Hi Mike,

As Glenn suggested, I've seen some pretty black metal oxides.  In
particular, a colleague of mine had some pretty black films using
reactively sputtered copper (Copper target with Ar/O gas flow) to form CuO
(cupric oxide).  You may have to play around with the power/O2 flow, but
you could probably get something relatively low temperature and reasonably
black.  You may have to check on the electrical properties afterwards to
see if it would suit your purposes.  Alternatively, you could deposit a
very thin copper film and then try using an O2 plasma..

I believe CrOx is sometimes used for black films as well (including the
black matrix for some LCDs).  In fact, you may be able to find some useful
materials if you start looking into what else they're using as a black
matrix.

Good luck,
Alasdair

PS:  Regarding black silicon, after a quick look it does appear as though
some people are able to get back films using PECVD a-Si:H, so it may be an
avenue for you to explore as well.  I don't personally have any experience
with it, so I can't offer you any advice in that regard.


On Thu, Jan 5, 2012 at 10:03 AM, Mike Whitson  wrote:

> Hello all,
>
> I'm trying to identify possible materials / vendors for a broadband
> (vis-MWIR) optical absorbing layer to be integrated in an optical MEMS
> device.  In the past, we've used a spin-coatable black polyimide for the
> purpose (purchased from Brewer), but they no longer make or sell the
> material.  Wondering if anyone has suggestions for an alternative vendor or
> material.  What we're looking for:
>
> * High broadband optical absorption.  Ideally a single material spanning
> the entire range from ~300-5000 nm would be good, but sets of materials
> with broad absorption bands (eg one for visible, one for 3000 - 5000 nm)
> would also work.  Ideally absorption should be high enough to perform well
> at sub-wavelength coating thicknesses.
>
> (Good absorption at i- and g-line wavelengths to act as a kind of BARC
> during photolithography would be a bonus, but not a requirement.)
>
> * Spin coatable.
>
> * Electrical resistivity as high as possible.  Given that one way to make
> such a material is by impregnating carbon black in a polymer matrix, I
> understand that getting a truly insulating material may be tough.
>
> * Patternable.  Ideally a diretly photopatternable material would be
> wonderful; if not, something amenable to a lift-off or etch process (say O2
> RIE with a hard mask) would be sufficient.
>
> * Long life.  This will be a permanent part of the optical device;
> polymers that can be crosslinked or otherwise cured would be preferable.
>
> If anyone has suggestions for vendors or even particular materials, I'd be
> grateful.
>
> -Mike