the substrate

[Timothy C. May]

At 6:48 PM -0800 4/12/97, *****Jay Jason LaBelle***** wrote:
>What exactly happens to the substrate that causes data to be somewhat
>readable after a specific bit pattern has been stored there for a long time?
>

I really hate these short, ambiguous questions.

If I understand your question, it depends on the technology, In traditional
silicon devices, either NMOS or CMOS, using SiO2 as the dielectric in the
storage capacitors and/or transfer gates, longterm storage of a fixed bit
pattern can produce residual threshold shifts. This can be caused by
trapping in the oxide, or even by short channel effects injecting electrons.

DRAMs and SRAMs have different imprinting characteristics.

(Interestingly, exposure to gamma or beta radiation uniformly can "freeze
in" a stored bit pattern for later readout under special conditions.)

I suggest a good book on semiconductor device physics, such as Andy Grove's
book, or Sze's standard textbook.

--Tim May

Just say "No" to "Big Brother Inside"
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