本實驗以四種金屬材料作為電極，探討不同金屬作為薄膜電晶體(TFT)之S/D電極對電性造成的影響，透過實驗量測與計算不同金屬電極之ZTO-TFT的接觸電阻，並對材料性質分析結果做討論。
製程上，以SiO2/p+Si作為基板(p+Si作為閘極，SiO2作為介電層)，將配好的ZTO前驅液，以旋轉塗佈方式製作ZTO主動層，再以微影製程以及濕式蝕刻法定義出ZTO主動層面積，最後以電子束蒸鍍的方式鍍製鋁(Al)、鉬(Mo) 、鈦(Ti)、鉑(Pt)四種金屬作為電極。
首先透過量測ID-VG曲線來計算四種電極材料的TFT電性表現參數值，包含電流開關比(on/off ratio)、場效載子遷移率(field effect mobility, μFE)、次臨界擺幅(S.S)、開關電壓(VON)等，計算結果顯示使用不同電極材料下之場效載子遷移率(field effect mobility, μFE)變化甚大，其中以鉬(Mo)作為電極的TFT其載子遷移率(field effect mobility, μFE)平均值達到5.75cm2/Vs，以鋁(Al)作為電極的TFT則最差，只有0.96cm2/Vs。
在考慮電極影響及計算電極材料與ZTO-TFT的接觸電阻上，使用External load resistance method來計算。方式為將多個不同歐姆值的電阻，分別外接串聯在TFT的源極端使之與量測儀器Agilent 4156C形成迴路，藉由量測不同電阻對汲極端的電流值(ID)變化，進而推導出金屬與ZTO-TFT的接觸電阻值。實驗中，鋁(Al)、鉬(Mo) 、鈦(Ti)、鉑(Pt)四種金屬作為電極(S/D)的接觸電阻分別約為21913Ω、1162Ω、11460Ω、2949Ω，依照結果可以推測越小的接觸電阻值對於電晶體有最佳的場效載子遷移率(μFE)。由於場效載子遷移率(μFE)的計算上未考慮接觸電阻的影響，利用External load resistance method則有考慮接觸電阻的前提下，利用以-RL0(VG)對(VG-VTH-0.5VD)-1的作圖，可由其直線的斜率值求得ZTO的載子遷移率，定義為本質載子遷移率(μ_i)，計算結果為鋁(Al)、鉬(Mo) 、鈦(Ti)、鉑(Pt)四種金屬下的ZTO本質載子遷移率(μ_i)分別為4.83cm2/Vs、5.32 cm2/Vs、5.31 cm2/Vs、5.34 cm2/Vs，顯示除了Al金屬下的ZTO性質發生改變外，其餘電極材料並不會影響ZTO性質。
在材料分析方面，藉由TEM剖面確定ZTO主動層的厚度為5.2nm，並且由ZTO在不同金屬電極材料下的微觀組織觀察，得知在有蒸鍍金屬鉬(Mo)、鉑(Pt)、鈦(Ti)下的ZTO與無蒸鍍電極材料(僅碳保護層)的ZTO內部結構皆呈現非晶態(amorphous)，而蒸鍍鋁(Al)金屬下的ZTO則呈現部分結晶，並且在鋁與鈦金屬在跟ZTO間均可發現一層的非晶層。
接著利用XPS縱深分析，分別對有、無電極材料下的ZTO內部化學組成及鍵結變化進行觀察，由Al 2p，Mo 3d，Pt 4f，Ti 2p的XPS分峰結果，在電極材料/ZTO界面層均發現有金屬電極氧化物的束縛能態，並由氧化態的特徵峰值所占整體面積比例我們可以得知氧化程度為Al>Ti>Mo>Pt。為了分析在不同電極下的ZTO氧空缺濃度，由在界面層O 1s中，我們還得考慮氧分別與Al、Mo、Pt、Ti四種金屬形成鍵結(MOx)的束縛能峰值與ZTO層的峰值差異。ZTO (MOx)的束縛能約530.2eV(標記為O1)，ZTO中的氧空缺則為531.6eV(標記為O2)，而氧與金屬Al、Mo、Pt、Ti鍵結(MOx)的束縛能及其缺陷峰值則分別標記為O3及O4。為了得到ZTO中的氧空缺濃度，利用O2/(O1+O2)來得到各自的結果，沒有電極材料的單層ZTO結果約26%，而Al、Mo、Pt、Ti下的ZTO結果分別為65%、27%、27%、23%，可以發現Mo、Pt、Ti三種金屬對ZTO薄膜中氧空缺濃度不會產生太大的改變，而Al金屬卻大大增加ZTO中的氧空缺濃度，可能代表Al與ZTO界面生成的氧化鋁層主要是來自ZTO中氧擴散而來。另外，在界面層中的Sn 3d5/2分峰結果顯示，除了有ZTO中氧化錫(SnOx)束縛能峰值(487eV)外，有另一個次要峰值(約485eV)出現，其峰值近似中性錫原子的束縛能態，代表氧空缺濃度可能導致ZTO層中錫氧鍵結(Sn-O bond)強度減弱，亦或電極材料原子擴散進ZTO中造成錫離子被還原趨於中性。無電極材料的單層ZTO其485eV的峰值所占整體僅約4.5%，而Al、Mo、Pt、Ti下的ZTO結果分別為39.2%、25.2%、8.9%、54.9%，從這裡暗示出Pt幾乎不與ZTO產生交互作用，並可推測界面處生成的電極氧化物(AlOx、MoOx、TiOx)其氧原子是ZTO層中的錫氧鍵結(Sn-O bond)斷鍵後，再擴散而來，導致ZTO中的錫離子被還原。

