From: davec@ultra.com (Dave Chapman {Ultra IBM SW Manager})
Subject:  Long-Term Information Storage
Summary:  Technology exists for thousand-year text storage
Organization: Ultra Network Technologies
Date: Wed, 8 Apr 92 02:43:15 GMT

   Thinking about the problem of storing documents for
several thousand years (about 10 years ago), I came up with
the idea of steel microfilm.
   Using chip technology, thin steel microcards could be
coated with photoresist, exposed to an image, and then
selectively etched.  The result would be a microcard made
of thin stainles steel, about 3x5" (75x125 mm), holding
about 20 or 50 pages of images.  A "shoebox" of cards 0.1 mm
thick would contain 2000 cards, or 50,000 pages.
   In 1982, at Yale's EE Department, I did a little work on
the project:  Using 35 mm black and white film, four negatives
were used.  One was Hokusai's "View of Mt. Fuji" (I forget
which one), and the others were English text.  We had a great
deal of trouble getting the images onto a test wafer,
because the optics were all set up to use circular chip masks.
Eventually, the system imaged properly onto the wafer, and
work stopped.  It was possible to read the micro-images,
and I am confident that the images could have been etched onto
(for example), an aluminum-coated silicon wafer.
   Work stopped because of limited time, and because it became 
obvious that, while the lab was set up to etch circular silicon
objects, rectangular steel objects would require a lot of
technology development.
   Stainless steel objects are presumed to have an extremely 
long life.  A box of such cards would have three main failure
modes:  Slumping, embrittlement, and sticking together.
Slumping requires that a grade of stainless steel be chosen
such that the crystal structure is well-defined, without too
many amorphous or microcrystalline zones.  Embrittlement 
requires that the material have a low diffusion constant, and
that the alloy not contain too many different metals.  In a
certain sense, the requirements for slump and embrittlement
contradict each other.  I suspect that a high nickel alloy would
be best, with either iron/nickel or iron/nickel/chromium
being optimal.
   The cards would first be coated with a thin film of either 
silicon oxide or aluminum oxide.  This would be a combination 
protective layer/anti-reflection coating.  When viewing the cards, 
the background should appear to be brown, and the etched letters 
should appear to be reflective.
   Sticking together is solved by coating the cards with something
which is soft, does not diffuse into the stainless steel,
and is non-corrosive.  Candidate materials include gold, silver,
copper, lead, polyethylene, indium oxide, calcium flouride,
germanium oxide, cellulose, nylon, paraffin, and magnesium silicate.
None of these materials is optimal.  Today, I would use paraffin,
which is a mixture of C12H26, C13H28, and C14H30.
   The design life of these records is 5000 years.  I suspect 
that 10,000 year life would be more typical (assuming that none
of the cards are used as razor blades).  Isolated examples
could servive considerable longer than that, although the
technology required to recover the information would increase
over time.
   To bring this technology into the 1990's, you could also
make stainless steel CDs and CD-ROMs.
   I would envision a typical "shoebox" intended for long-term
storage as containing a micro-card viewer, as well as a cartoon
introduction to English, a dictionary, an almanac, and various
other general information.  The intent is that someone with
Neolithic or Bronze Age technology should be able to figure 
out how to read the cards, 5000 years from now.


-Dave Chapman

davec@ultra.com		or perhaps	dchapman@ultra.com


Newsgroups: sci.archaeology