電子槍蒸鍍之絕緣層對雙層石墨烯電性之影響

Abstract

本論文探究電子槍蒸鍍技術應用在雙閘極石墨烯元件之可行性，實驗先對三種常用之絕緣材料Al2O3、SiO2、MgO進行漏電及電容分析，發現Al2O3及MgO蒸鍍出的薄膜有較小的漏電流，適宜做為閘極絕緣層之材料。並在不同環境下對石墨烯元件進行量測並比較；在大氣環境下及氮氣吹拂環境下，易因水氣的吸附造成量測上的誤差。而真空環境能避免水氣的問題並減少量測上的雜訊產生。 而在真空環境下，探究三種絕緣材料對於石墨烯元件的影響。電子槍蒸鍍技術之絕緣材料會降低石墨烯元件的載子移動率，而蒸鍍過程中的charge trapping會造成石墨烯元件電中性點(charge neutral point；CNP)的變動，而透過HSQ作為蒸鍍絕緣材料及石墨烯當中的緩衝層，對於電中性點的變動有所改善。最後將Al2O3、MgO及HSQ與MgO複合結構做成雙閘極石墨烯元件。並透過上下閘極電場的施加與調變進行雙層石墨烯能間隙的調控。

We investigated the effect of e-beam evaporated dielectric layers on the electrical performance of bilayer graphene. The comparison of leakage current and capacitance-voltage characteristics in MOS (metal–oxide–semiconductor) structure with various e-beam evaporated dielectric layers such as, Al2O3, SiO2 and MgO is presented. For MOS with Al2O3 and MgO, the leakage current density is low compared with MOS with SiO2 . Therefore, Al2O3 and MgO were chosen as the gate dielectric layer for dual-gated bilayer graphene devices. The graphene device measurement in different environment was carried out .We found that water vapor severely affected the charge neutral point (CNP) and the carrier mobility of the graphene when the measurement was performed in air and in N2. Therefore, the measurement in vacuum was preferred to avoid the influence of water vapor. We found that all three e-beam evaporated dielectric layers decrease the mobility. And also shift the CNP of the graphene device toward negative bottom gate bias. Introducing HSQ buffer layer prior to the deposition of dielectric layer could compensate the shift of the CNP. Finally, dual-gated BLG devices were fabricated with Al2O3 , MgO and HSQ+ MgO as dielectric layers, respectively. The band gap opening of these devices was observed by properly tuning the top gate and bottom gate voltages.