This is with regards to the two techniques used to program and erase FLASH memory in the memory lecture. There were discrepancies between the content discussed in the lecture notes and further readings I’ve done on the topic.

The lecture note seemed to mention that Hot Injection Technique is used to program the FLASH while the Fowler-Nordheim Tunneling Technique is used to erase the memory. However from what I read online, it seemed that both techniques could be used to either program or erase the memory.

The underlying principle of Hot Injection Technique seemed to be providing the electrons with high enough energy to overcome the potential barrier between the oxide layer. (Traditional physics model)

The underlying principle of Fowler-Nordheim Tunneling Technique seemed to be based on quantum physics which explains a probability that an electron could tunnel (quantum tunneling) through the oxide layer. This probability could be increased by a few factors, usually through the decrement of the oxide layer to reduce potential barrier or increment of voltage.

There seemed to be a two variation of how things are:

1) Hot injection is used to program, Fowler-Nordheim is used to erase.

2) Both techniques are use in conjunct in modern chip and are used for both programming and erasing.

[Jason] Yes, both techniques could be used. Specifically which technique applies depend on the technology node. There is no need to understand the quantum physics principle of either technique. “Hot injection is used to program, Fowler-Nordheim is used to erase.” is typically the most likely situation.

Could you kindly verify the above information.

Lastly, just to verify if I’ve got the content right. By programming the FLASH memory we are assigning the logic value of “0” to the memory cell. This is because once the P-substrate is charged, it shields the channel region and prevents a channel between source and drain, causing a logic of “0”.

[Jason] Between program and otherwise, the threshold voltage (VTH) shifts. The VTH value decides if the cell stores “1” or “0”.  The decoding circuit may be implemented to decode as designed.

Reference: http://www.cse.scu.edu/~tschwarz/coen180/LN/flash.html

Cheers,

Raymond