Biomedical Engineering Reference
In-Depth Information
of.silicon..his.membrane.is.coated.with.either.an.aluminum.or.a.multilayer.dielectric.ilm..he.bottom.
of. the. mirror. layer. is. metalized. with. conductive. gold. to. deine. the. counter. electrode. for. actuation. of.
the.mirror..he.mirror.is.actuated.by.applying.voltage.to.the.conductive.gold.actuator.pads.deined.on.
the.silicon.pad.array.substrate..Figure.8.27.(bottom).shows.a.cross.section.of.the.membrane.structure,.
including.the.top.aluminum.relective.coating,.the.middle.structural.silicon.nitride.membrane,.and.the.
bottom.gold.conductive.coating..A.thin.chromium.layer.is.sometimes.used.to.increase.adhesion.for.the.
aluminum.relective.layer.and.the.gold.conductive.coating..he.total.thickness.of.the.metalized.mem-
brane.is.approximately.1.25.μm.thick..he.silicon.frame.chip.is.bonded.to.the.silicon.pad.array.substrate.
using.lip-chip.solder.bonding.with.precision.spacer.beads.to.deine.the.gap.
Push-Pull Membrane Mirror :.Adaptica.has.designed.and.fabricated.a.push-pull.membrane.DM.by.
adding.additional.transparent.electrodes.over.the.top.side.of.the.mirror.membrane,.in.addition.to.the.
usual.backside.electrodes.that.are.used.in.the.membrane.mirrors.from.Flexible.Optical.B.V..and.Agile.
Optics,.as.described.earlier..A.cross.section.of.the.Adaptica.mirror.is.shown.in.Figure.8.28..By.using.
Reflective coating
(Aluminum or multilayer dielectric)
Silicon nitride
mirror membrane
( ~ 1 μ m thick)
Silicon
frame
Silicon
frame
Solder bond
with precision
spacer beads
Silicon pad array
substrate
Conductive gold
coating on back
of membrane
Conductive gold actuator pads
Cross section of agile optics deformable mirror
Aluminum reflective coating
Chromium
adhesion
layers
Total thickness
1.25 μ m
Silicon nitride mirror membrane (1 μ m thick)
Gold conductive coating
Typical membrane structure
FIGuRE 8.27 MEMS.deformable.membrane.mirror.from.Agile.Optics.. Top :.A.bulk.micromachined.chip.pro-
vides.a.silicon.frame.that.supports.a.silicon.nitride.mirror.membrane..he.silicon.nitride.has.a.relective.coating.
(aluminum.or.a.multilayer.dielectric).on.the.front.side.of.the.mirror.and.a.gold.counter.electrode.on.the.back.side.of.
the.mirror..he.silicon.frame.chip.is.lip-chip.bonded.to.a.silicon.pad.array.substrate.using.precision.spacer.beads.
to.deine.the.gap.between.them..he.silicon.pad.array.substrate.has.conductive.gold.actuator.pads.that.can.be.biased.
to.delect.the.mirror.membrane.. Bottom :.A.cross.section.of.the.metalized.silicon.nitride.mirror.membrane..(Credit:.
From.Justin.Mansell,.Active.Optical.Systems,.LLC..With.permission.)
Transparent
electrodes on glass
Glass substrate
Electrodes
on PCB
Amplifiers array
0-300 V
FIGuRE 8.28 Push-pull.mirror.from.Adaptica..In.addition.to.backside.electrodes.that.are.deined.on.the.bottom.
side.PCB,.there.are.also.upper.electrodes.on.the.front.side.deined.in.transparent.conducting.indium.tin.oxide.(ITO)..
(Credit:.Adaptica,.Italy.)
 
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