NAND Flash Word Line Voltage Hold After Program Completion
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
NAND-type flash memory devices face challenges in maintaining the 2nd read condition for a long time after a program operation, leading to fluctuations in threshold voltage distributions and increased error rates due to the word line creep-up phenomenon, which affects data writing speed and accuracy.
Innovation Solution
After completing a program operation, maintaining the word lines at a voltage higher than ground potential to prevent immediate transition to the 1st read condition, thereby prolonging the 2nd read condition and reducing word line creep-up, ensuring consistent data retention and faster writing speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the word line voltage is immediately returned to ground potential after program operation, then the device can quickly transition to ready state, but the 2nd read condition cannot be maintained leading to threshold voltage fluctuations and increased error rates
Solution Approach 1:
The patent applies preliminary action by proactively maintaining the word line at elevated voltage immediately after program operation completes. This preliminary voltage maintenance prevents the immediate transition to ground potential, thereby preserving the 2nd read condition and preventing threshold voltage fluctuations before they can occur. The voltage is kept high for a predetermined period to ensure data retention accuracy is maintained during this critical transition window.
Solution Approach 2:
The patent implements beforehand cushioning by introducing a predetermined delay period where the word line voltage is maintained at elevated levels rather than immediately returning to ground. This cushioning period acts as a protective buffer that prevents the harmful word line creep-up phenomenon and threshold voltage distribution shifts from occurring, thereby cushioning against potential data retention errors during the critical transition phase.
2Reliability
If the word line voltage is maintained at high level after program operation, then word line creep-up is reduced and data retention is improved, but the device cannot quickly accept new operations
Solution Approach 1:
The patent applies partial action by maintaining the word line voltage at elevated levels for only a predetermined partial period after program operation, rather than continuously. This partial maintenance is sufficient to prevent word line creep-up and stabilize threshold voltages during the critical window, while allowing the system to transition back to normal operation afterward, thus balancing reliability improvement with operational productivity.
Solution Approach 2:
The patent implements periodic action through a structured voltage maintenance schedule where the word line is held at elevated voltage for a specific predetermined period after program completion, then transitions back to normal operating voltages. This periodic approach ensures threshold voltage stability during the critical post-program window while allowing the system to efficiently return to high-throughput operation mode.
3Speed
If the word line voltage transitions quickly to ground potential, then the device responds faster to new commands, but threshold voltage distributions shift causing increased error rates
Solution Approach 1:
The patent applies preliminary action by maintaining elevated word line voltage during the critical post-program period before allowing the voltage to transition to ground potential. This preliminary voltage maintenance prevents threshold voltage distribution shifts from occurring during the transition, thereby preventing increased error rates while still allowing relatively fast command response after the predetermined period elapses.
Solution Approach 2:
The patent implements beforehand cushioning by introducing a predetermined delay period that cushions against rapid voltage transitions. This cushioning period prevents the harmful effects of quick voltage changes on threshold voltage distributions, thereby maintaining manufacturing precision in terms of threshold voltage control while still enabling relatively fast overall system response.
Data Source
AI summary
A method of controlling a semiconductor memory device includes: applying a first voltage to a select word line; applying a second voltage to a first non-select word line and a second non-select word line; completing the program operation; applying a third voltage to the select word line; and applying a fourth voltage to a first non-select word line and the second non-select word line. Voltages applied to the select word line, the first non-select word line, and the second non-select word line are higher than or equal to the ground voltage in a period from when a control circuit receives a signal of starting a read operation to when the read operation starts. After the third voltage applied to the select word line, the fourth voltage applied to the first non-select word line and the second non-select word line, the read operation starts.