Investigation of PMMA Dielectric Layer Applied in Organic Thin Film Transistors

• Main Authors: Tsung-SyunHuang, 黃琮訓
• Other Authors: Yan-Kuin Su
• Format: Others
• Language: en_US
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/35779939515849450632

博士 === 國立成功大學 === 微電子工程研究所碩博士班 === 98 === The structure and electric characteristics of PMMA-based organic thin film transistor and their pentacene film grown on PMMA film have been investigated in this dissertation Four solvents, toluene, p-xylene, o-Dichlorobenzene, and chloroform were selected to dissolve PMMA and AFM was used to measure the grain size and roughness of pentacene grown on PMMA. Several material characterization techniques, such as X-ray diffraction (XRD), contact angle, X-ray photoelectron spectroscopy(XPS) and atomic force microscope (AFM) were performed to characterize the material quality. This study gave clear experimental evidence that the quality of pentacene grown on the PMMA dielectric layer dissolved in toluene is the best choice. The treatment of UV-ozone on ITO surface can reduces the leakage current through PMMA dielectric layer. With the UV-ozone cleaner treatment for ITO surface, the average number of pinholes in PMMA film deposited the ITO reduces from 47 to 19 (in 25 μm2 area). The leakage current density reduces from 1.5 to 2.0 × 10-2 A/m2. According to the analysis of XRD and AFM measurements, the optimum pentacene thickness grown on PMMA film was 60 nm. In this dissertation, we have also compared the performance of PMMA-based OTFTs with that of SiO2-based OTFTs, including pentacene film quality and electric characteristics. This study also gave clear experimental evidence that the quality of pentacene grown on the PMMA layer was better than that grown on SiO2 dielectric layer. XRD was used to measure the diffraction intensity in order to observe the crystalline quality of pentacene thin film on PMMA and SiO2. AFM was also used to measure the grain size and roughness of pentacene grown on PMMA and SiO2 and subsequently deduce a match in surface free energy between pentacene and PMMA. The maximum saturation field-effect mobility was 0.241 cm2/V s. It was also found that the electric characteristics of OTFT with PMMA dielectric layer were beter than that of OTFT with SiO2 dielectric layer. The excellent transfer characteristics of pentacene-based OTFTs with PMMA as dielectric layer were obtained: drain saturation current (3 μA at VGS = -50 V and VDS = -50 V), threshold voltage (VT = -11.5 V), on/off current ratio (7.7 × 104), and field-effect mobility (μsat = 0.48 cm2/Vs) were obtained by inserting the MoO3 buffer layer. The MoO3/pentacene interface was analyzed by XPS and found the C1s core level peak in MoO3/pentacene interface shifted to higher binding energy. For the energy barrier of 0.2 eV in Au/MoO3 interface, the carriers can sufficiently jump the energy barrier into MoO3 layer as VDS increases, and than efficiently inject into pentacene film. This is why the performance of OTFTs with MoO3 buffer layer can be enhanced as VDS is more than 1.7 V. Besides, the MoO3 buffer layer was also a protector against the penetration phenomena, which would cause interface dipole barrier. Therefore, excellent performance of pentacene-based thin film transistors will be achieved by inserting a MoO3 buffer layer.