Hi Jingbo,
you forgot to give the wavelength :-)
For mirror done with surface micromachining using the MUMPS process our
experience is as follow:
- the coating is Au, thus for wavelength at 800nm the reflectivity is greater
than 97%, but it drops to 40% only at 500nm.
- at 800 nm again the theoretical reflectivity of Poly-Si is 0.35, while the
transmittance of 1.5um layer will be about 3% and 1% for 2um thick poly.
This parameters can be obtained using Fresnel formulas and a databook.
- for the roughness, measured on different mirrors made using different
combination of structural layer we had between 2.3 and 2.6 nm RMS.
Interestingly the roughness was larger (3.2nm) on the polysilicon without the
Au layer.
- a last parameter that you may need is the radius of curvature, which depends
a lot on the stress in the layers :  for the run we tested, and 1.5um poly it
was 1.9mm while for 3.5um thick layer it was 22mm.
However if you look at the specification from Cronos, you'll see that it is
hard to predict this value, because the stress in the layer may vary
substantially...

The mirrors here were about 300umX300um.

For your last question, it seems it can be... but it depends on the
wavelength!
Hope it helps!
Franck

"-----Original Message-----
"From: Zhang JingBo [mailto:[email protected]]
"Sent: Friday, 18 January, 2002 17:39
"To: [email protected]
"Subject: [mems-talk] refractive index & reflectivity data wanted
"
"
"Dear All,
"
"I need some data of surface micromachined mirrors urgently and
"seek for your
"knowledge/experience.
"
"1. the typical refractive index (n) and extinction coefficient (k) of
"polysilicon layers
"2. the reflectivity (R) and the RMS roughness (sigma) of the
"mirror surface
"after Au coating.
"
"The required data are RMS roughness <15 nm and an ideal
"reflectivity >0.94. Do
"you think these requirement can be met?
"
"Your info is highly appreciated
"
"Dr Jingbo Zhang
"From Singapore
"
">>>  01/17/02 04:29AM >>>
"Hi all !
"I am Dr.P. Sergey Soukhoveev. Recently I have been developed
"some novel way
"in design and fabrication of ultra-high aspect ratio mems
"devices (nano- and
"um scale) by using fiber-glass technologi without any
"lithography. Right now
"I have been developed some different approaches to batch-fabrication of
"different microdevices (say for example 3d-dc-micromotors with
"magnetostatic
"bearings, micro-channel mems-devices, actuators for microwings, etc.).
"My problem is how to find any help to creat and realize my Programe for
"unusel 3d MEMS.
"Best Regards
"Sergey Soukhoveev
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