The development of heterogeneous-interfacial properties and device characteristics in P(VDF-TrFE-CTFE) based electronics

• Main Authors: Po-Han Chen, 陳柏翰
• Other Authors: Chih-Ting Lin
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/4ku3x3

博士 === 國立臺灣大學 === 電子工程學研究所 === 105 === Organic electronics have been developed for decades. Both organic semiconductors and organic conductors are intensively investigated. However, there are few pieces in the organic dielectric, which is also important in organic transistors. Since dielectrics not only function as protective layers in organic electronics but also determine essential characteristics of organic thin field transistors (OTFTs), it is important to explore different organic dielectrics and identify a good one for future applications of organic electronics. To address this point of view, in this dissertation, we aim to investigate a newly developed organic dielectric, Poly(vinylidene fluoride- trifluoroethylene-chlorotrifluoroethylene) terpolymer, or called P(VDF-TrFE-CTFE). P(VDF-TrFE-CTFE) has a high dielectric constant and inert characteristics to chemicals. Therefore, it is considered as a potential candidate for the gate dielectric in OTFTs and passivation layer in flexible electronics. To obtain material properties and fabrication conditions of P(VDF-TrFE-CTFE), in this thesis, it is analyzed by thermal analysis, X-ray diffraction, and atomic force microscope. Using cyclic voltammetry measurements, the energy levels of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) are estimated as -7.39 and -2.56 eV, respectively. As a consequence, the bandgap of P(VDF-TrFE-CTFE) can be experimentally estimated as 4.83 eV. Based on our experiments, P(VDF-TrFE-CTFE) has high dielectric constant (r > 45 at 1 kHz), high dielectric strength (EBD > 4.25 MV/cm), and high storage stability (> 1000 hours). Utilizing these advantages, P(VDF-TrFE-CTFE) based Schottky-barrier MISFET (metal-insulator-semiconductor field-effect-transistor) has low driving voltage, low threshold voltage (-1.5 V), steeper subthreshold swing (0.997 V/dec), higher on/off ratio (~ 5 orders), smaller hysteresis characteristics (V = 4.8 V), and high storage stability. These experiments demonstrate the potential of P(VDF-TrFE-CTFE) to be used as an organic dielectric in OTFTs. Utilizing developed P(VDF-TrFE-CTFE) based MIS (metal-insulator-semiconductor) devices, a phenomenon of thickness-dependency dielectric constant is experimentally verified. This is attributed to a low-k interface layer on P(VDF-TrFE-CTFE)/silicon interface. This could result from surface-tension constrained molecules and effects of interface trapped charge. Both of these effect dipole arrangements within the interface layer of P(VDF-TrFE-CTFE). These interfacial properties dominate characteristics of OTFTs with P(VDF-TrFE-CTFE) as gate dielectrics.