Multi-Level Memory Programming With Repeated Analog Verify
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Solution Overview
Problem
Existing memory devices face challenges in achieving precise threshold voltage distributions during programming, leading to read errors and inefficiencies, particularly in multi-level cell programming, due to memory cells not reaching their intended voltages and requiring additional error correction.
Innovation Solution
Implementing level-based programming with multiple analog program verify operations between programming pulses, including an additional analog verify operation to identify and further program memory cells that have failed previous verify operations, using control logic to apply specific voltage levels to bitlines for targeted programming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional programming operations are used with single verify operations, then programming time is reduced, but threshold voltage distribution precision deteriorates leading to read errors
Solution Approach 1:
The programming process is segmented into multiple programming pulses separated by multiple analog program verify operations. Each verify operation targets specific voltage levels (e.g., first analog program verify at 3.6V, second analog program verify at 4.0V), dividing the verification task into discrete stages that collectively ensure precise threshold voltage distribution while managing overall programming time efficiently.
2Measurement precision
If additional analog verify operations are implemented, then threshold voltage accuracy is improved, but device complexity increases
Solution Approach 1:
Different analog verify operations target different local voltage ranges with specialized voltage levels. The first analog program verify operation uses a first voltage level (3.6V) optimized for lower threshold voltage verification, while the second analog program verify operation uses a second voltage level (4.0V) optimized for higher threshold voltage verification. This localized optimization ensures high measurement precision for each voltage range without requiring a single complex verify mechanism.
3Manufacturing precision
If multiple programming pulses are used with level-based programming, then threshold voltage distribution is improved, but programming time increases
Solution Approach 1:
The programming process employs periodic action through alternating programming pulses and verify operations. The sequence repeats: programming pulse applied to memory cells, then first analog program verify operation, then second analog program verify operation, then another programming pulse. This periodic cycle ensures thorough verification at multiple voltage levels while maintaining efficient programming throughput by systematically rotating through the verification stages.
Data Source
AI summary
A method includes causing, in between applying programming pulses to selectively store data to multiple voltage levels of a plurality of memory cells, a second occurrence of a first analog verify operation to be performed on a first set of memory cells to identify one or more memory cells of a first subset of the first set of memory cells. The first subset of memory cells are those that failed the first analog verify operation and the one or more memory cells twice failed the first analog verify operation. A first occurrence of a second analog verify operation is performed at a second set of memory cells to identify a second subset of the second set of memory cells that failed the second analog verify operation.