自旋轉移力矩式磁阻隨機存取記憶體(Spin-Transfer-Torque Magnetic Random-Access Memory, STT-MRAM)是近幾年最有前途的 on-chip 內建記 憶體之一。然而，STT-MRAM 中的隧道磁阻元件 (Magnetic Tunnel Junction, MTJ) 存在一些可靠性的威脅，這些威脅會降低其耐用性、產生缺陷並導致 內建記憶體故障。最主要的可靠性問題是來自 MTJ 上的老化效應，也就是 與時間相關的介電層崩潰效應 (Time Dependent Dielectric Breakdown, TDDB)。此效應會隨著時間去影響 MTJ 的電阻值並且長久下來可能會導 致記憶體資料讀取錯誤。為了克服這一困難，在本篇論文中，我們提出了一 個在線老化偵測和老化補償的架構，透過動態監控電氣參數的偏差並提供 適當的補償以避免讀取錯誤。在線老化偵測機制可以通過偵測讀取電流來 識別老化的資料，然後老化補償機制可以調整讀取放大器的參考電阻，以容 忍 MTJ 老化引起的電阻值下降而發生的資料讀取錯誤。與現有的基於測試 的老化偵測技術相比，我們的機制可以在資料讀取的同時同步在線運行老 化檢測和補償，並且對於性能的影響小到可以忽略。模擬和分析結果表明， 我們所提出的技術可以在考慮製成工藝變化下成功偵測到老化資料，並使 整體 STT-MRAM 的可靠性提高至 25%。 ;Spin-transfer-torque magnetic random-access memory (STT-MRAM) is one of the most promising emerging memories for on-chip memory. However, the magnetic tunnel junction (MTJ) in the STT-MRAM suffers from several reliability threats which degrade the endurance, create defects, and cause memory failure. One of the primary reliability issues comes from time-dependent dielectric breakdown (TDDB) on MTJ, which deviates resistance value of MTJ over time and may lead to reading error. To overcome this challenge, in this paper we present an on-line aging detection and tolerance framework to dynamically monitor the electrical parameter deviations and provide appropriate compensation to avoid reading error. The on-line aging detection mechanism can identify aged words by monitoring read current and then the aging tolerance mechanism can adjust the reference resistance of the sensing amplifier to compensate the aging-induced resistance drop of MTJ. In comparison with existing testing-based aging detection techniques, our mechanism can operate on-line with read operations for both aging detection and tolerance simultaneously with negligible performance overhead. Simulation and analysis results show that the proposed techniques can successfully detect aging words under process variation and achieve at most 25% reliability improvement of STT-MRAMs.
