以焦耳熱效應與滲透理論為基礎的電阻式記憶體數值模擬

Abstract

在本論文中，我們利用了焦耳熱效應的模擬方式推斷出單極性電阻式記憶體中導電絲狀路徑的可能形貌以及利用滲透理論的模擬方式建構出一個可以進行電阻值切換的雙極性電阻式記憶體模型。 在焦耳熱效應的模擬中，我們遵循著過去有文獻指出在單極性電阻式記憶體中，導電絲狀路徑的可能形貌為圓錐形狀的依據，進行深入的數值方面模擬。後來藉由焦耳熱效應數值模擬所得到的結果，發現到單純考慮導電絲狀路徑為圓錐形狀是不夠的，而是必須要再額外考慮串聯電阻的效應才能完整解釋。 而在利用滲透理論的模擬中，我們也是參考之前的文獻成功地重新建構出一個可以進行電阻值切換的雙極性電阻式記憶體模型，而其中模擬用到最重要的部分為假設電阻式記憶體的電流傳導機制為缺陷協助電子穿隧的電流。 最後，我們利用電阻值切換的雙極性電阻式記憶體模型，進行統計與分析在實際雙極性電阻式記憶體量測上我們關切的電性參數，並且驗證了一些曾被提出可以降低的電阻式記憶體結構在電性參數的變動問題。然而目前這個模型仍尚未足夠完整，因此在最後提供了一些可以改善的方法使得這個阻值切換的電阻式記憶體模型將來能夠更接近真實的電阻式記憶體元件。

In this thesis, we use a physical model based on Joule heating effect to predict the probable filamentary shape existing in unipolar RRAM and also use the percolation theory to construct a bipolar RRAM model. In the Joule heating effect simulation, we followed the previous literature which claimed that the filament shape is conical in unipolar RRAM. Therefore, we use numerical simulation to investigate the issue in depth. However, utilizing numerical simulation results considering Joule heating effect, we found that it is sufficient to explain the unipolar RRAM electrical characteristics by adding a series resistance rather than only considering the filament morphology as conical shape. In the simulation based on percolation theory, we also followed the previous literature to construct successfully a bipolar RRAM model. Furthermore, the most important assumption in this simulation is that the trap assisted tunneling is the dominant electron conduction mechanism in oxides. Finally, we exploited the bipolar RRAM model to analyze the statistics of the RRAM electric parameters. Moreover, we also use this model to validate some experimental approaches reported in previous literature may reduce cycling variation. Although, this model is not mature enough, we provided some directions to further improve this model.