Nonvolatile Memory Page Buffer Circuit Read Margin Optimization
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Solution Overview
Problem
Flash memory devices face challenges in data reliability due to reduced read margin and errors caused by program and read disturbances, leading to vulnerabilities during read operations, especially as storage capacity increases and fabrication scales advance.
Innovation Solution
A nonvolatile memory device employs a page buffer circuit with multiple page buffers that perform sequential sensing operations to determine data states, using a control circuit to adjust read operations based on threshold voltage valleys, thereby reducing errors and enhancing performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If multi-level cells are used to increase storage capacity, then storage capacity is improved, but read margin is reduced
Solution Approach 1:
The patent performs a preliminary first read operation to determine the threshold voltage distribution and identify the valley point before executing the second read operation. This preliminary action allows the system to adaptively adjust read voltages for the subsequent read operation, thereby maintaining adequate read margin even in multi-level cells with reduced margins.
2Manufacturing precision
If fabrication scaling is advanced to increase density, then storage density is improved, but program and read disturbance errors increase
Solution Approach 1:
The patent implements a feedback mechanism where the results of the first read operation are used to determine the threshold voltage valley, which then informs the voltage settings for the second read operation. This feedback loop allows the system to compensate for disturbance errors introduced by fabrication scaling, thereby maintaining data accuracy despite increased density.
3Reliability
If sequential sensing operations are performed to determine data states, then data reliability is improved, but read operation time is increased
Solution Approach 1:
The patent divides the read operation into two separate sensing operations: a first read operation to determine threshold voltage distribution and a second read operation to read the actual data. This segmentation allows each operation to be optimized for its specific purpose, improving overall data reliability while managing read time through efficient sequential execution.
Data Source
AI summary
Nonvolatile memory device includes a memory cell array including pages, each of the pages including memory cells storing data bits, each of the data bits being selectable by a different threshold voltage, a page buffer circuit coupled to the memory cell array through bit-lines, the page buffer circuit including page buffers to sense data from selected memory cells, and perform a first read operation and a second read operation, each including two sequential sensing operations to determine one data state, and each of the page buffers including a latch configured to sequentially store results of the two sequential sensing operations, and a control circuit to control the page buffers to store a result of the first read operation, reset the latches after completion of the first read operation, and perform the second read operation based on a valley determined based on the result of the first read operation.