臺灣博碩士論文加值系統

由於快閃記憶體具有有限的編程/抹除次數(P/E cycles)限制，通常在超過該上限次數後，逐漸不堪使用，而其核心原因來自於快閃記憶體單元內的寫穿(wear-out)現象，在此現象的影響下，任何資料在快閃記憶體中都僅能在有限的時間內安全儲存，並隨著資料的保留時間增加，保留錯誤率持續上升，最終錯誤率超過ECC可糾錯能力而損壞。由於保留錯誤是快閃記憶體的主要錯誤，而其錯誤率又和不同狀態間存在相依的現象，建立在此基礎之上，現今有一些保留錯誤的緩解方法被提出，本文提出了一種在TLC快閃記憶體單元內的寫入頁面配置方法WPS以及字線寫入區塊分類WBC機制，前者的方案是以之前方法的權重計算為基礎，去設計一種新的編碼方式並且包括了新的Flag設計以及狀態編碼的優化；而後者是一種新的耗損平均機制，透過這二種新的方法可以減少保留錯誤率外並增加各個區塊的壽命。

Since NAND flash memory has limited P/E cycles, it could be unusable after exceeding the limited P/E cycles, and the main reason is the wear-out phenomenon in the flash memory cell. Under the influence of this phenomenon, any data can only be safely stored in the flash memory for a limited time (i.e., the retention time). As the retention time increases, the retention error rate continues to rise, and the final retention error rate could exceed the ECC capability. Since the retention error is the main error of the flash memory and its error rate is dependent on different states, some mitigation methods for retention errors are proposed. In the thesis, we propose a retention error mitigation method based on TLC NAND flash memory. The proposed method contains a write position selection scheme (including a new flag design and state coding optimization) and a word-line block classification mechanism for the wear-leveling issue. According to the experimental results, we can reduce the retention error rate and increase the lifetime of TLC NAND flash memory.

第一章 緒論 1
1.1 前言 1
1.2 論文架構 1
第二章 環境背景 2
2.1 NAND Flash Memory 2
2.2 NAND Flash Memory Organization 2
2.3 SLC、MLC、TLC架構 3
2.4 Architecture Restriction 4
2.5 Flash Translation Layer 5
2.6 ECC 6
2.7 Data Retention Errors 7
2.8 Bit-Flip Strategy 8
2.9 Refresh Mechanisms 9
2.10 Bad Block Management 10
第三章 研究動機與相關研究 12
3.1 研究動機 12
3.2 相關研究 13
第四章 基於TLC快閃記憶體的保存錯誤緩解 16
4.1 概述 16
4.2 Write Position Selection 18
4.2.1 Flag映射表設計 19
4.2.2 WPS狀態權重設計與權重計算 20
4.2.2.1 資料保留錯誤率推估方法 23
4.2.3 狀態編碼的優化設計 24
4.3 Word-line Block Classification 24
第五章 實驗與效能分析 30
5.1 實驗環境 30
5.2 實驗負載 31
5.3 實驗結果 33
5.3.1 工作負載的組成與分析 33
5.3.2 保留錯誤率分析 38
5.3.3 Word-line Block Classification保留錯誤率分析 44
第六章 結論 49
第七章 參考文獻 50

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