Flash Memory Refresh Controller for Charge Leakage
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Flash memory devices experience degradation in data retention characteristics due to charge leakage from floating gates, leading to a reduction in threshold voltage and potential read failures, as repetitive programming/erasing cycles stress the insulating films.
Innovation Solution
A flash memory device with a memory cell array, a page buffer circuit having a single latch structure, and a controller that detects improper voltage distributions and performs a refresh operation to maintain threshold voltages above a defined program-verifying voltage, using a refresh command generated based on stored refresh data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If flash memory devices are used for repetitive programming/erasing operations, then data storage capability is maintained, but charge leakage from floating gates increases causing threshold voltage degradation
Solution Approach 1:
The patent applies preliminary action by performing a refresh operation before the threshold voltage degradation becomes critical. The controller detects improper voltage distribution caused by charge leakage and executes a refresh operation to restore the threshold voltage to an appropriate level, preventing read failures before they occur.
Solution Approach 2:
The patent implements feedback by having the controller continuously monitor the voltage distribution of memory cells and detect when charge leakage causes improper voltage levels. Based on this feedback, the controller determines when a refresh operation is needed and executes it to maintain data retention characteristics.
2Productivity
If insulating films are subjected to repeated stress from programming/erasing cycles, then memory cell functionality is maintained, but film breakdown occurs leading to read failures
Solution Approach 1:
The refresh operation serves as a preliminary corrective action that restores threshold voltage before read failures occur. By detecting improper voltage distribution early and executing refresh, the system prevents the cumulative damage from programming/erasing cycles from causing insulating film breakdown and read failures.
Solution Approach 2:
The patent provides beforehand cushioning by implementing a refresh mechanism that compensates for charge leakage before it causes critical threshold voltage degradation. This cushioning effect maintains the insulating film integrity and prevents read failures by restoring voltage levels proactively.
3Quantity of substance
If threshold voltage distribution shifts to lower voltage levels over time, then charge storage is maintained, but read margin decreases causing read failures
Solution Approach 1:
The controller uses feedback to detect when threshold voltage distribution shifts to lower voltage levels causing improper voltage distribution. Based on this detection, the controller executes a refresh operation that restores the threshold voltage to appropriate levels, thereby maintaining read margin and preventing read failures while preserving charge storage capacity.
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
The solution enhances data retention characteristics and improves the reliability of flash memory devices by maintaining threshold voltages and preventing read failures through the refresh operation.
Implementation Method 1
Stored charge (e.g., electrons) may leak from a floating gate due to a number of mechanisms, including the emission of thermions
Implementation Method 2
Stored charge (e.g., electrons) may leak from a floating gate due to a number of mechanisms, including charge diffusion
Data Source
AI summary
A flash memory device is disclosed and includes a memory cell array comprising memory cells arranged in rows and columns, a page buffer circuit having a single latch structure and configured to read data from a selected page in the memory cell array, and a controller controlling the page buffer circuit to detect memory cells having an improper voltage distribution causes by charge leakage within the selected page.