Nonvolatile Memory Selective Erase via String Grouping
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Solution Overview
Problem
The increasing unit capacity of erase operations in nonvolatile memory devices leads to larger spare blocks for storing metadata, resulting in increased device size and reduced lifetime due to unnecessary erasures, as existing technologies erase entire memory blocks even when only a portion of the data needs to be modified.
Innovation Solution
The method involves dividing cell strings in a memory block into string groups and selectively applying an erase voltage to only the targeted string group, using control circuits to manage voltages and transistors, thereby erasing only the intended cells while keeping others unaltered.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the entire memory block is erased when only a portion of data needs to be modified, then the erase operation is simple to perform, but the device lifetime is reduced due to unnecessary erasures and the size of spare blocks increases
Solution Approach 1:
The memory block is divided into multiple string groups, allowing selective erasure of only the required segment (string group) rather than the entire block. This segmentation enables partial erasure operations, extending device lifetime by reducing unnecessary erasures while maintaining operational simplicity through controlled voltage application to specific string groups.
2Reliability
If the entire memory block is erased, then data integrity is maintained, but the size of spare blocks increases
Solution Approach 1:
The erase operation extracts and applies voltage only to the specific string group that requires erasure, rather than applying voltage to the entire memory block. This selective extraction reduces the amount of memory space that needs to be reserved as spare blocks, thereby reducing the overall device size while maintaining data integrity through controlled erasure.
3Reliability
If selective erasure of string groups is implemented, then the unit capacity of erase operation is reduced and device lifetime is extended, but the control circuit complexity increases
Solution Approach 1:
Different voltage levels and control signals are applied to different string groups based on their specific erasure requirements. The control circuit manages voltage application locally to each string group, enabling selective erasure that extends device lifetime while maintaining reasonable circuit complexity through localized control rather than global control.
Data Source
AI summary
An erase voltage is applied to channels of a selected string group to erase only the selected string group. A size and a number of the spare blocks for storing meta data are reduced and thus a size of the nonvolatile memory device is reduced by reducing unit capacity of the erase operation through grouping of the cell strings. Lifetime of the nonvolatile memory device is extended by having control over erasing some cell strings and not others. Control of cell strings for erasure includes allowing some control lines to float, in some embodiments. In some embodiments, ground select transistors with different thresholds and appropriately applied voltages are used to control erasure of particular cell strings. In some embodiments, biasing of word lines is applied differently to portions of a particular cell string to only erase a portion of the particular cell string.