Post Over-Erase Correction with Auto-Adjusting Verification
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Solution Overview
Problem
Conventional flash memory technologies face issues with gm degradation and increased OFF leak current due to repeated program and erase operations, leading to longer erase times and reduced read margins, necessitating improved post over-erase correction methods.
Innovation Solution
A post over-erase correction method with an auto-adjusting verification mechanism and leakage degree detection function that adjusts verification based on detected gm degradation and leakage levels, reducing erase time and risk of over soft-programming by modifying programming voltages and reference currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional POEC is executed with fixed verification current, then over-erased cells are repaired, but erase time increases and over soft-programming risk increases due to gm degradation
Solution Approach 1:
The patent applies dynamics by making the POEC verification current adjustable rather than fixed. The verification current is dynamically adjusted based on detected leakage degree, allowing the system to adapt to gm degradation while maintaining effective repair and controlling erase time
Solution Approach 2:
The patent changes the verification current parameter based on leakage degree detection. By adjusting this critical parameter according to actual cell conditions, the system optimizes the balance between repair effectiveness and erase time without causing over soft-programming
2Manufacturing precision
If POEC reference current is lowered to repair over-erased cells, then threshold voltage is restored, but OFF leak current increases due to gm degradation
Solution Approach 1:
The patent implements feedback by detecting the leakage degree and using this information to adjust the POEC verification current. This closed-loop approach ensures that threshold voltage restoration is achieved while compensating for gm degradation that would otherwise increase OFF leak current
Solution Approach 2:
The verification current parameter is changed based on leakage degree detection, allowing the system to restore threshold voltage while accounting for increased OFF leak current due to cycling-induced gm degradation
3Reliability
If POEC verification is严格执行 to reduce OFF leak current, then read margin improves, but erase time increases due to repeated programming
Solution Approach 1:
The patent makes the verification process dynamic by adjusting the verification current based on leakage degree. This allows the system to achieve sufficient read margin without unnecessarily repeated programming cycles that would increase erase time
Solution Approach 2:
The verification current parameter is adjusted according to leakage degree, enabling the system to achieve adequate read margin with fewer programming iterations and thus reducing erase time
4Device complexity
If POEC is executed with fixed parameters, then process is simple, but over soft-programming occurs due to gm degradation from cycling
Solution Approach 1:
The patent applies self-service by having the system automatically detect leakage degree and adjust verification current without external intervention. This self-adjusting mechanism prevents over soft-programming while maintaining process simplicity through automation
Solution Approach 2:
The verification current parameter is automatically changed based on leakage degree detection, preventing over soft-programming while keeping the process simple through automated adaptation rather than complex manual tuning
Data Source
AI summary
A post over-erase correction (POEC) method with an auto-adjusting verification mechanism and a leakage degree detection function detects gm degradation or leakage degree of flash cells before or after entering the POEC process. When a preset condition is satisfied, the auto-adjusting verification mechanism of the POEC is switched on to further reduce leakage current. After cycling, the POEC repairs Vt of over-erased cells to a higher level to solve leakage issues. The erase shot count increases due to slower erase speeds after cycling. Therefore, the cycling degree of flash cells is detected by observing the shot number that the erase operation used. When the leakage phenomenon becomes serious, the bit line (BL) leakage current, amount of repaired BLs, and over-erase correction (OEC) shot number will increase during the OEC procedure. Therefore, the leakage degree of flash cells can be detected by inspecting the above data.