Can noise on power supply rail cause bit-flip and damage floating gate flash? – KBA233933
Question: Can noise on the power supply rail cause a ‘bit-flip’, and damage on the S29AL-J, S29PL-J, and S29JL-J flash memory devices?
Answer: Bit flip may be a possible cause of a marginally programmed bit, also known as 'soft-programmed cell'. The presence of system noise or transients on the power supply rail during the programming operation can lead to 'under-programming' or ‘uncharged cell.’ High noise levels may disrupt or limit the programming threshold voltage (Vt) from reaching the required levels to fully program a cell. Although excessive noise may be present on the power supply rail, it is important to note that no permanent damage will occur.
When a ‘READ’ operation is performed, a marginally programmed bit can be read as '0' (programmed) or a '1' (erased). If read as a ‘0’ or a ‘1’ (respectively) passing the verification testing, the flash device becomes a probable candidate for a later pseudo single bit charge loss (pSBCL) failure.
A pSBCL cell is a physically good memory cell which had only been marginally programmed or erased. The cell has no physical anomalies and does not exhibit electron leakage from the floating gate with voltage or high-temperature stress. The subject cell has good data retention which is equal to a good bit. pSBCL is not a device-related failure but an application-induced failure, i.e., system noise or transients that are present on the power supply rail. Therefore, no such damage to the cell will occur.
To recover from a pSBCL failure, you should initiate a Chip Erase operation, or at the very least, a Sector Erase of the sector(s) of where the pSBCL occurred, and then re-program the data. This will ensure that the programming threshold voltage (Vt) has reached the required voltage levels to fully program the cell(s).