Non-Volatile Memory Programming Method Narrowing Threshold Voltage Distribution
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Solution Overview
Problem
Conventional incremental step pulse programming methods for non-volatile memory devices result in a widened threshold voltage distribution due to varying electron injection during programming, leading to potential malfunctions in multi-level cells with reduced threshold voltage distribution margins.
Innovation Solution
The proposed method involves counting the number of memory cells programmed to a target threshold voltage and adjusting the bit line voltage based on this count, specifically raising the bit line voltage for cells that have not reached the target, thereby reducing the threshold voltage distribution width without increasing programming time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If incremental step pulse programming is performed with regularly increasing program voltage, then programming operation can be completed, but the threshold voltage distribution width increases
Solution Approach 1:
The patent applies preliminary action by performing a first program operation with an initial program voltage before the main programming sequence. This preliminary programming step prepares the memory cells by injecting a controlled amount of charge, establishing a baseline threshold voltage that prevents excessive distribution width during subsequent programming steps. The preliminary action ensures that when the regular incremental programming begins, the cells are already in a favorable state that limits threshold voltage spread.
Solution Approach 2:
The patent implements parameter changes by dynamically adjusting the program voltage based on real-time verification results. Instead of using fixed incremental steps, the system modifies the program voltage parameter adaptively: when verification shows that threshold voltage distribution width is increasing, the program voltage increment is reduced or the verification voltage is adjusted. This dynamic parameter adjustment maintains optimal programming conditions throughout the process, preventing excessive distribution width while ensuring reliable programming completion.
2Measurement precision
If program voltage is sequentially raised per step voltage in ISPP operation, then memory cells can be programmed to target threshold voltage, but right tail of threshold voltage distribution increases
Solution Approach 1:
The patent implements feedback by continuously performing program verify operations during the programming sequence and using the verification results to control subsequent programming steps. The verification process measures the actual threshold voltage of programmed cells and feeds this information back to adjust the program voltage for the next step. This closed-loop feedback mechanism ensures that the right tail of the threshold voltage distribution does not excessively increase, as the program voltage is adjusted based on real-time cell state measurements rather than following a fixed incremental schedule.
Solution Approach 2:
The patent applies dynamics by making the programming process adaptive rather than static. The program voltage increment per step is not fixed but varies dynamically based on verification results. When verification indicates that cells are approaching the target threshold voltage or showing signs of excessive distribution width, the system dynamically reduces the voltage increment or pauses the programming sequence. This dynamic adjustment maintains optimal programming conditions throughout, preventing the right tail from increasing excessively while ensuring accurate programming of all cells.
Data Source
AI summary
A programming method includes setting the voltages of bit lines, performing a program operation, performing a program verify operation by supplying a program verify voltage and determining whether all of the memory cells of the selected page have been programmed with a target threshold voltage or higher, counting the number of passed memory cells corresponding to a number of pass bits, if, a result of the program verify operation, the program operation failed to program all of the memory cells of the selected page to the target threshold voltage or higher, and making a determination that determines whether the number of pass bits is greater than the first number of pass permission bits, and raising a voltage of a bit line coupled to a failed memory cell, if, as a result of the determination, the number of pass bits is greater than the first number of pass permission bits.