Date   : Sat, 22 Oct 2005 12:36:29 +0100
From   : "David Hunt" <dm.hunt@...>
Subject: Re: Space-Bar

>Further Information Question: Assuming the UV waves give the electrons in
>the EPROM circuit enough energy to 'go to' a higher energy orbit? Does
>passing the current through (using the EPROM burner) then give them a
>'bump off the energy level' to drop down to a more stable and permanent
>level when burning the EPROM??? Or am I completely off target. I only ever
>did Senior Chemistry & Physics, no electronics, so forgive me if I am
>completely off.

This is really a Physics question! Unless you're into the exotic end of
Electronics you probably won't have needed to touch on the atomic operation
of an EPROM.

Anyway, here is my stab at an explanation - it's been over 10 years since I
looked at this stuff;

An EPROM consists of an array of floating gates. A floating gate is a gate
that has a capacitor as its input. The capacitor is charged by the UV light.
An erased EPROM is all 1's. The capacitor cannot discharge because next to
the gate is a small gap. Electrons can be forced through this gap with a
high enough potential, e.g. 21V, this process is known as tunnelling. When a
programming voltage is applied the electrons can leave the capacitor and
thus a 0 can be created. A cell sensor is used to detect the amount of
charge on the gate, more than 50% it's a 1, less is a zero. However, if some
charge remains on the gate it will take longer to read as a zero, thus it is
important to make sure you follow the manufacturers programming
specifications. There is also some info. at the wiki;

<http://en.wikipedia.org/wiki/EPROM>

Dave ;)