3D Memory Erase-Verify Segmentation and Pass Voltage Masking
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Solution Overview
Problem
Three-dimensional memory systems face challenges in erase-verify operations due to differences in electric field effects across layers, leading to increased residual charges and potential erase-verify failures.
Innovation Solution
Implementing a method where multiple erase-verify operations are performed separately on different groups of memory cells within a memory cell string, using pass voltages to 'mask' residual charges and ensure successful erasure verification by applying distinct voltages to word lines connected to neighboring cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single erase-verify operation is performed on all memory cells in a 3D memory, then the operation is simple and fast, but residual charges cause erase-verify failures due to different electric field effects across layers
Solution Approach 1:
The memory cell string is divided into multiple groups (first group, second group, etc.) based on their vertical positions in the 3D stack. Each group is subjected to separate erase-verify operations, allowing independent control and verification of erasure for cells at different heights, thereby eliminating residual charge interference from upper or lower layers.
Solution Approach 2:
Before performing the erase-verify operation on a particular group of memory cells, preliminary actions are taken to apply pass voltages to word lines connected to neighboring cells. This preliminary voltage application masks residual charges that could interfere with the current operation, ensuring accurate verification.
2Measurement precision
If pass voltages are applied to mask residual charges, then erase-verify accuracy is improved, but the operation time and energy consumption increase
Solution Approach 1:
By segmenting the memory cell string into multiple groups and performing erase-verify operations on them sequentially rather than simultaneously, the patent applies pass voltages only when necessary for specific groups, minimizing the total time and energy consumption compared to a single comprehensive operation.
Solution Approach 2:
The erase-verify operation is performed continuously on different groups of memory cells without idle waiting. While one group is being verified, another group can be prepared or verified in parallel, maintaining continuous productive action and reducing overall operation time.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces the probability of erase-verify failures by effectively managing residual charges and ensuring accurate verification of memory cell erasure across varying layers in 3D memory systems.
Implementation Method 1
the effect of electric field of a erase-verify voltage applied on upper layers of the 3D memory is different from the effect of electric field of the erase-verify voltages applied on lower layers of the 3D memory
Implementation Method 2
In an erase-verify operation, the effect of electric field of a erase-verify voltage applied on upper layers of the 3D memory is different from the effect of electric field of the erase-verify voltages applied on lower layers of the 3D memory
Data Source
AI summary
An erase-verify method for a three-dimensional (3D) memory and a memory system are provided. The 3D memory includes at least one memory cell string including a plurality of memory cells, and the memory cells include a first group of memory cells and a second group of memory cells. Each of the memory cells is coupled to a word line. The method comprises the following steps. A first erase-verify operation is performed on the first group of memory cells. After performing the first erase-verify operation on the first group of memory cells, a second erase-verify operation is performed on the second group of memory cells in condition that the first group of memory cells are verified as erased successfully.