Controlling Pass Voltages To Minimize Program Disturb In Charge-Trapping Memory

摘要

Techniques are provided for preventing program disturb of unselected memory cells during programming of a selected memory cell in a NAND string which includes a continuous charge-trapping layer, either in a two-dimensional or three-dimensional configuration. In such a NAND string, regions between the memory cells can be inadvertently programmed as parasitic cells due to the program voltage and pass voltages on the word lines. For programmed cells, an upshift in threshold voltage due to a parasitic cell can be avoided by providing a higher pass voltage on an adjacent later-programmed word line than on an adjacent previously-programmed word line. For erased cells, an upshift in threshold voltage due to the parasitic cells can be reduced by progressively lowering the pass voltage on the adjacent later-programmed word line. The lowering can occur when memory cells of a lowest target data state complete programming.

主权项

1. A method for programming in a memory device, comprising:
programming selected memory cells connected to a selected word line (WLn) of a set of word lines, the selected memory cells are programmed to a plurality of target data states, and memory cells which are to remain in an erased state are also connected to the selected word line, the programming is performed by performing a plurality of program-verify iterations for the selected word line, each program-verify iteration of the plurality of program-verify iterations is performed by applying a program voltage followed by performing a verify test for one or more target data states of the plurality of target data states, and the program voltage is stepped up in the plurality of program-verify iterations; and during each program voltage, applying a first pass voltage to a word line (WLn+1) in the set of word lines which is adjacent to the selected word line and after the selected word line in a word line programming order, while applying a second pass voltage to a word line (WLn−1) in the set of word lines which is adjacent to the selected word line and before the selected word line in a word line programming order, wherein during one or more initial program-verify iterations of the plurality of program-verify iterations, the first pass voltage exceeds the second pass voltage by a difference, the first pass voltage becomes progressively smaller during subsequent program-verify iterations of the plurality of program-verify iterations, and the difference becomes progressively smaller during the subsequent program-verify iterations.