| Summary: | 碩士 === 國立交通大學 === 電子工程系所 === 92 === Recently, active matrix organic diode displays (AMOLEDs) become the most advanced technology in the market; organic light-emitting diodes (OLEDs) and organic thin film transistors (OTFTs) enable the fabrication of low-coat, flexible, full color flat panel displays. In this paper, organic thin film transistors based on poly (3-hexylthiophene) (P3HT) with the “bottom contact”structure, SiO2 as insulating layer, organic active layer grown with spin-coating have successfully been demonstrated.
In chapter 2, we used two kinds of solvents, xylene and chloroform, to dissolve P3HT. While weight percentage is as high as 0.3%, the P3HT cannot completely be dissolved in xylene and then many clusters of undissolved P3HT powder is observed. However, chloroform can dissolve high weight percentage of P3HT (> 2 wt%). Therefore, it is proved that chloroform is a good solvent for P3HT. Furthermore, we observed that the anomalous gate leakage current was suppressed by fabricating OTFTs with chloroform solution. As the weight percentage of P3HT is above 0.8%, it would cause obvious bulk leakage current. In summary, the P3HT OTFTs fabricated by 0.3% chloroform solution can acquire the lowest surface roughness and the better performance of devices than others.
In chapter 3, the OTFTs are treated with vacuum treatment, O2 treatment, N2 treatment, immersed in water or gate bias stress for different time. Since oxygen is a kind of dopant for P3HT, threshold voltage and leakage current of the OTFTs drastically increase with O2 treatment time. Vacuum and N2 treatments can be used to recover some of the lost performance through vacuum-induced expulsion of absorbed oxygen. As regards the OTFTs being immersed in water, the performance of electrical characteristics would not be affected. When a positive bias was applied to the gate electrode, it would lead to the dipole moment arranging in the P3HT polymer and positive threshold voltage shift. Negative gate bias stress causes negative threshold voltage shift.
In chapter 4, we use Pt, Au, Ni or Ti as S/D contact materials of OTFTs. Because the work function of Pt and Au are larger than the work function of P3HT, they can form better ohmic contact with P3HT than others. Nevertheless, it was observed that the crowding effect was occurred at the small drain bias for Ni as S/D contact material of OTFTs. Secondly, we adjusted the thickness ratio of adhesion/contact metals, such as Ti/Pt and Ti/Au. From experiment results, it was observed that contact resistance is weakly dependent on the thickness ratio of adhesion/contact metals.
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