Low Temperature Transistors and Sensors based on Oxide Semiconductor and Organic Semiconductor Materials

• Main Authors: Tsai, Wu-Wei, 蔡武衛
• Other Authors: Zan, Hsiao-Wen
• Format: Others
• Language: en_US
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/41876392252855371409

博士 === 國立交通大學 === 光電工程學系 === 100 === The development of flexible electronics and displays are crucial for nextgeneration electronics. Metal-oxide thin-film transistors (TFTs) and organic TFTshave higher potential than a-Si TFTs because of the following advantages：1) low-cost;2) solution fabrication process on a large area array system; 3) low fabrication temperature (< 200 ℃); and 4) the applications are on a flexible substrate. In the Chapter 2 of this dissertation, we proposed a high performance amorphous In-Ga-Zn-O (a-IGZO) thin film transistor with nano-dot doping (NDD).The nano dot structure creates many short channel and high concentration region in the channel region. Also, the performance of a-IGZO TFT can be controlled by the dots concentration and the Ar plasma treatment time. The proposed nano-dot doping reduces the effective channel length, lowers down the energy barrier, and enhances the effective field-effect mobility 19 times larger than that of the control sample without NDD. The proposed device is promising for the development of low-cost, lithography-free, and high-performance flexible electronics. In the Chapter 3 and Chapter 4 of the dissertation, we introduce the two organic photodetectors, including photodiode and phototransistor. In the Chapter 3, bilayered organic photo diodes with controllable carrier mobility in the p-type donor are demonstrated. Vertical carrier mobility of pentacene is demonstrated to be increased while the deposition rate is high. With C60 as the acceptor material and pentacene deposited at high deposition rate as donor material, the detection of 80-MHz signals is demonstrated. Using high mobility pentacene in stead of poly(3-hexylthiophene) (P3HT) to serve as the hole transport layer effectively improves the hole mobility over 1 orders and hence enlarges the operation bandwidth. The results enable the development of low-cost large-area organic image sheets for the detection of high-frequency signals. In the Chapter 4, we introduce a vertical polymer phototransistor with low operational voltage (-1.5 V). A blended polymer layer with both acceptor and donor materials was used as a IV channel material in the vertical space-charge-limited transistor (SCLT). Under illumination, we obtained external quantum efficiency (EQE) as high as 360% at 620nm. We propose the effects of base-field shielding as a means to explain high EQE. This proposition has been supported by two-dimensional simulation of the device. Moreover, we also study the pentacene-based organic thin film transistor (OTFT) as ammonia sensor in the Chapter 5 of this dissertation. Non-invasive ammonia sensors are attractive alternatives for the diagnoses of a variety of chronic diseases such as liver cirrhosis and renal failure. A low cost pentacene-based organic thin film transistor (OTFT) fabricated by a novel and simple process was demonstrated to be highly sensitive and specific for ammonia gas. Various measurement parameters that reflected OTFT device characteristics for ammonia detection were investigated. Significant variations of the turn-on current, intrinsic mobility, and threshold voltage (Vth) were observed while subthreshold swing (S.S.) was almost unchanged to the alteration of ammonia concentration. The OTFT device detected 0.5~5 ppm concentration ammonia gas at room temperature, which is in the critical range that can distinguish between healthy person and patients with liver cirrhosis and renal failure. The sensitivity of the device was further enhanced following a simple UV irradiation treatment to modify the functional groups on poly(methyl methacrylate) (PMMA) dielectric layer. Possible interference for ammonia detection such as humidity effect and selectivity among nitrogen, alcohol, carbon dioxide, acetone, methane and ammonia were also examined. We concluded that the proposed pentacene-based OTFT is a promising device for the future application in non-invasive medical diagnoses. In the Chapter 6 of this dissertation, an organic vertical transistor is investigated. In this work, I was cooperating with Dr. Yu-Chiang Chao, Dr. Chun-Yu Chen, Shu-Ling Jiang, Chun-Ming Chiang, and Ming-Che Ku. In the Chapter 6, the operation mechanism of vertical transistor is introduced. The turn-on current, on-off current ratio, current gain, and operation voltage of P3HT-based vertical transistor is 0.14 mA/cm2, 24310, 104, and 1 V. In order to improve the controllability and solve the accumulation of polystyrene spheres problems, the nano-imprint technology is used to replace the polystyrene spheres fabrication process and to from the grid structure.