五環素有機薄膜電晶體的特性探討

STUDIES ON CHARACTERISTICS OF PENTACENE ORGANIC THIN-FILM TRANSISTOR

楊琇如(Hsiu-Ju Yang)

指導教授 ： 郭欽湊

大同大學/工程學院/化學工程學系所/碩士(2007年)

摘要

本篇論文中最主要是針對五環素有機薄膜電晶體的特性改良，利用三種不同的矽氯烷處理劑來改善介電層的親水性質，進而促進有機薄膜電晶體的電特性。
在高真空下熱蒸發五環素與三種相關之絕緣層表面處理劑（OTS、PTS及PETS）組成的有機薄膜電晶體，測量其電性質，並以水接觸角、原子力顯微鏡、Ｘ光繞射光譜、場放射槍掃描式電子顯微鏡及半導參數儀（HP-4155C）設備分析自組裝層對五環素薄膜性質與元件性能之影響。
分析結果：水接觸角隨著濃度的增加而有增加的趨勢，在濃度0.1、0.5、1.0、1.5 wt% 其水接觸角分別為84°、85°、86°及90°；而PTS在濃度0.1、1.0、2.5 wt%的水接觸角分別為74°、76°及81°。
利用PTS對SiO2進行表面處理後，基板溫度120℃，蒸發溫度435℃為pentacene的最佳蒸鍍條件。可得場效位移率、開關電流比、門檻電壓和次臨界轉換斜率分別為9.97 ´ 10-2 cm2/Vs、2.28 × 107、-15.7 V和1.05 V/decade。
另利用各種濃度的OTS對SiO2進行表面處理，結果顯示濃度0.1 wt % OTS之效果最佳。場效位移率、開關電流比、門檻電壓和次臨界轉換斜率分別為3.57 ´ 10-1 cm2/Vs、1.76 × 107、-7.7 V和1.01 V/decade。
同理， PTS及PETS處理劑對場效位移率確有正面的影響。PTS在濃度2.5 wt%時，其場效位移率及開關電流比分別2.09 × 10-1 cm2/Vs、3.66 × 106；而PETS在濃度0.3 wt%時，其場效位移率及開關電流比分別2.28 ´ 10-1 cm2/Vs、3.99 × 107。使用OTS為自組裝層試劑能得到最好的元件性能，五環素有機薄膜電晶體場效位移率及開關電流比未處理二氧化矽元件可增加一到兩個次方。
由原子力顯微鏡及場放射槍掃描式電子顯微鏡的相片能夠得知五環素顆粒沉積的晶粒較小，大小也較為均一，且表面的平坦度也較佳，這使得五環素堆疊較緊密，而造成較少的電子陷阱（trap），因而提升OTFTS的電特性。
OTS濃度為0.1及0.5wt%的單晶相peak強度分別為1642及804，相對應的場效位移率為3.57 × 10-1 and 1.17 × 10-1 cm2/Vs；PTS濃度為0.5、1.5和2.5wt%的單晶相單晶相peak強度分別為1390、2090和4198，相對應的場效位移率為1.37 × 10-1、1.48 × 10-1 及2.09 × 10-1 cm2/Vs，因此由XRD也可以證明：單晶相peak強度越大，擁有較好的電性。
壓力下降會使空氣中的水氣減少，材質中 trap 較少，則OTFT的電特性提升。由0.1 wt% OTS處理後的元件特性看來，在壓力為4.6 × 10-2 torr時，可得場效位移率4.12 × 10-1 cm2/Vs、開關電流3.04 × 107；2.5 wt% PTS處理後，在壓力為4.9 × 10-2 torr時，場效位移率為2.09 × 10-1 cm2/Vs、開關電流108；0.3 wt% PETS處理後，在壓力為19 torr時，場效位移率為2.65 × 10-1 cm2/Vs、開關電流3.43 × 107。

