Flash Memory Step-Up Voltage Control for Write Reliability
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Solution Overview
Problem
Highly integrated flash memory devices face challenges in maintaining data reliability due to adjacent-cell interference, which increases threshold voltage distribution width and affects write time, requiring a method to reduce write time while preserving data reliability.
Innovation Solution
A non-volatile semiconductor memory device that dynamically adjusts the step-up voltage based on the distribution width of threshold voltage distributions during the write operation, ensuring smaller distribution widths and faster write times by varying the step-up voltage according to the determined distribution width of intermediate or midpoint threshold voltage distributions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a smaller step-up width is used in the step-up operation to reduce threshold voltage distribution width, then data reliability is improved, but write time increases and performance is reduced
Solution Approach 1:
The patent applies dynamics by making the step-up width adjustable rather than fixed. The step-up width is dynamically changed based on the memory cell's threshold voltage state and the current write operation progress. This allows the system to use smaller step-up widths when needed to maintain data reliability while using larger step-up widths when possible to reduce write time, thus resolving the contradiction between reliability and write speed.
Solution Approach 2:
The patent changes the parameter of step-up width based on the distribution width of threshold voltage. By monitoring the threshold voltage distribution and adjusting the step-up width accordingly, the system optimizes the balance between achieving narrow distribution widths (for reliability) and maintaining fast write speeds. This parameter adaptation resolves the fixed trade-off between reliability and write time.
2Quantity of substance
If multi-level storage scheme is used to increase storage capacity, then storage density is improved, but adjacent-cell interference increases and data reliability deteriorates
Solution Approach 1:
The patent applies local quality by tailoring the step-up width to the specific state of each memory cell or group of cells during the write operation. Rather than using a uniform step-up width for all cells, the system adjusts the step-up width locally based on the observed threshold voltage distribution width, which varies depending on the cell's current state and its susceptibility to adjacent-cell interference. This localized adjustment maintains reliability while enabling multi-level storage.
Solution Approach 2:
The patent implements feedback by monitoring the threshold voltage distribution width during the write operation and using this information to adjust subsequent step-up widths. The system measures the actual distribution width, compares it to target values, and modifies the step-up width in response to maintain optimal distribution narrowness. This feedback mechanism ensures data reliability in multi-level storage by continuously adapting to the actual cell states and interference conditions.
Data Source
AI summary
A control circuit applies a write pulse voltage to a selected word line to perform a write operation to 1-page memory cells along the selected word line. The circuit then performs a verify read operation to confirm whether the data write to the 1-page memory cells is completed. According to the result of the verify read operation, a step-up operation is performed out to raise the write pulse voltage by a step-up voltage. The control circuit changes the amount of the step-up voltage according to a distribution width of a first threshold voltage distribution generated in process of the write operation to the memory cells.