NAND Flash Memory Cell Block Write Strategy for Proximity Effect
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Solution Overview
Problem
In narrow-interval nonvolatile memory devices like NAND flash memories, the proximity effect between adjacent memory cells causes erroneous data reading due to capacitive coupling, leading to a prolonged programming time and slow write rate, especially in multivalued memory cells where the threshold voltage distribution is narrow.
Innovation Solution
The semiconductor memory device employs a dual write sequence strategy, where data is written to memory cells in a checkered pattern in the first cell block with a larger step-up voltage, and then copied to a second cell block with a smaller step-up voltage, allowing simultaneous read voltage application to adjacent word lines for efficient data detection and verification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the interval between adjacent memory cells is narrowed to increase microfabrication density, then storage capacity increases, but proximity effect between memory cells increases causing erroneous data reading
Solution Approach 1:
The memory cell array is divided into multiple independent cell blocks (first cell block, second cell block, etc.). During write operations, data is written to selected cell blocks while other blocks remain inactive, segmenting the capacitive coupling effect and preventing proximity interference from affecting all cells simultaneously.
Solution Approach 2:
Different cell blocks are assigned different operational states (active/write or inactive/standby) based on local requirements. The cell block configuration allows certain blocks to be in write mode while others are in standby mode, creating local quality differences that isolate proximity effects to specific regions.
2Manufacturing precision
If a small step-up voltage is used in program operation to narrow threshold distribution in multivalued memory cells, then data accuracy improves, but programming time increases and write rate decreases
Solution Approach 1:
Data is written in advance to a first cell block using a large step-up voltage for fast programming. Before actual read operations, the data is preliminarily copied to a second cell block using a small step-up voltage to narrow threshold distribution. This preliminary action separates the fast write phase from the precise read phase.
Solution Approach 2:
Data is copied from the first cell block to the second cell block before read operations. The second cell block serves as a copy with narrowed threshold distribution, allowing accurate reads without sacrificing write speed in the first block.
3Quantity of substance
If data is written to all memory cells in a cell block, then storage utilization improves, but proximity effect from adjacent cells causes threshold voltage fluctuation and erroneous reading
Solution Approach 1:
The operational state of cell blocks is dynamically adjusted during write and read operations. During writes to the first cell block, the second cell block is set to standby mode. During reads from the first block, the second block remains inactive. This dynamic state management isolates active cells from proximity effects of adjacent active cells.
Solution Approach 2:
The cell block structure acts as an intermediary that isolates groups of memory cells. By configuring certain blocks as active and others as standby, the patent creates buffer zones that mediate between adjacent active cells, reducing direct capacitive coupling and proximity effects.
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 reduces the influence of proximity effects, shortens programming time in the first cell block, maintains high write rates, and allows for precise data verification and reading, while maintaining storage capacity and reducing the number of write operations in the second cell block.
Implementation Method 1
The proximity effect is interference affected by the memory cell from an adjacent memory cell by capacitive coupling
Implementation Method 2
the word line drivers simultaneously apply a read voltage to two adjacent word lines
Implementation Method 3
sense amplifiers provided to correspond to each of the bit lines, the sense amplifiers detecting data stored in the memory cells
Data Source
AI summary
This disclosure concerns a memory including cell blocks, wherein in a first write sequence for writing data to a first cell block, drivers write the data only to memory cells arranged in a form of a checkered flag among the memory cells included in the first cell block, in a second write sequence for writing the data from the first cell block to a second cell block, the drivers write the data to all memory cells connected to a word line selected in the second cell block, and when the data is read from the first cell block or at a time of data verification when data is written to the first cell block, the word line drivers simultaneously apply a read voltage to two adjacent word lines, and the sense amplifiers detects the data in the memory cells connected to the two word lines.