3D NAND Flash Memory TVS Calibration Using Reference Pages
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Solution Overview
Problem
Existing threshold-voltage shifting algorithms for 3D NAND flash memory devices are inadequate due to abrupt changes in optimal voltage thresholds, leading to increased raw bit error rates and requiring repeated re-reading of failing pages, which is time and power consuming.
Innovation Solution
The method involves determining corrected threshold voltage shift values for a failing page by exploiting the TVS values of neighboring pages within the same memory block, using reference pages to infer optimal values without the need for additional read operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional threshold voltage shifting algorithms are used for 3D NAND flash memory, then the memory can be read with initial TVS values, but abrupt changes in optimal voltage thresholds lead to increased raw bit error rates and require repeated re-reading operations
Solution Approach 1:
The patent performs preliminary calibration of threshold voltage shift values for reference pages before actual read operations. By pre-determining corrected TVS values based on reference pages, the system prepares optimal read parameters in advance, avoiding the need for repeated read operations when read failures occur.
Solution Approach 2:
The patent copies TVS calibration data from reference pages to failing pages. Instead of performing separate calibration for each failing page, the system infers corrected TVS values for failing pages based on the calibration data from neighboring reference pages, significantly reducing the number of read operations required.
2Reliability
If repeated re-reading operations are performed to correct TVS values, then read success rate may improve, but power consumption increases
Solution Approach 1:
The system performs TVS calibration preliminarily on reference pages before actual data reads. By establishing corrected TVS values in advance through reference page calibration, the system eliminates the need for power-consuming repeated read operations to determine appropriate TVS values.
Solution Approach 2:
The patent copies corrected TVS values from reference pages to failing pages, avoiding repeated power-consuming read operations. The calibration data from reference pages is reused for multiple failing pages within the same block, significantly reducing overall power consumption.
3Measurement precision
If conventional TVS calibration is performed for each failing page, then accurate TVS values can be obtained, but the process is time and power consuming
Solution Approach 1:
The patent merges the calibration process for multiple pages by using reference pages to infer TVS values for failing pages. Instead of calibrating each page independently, the system combines calibration efforts by leveraging correlated TVS value changes across pages within the same block, maintaining accuracy while improving speed.
Solution Approach 2:
The system copies corrected TVS values from reference pages to failing pages, achieving accurate calibration without repeating the full calibration process for each page. This approach maintains measurement precision by using correlated TVS changes while dramatically improving calibration productivity.
Data Source
AI summary
Threshold voltage shift values, or TVS values, are calibrated for a non-volatile memory unit including strings of memory cells organized into memory pages, the memory pages being organized into blocks. The calibration involves a read operation to read a given page of the memory pages, based on given one or more TVS values for the given page. In response to a read failure of the read operation, the calibration determines one or more corrected TVS values based on one or more reference TVS values of one or more reference pages of the memory pages. The calibration subsequently performs a read operation to read the given page based on the one or more corrected TVS values. This calibration exploits TVS values of reference pages to determine corrected TVS values of the failing page, instead of finding appropriate TVS values by repeatedly re-reading the failing page.