Bit Line Voltage Compensation for Channel-to-Floating Gate Coupling
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Solution Overview
Problem
As memory devices become smaller, capacitive coupling effects during programming become more problematic, leading to increased programming speed and widened threshold voltage distributions in non-volatile memory devices, particularly in NAND flash memory systems.
Innovation Solution
The implementation of sensing circuits and programming techniques that optimize bit line management, including floating or driving bit lines to compensate for channel-to-floating gate capacitive coupling, and using voltage step-ups on unselected bit lines to counteract coupling effects, thereby maintaining intended programming speeds without additional verify operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If memory devices are scaled down to become smaller, then device size is reduced, but capacitive coupling effects increase causing programming speed to increase and threshold voltage distributions to widen
Solution Approach 1:
The patent applies preliminary anti-action by detecting capacitive coupling effects before they cause excessive programming speed increases, and applying compensating voltages to counteract the coupling effects. The system monitors threshold voltage changes and applies opposing voltages to bit lines or word lines to prevent the coupling-induced programming acceleration, thereby maintaining precise threshold voltage control despite device scaling.
Solution Approach 2:
The patent changes operational parameters dynamically by adjusting bit line voltages, word line voltages, or programming pulse characteristics based on detected capacitive coupling levels. The system modifies voltage magnitudes, pulse widths, or timing parameters to compensate for coupling effects, allowing precise control of programming speed and threshold voltage distribution even as device dimensions are reduced.
2Device complexity
If capacitive coupling effects are not compensated, then programming operation is simpler, but threshold voltage control precision deteriorates
Solution Approach 1:
The patent implements feedback control by continuously monitoring threshold voltage changes during programming operations and using this information to adjust compensating voltages applied to bit lines or word lines. The system measures actual programming progress and modifies control parameters in real-time to maintain precise threshold voltage control, creating a closed-loop control system that adapts to coupling effects without requiring overly complex open-loop compensation circuits.
3Manufacturing precision
If verify operations are added to compensate for coupling effects, then threshold voltage control is improved, but programming time increases
Solution Approach 1:
The patent applies preliminary action by pre-calculating or pre-establishing compensating voltage levels and timing sequences that account for expected capacitive coupling effects. The system prepares compensation parameters in advance based on device characteristics and programming conditions, allowing direct application of compensating voltages during programming without requiring iterative verify operations. This preliminary preparation enables precise threshold voltage control while maintaining fast programming speeds.
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 reduces capacitive coupling effects, ensuring precise control over programming speed and maintaining desired threshold voltage distributions, even in fast and slow programming modes, without increasing overall programming time or complexity.
Implementation Method 1
capacitive coupling effects become more problematic during programming
Implementation Method 2
electrons from the channel of a storage element to be injected into the floating gate
Data Source
Figure 1a~2
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Figure 4
AI summary
During programming of storage elements, channel-to-floating gate coupling effects are compensated to avoid increased programming speed and threshold voltage distribution widening. In connection with a programming iteration, unselected bit lines voltages are stepped up to induce coupling to selected bit lines, and the amount of coupling which is experienced by the selected bit lines is sensed. When a program pulse is applied, voltages of the selected bit lines are set based on the amount of coupling. The bit line voltage is set higher when more coupling is sensed. The amount of coupling experience by a given selected bit line is a function of its proximity to unselected bit lines. One or more coupling thresholds can be used to indicate that a given selected bit line has one or two adjacent unselected bit lines, respectively.