Scaling Effects Flashcards
Smaller things are less affected by __-
Volume dependent phenomenon: Inertia, mass, heat storage, magnetic force
Smaller things are more affected by __
SA dependent phenomenon: friction, heat dissipation, electrostatic force
As we scale down, ___ happens much more rapidly than -__
volume decreases much more rapidly than surface area. Thus,
(SA/ Vol) increase rapidly
How is stress related to scale?
Stress in members is directly proportional to size. As size decreases, internal stress decreases
How does scale effect the resonant f and Q factor of a cantilever?
- Resonant f increases rapidly
- Q factor (stored energy / lost energy) = much less sensitive to pressure
How does scale effect buoyancy?
Smaller bubbles have significantly less volume and more surface area- they are much less buoyant
What happens to flow regimes in the MEMs scale?
Since the Reynolds number is «< 1 for MEMs scale, flow is almost always laminar with no turbulence
What happens to diffusion n the MEMS scale?
T= 2Dl^2, where T is the diffusion time for distance l. Clearly, as scale decreases, diffusion time decreases proportionally
What happens to surface tension in the MEMs scale?
Surface tension scales linearly with decreasing size. Can damage or stick down MEMs structures, or this phenomenon can be use for assembly
What causes stiction?
- capillary forces
- van der waals force
- hydrogen bonding
- electrostatic attraction
What can stiction do during release?
when rinse water dries, stiction can permanently deform parts to that they stick to the substrate
What can help relieve stiction?
- surface treatments: self assembled monolayers, flourocarbon coatings, diamond like coatings
- dry gas phase etchants
- critical point etching that uses supercritical Co2 for release
