Read with look-back combined with programming with asymmetric boosting in memory

摘要

A read operation compensates for program disturb when distinguishing between an erased-state and a lowest programmed data state, where the program disturb is a function of the data state of an adjacent, previously-programmed memory cell on a common charge-trapping layer. A programming operation avoids program disturb of the programmed data states by using asymmetric pass voltages. Before reading the memory cells on a selected word line (WLn), the memory cells on the adjacent, previously-programmed word line (WLn−1) are read. The read operation for WLn uses multiple read voltages—one for each data state on WLn−1, and one of the read results is selected based on the data state of the adjacent memory cell. Other read operations distinguish between each pair of adjacent programmed data states using a read voltage which is independent of the data state of the adjacent memory cell.

主权项

1. A method for operating a memory device, comprising:
programming memory cells in a set of word lines in a word line programming order, the set of word lines comprise one word line, a first adjacent word line which is adjacent to the one word line and after the one word line in the word line programming order and a second adjacent word line which is adjacent to the one word line and before the one word line in the word line programming order, wherein one memory cell is connected to the one word line, another memory cell is connected to the second adjacent word line, the one memory cell and the another memory cell are arranged along a continuous charge-trapping film, the programming of the memory cells comprises applying a plurality of program pulses to the one word line while a first pass voltage is applied to the first adjacent word line and a second pass voltage is applied to the second adjacent word line, and the first pass voltage is higher than the second pass voltage during one or more initial program pulses of the plurality of program pulses; and subsequently, in response to a read command involving the one memory cell:
reading the another memory cell to determine a threshold voltage range among a plurality of threshold voltage ranges of the another memory cell, andafter the reading of the another memory cell:
performing a set of read processes for the one memory cell which distinguishes between an erased state and a lowest target data state of a plurality of target data states by applying a plurality of control gate read voltages to the one word line while sensing whether the one memory cell is in a conductive state, and selecting a result from one read process of the set of read processes based on the threshold voltage range of the another memory cell, andperforming additional read processes for the one memory cell for distinguishing between higher target data states of the plurality of target data states,wherein each read process of the additional read processes is independent of the threshold voltage range of the another memory cell.