以自組裝層改善五環素薄膜電晶體特性

IMPROVEMENT OF PENTACENE THIN FILM TRANSISTOR WITH SELF-ASSEMBLED MONOLAYER

林益陞(Yi-Sheng Lin)

指導教授 ： 郭欽湊

大同大學/工程學院/化學工程學系所/碩士(2006年)

摘要

真空蒸鍍五環素薄膜是報告中位移率最佳之有機半導體。五環素有機薄膜電晶體受到非常注意是因為它的優點如:低成本、大面積及低溫製程超越一般無機電晶體。五環素晶體中分子之間是靠相當於凡得瓦爾的力連接。因此，絕緣層(例：疏水性…)能夠影響五環素半導體的型態。本文目的是為了顯示藉由控制絕緣層與有機層界面表面處理劑改進有機薄膜電晶體性能。
我們發現藉由高真空下熱蒸發五環素與五種相關之絕緣層表面處理劑(HMDS、OTS、PTS及PETS)組成的有機薄膜電晶體電性質。然後我們使用Ｘ光繞射、原子力顯微鏡、X射線光電光譜、水接觸角及半導參數儀設備分析自組裝層、五環素薄膜性質與元件性能。
分析結果：場效位移率及開關電流比分別為0.34 cm 2 V –1 s –1、1.21 x 10 5 (上接觸式)及0.011 cm 2 V –1 s –1、2.31 x 10 4 (下接觸式)。原子力顯微鏡相片能夠看到五環素顆粒在電極區域較通道區域小很多，此不連續性為造成下接觸式較上接觸式電晶體差的原因。下接觸式五環素有機薄膜電晶體場效位移率及開關電流比分別達到0.1 cm 2 V –1 s –1 and 1.71 x 10 5 (OTS處理)。X射線光電光譜偵測表面50-100 Å的化學成份，證明OTS確實吸附在介電層上。同理，HMDS、PTS及PETS處理劑對場效位移率確有正面的影響。PTS與HMDS處理場效位移率及開關電流比分別0.11 cm 2 V –1 s –1、1.92 x 10 6 (PTS)與0.07 cm 2 V –1 s –1、5.29 x 10 5 (HMDS)。使用PETS為自組裝層試劑能得到最好的元件性能。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0.13 cm 2 V –1 s –1，4.17 x 10 6，- 2.4 V和0.8 V/decade。五環素有機薄膜電晶體場效位移率及開關電流比比未處理二氧化矽元件增加一到兩個次方。而且經PTS 和PETS處理過介電層之五環素有機薄膜電晶體性能可得一突出的次臨界轉換斜率。

關鍵字

五環素 ； 有機薄膜電晶體 ； 自組裝層 ； X射線光電光譜

並列摘要

The best mobility for organic semiconductors has been reported for vacuum-deposited pentacene film. Pentacene organic thin-film transistor (OTFT) has drawn great attention because of it is advantages over conventional inorganic electronics such as low cost, large-area, and low processing temperature. Pentacene interactions between molecules in the crystal are rather weak van der Weals interactions. Thus, the dielectric (ex: hydrophobic….) can influence the morphology of the pentacene semiconductor. The purpose of this work is to show the improvement of OTFT performance by controlling the surface treatments of dielectric/organic layer interface.
We investigated the electrical properties of the OTFTs using pentacene fabricated by thermal evaporation in high vacuum with the five kinds of dielectric surface treatments: as-prepared, hexamethyldisilasane ((CH3)3-Si-O-Si-(CH3)3) (HMDS), octadecyltrichlorosilane (C18H37SiCl3) (OTS), phenyltrichlorosilane (C6H5SiCl3) (PTS), and phenethyltrichlorosilane (C6H5C2H4SiCl3) (PETS) treatment. And we use x-ray diffractometer (XRD), atom force microscope (AFM), X-ray photoelectron spectroscopy (XPS), water contact angle, and semiconductor parametric test system (HP 4155C) equipments to analyze the properties of self-assembled monolayer (SAM), pentacene thin film, and the performance of the device, respectively.
From the result, the mobility and on/off current ratio of pentacene OTFT are 0.34 cm 2 V –1 s –1 and 1.21 x 10 5 (top-contact) and 0.011 cm 2 V –1 s –1 and 2.31 x 10 4 (bottom-contact), respectively. From the result of AFM images, it can be seen that grain size of pentacene thin film deposited on the electrode region are significantly smaller compared to that of the channel region on SiO2. That discontinuity causes for the inferior performance of bottom-contact pentacene transistors compared to that of top-contact devices. The mobility and on/off current ratio of bottom-contact pentacene OTFT with OTS-treated SiO2 can be achieved 0.1 cm 2 V –1 s –1 and 1.71 x 10 5, respectively. XPS detects the chemical composition of surfaces in the top 50-100 Å. The results confirm OTS adsorbed on the surface of gate dielectric. Similarly, HMDS, PTS, and PETS treatments can affect good influence in filed effect mobility. The mobility and on/off current ratio of pentacene OTFT are 0.11 cm 2 V –1 s –1, 1.92 x 10 6 of PTS-treated and 0.07 cm 2 V –1 s –1, 5.29 x 10 5 of HMDS-treated, respectively. The best performance of device can be obtained by using PETS as SAM reagent. The mobility, on/off current ratio, threshold voltage, and subthrshold slope of pentacene OTFT are 0.13 cm 2 V –1 s –1, 4.17 x 10 6, - 2.4 V, 0.8 V/decade of PETS, respectively, which are enhanced one to two orders of magnitude larger than those of untreated SiO2 device. Furthermore, the pentacene OTFT performance with PTS- and PETS-treated gate dielectric can be obtained an outstanding subthrshold slope.

並列關鍵字

Pentacene ； Organic thin-film transistor (OTFT) ； Self-assembled monolayer (SAM) ； X-ray photoelectron spectroscopy (XPS)

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