臺灣博碩士論文加值系統

二維過渡金屬硫化物，具有高載子遷移率的優勢與合適的能隙，因而成為近年來的熱門研究主題，但是目前的文獻中提到二硫化鉬場效電晶體其載子遷移率無法達到理論預測值，其原因為當金屬舆二維過渡金屬硫化物接觸後，產生過大的接觸電阻，使得載子於傳輸時受到阻礙，從而限制元件的性能，因此金屬電極和介電材料的選擇亦是影響二維半導體材料所製作場效電晶體元件效能的關鍵因素。
文獻中有以石墨烯作為二維半導體接觸電極，顯示出良好的接觸特性，少數層二硫化鉭在室溫也有金屬特性可作為接觸電極，因此提出探討不同金屬( Au, Ti/Au, Ti/Ni或In/Au ) 與二硫化鉭之接觸電阻與電子傳輸。本實驗利用機械剝離法，將二硫化鉭轉移至矽基板上，以電子束微影系統規劃電極設計，再以熱蒸鍍系統於材料表面沉積金屬薄膜製作出電極，進行電性量測以及變溫量測，以探討不同金屬接觸二硫化鉭之接觸電阻與電性傳輸上的差異。常溫下電性量測鈦金的接觸電阻最低為27.7 (Ω-μm)，金的接觸電阻最低為132.9 (Ω-μm)，銦金的接觸電阻最低為186.3 (Ω-μm)，鈦鎳的接觸電阻最低為620.8 (Ω-μm)，其結果顯示鈦金電極的接觸電阻為金電極接觸電阻的0.2倍、銦金電極接觸電阻的0.15倍、鈦鎳電極接觸電組的0.04倍。此外，變溫量測不同金屬電極接觸二硫化鉭的接觸電阻皆會隨著溫度的降低同時降低，接觸電組表現出金屬特性。實驗結果以鈦金電極接觸二硫化鉭之電阻最低，預期可提供更加良好的電性。

Because two-dimensional transition metal dichalcogenides (TMDs) exhibit a suitable energy gap and a high mobility, these novel materials attract much attention in recent years. The mobility of field-effect transistors (FETs) based on those TMDs, however, does not reach the theoretical prediction. The problem comes from a poor contact between metal electrodes and TMDs, leading to a high contact resistance. Thus, the device performances are degraded. The metal contact and dielectric interfacial effects are two key factors that affect the performances of FET devices based on TMDs.
In recent reports, it was demonstrated that graphene can be used as good metal electrodes on TMDs. Because few-layer tantalum disulfide (TaS2) shows a metallic behavior at room temperature, it could also be used as a good metal contact for TMDs. We therefore explore the contact effect of conventional metal electrodes on TaS2. In this experiment, we implement mechanical exfoliation to isolate few-layer TaS2 flakes and to transfer to silicon substrates. Then, the techniques of electron-beam lithography and thermal evaporation are adopted to pattern metal electrodes on TaS2 flakes. We investigate electron transport and contact resistance of TaS2 with several different metal electrodes, including Au, Ti/Au, Ti/Ni and In/Au. At room temperature, the Ti/Au metal electrode on TaS2 gives a low contact resistance of 27.7 (Ω-μm). In addition, the Au, In/Au, and Ti/Ni metal electrodes reveal contact resistances of 132.9, 186.3, and 620.8 (Ω-μm), respectively. All those contact metal presents a decreasing contact resistance with decreasing temperature. It is confirmed that Ti/Au metal electrode offers a low-resistance contact on TaS2 flakes.

摘要 i
Abstract iii
目錄 v
圖目錄 vii
表目錄 xiii
第一章 緒論 1
第二章 文獻回顧 2
2.1 二硫化鉭(TaS2)的基本特性與結構 2
2.2 凡德瓦金屬接觸 3
2.3 石墨烯接觸效應 6
第三章 實驗原理 9
3.1 接觸電阻 (Contact resistance, Rc) 9
3.2 TCR電阻溫度係數 ( Temperature Coefficient of Resistance ) 10
3.3 場效電晶體(Field-effect transistor) 10
第四章 實驗方法與步驟 15
4.1 製程儀器 15
4.1.1 二維材料對準堆疊系統 (Stacking-Aligned system) 15
4.1.2 電子束微影系統 (Electron-Beam lithography, EBL) 15
4.1.3 熱蒸鍍系統 (Thermal Evaporation) 16
4.1.4 高溫真空熱退火系統 (Vacuum Thermal Annealing) 18
4.1.5 電性量測探針系統 (Probe Station) 19
4.1.6 原子力顯微鏡 (Atomic Force Microscopy, AFM) 21
4.2 元件製程步驟及方式 22
4.2.1 基板清洗 22
4.2.2 二維材料機械剝離法 22
4.2.3 二維材料對準轉印 22
4.2.4 光阻塗佈 23
4.2.5 定位樣品與設計電極 23
4.2.6 電子束微影與顯影 23
4.2.7 熱蒸鍍 24
4.2.8 舉離 25
4.2.9 熱退火 25
4.3 量測系統介紹與步驟 25
4.3.1 電性量測 25
4.3.2 變溫量測 26
第五章 結果與討論 28
5.1 二硫化鉭基本特性 28
5.2 鈦金、金、銦金以及鈦鎳作為接觸電極下之二硫化鉭TaS2接觸電阻 30
5.2.1 探討金作為接觸電極下之接觸電阻與變溫分析 37
5.2.2 探討銦金作為接觸電極下之接觸電阻與變溫分析 39
5.2.3 探討鈦金作為接觸電極下之接觸電阻與變溫分析 41
5.2.4 金、銦金以及鈦金作為接觸電極下之變溫接觸電阻變化 44
第六章 結論 46
參考文獻 47

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