Flash Memory Program Voltage Adaptation
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Solution Overview
Problem
The incremental step pulse programming (ISPP) method for flash memory devices can lead to decreased threshold voltage distribution margin and errors when dealing with heterogeneous threshold voltage distributions, particularly due to the need for periodic program voltage increments.
Innovation Solution
A method is introduced where a program loop using a program voltage suitable for memory cell characteristics is executed, involving an Nth program loop with an Nth program voltage, followed by a program verify operation to count memory cells with threshold voltages greater than or equal to the verify voltage, generating a voltage revision value based on the count and operational conditions, which is then added to a subsequent Mth preset program voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If incremental step pulse programming (ISPP) method is used with constant program voltage increments, then program operation can be performed systematically, but threshold voltage distribution margin decreases and errors occur due to heterogeneous threshold voltage distributions
Solution Approach 1:
The patent applies dynamics by making the program voltage adaptive rather than fixed. The program voltage is dynamically adjusted based on real-time feedback from program verify operations and counted memory cell states. This allows the programming system to adapt to heterogeneous threshold voltage distributions across different memory cells, resolving the contradiction between systematic programming and adaptability to cell variations.
Solution Approach 2:
The patent implements feedback mechanisms where program verify operations continuously monitor memory cell states during programming. The results of these verify operations and the counted number of memory cells with threshold voltages above the verify voltage are fed back to adjust subsequent program voltages. This feedback loop enables the system to maintain reliability by adapting to actual cell characteristics rather than relying on fixed voltage increments.
2Productivity
If program voltage is increased to accommodate heterogeneous threshold voltage distributions, then more memory cells can be programmed, but program operation speed decreases due to multiple voltage adjustment steps
Solution Approach 1:
The patent applies preliminary action by performing program verify operations and counting memory cell states at strategic points during the programming process. This preliminary assessment of cell states allows the system to predict the optimal program voltage for subsequent operations, avoiding the need for multiple trial-and-error voltage adjustments and thereby maintaining high programming speed while ensuring reliability.
Solution Approach 2:
The patent changes the program voltage parameter dynamically based on counted memory cell states and verify operation results. Instead of using fixed voltage increments, the system adjusts the voltage parameter adaptively, changing it in response to actual cell characteristics. This parameter change strategy enables the system to maintain both speed and reliability by optimizing voltage selection based on real-time feedback.
3Manufacturing precision
If multiple program loops are executed with fixed preset voltages, then programming can be completed for all memory cells, but the threshold voltage distribution becomes non-uniform across different cell groups
Solution Approach 1:
The patent applies local quality by tailoring program voltages to specific memory cell groups based on their individual characteristics. Instead of applying a uniform voltage schedule to all cells, the system determines optimal voltages for each cell group based on their threshold voltage distributions and programming progress. This localized approach ensures uniform threshold voltage distribution across different cell groups while managing complexity through systematic voltage determination methods.
Solution Approach 2:
The patent changes program voltage parameters differently for different memory cell groups based on their specific characteristics and programming states. Each cell group receives customized voltage adjustments rather than a blanket voltage schedule. This parameter differentiation approach achieves uniform threshold voltage distribution across diverse cell groups while maintaining manageable system complexity through structured voltage control strategies.
Data Source
AI summary
A method of programming a flash memory device, which is a nonvolatile memory device including a plurality of pages, includes executing an Nth program loop of a program operation by applying an Nth selected program voltage to a selected word line from among the plurality of pages, and performing a program verify operation by applying a program verify voltage to the selected word line, counting the number of memory cells having a threshold voltage which is greater than or equal to the program verify voltage, from among memory cells connected to the selected word line, generating a program voltage revision value based on a result of the counting and an operational condition of the Nth program loop, and adding the program voltage revision value to an Mth preset program voltage of an Mth program loop executed after the Nth program loop where M>N.