3D Memory Read Voltage Control to Prevent String Pinch-Off
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Solution Overview
Problem
In three-dimensional memory devices, the application of uniform read and pass voltages to selected and unselected word lines leads to pinch-off in unselected strings, generating hot electrons and degrading the reliability of read operations due to varying channel voltages.
Innovation Solution
A memory device that applies different pass voltages to unselected word lines based on their distance from the selected word line, using a voltage generator to control these voltages during a read operation, ensuring uniform channel potentials and preventing pinch-off.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If uniform pass voltage is applied to all unselected word lines, then the circuit design is simple, but pinch-off occurs in unselected strings causing hot electron generation and read operation degradation
Solution Approach 1:
The patent applies different pass voltages to different groups of unselected word lines based on their distance from the selected word line. Specifically, unselected word lines adjacent to the selected word line receive a first pass voltage, while other unselected word lines receive a second pass voltage. This local differentiation prevents pinch-off in unselected strings while maintaining reasonable circuit complexity.
Solution Approach 2:
The patent segments the unselected word lines into multiple groups and applies different pass voltages to each group. The unselected word lines are divided into those adjacent to the selected word line and those not adjacent, with each group receiving appropriately differentiated voltage levels to prevent hot electron generation.
2Reliability
If different pass voltages are applied to all unselected word lines, then read operation reliability is improved, but the control complexity increases
Solution Approach 1:
The patent implements local quality by applying differentiated pass voltages only where necessary - specifically to unselected word lines adjacent to the selected word line - while applying a different voltage to other unselected word lines. This targeted approach improves reliability without requiring complex control for all word lines.
Solution Approach 2:
The patent employs dynamic voltage control where the pass voltage level is adjusted based on the position of unselected word lines relative to the selected word line. The voltage generator dynamically selects appropriate voltage levels for different groups of unselected word lines during the read operation.
3Stability of the object's composition
If high pass voltage is applied to prevent pinch-off, then channel potential uniformity is improved, but hot electron generation increases due to voltage differences
Solution Approach 1:
The patent applies higher pass voltage locally to unselected word lines adjacent to the selected word line where pinch-off is most likely to occur, while applying lower pass voltage to other unselected word lines. This localized voltage differentiation maintains channel potential uniformity in critical areas while minimizing voltage differences that cause hot electron generation.
Solution Approach 2:
The patent changes the pass voltage parameter based on the position of unselected word lines. By adjusting the voltage level according to proximity to the selected word line, the patent maintains sufficient channel potential uniformity to prevent pinch-off while reducing excessive voltage differences that would generate hot electrons.
Data Source
AI summary
The present disclosure relates to a memory device, and a method of operating the memory device that includes a memory block including memory cells. The memory device also includes a voltage generator configured to apply a read voltage and pass voltages to word lines coupled to the memory block. The voltage generator is configured to apply the read voltage to a selected word line among the word lines and apply different pass voltages to unselected word lines symmetrical to each other with respect to the selected word line depending on distances to the selected word line, during a read operation on the memory block.