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From: chuck@marie.mit.edu (CHUCK PARSONS 617-253-4157)
Newsgroups: comp.sys.next
Subject: Re: parity is for farmers?
Message-ID: <25MAY91193001@marie.mit.edu>
Date: 26 May 91 00:30:01 GMT
References: <1991May21.232331.24888@cs.umn.edu> <1991May22.234515.24685@milton.u.washington.edu> <64346@bbn.BBN.COM>
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In article <64346@bbn.BBN.COM>, adoyle@bbn.com (Allan Doyle) writes...
>In article <1991May22.234515.24685@milton.u.washington.edu> mrc@milton.u.washington.edu (Mark Crispin) writes:
> 
>True enough, but whatever happened to the Alpha particle hits we
>were hearing so much about a few years ago. Alpha particle hits would
>affect only single bits by flipping the bit or erasing or setting
>the bit. I was under the impression that the newer memories were
>getting increasingly vulnerable since the bit size was shrinking and
>the energy needed to flip a bit was decreasing. Have the semiconductor
>manufacturers figured out how to shield the chips with a special
>coating or something?
> 
  Alpha particles don't go very far. They will pass through a few
centimeters of air or a few hundred microns of silicon, certainly
not through the case of any chip. The alpha particles come from
radioactive elements in the silicon and other parts of the chip
themselves that basically make it impossible to shield against them.

  You can use purer materials, our design to minimize the amount of silicon
kept depleted. The alpha particle can cause some crystal damage and
it liberates free charge. The crystal damage is a culmultive problem.
The free charge isn't necessarily a problem. It causes leakage across
depleted regions and can cause perment static charges to build up in oxide.
But in any of the silicon that is definatly p or n its not a problem.

  I believe that is a major reason that silicon on insulator designs are
more radiation resistant, you get rid of the enormous back biased substrate
/well diode.

Chuck@mitlns.mit.edu