Back Gate Operation with Elevated Threshold Voltage

摘要

In a three dimensional NAND memory, increased threshold voltages in back gate transistors may cause program failures, particularly along word lines near back gates. When back gate transistor threshold voltages cannot be returned to a desired threshold voltage range then modified program conditions, including increased back gate voltage, may be used to allow programming.

主权项

1. A method of operating a block of a three dimensional nonvolatile memory array comprising:
applying a first set of programming conditions that includes a first back gate voltage that is applied to a back gate of the block for programming operations during a first period of operation; performing one or more back gate tuning operations on the back gate of the block to maintain threshold voltage of a back gate transistor in a target range; subsequently determining that the threshold voltage of the back gate transistor remains higher than the target range after back gate tuning; and subsequently, replacing the first set of programming conditions with a second set of programming conditions that includes a second back gate voltage that is applied to the back gate of the block for programming operations during a second period of operation, the second back gate voltage being larger than the first back gate voltage.