Managing Circuits for Proactive Bad Block Identification in Non-Volatile Memory
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Solution Overview
Problem
Non-volatile memory devices, such as NAND flash memory, often suffer from short circuits between word lines and memory holes or local interconnects, leading to data loss and operational failures during erase, program, and read operations, which are difficult to detect and mitigate during manufacturing.
Innovation Solution
A memory apparatus with managing circuits that proactively identify potential bad blocks by applying stress and determining whether to retire them to a grown bad block pool or return them to normal operation based on the stress results, thereby preventing data loss from uncorrectable errors caused by word line to memory hole or local interconnect short circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If manufacturing testing is performed to detect short circuits, then reliability is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent applies preliminary action by performing proactive identification and stress testing of potential bad blocks during manufacturing before the memory device is deployed. The managing circuit identifies blocks that may have latent short circuit defects and applies stress to accelerate defect manifestation, allowing detection before field operation. This resolves the contradiction by moving the detection action to the manufacturing stage, improving reliability without requiring complex ongoing testing mechanisms.
2Reliability
If stress is applied to all blocks to identify potential bad blocks, then reliability is improved, but productivity decreases due to increased processing time
Solution Approach 1:
The patent applies local quality by selectively applying stress only to blocks identified as potential bad blocks, rather than uniformly stressing all blocks. The managing circuit first performs a preliminary identification phase to flag suspicious blocks, then applies stress selectively to those specific blocks. This differentiated approach maintains high reliability by targeting potential defects while preserving productivity by avoiding unnecessary processing of good blocks.
Solution Approach 2:
The patent segments the block population into different categories: normal blocks, potential bad blocks, and grown bad blocks. This segmentation allows the system to apply different processing strategies to different groups, with stress testing focused specifically on the potential bad block segment. The segmentation resolves the contradiction by isolating the reliability-critical operation to a subset of blocks rather than the entire population.
3Reliability
If potential bad blocks are retired to grown bad block pool, then data loss is prevented, but usable capacity decreases
Solution Approach 1:
The patent applies preliminary action by retiring blocks to the grown bad block pool proactively during manufacturing, before field defects can cause data loss. By identifying and retiring potential bad blocks in advance, the system prevents future data loss events. The principle resolves the contradiction by performing the capacity-reducing action (retirement) during manufacturing when it has minimal impact on the customer experience, rather than losing capacity later due to uncorrectable errors in the field.
Solution Approach 2:
The patent creates a cushioning mechanism by maintaining a grown bad block pool that absorbs potential failures before they affect operational blocks. The managing circuit monitors and manages this pool, ensuring that blocks are retired to the cushion pool before they can cause data loss in active use. This beforehand cushioning resolves the contradiction by proactively reducing capacity to prevent future data loss, making the capacity loss visible and controllable during manufacturing rather than catastrophic in the field.
Data Source
AI summary
A memory apparatus and method of operation is provided. The apparatus has blocks each including non-volatile storage elements. Each of the non-volatile storage elements stores a threshold voltage representative of an element data. The apparatus also includes one or more managing circuits configured to erase at least one of the blocks in an erase operation and program the element data in a program operation. The one or more managing circuits are also configured to proactively identify ones of the blocks as potential bad blocks and selectively apply stress to the ones of the blocks identified as the potential bad blocks and determine whether the potential bad blocks should be retired from the erase and program operations and put in a grown bad block pool or released to a normal block pool used for the erase and program operations based on a judgment after selectively applying the stress.