Investigation On New Structure Thin Film Transistors And Their Electrical Properties

Organic transistors have attracted considerable interest because they are lightweight, flexible, inexpensive, and highly efficient over large areas. As a result of these characteristics, organic transistors are expected to find use in a variety of applications, including electronic barcodes, displays, and sensors. Until now, their performance has been inferior to inorganic transistors because of their lower mobility values (typical mobility ranges are 1–10 and 500–10000 cm2/Vs for organic and inorganic semiconductors, respectively). Attempts to enhance the performance of organic transistors have relied on designing new type of device structures. In addition, increasing attention has been paid to nano- or microstructured materials during past decades because of their intriguing optical and electronic properties. Of particular interest in this regard is one-dimensional (1D) organic nano- or microstructures on various substrates with high length/diameter aspect ratio, since such highly ordered functional materials are potential candidates as active components in a wide range of research field including gas sensors, organic light-emitting diodes (OLED), organic field effect transistors (OFET), optical waveguide fibers, photodetectors, and solar cells, etc. The quantum size effect of micro- and nano-structured semiconductors could induce novel optical and electronic properties when compared with those of thin-film transistor materials. The 1D alignment facilitate carrier transport hence improve the charge mobility of the electronic devices, however, the on/off current ratio (Ion/Ioff) of the 1D semiconductor is commonly lower than that of thin-film transistors. To fabricate integrated optoelectronic devices, it is important to control the assembly and alignment of the nano- or microwires in desired position on the substrate. Thus, the development of efficient self-assembly approach is highly important toward unique 1D micro- or nanostructured materials for semiconducting transistors.In this thesis, we reported two strategies, (a) designing novel device structure and (b) constructing ordered 1D nano- semiconducting materials, for high performance field effect transistors. Our approach to resolving first issue is to employ a self-aligned type transistor for organic semiconducting materials which usually employed in inorganic thin-film transistors. As for the second issue, A simple electronspun approach allows us controllably synthesize large quantities of well-defined 1D ultralong nanofibers. Field effect transistor devices based on the 1D fibers fabricated in situ on SiO2 substrate exhibited excellent semiconducting properties.1. Na2Ti3O7 nanowires with diameters of about 80–130 nm and lengths up to several tens of micrometers are synthesized via a simple hydrothermal method and characterized by the field-emission scanning electron microscopy and X-ray diffraction. Back-gate field-effect transistors based on these nanowires are fabricated on indium tin oxide glass substrates with polymethyl-methacrylate-co-glyciclyl-methacrylate as the gate insulator layers. Typical p-type semiconductor material properties are observed in our investigations. The field-effect mobility is about 0.1 cm2/Vs. The capacitance per unit area of the dielectric is 3.43 nF/cm2 (dielectric constant, k = 3.9). The on/off ratio is around 103.2. For the first time, we tried to apply the self-aligned device structure to organic thin film transistors. This type of device fabrication has the following two advantages: firstly, a top-gate top-contact self-aligned field effect transistor can be constructed by three-time vacuum evaporations, significantly simplifying the device fabrication process. Secondly, the transistor fabricated by this method exhibits excellent conducting properties. The mobility achieved 2.68 cm2/Vs and Ion/Ioff of the transistor achieved about 104, demonstrating its potential for practical application.3. Electrospining has received steadily increasing interest due to its ability to produce nanometer-sized fibers with a high level of reinforcement. A large number of polymers have been electrospun into nanofiber with fiber diameters typically ranging from 50 to 500 nm. Considering this point, we employed this methodology to fabricate polythiophene nanofiber based transistors in the present study. In this method, the electro-spun polymer PAN (polyacrylonitrile) are used as the template and conducting polythiophene are then coated on the surface of the core PAN fibers by in-situ deposition polymerization. The polythiophene nanofiber prepared by this method can be directly deposited on glass substrates pre-coated by Si insulator with highly ordered alignment. Then source-drain electrodes (Au) were evaporated through shadow masks. This device exhibits typical p-type semiconducting properties. The transistor reached maxima Ion/Ioff of about 0.4×106. The calculated mobility is 14.9 cm2/Vs; this value is even higher than the mobility of P3HT.4. Firstly, a multi-gate double-channel Poly-Si TFT structure has proposed. Open-state current of the transistor double than multi-gate single-channel Poly-Si TFT transistor; Only P-channel 3T pixel drive circuit for AM-OLED has designed and simulated with Hspice software. The 3T pixel circuit has simplified the process. The pixel circuit design has certain advantages and advanced; At last, a LTPS-TFT-AMOLED test method has invented.