Nonvolatile Memory Read Voltage Optimization via On-Chip Valley Search
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Solution Overview
Problem
Existing nonvolatile memory devices face challenges in accurately reading multi-bit data from flash memories due to variations in threshold voltage distributions caused by word line coupling, leading to read errors and reduced reliability.
Innovation Solution
A read method for nonvolatile memory devices that performs an on-chip valley search (OVS) operation by dividing data into pages and performing multiple sensing operations at different read voltages to determine optimal read voltages, and selectively performing data recover read operations based on the results to minimize read errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If multi-bit data is read from flash memory cells, then storage capacity is improved, but read accuracy deteriorates due to threshold voltage distribution variations
Solution Approach 1:
The patent performs preliminary sensing operations to detect threshold voltage distribution characteristics before the actual data read operation. By conducting N sensing operations (where N≥3) at different read voltages to identify valley points in the threshold voltage distributions, the system prepares optimal read voltage information in advance, which is then used to guide the subsequent data read operation, thereby improving read accuracy for multi-bit data
Solution Approach 2:
The patent implements a feedback mechanism where the results of preliminary sensing operations are used to dynamically adjust read voltage selection. The valley search operation continuously monitors threshold voltage distributions and feeds back optimal voltage information to the read operation, enabling adaptive voltage adjustment that compensates for variations in threshold voltage distributions caused by word line coupling and other factors
2Measurement precision
If multiple sensing operations are performed to determine optimal read voltages, then read accuracy is improved, but operation time increases
Solution Approach 1:
The patent performs N sensing operations where N≥3, which is more than the minimum required for basic reading. This excessive action ensures that sufficient data points are collected to accurately identify valley points in threshold voltage distributions, thereby determining optimal read voltages with higher confidence while maintaining acceptable operation time through efficient processing of the additional sensing data
3Ease of operation
If data is divided into M pages for individual reading, then data organization is improved, but read complexity increases
Solution Approach 1:
The patent divides multi-bit data stored in each memory cell into M separate pages (where M≥3), with each page representing a specific bit position. This segmentation allows independent reading and processing of each bit plane, simplifying the overall read operation by breaking down complex multi-bit retrieval into manageable single-bit operations that can be handled using standard sensing circuits and logic
Data Source
AI summary
Provided is a read method for a nonvolatile memory device for reading data with an optimum read voltage. The read method includes reading data of a first set of memory cells connected to a first word line, by dividing the data of the first set of memory cells into M pages and individually reading data from the M pages. The reading data includes performing an on-chip valley search (OVS) operation on a first valley of two adjacent threshold voltage distributions of the first set of memory cells when reading each of the M pages, and performing a data recover read operation via a read operation on a second word line adjacent to the first word line, based on a result of the OVS operation. In the data recover read operation, a read operation on the first word line is not performed.