Multi-Word Line Erratic Programming Detection

摘要

Techniques are presented to detect word line failures (such as word line to word line shorts, control gate to substrate shorts, broken word lines, and so on) in non-volatile memory arrays. A first simultaneous read of multiple word lines is performed, followed by a second simultaneous read of the same word lines, where the read conditions of the two reads are shifted by a margin. For example, one of the read could use a standard read voltage on the word lines, while the other read could shift these levels slightly higher. The results of the two reads can then be compared on a bit line by bit line basis, XOR-ing the results to determine is the set of word lines may include any defective members.

主权项

1. A method of determining whether a memory circuit, including an array of a plurality of memory cells formed along word lines and bit lines, has defective word lines, the method comprising:
performing a program operation to write to one of two or more data states to each of a plurality of memory cells formed along a first plurality of selected word lines and a first set of one or more selected bits lines; subsequently performing first and second composite sensing operations, each including:
concurrently applying to each of the first plurality of selected word lines a corresponding sensing voltage to distinguish between a first pair of the data states, wherein the values of the sensing voltages for the second composite sensing operation are shifted by a margin voltage relative to the corresponding sensing voltages for the first composite sensing operation; andconcurrently performing, for each of the one or more selected bit lines, a first combined sensing operation of the corresponding plurality of memory cells along the plurality of selected word lines while said sensing voltages are applied thereto, where the result of the first combined sensing operation for each of the selected bit lines is dependent upon the state of the plurality of memory cells therealong on the first plurality of selected word lines; performing a comparison of the results of the first composite sensing operation to the result of the second composite sensing operation on a bit line by bit line basis for each of the first set of selected bit lines; and based upon the comparison, determining whether the first plurality of bit lines includes any defective word lines.