The study of organic thin-film transistors with high-k gate dielectrics and Ni-doped magnetic organic semiconductors

• Main Authors: Tsung-YehHo, 何宗曄
• Other Authors: Wei-Yang Chou
• Format: Others
• Language: en_US
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/49376573629881491400

博士 === 國立成功大學 === 光電科學與工程學系 === 102 === The organic material has become an emerging research field because of its flexibility, low cost, and low temperature process capabilities. The work presented in this dissertation is divided into three parts according to the type of organic material. Part one deals low voltage-operating organic thin-film transistors with high-dielectric constant (high-K) materials for the device’s gate dielectrics. The surface properties of these high-K materials must match those of organic semiconductors. A modification material coated on high-K dielectric is needed, and polyimide (PI) is a promising modifier to reduce the surface energy and the interface trap states (in the level of 1010 cm-2 eV-1) of the high-K dielectrics. In this study, surface characteristics of the dielectrics were identified and interface analyses at the dielectric/organic semiconductor interface were conducted through combined electrical force microscopy and impedance-admittance investigation. When the organic semiconductor pentacene was grown on the PI-modified dielectrics, the atomic force microscopy (Atomic Force Microscope, AFM) images and X-ray diffraction (XRD) analyses showed larger grain size and higher crystallinity than those on native high-K dielectrics. Although the gate field was decreased by inserting a PI layer, the effective gate field was compensated by an electric dipole-induced dipole field embedded in the PI layer. Using polyimide-modified high-K materials as the gate dielectric, high performances (S. S. 〈 1 V per decade,  above 0.1 cm2 V-1 s-1, and on/off ratio 〉 105) and low voltage-operating (〈 5 V) pentacene-based thin-film transistors were achieved. Recently, a great demand for high-performance nonvolatile memory devices has arisen for use in portable electronic devices. Therefore, active research has been performed to study the fabrication of high performance nonvolatile memory devices with fast writing/reading, high density data storage, writing/reading stability, long retention time and low power consumption. The part two of this dissertation, magnetic material nickel and an organic material pentacene were co-deposited on top of the PI layer. The AFM and magnetic force microscopy (MFM) images show that the magnetic domain distribution of nickel is very similar to the morphology of the pentacene grain. Magnetic organic pentacene film was attributed to the thin-film phase, as determined from XRD results. The magnetic-field- and temperature-dependent magnetic moments analyses by superconducting quantum interference device (SQUID) show that all the samples exhibited room-temperature ferromagnetism. Polarized Raman spectra of magnetic organic films show that the local π-electron clouds of pentacene form “bridges”, giving the nickel electrons a coherent spin transport. Topographically patterned polymer films and surfaces, having sub-micron scale resolutions are important in a host of scientific and commercial applications like thin film transistors (TFT), solar cells, organic light emitting diodes (OLED), optical sensors, optoelectronic devices, etc. In part three, flexible composite micro/nano molds (h-PDMS/PDMS) with four ridge widths (400, 600, 800, and 1200 nm) were replicated from silicon molds. For the nano-imprinting fabrication process, four types of PI nano-groove with ridge widths of 400, 600, 800, and 1200 nm were created.