NAND Flash Programming via Pre-Program Voltage Control
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Solution Overview
Problem
The challenge in non-volatile memory devices, particularly in NAND flash memory, is the widening of threshold voltage distributions due to interference, back pattern dependency, and source line resistance, which affects the programming of multi-level cells and increases interference between memory cells as device size shrinks.
Innovation Solution
A method of programming non-volatile memory devices involves pre-programming selected word lines with a lower pre-program voltage, followed by applying a program voltage, and using pass voltages to reduce the width of threshold voltage distributions, specifically targeting erase cells to minimize interference by keeping their threshold voltage close to 0V.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If program voltage is increased to affect programming of MLC, then programming capability is improved, but threshold voltage distribution width increases
Solution Approach 1:
The patent applies preliminary action by performing a pre-program operation before the main program operation. In the pre-program operation, a pre-program voltage (lower than program voltage) is applied to program cells that will be erased, shifting their threshold voltage to a predetermined level. This preliminary action prepares the cells to receive the main program operation without causing excessive threshold voltage shift, thereby maintaining narrow threshold voltage distribution while enabling effective programming.
2Productivity
If device size is reduced, then integration level is improved, but interference between memory cells increases
Solution Approach 1:
The patent applies local quality by differentiating the treatment of memory cells based on their operational state. Specifically, it identifies program cells (to be programmed) and erase cells (to be erased) and applies different voltage sequences and timing to each type. This localized differentiation allows the system to maintain narrow threshold voltage distributions in erase cells while still achieving high integration density, thereby reducing interference effects.
3Adaptability or versatility
If threshold voltage distribution width is made narrow for MLC, then data storage capability is improved, but programming difficulty increases
Solution Approach 1:
The patent applies segmentation by dividing the programming operation into two distinct phases: a pre-program operation and a main program operation. The pre-program operation uses a lower pre-program voltage to preliminarily program erase cells, while the main program operation uses higher program voltage for program cells. This segmentation allows the system to achieve narrow threshold voltage distributions necessary for MLC while managing programming complexity through structured, multi-stage operations.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach narrows the threshold voltage distribution of erase cells, reducing interference and improving programming efficiency by minimizing the shift in threshold voltages during programming operations.
Implementation Method 1
The number of data bits that can be stored in a memory cell depends upon the number of threshold voltage distributions that can be represented by the memory cell
Implementation Method 2
Capacitance coupling is generated between floating gates between the second to ninth memory cells C1 to C8 surrounding the first memory cell C0
Data Source
AI summary
A programming method of a non-volatile memory device may include providing a memory device in which a first word line is preprogrammed in an erase operation of a memory block, pre-programming a second word line according to a program command, and programming the first word line.