22 Jan
2003
22 Jan
'03
4:40 a.m.
From: "Arno Kletzander"
<Arno_1983(a)gmx.de>
Hello everybody, this is something I've been wondering about for some time
now. Perhaps here is the place to ask, since it's about one of the "inner
secrets of silicon":
Tony Duell wrote:
erased
The 8751 is the EPROM version of the 8051
microcontroller. It's otherwise
identical to it.
If it's in a ceramic package with a quartz window, then you can erase it
like any other EPROM and reprogram it. If it's in the plastic package,
then it's the OTP version.
If in fact the same die was used in both components, then it's only the
plastic (which is impenetrable to the commonly-used ultra-violet light) that
prevents the OTP variant from being erased and reprogrammed.
However, there are kinds of radiation similar to light which *will*
penetrate the plastic housing...you see where this goes? Will the memory be when you, say, X-ray the OTP component, will it stay
unaffected, or is the
thing just going to die?
(just outta curiosity)
Arno Kletzander
Hi
The trick is impart just enough energy to the electrons
to get them to tunnel through the insulation. If you start
hitting things too hard, you'll start to damage the crystal
structure. UV light will both penetrate into the floating
gates and react with the desired amount. One could use
x-rays to erase the chip but you'd need an intensity that
is great enough that it would also damage the chip. The amount of
x-ray energy captured by the gate in a normal x-ray picture
is quite small. Since x-rays go through greater depths without
reacting and have higher energies, they will most likely damage
the chip while erasing the charge on the gates. Materials
change the amount of transparency at differing frequencies
of electromagnetic energy. UV is just right to penetrate
the silicon oxide cover and be absorbed by the poly-silicon
gates.
It is interesting that the flight at high altitudes is
probably more damaging to electronics than the inspection
x-ray at the gate.
Dwight