Flash Memory Read Disturbance Prevention via Voltage Control
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Solution Overview
Problem
Flash memory devices experience read disturbance due to leakage currents during reading and reading verification operations, which can inadvertently program unselected memory cells and reduce the reliability of the device.
Innovation Solution
The solution involves specific voltage control methods, including applying a selection voltage to the selected word line and a higher voltage to unselected word lines and selection lines, while ensuring the channel voltage is discharged into a bit line or common source line, thereby preventing hot-electron injection and reducing read disturbance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a reading operation is performed on a flash memory cell, then data can be read from the selected memory cell, but leakage current is generated through the channel region causing read disturbance
Solution Approach 1:
The patent applies different voltage levels to different regions (selected vs. unselected word lines, string selection line, ground selection line) to create localized electrical conditions that prevent leakage current in unselected cells while allowing reading in the selected cell. Specifically, unselected word lines are driven at a first voltage level while the selected word line receives a selection voltage, creating local voltage differences that control current flow paths.
Solution Approach 2:
The patent changes voltage parameters dynamically during the reading operation. The control circuit drives unselected word lines at a first voltage level, then drives the string selection line and ground selection line at a second voltage level (higher than the first). This parameter change prevents channel boosting and eliminates the voltage difference that would cause leakage current and read disturbance.
2Reliability
If unselected word lines are driven at high voltage to prevent channel boosting, then read disturbance is reduced, but voltage control complexity increases
Solution Approach 1:
The control circuit performs multiple functions using the same voltage control mechanism. By driving unselected word lines at a first voltage and then driving the string selection line and ground selection line at a second voltage, the same control approach prevents channel boosting, eliminates read disturbance, and maintains proper cell selection. This multi-functional approach reduces overall system complexity despite the multiple voltage levels.
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 effectively minimizes read disturbance, enhancing the reliability of flash memory devices by preventing unintended programming of unselected memory cells during reading operations.
Implementation Method 1
This leakage current can inadvertently program an unselected memory cell by a hot-electron injection effect, which is referred to as 'read disturbance.'
Data Source
AI summary
A method of reading a flash memory device can include driving a selected word line by applying a selection voltage thereto and driving unselected word lines by applying a first voltage thereto, driving the unselected word lines and first and second selection lines by applying a second voltage that is higher than the first voltage thereto, and reading data from a memory cell that is coupled to the selected word line.