Memory Read Offset Selection for Slow Charge Loss Errors
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Solution Overview
Problem
Memory systems face increased bit error rates due to slow charge loss (SCL) causing threshold voltage shifts, leading to higher read error handling trigger rates and adverse system performance, as existing methods fail to accurately select read types based on SCL time and temperature variations.
Innovation Solution
Implementing a read management component that tracks read offset categories for memory cells, determining current SCL and temperature data to selectively apply different read types, such as valley tracking or adjusted read offset voltages, to maintain low error handling trigger rates while minimizing performance degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional fixed read offset voltages are used, then device complexity is low, but bit error rate increases due to threshold voltage shifts from slow charge loss
Solution Approach 1:
The patent implements dynamic read offset voltage adjustment by tracking slow charge loss time and temperature variations. The read management component selectively applies different read types (first read type with first read offset voltages, second read type with second read offset voltages) based on current SCL time and temperature conditions, making the read operation adaptive rather than fixed.
Solution Approach 2:
The patent changes the read offset voltage parameter based on SCL time and temperature conditions. By determining current read offset category corresponding to SCL time ranges and selecting appropriate read offset voltage sets, the system adjusts critical read parameters to compensate for threshold voltage shifts caused by slow charge loss and temperature variations.
2Reliability
If read offset voltages are adjusted to compensate for SCL, then bit error rate decreases, but system performance degrades due to additional read type selection overhead
Solution Approach 1:
The patent performs preliminary tracking of slow charge loss time and categorization of read offset categories before actual read operations. By determining current read offset category in advance and pre-selecting appropriate read types based on SCL time ranges, the system prepares the optimal read configuration beforehand, minimizing runtime decision overhead.
Solution Approach 2:
The patent implements feedback mechanisms by monitoring temperature variations and SCL time, then using this information to selectively apply appropriate read types. The read management component continuously adjusts read offset voltages based on feedback from SCL tracking and temperature sensing, optimizing read operations under varying conditions.
3Manufacturing precision
If multiple read types are implemented to handle different SCL time ranges, then manufacturing precision of read operations improves, but device complexity increases
Solution Approach 1:
The patent segments the SCL time range into multiple categories (first set of read offset voltages for first SCL time range, second set for second SCL time range, etc.). By dividing the continuous SCL time variable into discrete ranges and associating each range with specific read offset voltage sets, the system achieves precise read operations for different aging stages while managing complexity through structured categorization.
Solution Approach 2:
The patent applies different read offset voltage characteristics to different SCL time ranges and temperature conditions. Each read type is optimized with specific read offset voltages tailored to its target SCL time range, providing locally optimized read precision for each operating condition rather than using a uniform approach.
Data Source
AI summary
An example method includes tracking, via a controller external to a memory device comprising a plurality groups of memory cells, respective read offset categories for the plurality of groups of memory cells. The method can include: in response to receiving a read request targeting a group of memory cells of the plurality of groups of memory cells, determining a current read offset category corresponding to the group of memory cells; selecting, based at least on the determined current read offset category, one of multiple read types to execute to read the group of memory cells; and executing the selected one of the multiple read types to read the group of memory cells.