Dynamic Read Voltage Adjustment for Nonvolatile Memory
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Solution Overview
Problem
Nonvolatile memory systems face challenges in maintaining accurate read operations due to variations in threshold voltage levels over time, leading to potential data loss or errors, especially when programming operations are performed across different pages.
Innovation Solution
A method and system that determine the elapsed time since a programming operation and adjust the read voltage based on this elapsed time and the number of erase operations, using an access mark system to manage and reset these values, thereby optimizing read operations and reducing errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed read voltage is used for all programming operations, then the device complexity is reduced, but the reliability of read operations deteriorates due to threshold voltage variations over time
Solution Approach 1:
The patent applies dynamics by transitioning from a fixed read voltage to a dynamic read voltage that changes based on the elapsed time since the last programming operation. The control circuit adjusts the read voltage according to time-dependent characteristics of the memory cell, allowing the system to adapt to threshold voltage variations without requiring complex additional hardware structures.
Solution Approach 2:
The patent implements parameter changes by modifying the read voltage parameter based on the elapsed time since programming. The control circuit determines the appropriate read voltage level by referencing the time that has passed since the programming operation, thereby compensating for threshold voltage drift without increasing device complexity.
2Reliability
If the read voltage is adjusted for each programming operation, then the reliability of read operations is improved, but the device complexity increases due to additional control mechanisms
Solution Approach 1:
The patent applies self-service by enabling the control circuit to automatically determine and adjust the read voltage based on the elapsed time since programming. The system uses internally stored timing information and erase operation counts to autonomously select the appropriate read voltage without requiring external intervention or complex additional control mechanisms.
Solution Approach 2:
The patent implements feedback by using the elapsed time information and erase operation count as feedback parameters that influence the read voltage selection. The control circuit continuously monitors these parameters and adjusts the read voltage accordingly, creating a closed-loop system that improves reliability without significant complexity increase.
3Measurement precision
If timing information is stored for each memory block, then the read voltage can be accurately adjusted, but the memory capacity is reduced due to overhead storage requirements
Solution Approach 1:
The patent applies segmentation by dividing the timing information storage into separate fields within the spare area of each memory block. Instead of using a unified large storage structure, the timing information is segmented into discrete fields that can be efficiently managed and accessed, minimizing the overhead impact on usable memory capacity.
Solution Approach 2:
The patent implements discarding and recovering by utilizing the spare area of memory blocks for storing timing information, which would otherwise be wasted space. By recovering and repurposing this unused capacity for timing storage, the system achieves precise elapsed time determination without significantly reducing the usable memory capacity for data storage.
Data Source
AI summary
An elapsed time with respect to a programming operation on a memory cell of a nonvolatile memory is determined, a read voltage is adjusted based on the determined elapsed time and a read operation is performed on the memory cell using the adjusted read voltage. Determining the elapsed time may be preceded by performing the programming operation in response to a first access request and determining the elapsed time may include determining the elapsed time in response to a second access request. Memory systems supporting such operations are also described.