Biomedical Engineering Reference
In-Depth Information
in.Figure.8.39..he.square.and.circular.actuators.supported.by.folded.springs.were.found.to.tilt.when.
they.were.actuated,.which.led.to.premature.pull-in.(Fernandez.2010)..he.X-beam.actuators.used.ixed-
guided.springs,.which.are.stifer.than.the.folded.springs..he.ixed-guided.springs.provide.a.nonlinear.
restoring.force.when.they.are.displaced.more.than.the.thickness.of.the.spring.layer,.and.if.the.actua-
tor. starts. to. tilt,. the. corner. that. tilts. down. the. most. further. stretches. the. spring,. increasing. the. non-
linear.spring.force..his.provides.a.feedback.mechanism.for.vertical.displacement.rather.than.tilting..
he.trade-of.for.the.stifer.nonlinear.spring.is.an.increased.actuation.voltage..he.actuator.shown.in.
Figure 8.40.required.377.V.to.obtain.a.displacement.of.9.7.μm..To.decrease.the.actuation.voltage,.either.a.
smaller.gap.or.more-lexible.springs.must.be.used..he.gap.on.this.actuator.was.28.5.μm.and.the.average.
thickness.of.the.spring.layer.was.∼3.5.μm..he.gap.can.be.decreased.to.20.μm.and.the.spring.layer.to.
∼2.μm.to.decrease.the.actuation.voltage.
Gold. mirror. layers. were. electrodeposited. on. top. of. the. actuator. arrays. to. fabricate. DMs.. Gold. is. a.
good.relector.in.the.IR.spectrum,.as.used.in.astronomy.and.two-photon.microscopy,.and.it.does.not.
tend.to.oxidize,.so.it.can.be.packaged.without.a.mirror.to.protect.it.from.the.environment..his.elimi-
nates.two.passes.through.a.glass.surface.as.would.be.required.for.DMs.packaged.behind.a.protective.
window..he.small.deformations.that.can.be.seen.on.the.mirror.surface.shown.in.
Figure.8.41
.result.from.
residual.tensile.stress.in.the.electrodeposited.gold.layer..hese.deformations.result.from.torques.placed.
(a)
(b)
(c)
FIGuRE 8.39
Solid. models. of. diferent. electrostatic. actuator. designs.. (a). Square. actuators. supported. by. eight.
folded.springs.at.the.corners..(b).Circular.actuators.supported.by.four.folded.springs..(c).X-beam.actuators.sup-
ported.by.four.ixed-guided.beams..(From.Fernandez,.B..R..and.J..Kubby,.
J Micro/Nanolitho MEMS MOEMS.
,.9,.
041106-1,.2010.)
FIGuRE 8.40
White. light. interferogram. showing. an. X-beam. actuator. displaced. by. 9.3. μm. at. 377. V.. (From.
Fernandez,.B..R..and.J..Kubby,.
J Micro/Nanolitho MEMS MOEMS.
,.9,.041106-1,.2010.)
