Study on the Electrical Properties and Schottky Contact Characteristics of Organic Thin Film Transistors with Metal/Novel Material Source and Drain

• Main Authors: Chia-Hao Chang, 張家豪
• Other Authors: Chao-Hsin Chien
• Format: Others
• Language: en_US
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/79029430072282003633

碩士 === 國立交通大學 === 電子工程系所 === 95 === In this thesis, pentacene thin-film transistors (pentacene TFTs) were fabricated to study the influences of pentacene deposition condition and contact material on the device performance and contact resistance. On the foundation of the results of electrical characteristics and surface morphology, the probable mechanisms of the effect of deposition conditions and contact materials on the performance were intensively discussed in attempt to achieve superior performance and low contact resistance of pentacene TFTs. By varying deposition temperature and rate, and thickness of pentacene active layer, we found that higher deposition temperature and lower deposition rate could lead to highly crystalline order and less defects in pentacene active layer, which result in turn result in higher mobility and on/off current ratio. Schottky contact between pentacene and metal electrodes results in a large unwanted contact resistance. Therefore, we used Au and Pd, which have the approximate work functions, as the contact materials. For firmly sticking Au and Pt to the substrate, Ti adhesion layer is needed. However, this additional layer will induce large injection barrier of Schottky contact because of the huge work function difference between Ti and pentacene. Thus, we also studied the effect of the adhesion layer thickness on the performance in order to get the optimized composition. From the results, pentacene TFTs with Pd as the contact material and thin Ti adhesion layer depicted superior performance because of the better contact properties and the reduced injection barrier of Pd than Au. In addition, in order to improve the performance of pentacene TFTs, HMDS surface treatments on gate dielectric was also conducted. In the final part of this thesis, we introduced multi-walled carbon nanotubes (MWCNTs) to be the contact material and studied the effects of MWCNT S/D on the performance. From the results, we found that superior performances and lower contact resistance were achieved, because of its excellent contact properties and lager contact area to pentacene. The highest mobility and on/off current ratio, and lowest contact resistance were 0.16 cm2/Vs, 10^7, 10^8 Ω-μm, respectively.