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A Closer Look at Read Disturb Errors

Read Disturb Error

 

When NAND flash memory is used only for read operations, many designers believe that they do not have to worry about product lifespan, since no writing is occurring. In reality, even read operations can eventually wear the flash memory out, as repeated read operations can lead to inadvertent reprogramming and damage caused by cross-coupling noise. When these issues occur, they are called read disturb errors. Fortunately, industrial-grade NAND flash memory typically comes with read leveling and ECC integrated to mitigate these risks.

 

Read-Only Flash Memory Applications

Read-only flash memory can occur in multiple applications, but is particularly common in gaming. This happens because the data is written to the card once and then read repeatedly when the device is being used. Users do not create new data, so write operations are not occurring. This is the same across any application in which data is loaded one time but read repeatedly without any additional input from users.

 

Read Disturb Errors

When read operations are executed, the line of data that is being read is biased to a voltage between the states that need to be detected, so that it can be read effectively. The data lines that are not being read are biased to a high voltage state. This ensures that every cell on the NAND string is conducting, which is required so that the cells being read will pass through the sense amplifier. The problem is that the lines that are not being read become slightly programmed through the high voltage bias. Every time that same read operation occurs, the lines become slightly more programmed, which in turn causes a read disturb error.

 

Cross-coupling noise also causes read disturb errors. As the geometry of a cell shrinks, the cross-coupling noise gets even more intense. If the memory is functioning in a high-temperature environment, the noise gets worse still, triggering a read disturb error.

 

Error Prevention

For industrial users, the key to reducing read disturb errors is to choose SLC over MLC flash. Although MLC flash is acceptable for consumer products, industrial applications need the reliability of SLC. SLC flash comes with read wear leveling and ECC integrated into the memory device, so that the common causes of read disturb errors are corrected.

 

To learn more about read disturb error prevention and the other features of SLC flash memory, contact Delkin. Our product specialists are available to answer your questions today.

 

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