Flash Memory Read Recovery via Edge Word Line Voltage Control
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Solution Overview
Problem
Flash memory devices experience threshold voltage distortion due to hot carrier injection (HCI) during read operations, leading to read failures, as the threshold voltages of memory cells change, causing the erase state to overlap with program states.
Innovation Solution
A flash memory design that applies specific recovery voltages to unselected word lines during read operations, depending on whether the selected word line is an edge-adjacent word line or not, to reduce threshold voltage distortion. This involves a read recovery voltage generator that provides different recovery voltages based on the selected word line, mitigating channel voltage differences and thereby reducing HCI effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If read operation is performed on edge word line, then data can be read, but threshold voltage distortion occurs due to hot carrier injection
Solution Approach 1:
The patent applies preliminary anti-action by applying a recovery voltage to unselected word lines before threshold voltage distortion can occur. When an edge word line is selected for reading, the peripheral circuit detects this and applies a recovery voltage to other unselected word lines to prevent hot carrier injection and threshold voltage distortion before it happens.
Solution Approach 2:
The patent applies local quality by providing different recovery voltages to different word lines based on their position. Edge word lines (adjacent to selection lines) receive different recovery voltage treatment compared to inner word lines, as they are more susceptible to hot carrier injection effects. This localized approach targets the specific regions where distortion occurs most severely.
2Reliability
If different recovery voltages are applied to unselected word lines, then threshold voltage distortion is reduced, but device complexity increases
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the recovery voltage parameter based on which word line is selected. The peripheral circuit changes the voltage parameter applied to unselected word lines depending on whether an edge word line or inner word line is selected, optimizing distortion prevention while managing circuit complexity through controlled parameter variation.
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 effectively reduces threshold voltage distortion at edge word lines, enhancing read operation reliability by minimizing the overlap of erase and program states, thus preventing read failures.
Implementation Method 1
Threshold voltage of memory cells may change due to coupling noise, program disturbance, read disturbance, hot carrier injection (HCI), and the like.
Implementation Method 2
Distortion of the threshold voltage due to HCI occurs at an edge word line.
Data Source
AI summary
Disclosed is a flash memory including first to third memory cells connected to a cell string, a first selection line configured to select the cell string, a second selection line configured to select a connection with a common source line, a first word line connected to the first memory cell and positioned adjacent to the first or second selection line, a second word line connected to the second memory cell and adjacent to the first word line, and a third word line connected to the third memory cell and positioned between the second word line and the first or second selection line. Wherein during a read operation, a first recovery voltage is applied to unselected word lines when the selected word line is the second word line, and a second recovery voltage is applied to the unselected word lines when the selected word line is not the second word line.