Several years ago, I experimented with the use of CYTOP, a spinnable amorphous
perfluoropolymer, for a very similar purpose.  (I was bonding PZT to Si and
lapping the PZT to about 50 µm.)  I don't have info on the chemical resistance
of CYTOP to KOH, but I'd expect a fluorinated polymer to be fairly inert.  CYTOP
isn't really designed as an adhesive, but it worked "well enough" for my
purposes - when I put the bonded unimorph into a tensile tester, the mounting
adhesive always failed before the CYTOP bond.  I have one reference citing a
bond strength around 4 MPa.

If you're doing wafer-to-wafer in a bond aligner, this probably isn't an issue
for you, but the biggest problem I faced was surface-surface wedge correction;
if the surfaces aren't parallel, the effective bond area becomes tiny.

Looking back to my notes from that time, I note some references to the use of
eutectic (solder), and Au and glass thermocompression bonding for such purposes
as well.  If your layers can tolerate the higher temperatures and pressures
required, those might be a more robust alternative to polymers.  Here are a few
relevant citations I have lying around:


K. Tanaka et al. : “Fabrication of Microdevices Using Bulk Ceramics of Lead
Zirconate Titanate”, Japanese Journal of Applied Physics, Vol.44, No.9B,
pp.7068-7971 (2005)

K. Oh et al. : “A Low-Temperature Bonding Technique Using Spin-On Fluorocarbon
Polymers to Assemble Microsystems”, Journal of Micromechanics and
Microengineering, Vol.12, pp.187-191 (2002)

K. Tanaka, E. Takata, and K. Ohwada : “Anodic Bonding  of Lead Zirconate
Titanate  Ceramics to Silicon  With  Intermediate  Glass Layer”, Sensors and
Actuators A, Vol.69, pp.199-203 (1998)

K. Turner et al. : “Bonding of Bulk Piezoelectric Material to Silicon Using a
Gold-Tin Eutectic Bond”, Materials Research Society Symposium Proceedings,
Vol.687, pp.B3.2.1-B3.2.6 (2002)

J. Cheong et al. : “Reliable Bonding Using Indium Based Solders”, Proceedings of
SPIE, Vol.5343, pp.114-120 (2004)


Good luck,
Mike Whitson


On Aug 11, 2010, at 8:45, James Paul Grant wrote:

> Hello all,
>
> Does anyone know of a permanent spin on 'glue' that is temperature stable (up
to 140oC), KOH resistant, transparent and is not attached by acetone?
>
> It might help if I explain why I require such a glue:
>
> I'd like to permanently bond a lithium niobate wafer to a slicon wafer. The
Lithium niobate wafer will then be lapped down to a thickness or around 10
microns. Next I would like to etch a 1 mm by 1 mm window in the silicon
structure such that the 10 microns of lithium niobate is essentially free
standing.
>
> Has anybody got any experience of such a technique?
>
> Any comments are most welcome.
>
> James