Nonvolatile Memory Verification via Adaptive Charge Sharing
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Solution Overview
Problem
Nonvolatile memory devices face challenges in maintaining retention quality due to variations in threshold voltage states between memory cells, leading to inefficient verification operations and potential charge loss.
Innovation Solution
The nonvolatile memory device employs an adaptive verification method by reading an adjacent word line to determine the program state, adjusting charge sharing between the selected memory cell and a sensing node, and modifying verification conditions such as sensing time or voltage level based on the read results to improve retention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If verification operations are performed with fixed parameters for all memory cells, then the operation process is simple, but retention quality deteriorates due to threshold voltage variations between cells
Solution Approach 1:
The verification operation parameters (sensing time, charge sharing amount) are changed dynamically based on the program state of adjacent memory cells. The control logic adjusts these parameters adaptively: when adjacent cells are in erased state, larger charge sharing and longer sensing time are applied; when adjacent cells are programmed, smaller charge sharing and shorter sensing time are used. This dynamic adjustment resolves the contradiction by optimizing retention quality for different cell states without requiring completely separate verification processes.
Solution Approach 2:
The invention changes physical parameters of the verification operation based on detected conditions. Specifically, the sensing time duration and charge sharing amount are modified according to the threshold voltage state of adjacent cells. This parameter adaptation allows the verification process to maintain high reliability across different memory cell states while avoiding the need for completely different verification methodologies.
2Measurement precision
If charge sharing between selected memory cell and sensing node is increased to improve verification accuracy, then measurement precision improves, but charge loss increases affecting retention
Solution Approach 1:
The charge sharing amount is adjusted as a variable parameter based on the program state of adjacent memory cells. When adjacent cells are in erased state, the selected cell experiences greater threshold voltage dispersion, so larger charge sharing is applied to achieve adequate verification accuracy. When adjacent cells are programmed, the selected cell has smaller threshold voltage dispersion, so smaller charge sharing suffices. This adaptive parameter adjustment resolves the contradiction by matching charge sharing magnitude to actual verification needs, minimizing unnecessary charge loss while maintaining adequate measurement precision.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the retention quality of memory cells by optimizing verification operations based on the program state of adjacent cells, reducing charge loss and improving the dispersion of memory cells, thereby improving overall memory retention.
Implementation Method 1
verifying the selected memory cell by adjusting charge sharing between the selected memory cell and a sensing node, which is connected to the selected memory cell through a bit line
Data Source
AI summary
An operation method of a nonvolatile memory device includes applying a program voltage to a selected word line and programming a selected memory cell connected to the selected word line; reading an adjacent memory cell connected to an adjacent word line of the selected word line; and verifying the selected memory cell by adjusting charge sharing between the selected memory cell and a sensing node, which is connected to the selected memory cell through a bit line.