3D NAND Memory Data Redundancy via Error Rate Segmentation
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Solution Overview
Problem
Three-dimensional NAND memory systems face challenges in data reliability due to varying error rates across different memory hole diameters, leading to uncorrectable data errors that existing error correction codes cannot address effectively.
Innovation Solution
Categorizing word lines in a three-dimensional NAND memory array based on predicted error rates, using an Exclusive OR (XOR) operation to combine data from high and low risk categories, and storing the XOR data separately to enable recovery of uncorrectable data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If data is stored in memory cells with small memory hole diameters, then storage capacity is increased, but error rate increases making data uncorrectable by existing ECC
Solution Approach 1:
The patent segments the memory array into multiple zones based on memory hole diameter characteristics. Each zone is independently managed with zone-specific ECC codes, allowing error correction strategies to be tailored to the reliability characteristics of each segment. This segmentation enables high-density storage in zones with smaller memory holes while maintaining overall system reliability through differentiated error handling.
Solution Approach 2:
The patent changes the ECC parameters dynamically based on the memory hole diameter characteristics of different zones. Zones with smaller memory holes (higher error rates) are allocated stronger ECC codes with higher redundancy, while zones with larger memory holes (lower error rates) use lighter ECC codes. This parameter adaptation resolves the contradiction by matching error correction strength to actual error rates, enabling both high storage capacity and data reliability.
2Reliability
If stronger error correction codes are applied to all data, then data reliability is improved, but storage efficiency decreases due to increased redundancy overhead
Solution Approach 1:
The patent applies local quality by assigning different ECC strengths to different zones based on their specific error characteristics. Instead of uniformly applying strong ECC across the entire memory array, each zone receives error correction capability matched to its local reliability needs. This resolves the contradiction by concentrating redundancy overhead only where actually needed, improving data reliability in high-error zones while preserving storage efficiency in low-error zones.
3Quantity of substance
If memory hole diameter is reduced to increase density, then storage density is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent performs preliminary characterization of memory hole diameters during manufacturing or initial operation, before data storage begins. This preliminary action creates a map of zone reliability characteristics that guides subsequent data placement and ECC allocation. By performing this characterization in advance, the system can achieve high storage density through small memory holes without requiring extremely tight manufacturing precision, as zones with varying hole diameters are systematically managed through zone-based ECC.
Data Source
AI summary
Layers in a multi-layer memory array are categorized according to likely error rates as predicted from their memory hole diameters. Data to be stored along a word line in a high risk layer is subject to a redundancy operation (e.g. XOR) with data to be stored along a word line in a low risk layer so that the risk of both being bad is low.