Sense Amplifier Latch Control for NAND Flash Threshold Distribution
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Solution Overview
Problem
Current non-volatile semiconductor storage devices face challenges in efficiently managing and reducing the threshold distribution width in NAND flash memory cells, which affects data storage and retrieval efficiency.
Innovation Solution
A non-volatile semiconductor storage device with a sense amplifier that supplies four types of voltages to memory cells, allowing for precise control of threshold distributions by using a dynamic latch to temporarily hold information and adjusting voltages based on verify results, thereby reducing the threshold distribution width.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional voltage supply methods are used in NAND flash memory, then the device structure remains simple, but the threshold distribution width cannot be effectively reduced
Solution Approach 1:
The sense amplifier is divided into multiple latches (first latch, second latch, third latch) that independently hold different voltage information. This segmentation allows precise control of threshold distribution by separating the control of different voltage levels, enabling the reduction of threshold distribution width while managing device complexity through functional decomposition
Solution Approach 2:
The sense amplifier employs dynamic latches that can switch between different states to supply different voltage patterns dynamically. The latches transition between holding various voltage information based on write operations and verify results, providing adaptive voltage control that reduces threshold distribution width without requiring a permanently complex structure
2Manufacturing precision
If multiple write operations are performed to reduce threshold distribution, then the threshold control precision improves, but the writing time increases
Solution Approach 1:
The first latch pre-holds information about the threshold distribution state before write operations commence. This preliminary preparation allows the sense amplifier to immediately supply appropriate voltages during writing, reducing the need for multiple iterative write operations and thereby decreasing total writing time while maintaining precise threshold control
Solution Approach 2:
The sense amplifier uses verify results as feedback to adjust subsequent voltage supply patterns. The latches update their held information based on verify outcomes, enabling the system to converge to the desired threshold distribution in fewer write-verify cycles, thus improving precision without proportionally increasing writing time
Data Source
AI summary
According to one embodiment, a semiconductor storage device includes a memory cell array having memory cell capable of holding N-bit data; and a sense amplifier comprising a first latch holding information on a threshold distribution, a second latch holding write data, and a third latch holding lower information of the N-bit data, and supplying a first to a fourth voltages to the memory cell to write the data to the memory cell using the first to fourth voltages. The sense amplifier supplies the first to third voltages to the memory cell based on information in the second and the third latches, and based on a result of transfer of the information held by the first latch to the second latch, supplies the fourth voltage or the first voltage to the memory cell.