傳統的電阻式記憶體在突觸元件最大的問題在於在元件的SET或RESET常常會有突升式或者突降式的電阻轉換，這造成在類神經網路神經元與神經元之間突觸的權重沒辦法完整的模擬，故越來越多人提出以雙層元件以達到漸進式的阻態轉換來滿足突觸元件的應用。此次研究吾人提出以Ta/WOx/ZrOx/Pt元件來模擬一系列突觸元件的操作。
第一部分吾人探討元件的直流偏壓操作，首先吾人先比較Ta/ZrOx/Pt及Ta/WOx/Pt兩個元件的電流電壓特性曲線，發現兩個試片皆沒有阻態轉換的現象，其中Ta/WOx/Pt的量測結果十分導電而Ta/ZrOx/Pt則相對介電，然而在量測Ta/WOx/ZrOx/Pt試片時卻發現其結果與上述兩者十分不一樣，其電流電壓行為為一漸進式的阻態轉換。為了了解各層材料對於電性的影響，吾人製作了一系列不同WOx及ZrOx厚度及改變電極材料的試片以比較其電流電壓特性曲線的差異，利用上述的實驗結果，提出一阻態轉換機制。根據WOx及ZrOx能帶圖能階相對位置的關係，吾人發現在ZrOx中靠近WOx/ZrOx界面有一蕭基特式能障形成，藉由外加電壓的施加，材料中帶正電的氧空缺會聚集或遠離WOx/ZrOx界面，造成該蕭基特式能障穿隧寬度的減少與增加來達到電子穿隧WOx/ZrOx界面的難易程度，使得元件的電流增加與減少為漸進式的，其整體導電行為較類似於界面性的阻態轉換機制。
第二部分吾人利用Ta/WOx/ZrOx/Pt元件操作了一系列突觸元件的操作。首先吾人藉由五十次連續相同脈衝的刺激來達到元件的增益與抑制，結果顯示良好的線性程度與重複性，這使元件未來應用在類神經網路的訓練是十分有潛力的。另外吾人也成功的模擬出成對脈衝促進(PPF)及脈衝時序依賴可塑性(STDP)兩種真實生物體的反應，結果也與真實生物體的現象十分吻合。最後吾人為了提升元件操作的方便性，以一單一脈衝刺激來達到元件的多重阻態操作，藉由-4V/-5V/ -6V/-7V/-8V/-9V/-10V 500ms的單一脈衝刺激，成功定義出7個阻態，並且還有去比較不同厚度疊層的元件在7種阻態分布的情況，結果顯示厚度加厚的試片電阻態分別的狀況界為優異。
第三部分吾人將元件做成一3×3的陣列結構來模擬陣列結構下電流電壓特曲線與MIM結構的差異，並且就由±1/2 VP的整流電壓來防止潛行電流(Sneak path)的發生。實驗結果發現在陣列結構下元件還是能夠展現優異的電性表現，並且有利於未來元件尺寸微縮下突觸元件的應用。

SUMMARY
In the first section of this study, the DC voltage sweeping operation of the Ta/WOx/ZrOx/Pt and associated devices are examined. First, neither the Ta/WOx/Pt nor the Ta/ZrOx/Pt device exbibits resistive switching behavior. The Ta/WOx/Pt device is quite conductive while the Ta/ZrOx/Pt device is relatively insulated. However, Ta/WOx/ZrOx/Pt devices exbibits gradual resistive switching. By comparing the results of XPS and conduction mechanism fitting, we proposed a mechanism to explain the resistive switching.
In the second section, we have demonstrated the potentiation and depression behavior of the Ta/WOx/ZrOx/Pt device by applying a series of identical electrical pulses (N=50). The current responses of potentiation and depression operations show good linearity and repeatability. It is promising for the application of artificial neural networks in the future. In addition, we also have successfully simulated paired-pulse facilitation (PPF) and spike-timing-dependent plasticity (STDP). Additionally, we demonstrated an arbitrarily switching among multiple states using a single pulse (of different pulse heights) stimulus to achieve seven resistive states.
In the third section, we made the device as 3×3 crossbar array structure to compare the I-V characteristics with the simple planar MIM sandwich structure. It is found that the device can still exhibit excellent resistive switching performance, and it is beneficial to the future application of synaptic devices under the miniaturization of device sizes.

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