Memory Sensing With Asymmetric VREADK Pass Voltages
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Solution Overview
Problem
Existing non-volatile memory devices face reliability issues due to neighboring word line interference (NWI) during sensing operations, which affect data retention and accuracy.
Innovation Solution
Applying different pass voltages to neighboring word lines located on opposite sides of a selected word line, with a first voltage applied to one neighboring word line that was previously programmed and a second voltage applied to the other neighboring word line that was in an erased condition, to reduce interference and improve sensing accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single pass voltage is applied to all neighboring word lines during sensing, then the device complexity is reduced, but neighboring word line interference increases and sensing accuracy deteriorates
Solution Approach 1:
The patent applies different pass voltages to different neighboring word lines based on their individual states (programmed or erased). Specifically, a first pass voltage is applied to a first neighboring word line and a second pass voltage is applied to a second neighboring word line, where the voltages differ according to the respective states of these word lines. This local differentiation reduces neighboring word line interference and improves sensing accuracy without requiring complete system-wide complexity increase.
2Reliability
If different pass voltages are applied to neighboring word lines based on their state, then neighboring word line interference is reduced and sensing accuracy is improved, but the device complexity increases
Solution Approach 1:
The patent determines the state of each neighboring word line (whether programmed or erased) before applying the sensing operation. Based on this preliminary state determination, the appropriate pass voltage is selected and applied to each neighboring word line. This preliminary action ensures that the correct voltage is applied in advance, reducing interference and improving reliability while managing complexity through proactive voltage selection rather than reactive adjustment.
3Object-affected harmful factors
If the effective channel length is increased to reduce DIBL, then neighboring word line interference is reduced, but the device area increases
Solution Approach 1:
The patent changes the voltage parameters applied to neighboring word lines during sensing operations. By applying different pass voltages (first pass voltage to first neighboring word line, second pass voltage to second neighboring word line) based on their programmed or erased states, the patent effectively reduces DIBL and neighboring word line interference through parameter optimization rather than physical dimension changes, thereby avoiding increased device area.
Data Source
AI summary
The memory device includes a memory block with a plurality of memory cells that are arranged in a plurality of word lines. The plurality of word lines include a selected word line, a pair of neighboring word lines that are immediately adjacent the selected word line, and a plurality of non-neighboring word lines that are not immediately adjacent the selected word line. Circuitry can perform a sensing operation on at least one memory cell in the selected word line. During the sensing operation, the circuitry is configured to apply a reference voltage to the selected word line, apply different first and second pass voltages to the neighboring word lines, and apply a third pass voltage that is different than the first and second pass voltages to the plurality of non-neighboring word lines. The circuitry is further configured to sense a threshold voltage of the at least one memory cell.