| In recent years, oxide semiconductors have attracted much attention in the field of electronic engineering, due to its earth abundant, better ambient stability, environmental friendly, easy processing and the potential application in displaying devices. Amorphous InGaZnO thin film semiconductor is a good candidate for next generation transistors, as a driver in liquid crystal display (LCD) or organic light-emitting diode (OLED) of mobile or tablet PC, due to its long range uniformity and excellent electrical performance after even after a low temperature annealing. To fabricate a high performance thin film transistors (TFTs), we should focus not only the active layer, but also the dielectric layer. Replacing the conventional thermal grown SiO2 to high-K gate dielectric is a feasible way for energy conservation, because of the minimized device operation voltage and the amplified device mobility. Among all kinds of high-K materials, Al2O 3 is an excellent insulator on account of large bandgap, proper band alignment with highly doped silicon and excellent capacitance performance. In addition, the large abundant of aluminum also favors of low cost fabrication.;In Chapter 3, acetylacetone assisted solution-processed In-Ga-Zn-O (IGZO) TFTs using Al2O3 as gate dielectrics were investigated. Normally fully covered Al2O3 thin films are difficult to achieve by spin coating with conventional solvent, such as 2- methoxyethanol, due to the poor wettability of highly doped silicon. Here a conventional aluminum nitrate solution with an additive was designed, to successfully spin coat robust continuous Al 2O3 thin films. For active layer fabrication, we utilized the combustion process to lower processing temperature, which could be confined in the range from 220 °C to 300 °C, without losing the device performance.;In Chapter 4, the effects of oxygen-plasma treatment on solution-processed Al2Ox gate dielectrics for IGZO TFTs were investigated in this paper. By utilizing the facile solution as described in Chapter 3, combining with oxygen-plasma treatment on gate dielectrics, the combustion-processed IGZO TFTs which were annealed at a temperature of 300°C, showed a mobility of 7.3 cm2V--1s--1, a threshold voltage of --0.3 V, an on-off current ratio of 1x10 5, a subthreshold swing of 160 mV/decade, when operating with a voltage ranging from --2 V to +5 V. Our experimental results demonstrate that oxygen-plasma treatment can remarkably improve dielectric performance. This is presumably due to the passivation of interfacial and bulk traps, and the reduced concentration of oxygen vacancies.;In Chapter 5, basing on the solution processed low-voltage IGZO TFTs, we have successfully fabricated a solution-processed poly[N-9″ -hepta-decanyl-2,7-carbazolealt-5,5-(4',7 '-di-2-thienyl-2',1',3'benzothiadiazole) (PCDTBT) capped IGZO phototransistors with Al2Ox serving as gate dielectric. Photons with the wavelengths (lambda) of 532 nm and 635 nm were absorbed through the layer of PCDTBT to generate electron-hole-pairs (EHPs). After the separation of EHPs, electrons were injected into IGZO layer through the p-n junction formed between the IGZO (n-type semiconductor) and the PCDTBT (p-type semiconductor). The photo-generated carriers boosted the drain current (IDS) of the transistors as well as brought about the negative threshold voltage shift (Delta Vth). Significant enhanced detection performance was achieved under the light at 532 nm. The highest photoresponsivity reached up to 20 A/W while the photoresponse rise time came to 10 ms and the fall time came to approximate 76 ms, which was much faster than trap-assisted IGZO visible light detection. The fabricated phototransistors favored the application of visible-light detectors and/or optical switches.;In Chapter 6, the capping effect of PCDTBT was investigated in depth by comparing the electrical performance and the negative bias illumination stress (NBIS) stability on the capped InOx, InZnOx and InGaZnOx. After the formation of the p-n junction, the diffused electrons and holes recombined immediately. A significant positive shift of threshold voltage meanwhile improved transfer hysteresis (threshold voltage shift between transfer forward and reverse sweep), indicating a remarkable reduced channel free carrier concentration and trap states as well. The PCDTBT plays an important role not only as a back channel passivation layer, but also a visible light absorption layer. Improved NBIS stability was achieved owing to the dominant absorption of photons through PCDTBT layer rather than the oxide semiconductors, weakening the photo-excitation and the followed ionization of neutral oxygen vacancies within oxides. In addition, the transfer hysteresis was also suppressed for PCDTBT capped transistors under NBIS. By employing PCDTBT as both a passivation and photon absorption layer, only a complementary voltage is needed to offset the NBIS effect. |
