A Research Of Processing And Interfacial Performances Of A-IGZO Thin Film Transistor

Amorphous indium gallium zinc oxide (a-IGZO), born in 2003, has opened a new gate of amorphous oxide semiconductor materials for the whole world. Thanks to its compact and flat thin film, ultra transparence in visible light area, brilliant semiconductor characteristics even in amorphous state whose electron mobility is over 5 cm2·V-1·s-1, the a-IGZO has become the ideal semiconductor material for flexible and transparent thin film transistor (TFT) of next generation. This paper mainly researches the processing methods of a-IGZO TFT, such as direct current magnetron sputtering, spin coating and vaporing, and the influence of devices structures and interface contact performance between a-IGZO thin film and different kinds of dielectric layers.Firstly, the research progress of oxide TFT is reviewed, the history and advantages compared with other semiconductor materials are summarized. Then with the help of scanning electron microscope (SEM) and atomic force microscope (AFM), the superficial feature of a-IGZO thin film is tested. It turns out that the thin film processed by magnetron sputtering keeps compact and flat; it is also in amorphous state.Secondly, two organic materials are chosen as insulator of a-IGZO TFT by spin coating:polymethyl methacrylate (PMMA) and polyvinyl alcohol (PVA). Based on these two materials, top-gate and bottom-gate devices are examined. The experiment result shows that the damage of insulator from high sputtering power is an inconvenient truth. In terms of performances of devices with different insulator thickness or magnetron sputtering power, those suffering high sputtering power or thin insulator are more likely to conduct between gate and drain. By contrast, high power has less impact on top-gate TFTs, for they need-form a-IGZO in advance before insulators are fabricated. Hence the off drain current of top-gate TFTs are lower. However, when considering electron mobility, bottom-gate TFTs are much better. According to consequences of AFM test, the a-IGZO thin films grown in insulator are less rough then those in glass substrate. Another conclusion is that PVA is more suitable than PMMA as the insulator of a-IGZO TFT, because dielectric constant of PVA is larger than PMMA’s, which makes TFTs based on PVA have larger mobility and on off ratio.In next part, staggered bottom-gate and coplanar bottom-gate TFTs are in comparison. TFTs based on PMMA and PVA are tested respectively. All results prove that coplanar bottom-gate TFTs have larger mobility and lower threshold voltage.Next, using PVA as insulator, and a conducting a-IGZO buffer layer between insulator and active layer makes the best a-IGZO TFTs in this paper, whose mobility is 11.59 cm2·V-1·s-1 and threshold voltage is 0.18 V, which can match the counterpart with traditional inorganic insulator. It turns out that it is significant for TFTs’ performance improvement to have a conducting a-IGZO buffer layer and interface contact performance between insulator and buffer layer is also very important for high performance TFTs.The last part is about a-IGZO TFTs with solution Al2O3. TFTs with traditional solution Al2O3 and combustion solution Al2O3 are made respectively. The outcome shows combustion solution Al2O3 is not better than former, except for lower annealing temperature. The next experiment is to compare the impact of different annealing temperature of solution Al2O3, which demonstrates 200℃ is the most suitable temperature.