Charge Loss Detection Using Multiple Sampling Scheme
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Solution Overview
Problem
In memory sub-systems, particularly in non-volatile memory devices like NAND, charge loss detection is challenging due to variations in threshold voltage distributions over time and temperature, leading to read disturb errors and inaccurate detection of open and cycled blocks.
Innovation Solution
Implementing a multiple sampling scheme where a first current is obtained at a saturation voltage, and a second current is sampled during a ramp-down period, allowing for quick identification of voltage shifts and adjustment of read voltages to account for charge loss, thereby improving the detection of charge loss in memory cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single sampling point is used for charge loss detection, then the detection process is simple and fast, but the detection accuracy is insufficient due to variations in threshold voltage distributions over time and temperature
Solution Approach 1:
The patent divides the charge loss detection process into multiple sampling points taken at different times during the read operation. Instead of using a single sampling point, the system performs multiple measurements (first read operation, second read operation, etc.) at different moments, allowing it to capture the dynamic variations in threshold voltage distributions caused by time and temperature changes, thereby improving detection accuracy while managing complexity through structured segmentation
Solution Approach 2:
The patent implements periodic sampling of the memory cell threshold voltages at regular intervals during the read operation. By performing read operations at multiple periodic time points and comparing the results, the system can detect charge loss more accurately by observing changes over time, transforming a static single-point measurement into a dynamic multi-point periodic measurement scheme
2Measurement precision
If multiple sampling points are used for charge loss detection, then the detection accuracy improves, but the detection time and processing complexity increase
Solution Approach 1:
The patent performs preliminary read operations at multiple sampling points before making the final charge loss determination. By提前 conducting these measurements and storing the results, the system prepares the necessary data in advance, allowing for efficient comparison and analysis when determining whether charge loss has occurred, thus reducing the critical path time for the detection decision
Solution Approach 2:
The patent combines multiple read operations and their associated measurements into a unified charge loss detection process. By merging the data from multiple sampling points and processing them together through a consolidated analysis routine, the system achieves accurate charge loss detection while avoiding the time penalty of completely separate detection operations, efficiently utilizing the collected measurement data
3Productivity
If traditional single-point detection is used, then the process is fast, but read disturb errors increase due to inaccurate detection of open and cycled blocks
Solution Approach 1:
The patent implements a feedback mechanism where the results from multiple read operations at different sampling points are compared and analyzed. The system uses this feedback information to dynamically adjust its determination of whether charge loss has occurred, allowing it to maintain fast detection speeds while improving reliability by using the cumulative feedback from multiple measurements to make more accurate decisions about block states and reduce read disturb errors
Data Source
AI summary
A memory device includes a memory array and control logic, operatively coupled with the memory array, to perform operations including causing a first current to be obtained with respect to cells of a wordline maintained at a first voltage, determining that the cells are at a second voltage lower than the first voltage, in response to determining that the cells are the second voltage, causing a voltage ramp down process to be initiated, causing a second current to be sampled with respect to the cells during the voltage ramp down process, and detecting an existence of charge loss by determining whether the second current satisfies a threshold condition in view of the first current.