carried out.

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• Parallel MEMS project in our group
• From the result of this study, the most
  promising candidates are then screened on
  Friction testers (from M. Dugger, Sandia National
  Laboratory) to study the frictional and wear
  characteristics.
• Publication
• This work was already submitted to Tribology
  Letters.
• Polysilicon deposition technique using MBE

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• 4 Month Plan
• Study VPL uptakes on different SAMS coating
  (PFTSperflourodecyltrichlorosilane)
• Test the bound and mobile lubricants on the
  actual MEMS devices and compare the result.
• Silicon wafers (1cmx1cm) will be coated with
  different bound and mobile lubricants to be
  analyzed and studied
• Nanoindentation
• Ellipsometry
• AFM
• Auger Electron Spectroscopy.

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Future Work

• Take QCM data on different combinations of bound
  plus mobile lubricants
• PFTS and OTS
• Ethanol
• Trifluorolethanol
• Fomblin PFPE lubricants
• Publish results of these findings and the results
  of silicon wafer studies

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