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f ot i e o c What is Stiction?
At the micro-scale, the forces associated with the stiction effect
are often greater than other micro-forces.
As a result, if stiction is present in a micro-system, it can dominate
the system. This usually has negative effects, such as microobjects sticking together with no way to separate them, or high
amounts of dissipative loss between two objects in sliding contact. © N. Dechev, University of Victoria 25 Stiction vs. Friction
Friction occurs between two objects in contact with each other and
a normal force Fn, between them. The frictional force Ff depends
on the coefficient of friction, and is independent of contact area, as
Fn In this sense, if the normal force is removed, the force of friction
will be gone.
Stiction is an adhesion force that will occur ‘upon contact’
between objects, and will keep the two objects in contact
indefinitely, even if the initial force that brought the two objects
together is gone.
Stiction is directly proportional to surface area of contact.
© N. Dechev, University of Victoria 26 The Causes of Stiction for MEMS
Stiction will occur upon contact between micro-objects, so a good
question may be:
Why did that contact occur in the first place?
Fluid surface tension effects due to the drying process after
the HF release of sacrificial layers
Shock loading or rapid acceleration that can bring two
Inadequate stiffness of supporting micro-beams against
gravity or normal operation
Desired contact by design © N. Dechev, University of Victoria 27 The Causes of Stiction for MEMS
Once contact has occurred, there are four major phenomena that
individually contribute to the ‘overall effect’...
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