You can easily make a torsion hinge from polysilicon for a 45 degree
rotation -- just make it long enough.  For a rectangular cross section
of width t, the strain in the material is
e = 2 * pi * theta * ( t/2 ) / L
where L is the length of the torsion beam, and theta is the deflection
angle.  For poly-Si, the fracture strain is about 2%, so for a safety
factor of 2 and a beam width and thickness of 2 um, the length should be
L = (2 * pi * pi/4 * 2 um / 2 / (2%/2) = 493 mm.
If this is too long, you can make a folded torsion beam to effectively
increase the length, something that might look like this:

--------------------------
                         |
   -----------------------
   |
   --------------------------(mirror attached here)


Good luck!

Rob Conant
UC Berkeley
http://www-bsac.eecs.berkeley.edu/~rconant



-----Original Message-----
From: Rose Zhang [mailto:zhang@ino.qc.ca]
Sent: Friday, March 05, 1999 6:44 AM
To: MEMS@ISI.EDU
Subject: MEMS: micro-mirror


Hello!

We are trying to design a micro-mirror with a deflection angle of 40 to 45
degree. However, if we use torsion hinge, the stress of the hinge at 45
degree exceeds the yield strength of most materials. I wonder whether you
have any suggestion about what materials and what hinge types are best
suitable for this kind of application.

Your help would be greatly appreciated.

Rose Zhang
Photonics Materials & Processes
Nationa Optics Institute
369 rue Franquet, Ste-Foy
Que, Canada
Tel: (418)657-7406x506
Fax:(418)657-7009