Back in Singapore
after a few days in Kuala Lumpur
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| KL Skyline |
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| Petaling Street KL |
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| Guan Di Temple KL |
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Guan Di Temple KL
Singapore Skyline
from Top of Ion Orchard
A few more
thoughts on reliability issues for MEMS (Micro Electro Mechanical Systems).
Stiction
Why is it such a HUGE problem?
- Forces
attracting the surfaces > forces pulling them apart (spring forces)
- In the
macro world not a big problem but in the micro world it is
- Surface
area scales with dimensions squared but volume and mass scale with dimension
cubed
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| Elephants Don't Climb Walls |
Forces that
attract surfaces:
- Capillary
forces (Long range micrometres, moist environment, rough surfaces)
- Electrostatic
forces (Long range, micrometres, dry environment smooth or rough surfaces)
- Hydrogen
bridging (Close range, OH terminated
smooth surfaces in a dry environment)
- Van der Waal’s
forces (Short range, smooth surface close together in a dry
environment, hydrophobic )
What can be done about it?
- For capillary induced stiction reducing the relative humidity can help
if the packaging allows it. Not always possible
- Minimise surface contact area:
- For bending cantilevers, try to have an arc shape rather than and
"s" shape to minimise surface area of contact.
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Minimise area of ContactImage based on http://www.me.unm.edu/~zleseman/news/news.htm
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- Create
surface roughness or dimples on contact surfaces
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Three-mask process for cantilever:
(a) mask I, dimples in oxide
(b) mask 2, anchor in oxide
(c) structural poly deposition and mask 3, poly pattern
(d) sacrificial oxide layer etching
From:Introduction to Microfabrication, Sami Franssil, John Wiley, 2010
- Coat surfaces with low surface energy materials such as diamond like carbon (DLC),
Self Assembly Monolayers (SAMs)
From::
Vapor-Phase Self-Assembled Monolayers for
Anti-Stiction
Applications in MEMS, Yan Xin Zhuang et al
Journal Of
Microelectromechanical Systems, 16(6), pp1451-1460, 2007
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