介電層氫氧基對五苯環有機薄膜電晶體的影響

Abstract

有機薄膜電晶體相對於傳統的非晶矽薄膜電晶體有許多優點，如：低溫製程、低成本、可撓性…等，但於此同時，元件可靠度低和壽命短則是其應用上最大的弱點。缺陷捕捉載子是目前公認造成有機薄膜電晶體臨界電壓飄移和遷移率裂化的最主要原因。 此論文主要研究有機薄膜電晶體中氫氧基受環境影響而產生缺陷的機制。我們使用聚甲基丙烯酸甲酯(PMMA)和聚乙烯酚(PVP)做為介電層表面處理材料，做出二種不同的有機薄膜電晶體，其中PVP處理的表面存在有氫氧基。 首先由光環境和暗環境中量測二種元件的遲滯效應，推論氫氧基應該可以形成捕捉電子的缺陷，而照光則會在有機半導體中產生電子電洞對，提供被捕捉電子的來源。接著比較二種元件在光環境和暗環境中做閘極正偏壓實驗，推論閘極正偏壓會導致有機半導體能帶彎曲，使原來不被填滿的缺陷態傾向被光產生的電子填滿，造成臨界電壓飄移。真空環境中閘極正偏壓的量測進一步說明，氫氧基要形成電子缺陷，應該是需要與大氣中的水氣和氧氣結合才行，此種缺陷不論是在光環境或是暗環境下，都會造成臨界電壓飄移。 針對以上缺陷產生的機制，設計適當保護層可以使有機薄膜電晶體更進一步朝向實用化。相反的，氫氧基使元件特性對水氧有明顯的變化，說明了有機元件在水氣和光偵測器上應用的可能性。

Organic thin film transistors compared with the conventional amorphous silicon thin film transistors have many advantages, such as: low-temperature process, low cost, flexible ... and so on. However, poor reliability and short life time is its application greatest weaknesses. So far, carrier capture defects are recognized as the main reason that causes threshold voltage shift and mobility degradation. In this thesis, dielectric hydroxyl groups (OH groups) defects forming mechanism influenced by the environment is studied. We use methyl methacrylate (PMMA) and poly-4-vinyl phenol (PVP) as the dielectric surface treatment material and make two kinds of OTFTs. PVP-OTFTs have OH groups on its interface while PMMA-OTFTs do not. By comparing PMMA and PVP devices’ hysteresis in dark and under light, we find OH groups can form defects and trap electrons. Illumination will photogenerate electron-hole pair in the organic semiconductor and provides the source of trapped electrons.Then, PMMA and PVP devices positive gate bias stress experiment in dark/light environment indicated that positive gate bias stress can make semiconductor’s energy band bending, some originally do not filled defect states will tend to trap photogenerated electrons and thus cause threshold voltage shift. In addition, positive gate bias stress experiment taken in vacuum environment further proved OH group should react with H2O and O2 in the air then electron defects could be formed. OH groups defects can cause threshold voltage shift on matter it was in dark or light environment. In order to realize OTFTs’ application, passivation layer that could protect organic semiconductor from environment effect is needed. On the other hand, significant threshold voltage shift caused by OH groups implicate OTFTs application on moisture/light sensor.