Nonvolatile Memory Block Erase Verification with Delta Detection
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Solution Overview
Problem
Flash memory devices face challenges in accurately verifying the erase state, leading to potential data reliability issues due to soft defects in memory cells, which are not detected by conventional verification methods.
Innovation Solution
The proposed solution involves an operation method for a nonvolatile memory device that includes performing an erase operation, followed by a block verification using a 0-th erase verification voltage, and subsequent delta verification using a different erase verification voltage to detect soft defects by comparing delta counting values across wordline groups.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional block verification using a single erase verification voltage is performed, then the verification process is simple and fast, but soft defects in memory cells are not detected, leading to data reliability issues
Solution Approach 1:
The verification process is segmented into multiple stages: initial block verification using a first erase verification voltage, followed by delta verification using a second erase verification voltage. This segmentation allows detection of soft defects that would be missed by a single verification stage, thereby improving data reliability without requiring complete redesign of the verification system
Solution Approach 2:
The initial block verification using the first erase verification voltage is performed as a preliminary action before the more complex delta verification. This preliminary verification quickly identifies obviously failed blocks, allowing the system to avoid unnecessary complex verification on already-failed blocks while ensuring thorough checking of potentially good blocks
2Reliability
If multiple verification operations including delta verification are performed, then soft defects are detected improving reliability, but the verification time and process complexity increase
Solution Approach 1:
The system performs partial verification on all blocks using the first erase verification voltage, then performs excessive (additional) delta verification only on blocks that pass the initial verification. This approach ensures thorough reliability checking while avoiding the time penalty of performing full complex verification on every block
Solution Approach 2:
The verification process uses feedback from the initial block verification results to determine which blocks require delta verification. Blocks that fail the initial verification are immediately identified and excluded from further verification, while blocks that pass are subjected to delta verification. This feedback mechanism optimizes verification time based on actual block states
Data Source
AI summary
An operation method of a nonvolatile memory device which includes a memory block having wordlines includes performing an erase on the memory block, performing a block verification on the memory block by using a 0-th erase verification voltage, performing a delta verification on the memory block by using a first erase verification voltage different from the 0-th erase verification voltage when a result of the block verification indicates a pass, and outputting information about an erase result of the memory block based on the result of the block verification or a result of the delta verification. The delta verification includes generating delta counting values respectively corresponding to wordline groups by using the first erase verification voltage, generating a delta value based on the delta counting values, and comparing the delta value and a first reference value.