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  • 學位論文

有機高介電材料P(VDF-TrFE-CTFE)異質接面性質之探討與元件研發

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

指導教授 : 林致廷
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摘要


有機薄膜電晶體研究中,有機半導體材料及有機導電分子已被廣泛的研究,相較於前述,有機介電質材料則較少有學者進行仔細地探討。而在一個完整的薄膜電晶體上,好的介電質材料不但提供更好的電氣特性,在另一方面,因為有機半導體與導電高分子材料對於環境因子皆非常敏感,良好的有機介電質材料亦可有效地保護軟性電子材料。所以,有機介電質材料將會是未來軟性電子實際應用時所需進行的重要發展方向。有鑒於此,本論文針對一新穎之有機高介電材料聚偏氟乙烯-三氟乙烯-三氟氯乙烯(Poly(vinylidene fluoride- trifluoroethylene-chlorotrifluoroethylene), P(VDF-TrFE-CTFE))作為有機電晶體之絕緣層及保護層之可能進行探討。 首先針對P(VDF-TrFE-CTFE)本身之材料特性進行分析,利用熱分析及X-射線繞射分析建構P(VDF-TrFE-CTFE)薄膜之製程條件,並利用循環伏安法架構材料能帶圖,材料之最高佔有軌域(highest occupied molecular orbital, HOMO)及低空軌域(lowest unoccupied molecular orbital, LUMO)分別於真空能階下方7.393 eV及2.565 eV處,能隙約4.83 eV。 實驗中也驗證了此材料擁有高介電常數(r > 45 @ 1 kHz)、高介電質強度(EBD > 4.25 MV/cm)及高的儲存環境穩定性( > 1000 小時)。利用P(VDF-TrFE-CTFE)作為有機電晶體之絕緣層,也使得電晶體擁有較佳的開/關比(on/off ratio > 5 order)、較低的臨限電壓(Vth = -1.5 V)、較好的次臨限斜率(SS = 0.997 V/dec)、較小的遲滯曲線(4.8 V)及降地操作偏壓,並可提升元件的環境穩定性。 此外針對介電常數與厚度之相依性現象,本論文也提出推論並驗證,研究結果指出由於靠近矽基板處之P(VDF-TrFE-CTFE)電偶極排列會受到介面陷阱電性的影響,導致P(VDF-TrFE-CTFE)/矽介面處生成低介電常數介面層,進而影響介電質之電容值或介電常數。

並列摘要


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.

並列關鍵字

P(VDF-TrFE-CTFE) dielectric high-k OTFTs

參考文獻


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