Look ahead read method for non-volatile memory

摘要

A read operation for selected memory cell on a selected word line compensates for program disturb which is a nonlinear function of the data state of an adjacent memory cell on an adjacent word line. When a command to perform a read operation for the selected memory cell is received, a read operation is first performed on the adjacent memory cell to determine its data state, or to classify the adjacent memory cell into a threshold voltage range which includes one or more data states, or a portion of a data state. The selected memory cell is then read using a baseline control gate voltage which does not provide compensation, and one or more elevated control gate voltages which provide compensation, to distinguish between two adjacent data states. An optimal sensing result is selected based on the data state or threshold voltage range of the adjacent memory cell.

主权项

1. A method for reading in a memory device, comprising:
in response to a read command involving a selected memory cell which is connected to a selected word line, reading an unselected memory cell which is connected to an unselected word line, the unselected memory cell is adjacent to the selected memory cell, the reading of the unselected memory cell determines a threshold voltage range among a plurality of threshold voltage ranges of the unselected memory cell; and after the reading of the unselected memory cell, performing each read process of a plurality of read processes for the selected memory cell by applying voltages to the selected word line while sensing whether the selected memory cell is in a conductive state and selecting an optimal result from the sensing based on the threshold voltage range of the unselected memory cell, wherein:
the read processes distinguish between data states among a plurality of data states;among voltages applied to the selected word line during at least one read process of the plurality of read processes, a lowest voltage provides the optimal result when the threshold voltage range of the unselected memory cell is below the lowest voltage and at least one elevated voltage provides the optimal result when the threshold voltage range of the unselected memory cell is above the lowest voltage; andover the plurality of read processes, a number of the voltages applied to the selected word line becomes progressively smaller as the plurality of read processes distinguish between progressively higher data states among the plurality of data states.