What Are Ultraviolet LED's Good For?

So this was before the 1701 and MM5203? Were they just experimental parts, or some of them sold?

It just seems odd that it doesn't work at all on contemporary EPROMs/OTPROMs. What changed?

On a sunny day (Sat, 28 Apr 2007 17:36:28 -0700) it happened John Larkin wrote in :

So what is the effect on FLASH when passing your mp3 player or notebook through an airport X ray check?

Probably none. It takes a lot of time and effort to erase a flash memory with UV.

Here's the important observation that comes out of these facts: FLASH devices can usually also be erased using UV light since they have a similar transistor structure to UV-EPROM devices. The encapsulation around a FLASH device normally prevents any UV light from effectively reaching the die, but since the PIC devices had the plastic around them removed, I can now attempt to apply UV light to see what happens.

I performed a simple experiment where I programmed the PIC device with a ramping pattern (0×00->0xFF over and over again) and then tossed it in my UV-EPROM eraser for the length of oh, about a good long shower and some email checking. When I took the device out of the eraser, I found that indeed the FLASH memory was blanked to it's normal all 1's state, and that the security fuses were unaffected. Significantly, if I did not bake the PIC device for long enough, I would get odd readings out of the array, such as all 0's, a phenomemon that I do not understand. I'm supposing it could be due to some effect involving incomplete erasure and the reference bitlines used to drive the reference leg of the sense amps on the FLASH array. Also note that the UV light works just as well on the EEPROM array.

Clearly, the metal shields over the security fuses were provisioned to thwart attempts to selectively erase the security fuses while leaving the FLASH memory array unaffected.

The picture above illustrates the problem I have (and its solution) (click on the image for a larger, clearer version). In order for the FLASH memory transistor to be erased, high-intensity UV light must strike the floating gate. The metal shield effectively reflects all of the incident light.

However, due to the optical index mismatch between the oxide and the silicon interfaces, light at certain angles will reflect off of the silicon surface. In order to witness an example of this reflective effect, jump in a swimming pool and submerse your head and look up at the water-air interface. You will note that the water looks highly reflective at an oblique angle. This is due to the index mismatch between water and air causing total internal reflection of light.

This reflection can be used to cause the UV light to bounce up and the metal shield, and bounce back onto the floating gate. Thus, by angling the PIC inside the ROM eraser, I can get enough light to bounce into the FLASH memory transistor region and cause erasure. After a couple of attempts, I developed a technique that seems to work relatively well.

On a sunny day (Sun, 29 Apr 2007 03:12:27 -0700) it happened "Alexander Von Helmholz" wrote in :

Good hacking :-) I wondered for a moment if Microchip should have use '1' for active on the fuses, but then you could not read it first time......

OK, tested, it lights up :-)

Cool...

You can now fix yourself a glowing gin and tonic cocktail as a discovery award. :) D from BC

Or they are useful for finding counterfeit bills.....

- Tim -

I recently bumped into this detail and thought I'd add it this old thread..

Clipped from

" Athlete's foot can also be detected with the use of an Ultraviolet LED flashlight, under 395Nm illumination (the most common UV LED frequency) the fungal patches will flouresce with a reddish-orange color. " D from BC