Word line ramping down scheme to purge residual electrons

摘要

Techniques are disclosed for accurately sensing memory cells without having to wait for a voltage that creeps up on word line after a sensing operation to die down. In one aspect, a read pass voltage is discharged in a manner that purges residual electrons from a memory string channel after a sensing operation. A control circuit may begin to discharge the read pass voltage from memory cell control gates at different strategic times in order to provide a path for residual electrons to leave the channel. Because residual electrons have been purged from the channel, no or very few electrons will be trapped in shallow interface traps of the memory cell if the word line voltage does creep up following sensing. Thus, the word line voltage may still creep up after the sensing operation without changing a threshold voltage of the memory cell.

主权项

1. A non-volatile storage device, comprising:
a NAND string of non-volatile storage elements, the non-volatile storage elements each having a control gate, the NAND string having a first select gate at a first end and a second select gate at a second end, the control gates include a first cluster of control gates, one or more clusters of control gates between the first cluster and the first select gate, and one or more clusters of control gates between the first cluster and the second select gate; and a control circuit in communication with the NAND string, the control circuit is configured to:
sense a first non-volatile storage element on the NAND string, including the control circuit configured to apply a read pass voltage to the control gates of unselected non-volatile storage elements of the NAND string;apply a read pass voltage to the control gate of the first non-volatile storage element after the first non-volatile storage element is sensed;begin to discharge the read pass voltage from the control gates of the first cluster prior to beginning to discharge the read pass voltage from the control gates in any of the other clusters and while the first select gate and the second select gate are in a conductive state; andsense a second non-volatile storage element on the NAND string after the read pass voltage on the control gates of the non-volatile storage elements of the NAND string is discharged to a steady state voltage.