金屬碘化物於電子元件之研究

Abstract

金屬鹵化物為當今熱門研究主題之一，其中最為注目的鈣鈦礦材料具有優越的光電特性，已被廣泛應用於光電、電子元件中，例如電阻式記憶體。由於低製成成本、高可調變性及可媲美或甚至更高的效能，可望取代傳統製成的材料。但材料中含有有毒元素鉛及大氣下結構不穩定性問題，因此本論文將無毒金屬鹵化物材料(碘化鉍)取代鈣鈦礦作為電阻式記憶體阻值切換層。本論文可以分成兩部分，前半部分探討以鉛鈣鈦礦材料為主動層其元件的異常現象：光浸潤效應以及可調變光電流方向現象，並利用調變元件結構抽絲撥繭找出主要因素為哪層或是哪些異質結構影響，並且利用光電子能譜探討載子於介面能階傳輸機制以及材料於持續照光下，材料原子間鍵結變化，並且提出可能機制。而後半部分探討層狀碘化鉍材料做為軟性電阻式記憶體阻值切換層可行性，在探討其與下電極材料間的交互作用中發現，電極基材的化學特性對於碘化鉍的表面形貌、化學鍵結、結晶性以及電阻切換特性有莫大的影響，亦發現碘化鉍缺陷(金屬鉍)的含量對於生成電壓有很大的影響，因此本文提出三種方法改善碘化鉍的表面形貌、化學鍵結及結晶性：透過使用金屬銀當作下電極緩衝層、自組裝分子介面改質以及凡德瓦爾材料作為緩衝層，其中以凡德瓦爾材料作為緩衝層最具廣泛性，其元件可達成無需生成電壓、低操作電壓以及高記憶體視窗，且具高彎折忍受力。本研究不只展現碘化鉍作為可撓式電阻式記憶體切換層的高潛力，其與金屬材料交互作用的探討，亦將有助於其他碘化鉍元件的應用與設計。

A widely known metal-halide materials, halide perovskite, possess numerous fascinated and desired properties, and their applications on optoelectronics and electronics also demonstrate competitive or even superior performance but in more cost-efficient manner in comparison to traditional technology. However, some abnormal properties including light soaking effect and switchable photocurrent phenomena were also observed in metal-halide-perovskite-based devices and remained ambiguous. In this dissertation, irreversible enhancement under light irradiation and switchable photocurrent phenomena were observed in the perovskite-based device, and the underlying mechanisms and triggered conditions were studied via photoemission spectroscopy and device engineering. The switchable photocurrent phenomena in the perovskite hint high potential of the halide perovskite for use as memory device. However, the toxic content and structural instability impede its commercialization. Alternatively, a nontoxic metal halide material, BiI3, was used as an insulator in the capacitor-like M-I-M structure. Subsequently, the resistive switching behavior, morphology, crystallinity, roughness, and chemical interaction of the BiI3 on the various metal substrates, including metal, silicon, and two-dimensional materials, were studied in detail. As a result, it reveals that rough surface, chemical reaction, and metallic Bi content are critical factors in performance of BiI3-based RRAMs especially in forming voltage and device stability. Therefore, the improvement of the BiI3 film quality is our main concern in the following chapters and is fulfilled by several methods, including introducing thin Ag buffer layer, surface modification via self-assembly monolayer molecular, and inserting van der Waals materials as buffer layer. Finally, the device with the copper foil/h-BN/BiI3/Au structure exhibited forming-free nature, high on/off ratio, excellent data-retention, high voltage sweep endurance, and superior bending endurance, evidencing the high potential of BiI3 as resistive switching layer in RRAMs. In addition, our fundamental study on the interaction of BiI3 with other materials including Au, Ag, Si, graphene would shed light on the architecture design and mechanism investigation of the devices based on BiI3.