有機鐵電材料 P(VDF-TrFE) 介電特性於異質接面性質之探討

The study of dielectric characterization of P(VDF0.75-TrFE0.25) on the Si/SiO2 surface

陳昱佳(Yu-Chia Chen)

指導教授 ： 林致廷

國立臺灣大學/電機資訊學院/電子工程學研究所/碩士(2019年)

https://doi.org/10.6342/NTU201903617

摘要

近年來，有機薄膜電晶體已被廣泛研究，大多數有機薄膜電晶體採用二氧化矽作為絕緣層；然而二氧化矽製程溫度對於有機薄膜電晶體未來發展將會受限，利用有機介電材料之製程溫度較低之特性，可以有效的克服製程溫度上的問題。因此本篇論文針對偏二氟乙烯-三氟乙烯共聚物(poly(vinylidene fluoride-trifluoroethylene)),P(VDF-TrFE)作為金氧半導體元件進行 P(VDF-TrFE) 與矽之介面性質探討。在論文第二章中，對此元件進行了基本的電性分析，包括:漏電流、介電常數、P(VDF-TrFE) 與矽之介面層特性，並且透過電導法計算P(VDF-TrFE) 與矽之介面捕陷電荷。且由介面層分析的結果可得知在P(VDF-TrFE) 與矽之介面處生成低介電常數介面層，因此在論文第三章中，我們探討了低介電常數介面層形成之原因，並且提出介面捕陷電荷影響接近介面層之P(VDF-TrFE)之電偶極非線性極化之推論，導致低介電常數介面層效應更為明顯，也透過實驗的方式去驗證此推論。為了避免此機制導致元件之穩定度降低,在論文第四章中，利用二氧化矽做為緩衝層之元件進行分析並將結果與未使用緩衝層之元件進行比較；由比較結果可得知有緩衝層之元件，其電性特性明顯提升，如較低的漏電流，較高之介面常數值以及較不明顯之低介電常數介面層；此外也發現使用SiO2作為緩衝層之元件,其漏電流在閘極偏壓約為＋20V時出現電流劇烈上升之現象，藉由比較有無SiO2緩衝層元件漏電流特性差異,我們也提出SiO2與P(VDF-TrFE)之間所形成之氧空缺為造成此現象之主要因素。

關鍵字

P(VDF-TrFE) ； 高介電值 ； 鐵電材料 ； 壓電材料

並列摘要

Recently, the organic thin-film transistors (OTFTs) have attracted a lot of attentions. Most of OTFTs studies utilize general organic dielectric materials, such as Polyvinylpyrrolidone (PVP), as an insulator in the transistor structure. However, the typical organic dielectric materials usually have low dielectric constant and suffers from leakage. In order to overcome this issue, we investigate the electrical characteristics of high-k organic material poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) with MIS structure in chapter 2, such as leakage current, dielectric constant, and the interfacial characteristics between P(VDF-TrFE) and silicon junction. The interface trap density can be calculated by conductance method. In chapter 3, we suggest that the interface trap charges induce lower dielectric constant interface layer in an organic ferroelectric capacitor, and we though the experimental to confirm this mechanism. In order to avoid the above phenomenon, we use the SiO2 as the buffer layer. The electrical characteristics of metal-ferroelectric-oxide-semiconductor (MFOS) and metal-ferroelectric-semiconductor (MFS) capacitors are compared in chapter 4. Comparing these two experiment results, we find the MFOS device which has lower leakage current, higher dielectric constant, and better interfacial characteristic. The dielectric constant of MFOS capacitor remarkable larger than MFS capacitor when the poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) copolymer thickness thinner than 300 nm. In addition, the leakage current increase seriously at 20 V gate bias voltage. We propose the mechanism to describe this phenomenon which is caused by the oxygen vacancies between P(VDF-TrFE) and SiO2 interface.

並列關鍵字

P(VDF-TrFE) ； dielectric ； high-k ； ferroelectric ； piezoelectric

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