Post by Axel SchwenkeWenn du einen (Zahn-)Arzt kennst, gib ihm den Chip, daß er ihn
mal röntgt. Danach ist er dann leer :)
Jed Margolin ( http://www.jmargolin.com/patents/eprom.htm )
hat mal Dov Frohman gefragt:
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The 1702 was introduced to the world in the May 10, 1971 issue
of Electronics Magazine in an article written by Dov Frohman,
the inventor of the EPROM. It contains a very curious paragraph:
" Erasure, however, has to be accomplished by non-electrical
methods, since the gate electrode is not accessible electrically.
Shining ultraviolet light on any part of an unpackaged device
causes a photocurrent to flow from the floating gate back to
the silicon substrate, thereby discharging the gate to its initial,
uncharged condition. This method of erasure allows complete
testing and correction of a complex memory array before the
package is finally sealed. Once the package is sealed, information
can still be erased by exposing it to X radiation in excess of
5 X 10**4 rads, a dose which is easily attained with commercial
X-ray generators."
X-rays? X-RAYS??
According to Dr. Frohman who was still working for Intel when I
spoke to him in 1993, they ended up deciding to ship the part
with a window because erasing the EPROM with X-rays created
surface states in the silicon that required annealing. What
this means is that the X-rays disrupted the crystal structure
at the surface of the silicon which could be fixed by annealing
in which sufficient thermal energy is supplied to the damaged
layer of atoms so they can rearrange themselves. Since the
underlying wafer is single-crystal, it serves as a seed for
the epitaxial regrowth of the layer being treated. Generally,
the required temperature is between 450 degrees Celsius and
something less than the melting point of silicon which is
1410 degrees Celsius.
In other words, to erase your EPROM you would first have to X-ray it
and then put it in an oven at about 600 degrees Celsius. The effects
of this process on the reliability of the part would have required
extensive testing so they decided on the window instead.
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Die 600´C macht das OTP-Plastikgehäuse nicht mit. Insofern ist
ist es letztlich doch urban-legend, selbst wenn es einen wahren
Kern hatte.
MfG JRD