本論文主要在探討如何透過化學修飾介電層表面來製作高效能的有機場效電晶體，並進而利用電晶體可放大電流訊號之特性，來作為靈敏的氣體偵測器元件。由於氣體偵測器需要操作於相對高溫(～150 ℃)的條件，以利於偵側器能夠持續操作，因此介電層與有機半導體材料的選擇，變得更加嚴苛。本實驗選定酞菁氧鈦(titanyl phthalocyanine, TiOPc)作為半導體材料，其酞菁(phthalocyanine)環熱穩定性佳，且環與環之間的距離可以接近至3.14 Å，因此具有高的載子遷移率。介電層修飾分子則選用磷酸正十八酯(n-octadecylphosphonic acid, ODPA)，並透過於基材上成長氧化鋁薄膜來輔助ODPA形成自組裝單層分子，藉由ODPA熱穩定性優異之特性，於高溫成長高結晶性之TiOPc薄膜，進而提升元件性能。
在薄膜的特性方面，我們運用了多重的實驗技術，如原子力顯微鏡(AFM)、接觸角量測儀(contact angle analyzer)、X光光電子能譜(XPS)、X光繞射(XRD)與近緣X光吸收細微結構能譜術(NEXAFS)等技術對薄膜之表面形貌、親疏水性、表面覆蓋率、晶體結構及分子排列傾角等方面進行探討，並藉由XPS與紫外光光電子能譜(UPS)分析分別探討NO2氣體分子於TiOPc薄膜中之吸附方式、功函數與價帶變化。
ODPA透過NEXAFS與XPS能譜分析得知其熱穩定性約可達至120 ℃且覆蓋率高達90%以上。TiOPc薄膜經由NEXAFS分析發現，於100 ℃時，其分子較為直立，並從XRD結果得知TiOPc形成緊密排列的-phase，使得載子以更高效率於分子間躍遷，提升電洞傳輸效率，其元件之最佳載子遷移率可達1.45x10-1 cm2/Vs。最後將TiOPc薄膜電晶體應用於NO2氣體感測噐，經由量測其電性變化得知於一大氣壓下，其感測NO2氣體分子之偵測極限約為25 ppm，並由XPS與UPS能譜結果得知NO2未曾以化學吸附之方式吸附於TiOPc薄膜，而是以電洞摻雜(hole-doping)方式影響TiOPc，使TiOPc各內殼層電子訊號峰與HOMO能階位置皆往低束縛能方向位移，而此現象主要因其費米能階下沉而造成。綜合上述結果得知TiOPc薄膜成長於熱穩定性優異之ODPA上時，其晶相與元件效能已獲得相當大的改善，並擁有良好的感測NO2氣體分子之能力。

In this thesis, we report on the fabrication of a high-performance titanyl phthalocyanine (TiOPc) organic field effect transistor (OFET) on a chemically modified dielectric layer, and the utilization of the OFET for gas sensing application via the current amplification capability of OFET. The gas sensors often needs to operate at higher temperature for a continuous operation and thus the material choices of semiconductors and dielectrics could be stringent. TiOPc was selected as the active OFET material because of its good thermal stability and its potential for having high carrier mobility, thanks to its rather short  stacking distance (3.14 Å). The inorganic substrate of Al2O3 film (3 nm thickness) was first grown on SiO2 (300 nm thickness) via atomic layer epitaxial deposition, and the self-assembled monolayer of n-octadecylphosphonic acid (ODPA) noted for its higher thermal stability was then prepared on Al2O3 via solution immersion. The aluminum oxide layer plays a critical role in improving the interfacial bonding of phosphonate group and achieving a near saturated surface coverage of ODPA.
A plethora of techniques have been used to characterize organic thin films. The morphology, hydrophilicity, ODPA coverage, molecular orientation, and crystalline state of ODPA and TiOPc thin films can be characterized by atomic force microscopy (AFM), contact angle analyzer, X-ray photoemission spectroscopy (XPS), near edge X-ray absorption fine structure spectroscopy (NEXAFS) and X-ray diffraction (XRD), respectively. Moreover, the change of electronic structure induced by NO2 adsorption on TiOPc can be investigated by XPS and ultraviolet photoemission spectroscopy (UPS).
XPS result shows that the initial surface coverage of ODPA monolayer is over 90% and the ODPA monolayer remains structurally stable at least up to 120 °C, evidenced by XPS and NEXAFS data. The TiOPc thin film crystallizes into -phase on top of ODPA, as revealed by XRD patterns, and the nearly planar TiOPc molecules are found to be tilted from the surface by ~65° via NEXAFS, in accord with the crystallographic data. The TiOPc OFET achieves a modest mobility of ~1.45×10–1 cm2/Vs and possesses a sensing capability for NO2 with a detection limit approaching 25 ppm at 1 atm. XPS and UPS data indicate that NO2 interact weakly with TiOPc, resulting in no observable feature change in the spectra of Ti 2p, C 1s, and N 1s core levels as well as the HOMO band other than a shift toward lower binding energy by a maximum 0.3 eV. This binding energy shift is interpreted as an evidence of hole doping by NO2 on TiOPc semiconducting film. In conclusion, the present research shows that crystalline TiOPc thin film can be grown on ODPA/Al2O3/SiO2 substrate and the organic films exhibit a good thermal stability up to 120 °C. The resultant TiOPc OFET possess an improved mobility and is capable of detecting NO2 gas at a minimum sensitivity of 25 ppm.

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