增強型氮化鋁鎵/氮化鎵金屬-絕緣體-半導體高電子遷移率電晶體之臨界電壓模擬研究

Abstract

氮化鋁鎵/氮化鎵高電子遷移率電晶體近年來廣受注目，由於擁有優越的材料特性因此適合應用在高頻以及高功率元件上。然而傳統結構的氮化鋁鎵/氮化鎵高電子遷移率電晶體其臨界電壓(Threshold Voltage)操作於負電壓也就是空乏型(Normally On)並不方便於電路設計以及元件故障安全操作，於是增強型(Normally Off)是目前許多研究團隊研究的重點。加上隨著元件的尺寸縮小，非理想效應變得非常重要，尤其是閘極氧化層下載子的量子穿隧效應(Quantum Tunneling Effect)。 因此，在本研究中我們使用SILVACO 公司的電腦輔助軟體(TCAD)來模擬研究掘入式金屬-氧化物-半導體氮化鋁鎵/氮化鎵高電子遷移率電晶體，基於飄移-擴散載子傳輸方程式(Drift-Diffusion Transport Model)，使用量子穿隧模型(Density Gradient or Quantum Moments Model) 趨近實驗數據，以達成實際元件的真實情況，使元件未來發展上更具真實性和可靠度。此論文對掘入式閘極、高介電值閘極氧化物、閘極金屬進行綜合研究，了解對臨界電壓的正位移。 研究中發現，相較於Al2O3 (aluminum oxide) ，使用TiO2 (Titanium dioxide) 當作閘極氧化層，其最大互導係數為259 mS/mm，且具有高的崩潰電壓650V和較小的汲極漏電流(≈10-9mA/mm) ，且使用鉑(Pt)當作閘極金屬時其臨界電壓可增加為1.3V。

AlGaN/GaN high electron mobility transistor (HEMT) is extensive investigation in recent years, because of their superior material properties that suitable for high frequency and high power applications. However, the conventional structure of AlGaN/GaN HEMT whose threshold voltage is operated in the negative voltage that also called depletion mode (normally on); moreover, it is not convenient for circuit design and fail-safe operation. Therefore, Enhancement-mode (normally off) is the wild of many research teams studied. In addition to, the framework of devices is scale down accompanied with the non-ideal effects. It cannot be ignored, and especially carriers confinement in channel under the gate oxide. It is called the tunneling effect (quantum tunneling) Therefore, in this thesis work a physical simulation of AlGaN/GaN MOS-HEMT is developed using commercially available software ATLAS from SILVACO Int. Based on drift - diffusion carrier transport equations. The quantum tunneling model (density gradient model) calibrate to the experimental data so that it approaches actual device situation and reliability. In this thesis, a comprehensive study of approaches to achieve positive threshold voltage. We have investigated the influence of recess gate, gate oxides, gate metallization on the devices characteristics. In this study, it’s found that TiO2 (Titanium dioxide) as a gate oxide layer exhibits better transfer and output I-V curve compared to the gate recessed MOS-HEMTs with Al2O3 (aluminum oxide). The maximum transconductance of 259mS/mm, an off-state breakdown voltage of 650V, and a small drain leakage current (≈10-9 mA/mm). Furthermore, the Pt (platinum) substitute for Ni (nickel) as metal gate that threshold voltage can be increased to 1.3V.