Flash Memory Refresh Triggered by Temperature and Dual-Speed Read Comparison
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Solution Overview
Problem
Existing flash memory technologies face challenges in performing refresh operations at appropriate times, leading to potential read errors due to power supply issues and delayed timing, which can result in unnecessary refresh operations or missed refreshes.
Innovation Solution
A flash memory system that includes multiple memory cells, a sense amplifier, and a controller performing first and second read operations followed by a refresh operation, where data is compared across these operations to determine if rewriting is necessary, ensuring refreshes occur before read errors occur.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If refresh operation timing is specified by period (time), then the refresh operation can be scheduled regularly, but unnecessary refresh operations may be performed and the timing may be delayed when power supply is not turned on
Solution Approach 1:
The patent changes the basis for determining refresh timing from a fixed time period to a temperature-based parameter. The refresh operation is triggered when the temperature exceeds a predetermined threshold, rather than at fixed time intervals. This allows the system to adapt refresh timing to actual thermal conditions, performing refresh operations only when temperature-induced threshold voltage variation becomes problematic, thereby eliminating unnecessary refreshes while ensuring data integrity.
2Loss of time
If timer measures elapsed time after write operation, then the period can be tracked, but the timer cannot measure if power supply is not turned on
Solution Approach 1:
The patent employs temperature as a self-recording parameter that continuously reflects the thermal history of the flash memory without requiring active measurement or power consumption. The temperature itself serves as the trigger signal for refresh operations, eliminating the need for timers, counters, or other active monitoring components that would require power to function.
3Loss of information
If counter counts number of write operations, then the write frequency can be tracked, but the counter cannot count if power supply is not turned on
Solution Approach 1:
The patent uses temperature as a cumulative indicator of stress conditions that naturally accumulates during write operations and power-on periods. Instead of counting individual write operations, the system monitors the integrated thermal effect, which inherently reflects the cumulative impact of write operations on threshold voltage variation without requiring active counting mechanisms.
Data Source
AI summary
The present invention aims at providing a flash memory that can perform a refresh operation at an appropriate time before a read error occurs. The controller performs the first read operation in which the memory cell as the read target is made to draw out the potential of one of the bit lines, the bit line potential controller is made to draw out the potential of the other of the bit lines at the first speed, and concurrently, the sense amplifier is made to read data; the second read operation in which the memory cell as the read target is made to draw out the potential of one of the bit lines, the bit line potential controller is made to draw out the potential of the other of the bit lines at the second speed faster than the first speed, and concurrently, the sense amplifier is made to read data; and the refresh operation in which, when the data read by the first read operation and the data read by the second read operation are determined to be different, the data stored in the memory cell as the read target is rewritten.