Corrective Reads with Adjacent-Cell State Bins for Data Retention Loss
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Solution Overview
Problem
Memory devices experience reliability issues due to cell-to-cell interference and intrinsic charge loss, leading to widened threshold voltage distributions and increased bit errors, which are not effectively addressed by existing corrective read mechanisms.
Innovation Solution
Implementing corrective reads with improved recovery by assigning target cells to bins using a pre-defined operation on the cell state information of adjacent cells, such as a linear combination of threshold voltages, to reduce the number of reads and minimize read disturb effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If corrective reads are performed using traditional methods, then data integrity is maintained, but the number of reads increases and read disturb effects worsen
Solution Approach 1:
The patent applies preliminary action by performing reads on adjacent cells before reading the target cell. This preliminary read of adjacent cells provides state information that is used to determine the appropriate read level offset for the target cell, thereby preventing read disturb effects before they occur during the target cell read operation.
Solution Approach 2:
The patent applies local quality by adjusting the read level offset based on the specific state of adjacent cells. Each target cell receives a customized read level offset determined by the states of its neighboring cells, rather than using a uniform read level for all cells. This localized adjustment minimizes read disturb effects on individual cells based on their local neighborhood conditions.
2Object-generated harmful factors
If the number of reads is reduced, then read disturb effects are minimized, but recovery from data retention loss deteriorates
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the read level offset parameter based on the states of adjacent cells. Instead of using fixed read levels, the system modifies the read level offset parameter to account for charge loss and cell-to-cell interference, enabling effective data recovery with fewer reads.
Solution Approach 2:
The patent applies feedback by using the state information from adjacent cells to determine the appropriate read level offset for target cells. This feedback mechanism allows the system to adaptively adjust read parameters based on actual cell states, improving recovery from data retention loss while minimizing the number of reads required.
3Device complexity
If cell-to-cell interference is not addressed, then device complexity is reduced, but threshold voltage distribution widening increases
Solution Approach 1:
The patent applies the intermediary principle by using adjacent cells as mediators to detect and compensate for cell-to-cell interference. The state of adjacent cells serves as intermediate information that reveals the presence and magnitude of interference, allowing the system to adjust read levels without requiring complex direct measurement of interference between all cell pairs.
Data Source
AI summary
A read is initiated with respect to a target cell. A pair of adjacent cells includes a first cell and a second cell each adjacent to the target cell. First cell state information is obtained for the first cell and second cell state information is obtained for the second cell. A state information bin is determined by applying a pre-defined operation to the first cell state information and the second cell state information of the respective pair of adjacent cells. The target cell is assigned to the state information bin. Each state information bin defines a read level offset for reading the target cell.