Flash Memory Read Voltage Determination Using Mixed Mode Extrapolation
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Solution Overview
Problem
The challenge in determining the reading voltage between the Erase and A states in flash memory devices becomes more difficult with scaling, as generic cell voltage distribution algorithms are insufficient to handle the unique characteristics of the Erase state, particularly due to the lack of negative sensing capabilities, which can lead to inaccurate determination and reduced flash memory lifetime.
Innovation Solution
A mixed mode method and an extrapolation method are employed to determine the Er→A reading voltage, where the mixed mode method uses different techniques for the Er→A and other reading voltages, and the extrapolation method estimates the Erase state distribution by extrapolating from the visible part of the Erase state tail, combining and filtering cell voltage distribution data to identify read threshold voltage boundaries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If generic cell voltage distribution algorithms are used to determine reading voltage, then the process is simple, but the determination accuracy is poor for Erase state
Solution Approach 1:
The patent divides the reading voltage determination process into two distinct segments: a first technique for determining the first reading voltage (Vread1) and a second technique for determining the second reading voltage (Vread2). This segmentation allows each technique to be optimized for its specific function, with the first technique handling the Erase state detection and the second technique handling other states, thereby resolving the contradiction between accuracy and complexity.
Solution Approach 2:
The patent implements a dynamic approach by selectively applying different techniques based on the state being detected. The system dynamically switches between the first technique (optimized for Erase state with negative voltage distribution) and the second technique (optimized for other states), allowing the determination process to adapt to the specific characteristics of each state rather than using a static generic algorithm.
2Measurement precision
If the Erase state distribution is partially detectable due to lack of negative sensing capabilities, then the device complexity is reduced, but the reading voltage determination becomes inaccurate
Solution Approach 1:
The patent introduces an intermediary approach by using a first technique that acts as a mediator between the limited negative sensing capabilities and the requirement for accurate Erase state detection. This first technique processes the partially detectable distribution data through specific algorithms that compensate for the sensing limitations, enabling accurate determination of Vread1 despite the inability to directly sense the full negative voltage distribution.
Solution Approach 2:
The patent applies parameter changes by transforming the measurement parameters and processing approach when detecting the Erase state. Instead of attempting to directly measure the full voltage distribution, the system changes the detection parameters to work within the constraints of available sensing capabilities, using the first technique to interpret and utilize the partially detectable distribution data effectively.
3Quantity of substance
If flash memory scaling is continued to increase storage density, then the storage density is improved, but the reading voltage determination becomes more difficult
Solution Approach 1:
The patent applies segmentation by dividing the reading voltage determination into two distinct techniques, allowing the system to handle the increased complexity introduced by scaling. The first technique specifically addresses the Erase state detection challenges that become more pronounced with scaling, while the second technique handles other states, enabling the system to maintain accuracy despite higher storage density requirements.
Solution Approach 2:
The patent implements a dynamic determination process that adapts to the challenges posed by flash memory scaling. By dynamically selecting between the first and second techniques based on the state being detected, the system can effectively handle the increased difficulty of reading voltage determination that arises from continued scaling, while still achieving the desired storage density improvements.
Data Source
AI summary
A data storage device includes a memory and a controller. In a particular embodiment, a method is performed in the data storage device. The method is performed during a read threshold voltage update operation and includes determining a first read threshold voltage of a set of storage elements of a memory according to a first technique and determining a second read threshold voltage of the set of storage elements of the memory according to a second technique. The first read threshold voltage is different from the second read threshold voltage, and the first technique is different from the second technique.