3D NAND Read Voltage Setting for Accurate Valley Detection
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Solution Overview
Problem
Conventional methods for setting read voltage in memory devices result in inaccurate determination due to varying pass memory cell numbers, leading to potential data errors.
Innovation Solution
A multi-stage approach is employed to set read voltage intervals, adjusting them by a shift voltage value to identify consecutive equal numbers or minimum values, ensuring accurate read voltage setting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a fixed voltage interval is used to search for the valley of threshold voltage distribution, then the search operation can be performed, but the pass memory cell number varies excessively resulting in decreased accuracy
Solution Approach 1:
The patent divides the voltage search process into multiple stages with different voltage intervals. The first stage uses a first voltage interval to perform an initial search, and the second stage uses a second voltage interval (smaller than the first) to perform a refined search around the identified valley region. This segmentation allows the system to efficiently locate the general valley position first, then accurately determine the precise read voltage, thereby resolving the contradiction between search efficiency and measurement precision.
2Productivity
If the voltage interval is not set suitably, then the search operation can be performed quickly, but the pass memory cell number varies excessively leading to regional minimum value and data errors
Solution Approach 1:
The patent dynamically adjusts the voltage interval size based on the search stage and identified valley position. In the first stage, a larger first voltage interval is used to cover a broader range and perform the initial search efficiently. After identifying the valley region, the system transitions to the second stage where a smaller second voltage interval is used for precise localization. This dynamic adjustment of the voltage interval resolves the contradiction between search speed and precision by optimizing the interval size for each phase of the search process.
3Ease of operation
If a regional minimum value is determined as read voltage, then the search operation completes, but data may be read erroneously
Solution Approach 1:
The patent implements a feedback mechanism where the results of the first search stage are used to guide the second search stage. The valley position identified in the first stage becomes the basis for setting the search range in the second stage. Additionally, the system compares pass memory cell numbers across different voltage intervals and uses this feedback to determine the optimal read voltage, ensuring it is not merely a regional minimum but a globally optimal value. This feedback approach resolves the contradiction by maintaining operational simplicity while significantly improving data read accuracy.
Data Source
AI summary
A memory device and read voltage setting method are provided. The memory device may be a 3D NAND flash memory circuit, and provides a high-capacity storage medium with favorable performance. The read voltage setting method includes: performing read verify operations on multiple memory cells according to multiple first reading voltage intervals and obtaining multiple first pass memory cells numbers; shifting the respective first reading voltage intervals by a shift voltage value to obtain multiple second reading voltage intervals; determining whether there is at least one consecutive equal number or a minimum number of the pass cells numbers and setting a read voltage according to the at least one equal number or the minimum number.