化學氣相沉積石墨烯材料與單層石墨烯電晶體之研究

Abstract

石墨烯(Graphene)為一種二維材料，具有高導電性與高載子遷移率等特性，因此石墨烯被視為次世代電晶體的候選材料。本論文探討其材料特性與電晶體的電性表現，材料製備是利用化學氣相沉積於銅箔上成長石墨烯，再透過轉印的方式將石墨烯轉移到目標基板上。因為光學干涉的特性使石墨烯能在特定基板上以光學顯微鏡觀察，並透過拉曼頻譜的量測，可以分析石墨烯的厚度和品質。利用電流電壓量測和霍爾量測下，以化學氣相沉積成長的單層石墨烯具有2000 Ω/square的片電阻，其電洞載子遷移率為317 cm^2/V∙s，片電洞濃度為8.8×10^12 cm^(-2)，並在低溫霍爾量測下，得到活化能為24 meV。石墨烯與金屬的接觸阻抗是以TLM方式量測，其與Au/Ti的接觸電阻率為5.60×10^3 Ω∙μm，而與Au的接觸電阻率為6.65×10^2 Ω∙μm。 不同結構的電晶體設計於提升石墨烯電晶體的電性與製程的可靠性，通道上的保護層使場效載子遷移率從126 cm^2/V∙s 增加至226 cm^2/V∙s，而石墨烯最後轉印的方式減少了製程對石墨烯的影響，並提供更好的接觸阻抗，將場效載子遷移率提升至435 cm^2/V∙s。在降低了介電層的厚度後，閘極電場的控制能力增加，電流的開關比約為2.7倍，而量測的場效載子遷移率達834 cm^2/V∙s。

The characteristics of single-layer graphene material and transistors was discussed in this thesis. The graphene grown by chemical vapor deposition was transferred from Cu foil to the target substrate. The single-layer graphene is visible on specific substrate due to the light interference, and Raman spectroscopy was used to certify the thickness and the quality of the graphene. Measured by I-V measurement and Hall measurement, the sheet resistance is 2000 Ω/square, hole mobility is 317 cm^2/V∙s, and sheet hole concentration is 8.8×10^12 cm^(-2) for single-layer graphene. Hall measurement was conducted with varied temperature as well, and the activation energy of 24 meV was fitted. The contact resistivity was calculated by transmission line measurement, and it is 5.60×10^3 Ω∙μm and 6.65×10^2 Ω∙μm with the contact metal of Au/Ti and Au respectively. The transistors with different structure were fabricated to improve the electrical performance and the reliability of the procedures. Protection of channel and Graphene-last structure enhanced the field effect mobility from 126 cm^2/V∙s to 226 cm^2/V∙s and 435 cm^2/V∙s respectively. Furthermore, the insulator capacitance was increased with thinner dielectric layer. The on/off current ratio of 2.7 was observed, and the field effect mobility of 834 cm^2/V∙s was measured.