Select Transistor Threshold Voltage Check for NAND Flash Bad Block Detection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Non-volatile memory devices, such as flash memory, face performance deterioration due to changes in threshold voltage distributions of select transistors over time, leading to inefficient bad block checking operations that can prolong processing times and reduce device reliability.
Innovation Solution
A method for operating non-volatile memory devices that involves selecting specific select transistors within NAND strings and performing check operations on their threshold voltages, determining whether they fall within reference voltage ranges, and selectively skipping or performing program operations to classify memory blocks as bad, thereby optimizing the check process and reducing processing time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If comprehensive check operations are performed on all select transistors, then reliability is improved, but processing time increases
Solution Approach 1:
The patent performs a preliminary check operation on a first select transistor before checking other select transistors in the NAND string. This preliminary check allows early identification of bad blocks, enabling the system to skip or reduce subsequent checking operations on remaining transistors, thus reducing overall processing time while maintaining reliability through selective comprehensive checking.
Solution Approach 2:
The patent divides the checking process into segments: first checking a specific first select transistor, then conditionally checking other select transistors based on the first result. This segmentation allows the system to perform minimal necessary checks rather than comprehensive checks on all transistors, reducing processing time while maintaining adequate reliability through targeted verification.
2Measurement precision
If check operations are performed on all select transistors, then measurement precision is improved, but productivity decreases
Solution Approach 1:
The patent performs a preliminary check on a first select transistor to obtain initial threshold voltage information. This preliminary measurement provides sufficient precision to identify potential bad blocks, allowing the system to avoid time-consuming comprehensive checks on all transistors while maintaining adequate detection accuracy through selective verification.
Solution Approach 2:
The patent performs checking operations on only some select transistors rather than all transistors in the NAND string. By performing partial checking on strategically selected transistors (starting with the first select transistor), the system achieves sufficient measurement precision for bad block identification while significantly improving productivity through reduced operation count.
Data Source
AI summary
A method of operating a non-volatile memory device includes selecting a first select transistor from among a plurality of select transistors included in a NAND string, and performing a check operation on a first threshold voltage of the first select transistor. The check operation includes comparing the first threshold voltage with a first lower-limit reference voltage level, and performing a program operation on the first select transistor when the first threshold voltage is lower than the first lower-limit reference voltage level. When the first threshold voltage is equal to or higher than the first lower-limit reference voltage level, the check operation on the first threshold voltage is ended.