EPROM data retention

[1024MAK]

Following on from a comment in another thread (viewtopic.php?f=7&t=762#p6929)

This is interesting reading: http://www.ezoflash.com/willem_info/for ... 1144884107
This is likely to have been taken from ATMEL's UV Erasable EPROM, Application Note, The Benefits of Atmel’s RAPID™ Programming Algorithm. I have attached a copy.

ATMEL.pdf

(183.72 KiB) Downloaded 332 times

Microchip's 1997 Annual Reliability Report also makes interesting reading

Microchip 1997.pdf

(88.83 KiB) Downloaded 375 times

Q: What is the typical data retention time for STMicroelectronics' EPROM memories?
A: The typical data retention time for ST's EPROM memories is 20 years.

http://www.experts123.com/q/what-is-the ... ories.html

Some manufactures claim a much longer time. The Microchip data sheet for their 27C512A 512K (64K x 8) CMOS EPROM says

Data Retention > 200 years

See http://ww1.microchip.com/downloads/en/D ... 11173G.pdf

Mark

[RetroTechie]

It is simple: in UV erasable EPROMs (also one-time programmable versions, which use same internal technology), an 'empty' memory bit reads as a 1. And you can program a 0 into each bit. This is done by using the programming voltage (25/21/12~12.5V) to pull a bunch of electrons onto an isolated 'island' (the floating gate). Erasable by shining UV light through the window to kick those electrons off in under a half hour (a few weeks in sunlight). For any proper functioning EPROM this floating gate will be very well isolated from its surroundings. Read: able to keep that charge for many years.

But: no matter how well constructed, this isolation is never perfect. There will always be ways that allow small numbers of those electrons to find their way out of their 'cage' (cosmic radiation, tiny amounts of UV in normal lighting that might pass through a label, tiny amounts of moisture sealed inside the IC package, etc, etc). Thus that floating gate is leaky, and the 0 it keeps will flip back to a 1 if only you wait long enough.

That might take much longer than manufacturer said it should take. Or much shorter. Regardless of reason, 20 years is a long time, and for 20+ years ago programmed EPROMs it is not unheard of that some programmed bits flip back to erased state. Not "all the time", but it happens (I myself have seen it a few times). Simple as that.

Data Retention > 200 years

IC's buit today won't be functional anyway when they get 200 years old. So for all practical purposes, that is a bullshit claim. At best, it's an indicator of expected performance over shorter period like 10 or 20 years. So take a claim like that with a biiiig grain of salt...

[1024MAK]

Yes, as with any computer storage system, it is always wise to keep multiple back-up copies. So this applies to EPROM, EEPROM, and FLASH chips as well

With EPROM and some EEPROM or FLASH chips where a programmer is used, the way it programs the chips does partly determine the data retention time. If a chip is not programmed correctly, the chip may "forget" a lot sooner than ten years

But I agree, 10 to 20 years is the "normal" lifespan of the data in an EPROM.

I too was amused with the figure of 200 years for the now obsolete 27C512A I very much doubt that anyone will be testing this claim in 60 years time, let alone 200 years

Mark

[zx80nut]

I have many micros from around 1980, some of which contain EPROMS (in fact, my original ZX80 has an EPROM) and they are still working fine - so that's more than 30 years on.

Only one computer I have needed the EPROMS re-programming - a UK101 (from 1979) - many of the bits had gone back to 1's. However, not sure how well they were programmed originally, nor whether they were properly covered.

EPROMS that I have programmed myself for the BBC micro in 1983 (ish) are still fully programmed.

Grant.

[sirmorris]

I very much doubt that anyone will be testing this claim in 60 years time, let alone 200 years

<rubs hands together> Sounds like a challenge. Oh yes.

[Moggy]

I have many micros from around 1980, some of which contain EPROMS (in fact, my original ZX80 has an EPROM) and they are still working fine - so that's more than 30 years on.

Only one computer I have needed the EPROMS re-programming - a UK101 (from 1979) - many of the bits had gone back to 1's. However, not sure how well they were programmed originally, nor whether they were properly covered.

EPROMS that I have programmed myself for the BBC micro in 1983 (ish) are still fully programmed.

Grant.

Agreed the youngest of My EPROMS are 27 years old and still functioning, a few of them Memotech stuff Hi-res packs assembler etc.

Moggy.