# EPROM memory - the theoretical possibility of recovering data from memory after erasing the exposure with ultraviolet light?

I have a small question.

We have a EPROM memory.

Is there a theoretical possibility of recovering data from memory after deleting with ultraviolet light?

Is this theoretically possible? Or maybe it is impossible?

Anyone can give a source/reference (eg. scientific publication)?

• 0%................. Unless all your data is 1's. – StainlessSteelRat Apr 13 '18 at 19:34
• Well, you've linked a Wikipedia article... which cites a whole lot of articles. Here's some good research on what you're trying to find. These articles aren't hard to find. I typed in on Google, "Data remnants of EPROM memory after erasure". – KingDuken Apr 13 '18 at 19:34
• @KingDuken A nice read. – StainlessSteelRat Apr 13 '18 at 19:44

Dr. Sergei Skorobogatov from the Computer Science department of the University of Cambridge has written a rather sufficient article on this matter. In his research, he writes:

Even after an erase operation, the transistor does not return fully to its initial state, thereby allowing the attacker to distinguish between previously programmed and not programmed transistors, and thus restore information from erased memory.

in his abstract.

You may further investigate why in this research article as he provides physical depth of an EPROM module along with his methods of experimentations.

The Mathematical Theory of Communication, by Claude Shannon and Warren Weaver, is a good place to start.

A programmed EPROM has a signal (in the conductivity of its memory cell transistors) that can be read out, and has a large signal-to-noise ratio. Erasure reduces the signal, until the logarithm of the signal-plus-noise to noise ratio becomes zero.

There's a way to identi fy, from any given erasure efficacy, the amount of information in the EPROM after erasure (Shannon gives the formula, and Weaver explains it).

The usual circuitry in the EPROM will call all the erased bits '1' (all the words 'FF') because that defines the erasure level that is complete (in the hardware data sheet), so you can't expect the EPROM to simply plug into a socket and read out the erased parts. In that sense, there's no practical way to read the erased data, because the EPROM internal readout amplifiers have a threshold below which all inputs are interpreted as '1', which is the erased state as well as the unprogrammed state.

Even with signal-to-noise ratios in the zero range, however, one might use extraordinary readout procedures (like electron microprobing with power applied to the opened-up package of the EPROM). In theory, that allows one to identify all the erased bits, and get more than half of those identifications right. Guessing, one expects exactly half right, of course.