NAND Flash Memory Read Verification for Writing Speed
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Solution Overview
Problem
NAND flash memory devices face challenges in writing speed due to the need to set multiple threshold voltage distributions for multilevel data storage, leading to erroneous writing and decreased reliability, especially with variations in operating conditions such as temperature and voltage shifts during program verify operations.
Innovation Solution
A semiconductor memory device with a control unit that manages voltage generator circuits and data storage circuits to set and verify threshold voltages efficiently, allowing for accurate data reading and writing by adjusting read and verify operations across multiple levels, thereby improving writing speed and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If multiple threshold voltage distributions are set for multilevel data storage, then data storage capacity is improved, but writing speed deteriorates
Solution Approach 1:
The patent applies preliminary action by performing a read operation at a first level before the final write operation. This preliminary read allows the system to determine the number of cells between the first level and second level, which is used to verify whether the write operation should proceed. This advance checking prevents unnecessary write operations and reduces the overall writing time for multilevel data storage.
Solution Approach 2:
The patent implements feedback by using the read data from the first level to control subsequent write operations. The number of cells determined from the read operation provides feedback that indicates whether the threshold voltage distribution is appropriate, allowing the system to adjust or confirm the write operation parameters accordingly, thereby improving writing efficiency.
2Quantity of substance
If margin between threshold voltage distributions is narrowed to increase storage density, then data storage capacity is improved, but reading reliability deteriorates
Solution Approach 1:
The patent introduces an intermediary read operation at a first level that acts as a mediator between the threshold voltage distributions. By reading at this intermediate level and calculating the number of cells between levels, the system can accurately determine data states even when margins are narrow, thus maintaining reading reliability while enabling higher storage density.
Solution Approach 2:
The patent replaces direct threshold voltage comparison with a computational approach. Instead of relying solely on physical voltage margins, the system uses read data and computational logic to determine the number of cells between levels, substituting mechanical voltage separation with information processing to maintain reliability in narrow-margin scenarios.
3Adaptability or versatility
If voltage levels are shifted due to temperature and operating conditions, then adaptability is improved, but measurement precision deteriorates
Solution Approach 1:
The patent uses feedback from the preliminary read operation to detect voltage level shifts caused by temperature and operating conditions. By measuring the actual number of cells between levels and comparing it with expected values, the system can identify voltage drift and adjust subsequent operations accordingly, maintaining measurement precision across varying conditions.
Solution Approach 2:
The patent dynamically adjusts operating parameters based on detected conditions. When voltage level shifts are detected through the read operation, the system modifies subsequent read and write voltage levels to compensate for the drift, thereby maintaining accurate threshold voltage measurement and data integrity despite environmental variations.
Data Source
AI summary
A control unit reads data from a plurality of memory cells connected to one of the word lines in a read operation at a first level CR generated by a voltage generator circuit and in a read operation at a second level CR−x and finds the number of cells included between the first level and the second level from the data and, if the number is equal to or smaller than a specified value, determines the result of the read operation at the first level to be read data.