Date   : Sat, 22 Oct 2005 13:49:14 +0100 (BST)
From   : Pete Turnbull <pete@...>
Subject: Re: Space-Bar

On Oct 22 2005, 16:18, Peter Craven wrote:
>
> 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?

EPROMs are "floating gate" devices; each memory cell consists of a MOS
transistor with the gate isolated, and therefore floating.  If there is
 a static negative charge on the gate, ie excess electrons, the
transistor conducts and the resulting data shows up as a zero.  If
there's no excess, or not enough, the transistor doesn't conduct
(sufficiently) and the data in that location shows up as a one.  Now
give that gate a blast of UV of an appropriately short wavelength --
which means appropriately high energy - and the electrons will have
enough energy to jump or pass through the insulation and dissipate the
charge, thereby erasing the data back to a logic one.  Conversely,
apply a high enough voltage in the right place and you can force
electrons back onto the gate (which is why the programming voltage for
an EPROM is rather higher than the operating voltage).

-- 
Pete                                           Peter Turnbull
                                               Network Manager
                                               University of York