Nonvolatile Memory Threshold Voltage Stabilization
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Solution Overview
Problem
The threshold voltages of programmed nonvolatile memory cells in certain memory devices tend to change over time due to environmental and operational factors, leading to potential read data errors as the desired threshold voltage distributions are altered.
Innovation Solution
A method involving forward and reverse shifting of threshold voltages through multiple program loops with different sets of program pulses is employed to stabilize the threshold voltage distributions, ensuring that the nonvolatile memory cells maintain their programmed state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single program loop is executed to program nonvolatile memory cells, then the programming operation is completed efficiently, but the threshold voltage distribution becomes unstable and changes over time leading to read data errors
Solution Approach 1:
The programming operation is divided into multiple program loops (first program loop and second program loop) with different pulse configurations. The first program loop uses a first set of program pulses to achieve initial programming, while the second program loop uses a second set of program pulses with different characteristics (such as different pulse widths, amplitudes, or timing) to refine and stabilize the threshold voltage distribution. This segmentation allows each loop to serve a specific purpose in achieving both efficient programming and long-term stability.
Solution Approach 2:
The patent employs periodic programming actions through multiple program loops executed at different stages. The first program loop executes initially to program the memory cells, followed by a second program loop that executes afterward to adjust and stabilize the threshold voltage distribution. This periodic action ensures that the memory cells are programmed efficiently in the first loop and then stabilized in the second loop, preventing threshold voltage drift over time.
2Reliability
If multiple program loops with different pulse sets are executed to stabilize threshold voltage distributions, then the reliability of data storage is improved, but the programming time and operational complexity increase
Solution Approach 1:
The patent changes key parameters of the program pulses between the first and second program loops. The first set of program pulses has specific parameters (amplitude, width, timing) optimized for initial programming, while the second set of program pulses has modified parameters optimized for stabilizing the threshold voltage distribution. By systematically changing these parameters between loops, the patent achieves reliable data storage while minimizing the total programming time through optimized pulse configurations.
3Productivity
If the threshold voltage distribution is allowed to change naturally over time, then the programming operation remains simple and fast, but read data errors occur due to misinterpretation of changed threshold voltages
Solution Approach 1:
The patent performs a preliminary stabilizing action by executing the second program loop after the first program loop. This preliminary action adjusts and stabilizes the threshold voltage distribution before the memory device is used for normal read/write operations. By performing this stabilizing action in advance, the patent ensures that subsequent read operations can accurately interpret threshold voltages without errors, while the initial programming remains fast through the first program loop.
Data Source
AI summary
A method of driving a nonvolatile memory device, includes; forward shifting threshold voltages of nonvolatile memory cells by executing a first program loop with respect to the nonvolatile memory cells, and thereafter, reverse shifting the threshold voltages of the nonvolatile memory cells, and again forward shifting the threshold voltages of the nonvolatile memory cells by executing a second program loop with respect to the nonvolatile memory cells.