Reserved Memory Cells for Defect Position Marking in Flash
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Solution Overview
Problem
Non-volatile memory systems face challenges in identifying and managing defective data storage cells, which can lead to data distortion and reduced reliability, especially in bulk storage devices like flash memory cards, due to manufacturing errors or wear and tear, and existing error correction methods are inefficient.
Innovation Solution
The use of reserved or 'pilot' cells to identify and mark defective data storage cells, allowing for improved error correction by differentiating their voltage levels and storing information about defective cells, thereby enabling the system to omit or mark data from these cells during encoding and decoding processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If error correction codes and sophisticated defect management schemes are used to recover information from defective cells, then data reliability is improved, but device complexity and processing overhead increase
Solution Approach 1:
The patent applies preliminary action by pre-marking defective cell positions during manufacturing or initial characterization. The defect position information is stored in advance in the memory structure, so that during normal read/write operations, the system can immediately identify and handle defective cells without complex real-time analysis, thereby improving reliability while keeping the operational complexity low
Solution Approach 2:
The memory structure serves itself by using the same memory cells to store both data and defect position information. The system uses its own existing structure (memory cells and storage capacity) to manage defect information, eliminating the need for separate external defect management hardware or complex external processing schemes
2Reliability
If reserved cells are used to store defect position information, then error correction capability is improved, but storage capacity is reduced
Solution Approach 1:
The patent applies universality by making the reserved cells multi-functional. These cells serve dual purposes: they act as regular data storage cells when not containing defect information, and they store defect position information when needed. This allows the same physical structure to provide both error correction capability and storage capacity, maximizing the utility of each cell
Solution Approach 2:
The patent applies parameter changes by dynamically altering the function of memory cells based on their content. A cell can transition between storing user data and storing defect position information depending on the system's needs. This flexible parameter change allows the memory to adapt its configuration to balance error correction capability and storage capacity based on operational requirements
3Productivity
If defective cells are identified and marked as erasures during encoding and decoding, then error correction efficiency is improved, but processing time increases
Solution Approach 1:
The patent applies preliminary action by pre-identifying and marking defective cell positions before actual data read/write operations. The defect position information is prepared in advance and stored in the memory structure, so that during encoding and decoding, the system can immediately use this pre-prepared information to handle defective cells, improving error correction efficiency while minimizing additional processing time
Data Source
AI summary
Circuits, architectures, systems, methods, algorithms, software and firmware for indicating positions of defective data storage cells using reserved (e.g., “pilot”) cells. The circuit generally includes a memory having multiple subunits, each subunit containing multiple data storage cells and at least one reserved cell. The reserved cells store information identifying whether one or more data storage cells in a subunit are defective. The method of identifying defective memory positions generally includes determining the status of data storage cells in a multi-subunit memory; storing such status information in a reserved cell; and reading the reserved cell. In various embodiments, the reserved cells differentiate between fewer voltage levels and/or store a lower density of information than the data storage cells. The present invention improves error correction capabilities using cells that are typically already available in many conventional nonvolatile memories. In some cases, marking data from defective cells as erasures effectively doubles the error correction capability of the system. When the reserved cells contain more than one level, the overhead for a given level of fault coverage decreases as a function of memory size.