Solution-Processing Of Insulator Layers And The Research Of Its Performance

As an important part of organic thin film transistors(OTFTs), gate insulators’ quality directly affects the performance of the OTFTs. Therefore, it’s critical to gain good insulators for OTFTs devices with good performance. In this paper, the PVP was selected because of its high dielectric constant, good insulating property, and soluble in organic solvents which is good for preparing with solution process. After the PVP thin films and MIS structure devices were prepared, their optical properties and electrical properties were characterized with the help of spectroscopic ellipsometry, Semiconductor parameter analyzer and Impedance Analyzer, and the influence of solvent vapor-assisted spin coating and solvent vapor annealing(SVA) on the PVP thin films were discussed. The Specific researches are as follows :(1) Firstly, the influence of spin speed and PGMEA vapor-assisted spin coating on PVP films were studied by changing the spin speed and considering whether spinning coating with PGMEA solvent or not, the results showed that PVP film turned thinner with higher spin speed and PGMEA vapor-assisted spin coating. When the thickness of films were the same, the leakage current densities in unit area of the MIS structure which were prepared with PGMEA vapor-assisted spin coating PVP films were smaller than those without PGMEA. These indicated that the PGMEA vapor-assisted spin coating is an effective way to reduce the thickness and improve electrical properities of PVP films.(2) Secondly, the influence of SVA time on PVP films were investigated with Anisole. The relationship between the microstructure and the optical parameters of the PVP gate insulating films were analyzed based on effective medium approximation(EMA) model of Spectroscopic ellipsometry. The results showed that the gross thickness of PVP films were decreased with the increase of SVA time, and thickness of roughness layers were decreased at first and then increased with the increase of SVA time, the perfect time is 10 min. According to the J-V characteristics of MIS structure with this kind of films, it is showed that the leakage current density was decreased from 1.07×10-6A/cm2 to 6.85×10-8A/cm2 at 2 MV/cm when the SVA time increased from 0 min to 10 min, and then increased to 2.99×10-7 A/cm2 when the SVA time was 20 min. These indicated that we can obtain PVP films with less roughness and trap densities after being treated with SVA at the right time.(3) Finally, we investigated the effects of solvent relative vapor pressure to PVP films during SVA by changing the solvent pressure. The relationship between the microstructure and the optical parameters of the PVP gate insulating film were analyzed based on Cauchy model and EMA model of Spectroscopic ellipsometry. The results showed that the thickness of gross films(which were less than 30 nm) and roughness layer were decreased with the increase of vapor pressure, and the compactness of films turned better. According to the J-V characteristics of MIS structure made of this kind of films, it is showed that the leakage current density was decreased from 2.94×10-7A/cm2 to 4.2×10-8A/cm2 at 2 MV/cm as the vapor pressure increased from 0.21 to 0.82. The mechanism of leakage current is Poole-Frenkel effect when the electric field intensity is less than 1 MV/cm, then turned into Richardson-schottky launch when the electric field intensity increases from 1 MV/cm to 5 MV/cm. We also obtained ultra-thin PVP film(approximately 20 nm) whose capacitance per unit area reached 145 n F/cm2 when the pressure was 0.82.