關鍵字

薄膜電晶體 ； 五環素

並列摘要

The main aim of this thesis is the enhancement on the characteristics of pentacene organic thin film transistor. Three kinds of different chlorosilane treated agents were employed to modify hydrophilic character of dielectric layer, and promoted the electric characteristics of organic thin-film transistor (OTFT).
We investigated the electrical properties of the OTFTs using pentacene fabricated by thermal evaporation in a high vacuum with the three kinds of dielectric surface treating agent: octadecyltrichlorosilane (C18H37SiCl3) (OTS), phenyltrichlorosilane (C6H5SiCl3) (PTS), and phenethyltrichlorosilane (C6H5C2H4SiCl3) (PETS). Studies on properties of pentacene thin film and the performance of the device are affected by self-assembled monolayer (SAM) via the analysis of water contact angle, atom force microscope (AFM), X-ray diffractometer (XRD), field emission gun scanning electron microscopy (SEM), and semiconductor parametric test system (HP 4155C) have been carried out.
Water contact angle of OTS-treated SiO2 surface is 84°, 85°, 86°, and 90°for the OTS concentration of 0.1, 0.5, 1.0, and 1.5 wt%, respectively. Water contact angle of PTS-treated SiO2 surface is 74°,
76°, and 81°for the PTS concentration of 0.5, 1.0, and 2.5 wt%, respectively. Therefore, the analysis result that the water contact angle of SiO2 surface

increases with increasing the concentration of treating agent.
The optimal evaporated temperature of pentacene OTFT with PTS-treated SiO2 was substrate temperature at 120℃ and pentacene evaporation temperature at 435℃. The field-effect mobility, on/off current ratio, threshold voltage, and subthreshold slope of pentacene OTFT were 9.97 ´ 10-2 cm2/Vs, 2.28 × 107, -15.7 V, and 1.05 V/decade, respectively.
Through different concentration of OTS-treated SiO2 used, it is found that the best characteristics of OTFT occurs by 0.1 wt% OTS-treated SiO2. The field-effect mobility, on/off current ratio, threshold voltage, and subthreshold slope of OTFT were 3.57 × 10-1 cm2/Vs, 1.76 × 107, -7.7 V, and 1.01 V/decade, respectively.
For the same reason, PTS and PETS-treated SiO2 can improve the characteristics of OTFT. The field-effect mobility, and on/off current ratio of pentacene OTFT with 2.5 wt% PTS-treated SiO2 were 2.09 ´ 10-1 cm2/Vs, and 3.66 × 106, respectively. The field-effect mobility, and on/off current ratio of pentacene OTFT with 0.3 wt% PETS-treated SiO2 were 2.28 ´ 10-1 cm2/Vs, and 3.99 × 107, respectively. The best performance of device is obtained using OTS as self-assembly monolayer agent. The field-effect mobility, and on/off current ratio of pentacene OTFT with OTS-treated SiO2 were enhanced one to two orders of magnitude, larger than those of untreated device.

Photographs of Atom Force Microscope (AFM) and Scanning Electron Microscopy (SEM) showed that the size of crystals was smaller, and similar. The surface of pentacene was more flatness. Therefore, it lead to the packing of pentacene thin-film being more compact and less trap, hence enhanced OTFT’s electrical property.
The intensity of single crystal phase of pentacene thin film deposited on the surface of 0.1 and 0.5wt% OTS-treated SiO2 exhibits 1642 and 804, respectively. The corresponding field-effect mobility is 3.57 × 10-1 and 1.17 × 10-1 cm2/Vs. Similarly, the intensity of single crystal phase of pentacene thin film deposited on the surface of 0.1, 1.5 and 2.5wt% PTS-treated SiO2 exhibits 1390, 2090, and 4198, respectively. The corresponding field-effect mobility is 1.48 × 10-1, 1.48 × 10-1 and 2.09 × 10-1cm2/Vs. Therefore, XRD shows that the higher the intensity of single crystal / thin film phase, the better the electric properties.
The less amount of water in a air at lower pressure, resulting in the trap was less in the material. It enhanced the characteristics of OTFT. The field-effect mobility and on/off current ratio of pentacene OTFT with 0.1 wt% OTS treated SiO2 are 4.12 ×10-1 cm2/Vs and 3.04 × 107, respectively, at the pressure of 4.6 × 10-2 torr. The field-effect mobility and on/off current ratio of pentacene OTFT with 2.5 wt% PTS treated SiO2 are 2.09 ×10-1 cm2/Vs and 108, respectively, at the pressure of 4.9 × 10-2 torr. The field-effect mobility and on/off current ratio of pentacene OTFT with 0.3 wt% PETS treated SiO2 are 2.65 ×10-1 cm2/Vs and 3.43 × 107, respectively, at the pressure of 19 torr.

並列關鍵字

PENTACENE ORGANIC THIN-FILM TRANSISTOR

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