Is there a retention period for flash data?

No matter what storage technology is used, the data stored cannot be saved forever and will remain in flash memory for a certain period of time.

Data retention is a matter of data retention time. When the expiration date is reached, the data will be in error, indicating that ECC cannot successfully correct the data read from the flash memory.

We know that flash memory usually has the following errors:

 

1. Electrical problems:

For example, due to weak soldering or chip failure, normal commands cannot be executed or the data error rate is abnormally high. This issue will be discovered during factory testing of the flash memory or SSD.

 

2. Reading, writing and wiping failed:

Basic command execution failed, the result can be read through the status bits. These problems may also occur during use of the chip, but the probability is very small.

 

3. ECC error correction failed:

In fact, the data error rate is too high and exceeds the error correction capability of the error correction algorithm. Data retention is one of the main culprits. The mechanism of flash memory storage is to transfer electrons to the floating gate layer through quantum tunneling and stay there. As time goes by, there is still a certain possibility that electrons will leave the floating gate layer and return to the channel. Leaving more electrons may lead to the result of unit reading, that is, data errors.

 

Data retention is related to the thickness of the oxide layer under the floating gate layer. After all, the thicker the oxide layer, the less likely the electrons are to leave. Research shows that if the oxide layer thickness is 4.5nm, the theoretical data can be preserved for 10 years.