In this study, we investigated the influence on the electrical performance of solution-processed ZTO TFT using four kinds of different metal materials as S/D electrodes. The contact resistance of ZTO-TFTs with different metal electrodes and calculated. High-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) depth profile were also used to study the microstructure and the chemical state of the metal/ZTO interfaces.
For the fabrication process, SiO2/p+Si is used as the substrate (p+Si as the gate and SiO2 as the dielectric layer). The solution-processed ZTO precursor is spin-coated as the active layer, and then patterned by photolithography and wet etching. Finally, four kinds of metals including aluminum (Al), molybdenum (Mo), titanium (Ti), and platinum (Pt) were deposited by electron beam evaporation as the source/drain(S/D) electrodes.
The electrical parameters of ZTO-TFTs with four different S/D materials are extracted from the ID-VG curve, including the on/off ratio, the field effect mobility (μFE), the subthreshold swing (S.S.), and the turn-on voltage (VON). The main influence on the different S/D materials ZTO-TFTs was the calculated field effect mobility (μFE). The TFT using molybdenum (Mo) as S/D material showed the best result, while the TFT using aluminum (Al) as S/D material was the poorest.
The external load resistance method was used to calculate the contact resistance (RS+RD) between the S/D material and the ZTO active layer. We inserted external resistors with a suitable range connecting to the source terminal to form the series circuit. An equation model can be established after some manipulations. By plotting −RL0 versus 1/(VGS − VTH − 0.5VDS), the y-axis intersection gives contact resistance (RS+RD). We obtained the contact resistance between aluminum (Al), molybdenum (Mo), titanium (Ti), and platinum (Pt) as electrodes(S/D) and the ZTO layer. The result indicated the better field effect mobility (μFE) require the lower contact resistance beween S/D material and ZTO. Also, by plotting −RL0 versus 1/(VGS − VTH − 0.5VDS), the slope gives the intrinsic mobility(μi) of ZTO. The intrinsic mobility(μi) of ZTO-TFT fabricated by aluminum (Al), molybdenum (Mo), titanium (Ti), and platinum (Pt) showed similar value. This result was reasonable because the ZTO active layers were done by the same process.

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