Studies of temperature effects on electrical properties of ambipolar organic field–effect transistors and complementary inverters

• Main Authors: Chung-WeiHung, 洪崇瑋
• Other Authors: Horng-Long Cheng
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/07899793009597128627

碩士 === 國立成功大學 === 光電科學與工程學系 === 100 === This study investigates the influence of the operating temperature, ranging from 300 K to 400 K, on the electrical characteristics of pentacene- based ambipolar organic thin-film transistors and complementary-like inverters. The study can be divided into the following two parts: (1) the effects of temperature on the p-channel and n-channel electrical characteristics, respectively, of the ambipolar transistors were investigated; (2) complementary-like inverters were realized based on the pentacene-based ambipolar transistors, and named ambipolar inverters. We studied the effect of temperature on the electrical characteristics of the ambipolar inverters. Part 1: We fabricated the pentacene-based transistors using three kinds of gate dielectrics, including unmodified silicon dioxide (SiO2), poly(methyl methacrylate) (PMMA) modified SiO2, and poly(styrene) (PS) modified SiO2. The effects of operating temperature on the electrical characteristics of the corresponding devices were studied. When PMMA and PS modified SiO2 gate dielectrics were used, we observed that both hole- and electron- mobilities decrease with increasing temperature. In contrast, the transistor with unmodified SiO2 shows unipolar p-channel behavior and the observed hole mobilities are insensitive to temperature variations. Microstructural analysis using variable-temperature Raman spectra reveals that increasing temperature results in reduced intermolecular vibrational coupling energy and broadening of Raman peaks for the pentacene films, thereby reducing charge transport within active channel of transistors. This provides a reasonable basis for the lower hole- and electron-mobilities of pentacene-based ambipolar transistors at higher operating temperatures. Variable-temperature capacitance-voltage measurements of metal-insulator- pentacene-metal capacitors indicated that the flatband voltage shift toward the positive direction (i.e., shift to zero direction) as well as accumulation capacitance increases with increasing temperature, thereby providing an explanation for the threshold voltage shift of the corresponding transistors at higher temperatures. As operating temperature changes, the resulting changes in ambipolar electrical characteristics of pentacene-based transistors were attributed to the combined effects of electric field and thermal. Part 2: we studied the influence of operating temperature on the electrical characteristics of the pentacene-based ambipolar inverters. With increasing operating temperature, we observed a decrease in the hysteresis area, which is defined as the difference between forward and reverse switching voltages. This observation confirmed that the switching voltages of the investors are highly dependent on the threshold voltages of the individual p-channel and n-channel transistors. Finally, we found that the non-ideal noise margins of ambipolar investors could be improved by increasing the operating temperature, thus achieving more ideal operations.