NAND Flash Memory Programming Stability and Verification
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Solution Overview
Problem
In NAND flash memory devices, the threshold voltage of programmed memory cells remains unstable for a time interval after programming, leading to errors during verify operations, where cells may be incorrectly identified as passing or failing verification, resulting in expanded threshold voltage distribution.
Innovation Solution
Implementing a method where programming is followed by verification, with the option to increase programming voltage and repeat operations if pages fail verification, ensuring that verify operations are performed only after the threshold voltage has stabilized, and using a control unit with a page buffer and data storage circuit to manage program verification data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If verify operation is performed right after programming, then programming speed is improved, but measurement precision deteriorates due to unstable threshold voltage
Solution Approach 1:
The patent applies preliminary action by performing a preliminary programming operation before the final programming and verify operations. This preliminary programming allows the threshold voltage to stabilize before verification, ensuring accurate measurement while maintaining efficient programming flow. The control unit specifically waits for threshold voltage stabilization after the preliminary program before proceeding to verify the subsequent programming operations.
2Measurement precision
If verify operation is delayed until threshold voltage stabilizes, then measurement precision is improved, but productivity deteriorates due to increased programming time
Solution Approach 1:
The patent maintains continuity of useful action by overlapping programming operations with verification operations. While threshold voltage stabilizes after preliminary programming, the control unit continues to program additional pages without interruption. The verify operation is then performed on previously programmed pages, ensuring both accurate measurement and continuous productive operation throughout the programming process.
3Productivity
If threshold voltage is not allowed to stabilize, then productivity is improved by immediate verification, but reliability deteriorates due to programming errors
Solution Approach 1:
The patent uses preliminary action to perform an initial programming operation that establishes stable threshold voltages before verification begins. This preliminary programming serves as a foundation that ensures subsequent verify operations will be performed on stable, reliable data, preventing programming errors while maintaining overall process efficiency.
Solution Approach 2:
The patent applies beforehand cushioning by implementing multiple programming operations (including preliminary and iterative programming) before final verification. This creates a buffer or cushion of redundant programming steps that ensure threshold voltage stability and programming reliability, protecting against errors that would occur if verification were performed on unstable data.
Data Source
AI summary
Provided are a NAND flash memory device and a method of programming the same. The NAND flash memory device may include a cell array including a plurality of pages; a page buffer storing program data of the pages; a data storage circuit providing program verification data to the page buffer; and a control unit. The control unit may program the pages and verify the pages using the program verification data following the programming of at least two of the pages.