Semiconductor Memory Read Precision via Adaptive Potential
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Solution Overview
Problem
As NAND flash memory shrinks, adjacent cell coupling occurs, reducing data read precision due to shortening distances between charge storage layers, and faster read-out operations are necessary to mitigate these effects.
Innovation Solution
The semiconductor memory device employs a programming sequence where L page and U page programs are alternated between word lines to minimize threshold distribution fluctuations, using specific read-out potentials to distinguish between programmed values, and modifies reading conditions based on adjacent cell values to enhance read precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If NAND flash memory is shrunk to increase storage capacity, then storage density is improved, but adjacent cell coupling occurs and data read precision deteriorates
Solution Approach 1:
The patent applies preliminary action by performing a read operation on the adjacent cell (second memory cell) before reading the target cell (first memory cell). This preliminary read establishes the actual state of the adjacent cell, allowing the system to compensate for its coupling effect on the target cell's threshold voltage. By knowing the adjacent cell's state in advance, the system can adjust the read conditions for the target cell to maintain read precision despite the coupling effect caused by memory shrinkage.
2Productivity
If read-out speed is increased to mitigate adjacent cell coupling effects, then productivity is improved, but reading precision may deteriorate due to insufficient time for accurate threshold discrimination
Solution Approach 1:
The patent applies dynamics by making the read conditions adaptive rather than fixed. The read operation dynamically adjusts its parameters based on the state of the adjacent cell. Specifically, the system selects different read conditions (such as different pass potentials or verification potentials) depending on whether the adjacent cell is in a programmed or erased state. This dynamic adaptation allows the system to maintain high reading precision while operating at faster speeds, as each read operation is optimized for its specific context without requiring conservative timing margins.
3Quantity of substance
If the distance between charge storage layers is shortened to increase cell density, then storage capacity is improved, but adjacent cell coupling increases and threshold distribution stability deteriorates
Solution Approach 1:
The patent applies feedback by using the state information of the adjacent cell to adjust the read operation on the target cell. The system reads or determines the state of the adjacent cell first, then uses this information as feedback to modify the read conditions for the target cell. This feedback mechanism compensates for the threshold voltage shifts caused by adjacent cell coupling, thereby maintaining threshold distribution stability and read precision even when cells are densely packed with short distances between charge storage layers.
Data Source
AI summary
According to one embodiment, a control circuit applies a pass potential to a first word line and a preliminary read-out potential to a second word line. The control circuit reads data from a first memory cell transistor at a first condition in a case where a second memory cell transistor has been switched to an ON state and at a second condition in a case where the second memory cell transistor has been switched to an OFF state, by the applying of the preliminary read-out potential. The first condition enables the discrimination of a value of the first memory cell transistor in a case where the first memory cell transistor has a threshold in a relatively low distribution. The second condition enables the discrimination of the value of the first memory cell transistor in a case where the first memory cell transistor has a threshold in a relatively high distribution.