轉貼法二硫化鉬場效電晶體製程技術開發及特性改善之研究

Abstract

二維層狀過渡金屬硫屬化物近年來受密切關注，MoS2(二硫化鉬)也是其中之一，主要是用於通道材料且其擁有高電流開關比與高電子遷移率，然而，過高的接觸電阻限制了MoS2場效電晶體的電性且達到良好的歐姆接觸目前仍然是個挑戰，研究顯示MoS2場效電晶體是個蕭基能障電晶體，可由蕭基能障高度控制其電晶體特性，因此，很多研究聚焦在使用不同接觸金屬，然而多數研究顯示仍有無法忽視的蕭基能障存在，因此穩定且有效率降低接觸電阻的方法對於MoS2場效電晶體的製程十分重要。 本研究建立了一套穩定的轉貼法二維材料場效電晶體製程，此外，本論文展示了一些改善特性的嘗試，首先是使用氬電漿處理增加表面硫空位以增加二硫化鉬(MoS2)場效電晶體N型特性，電流提升了10倍。再者，使用氯化物參雜的方式增加表面電子濃度以提升電子穿隧機率藉此提高電流，電流從0.1µA/µm (微安培/微米)提升到了13µA/µm，有百倍以上的提升。最後，聚甲基丙烯酸甲酯(PMMA)被用於格絕電晶體於大氣環境以防止MoS2氧化以及參雜的逸散。

Transition metal dichalcogenides (TMDCs) materials attract many attention recently, and MoS2 is one of them. MoS2 has been used as a channel material, and owns high Ion/Ioff ratio and high mobility. However, high contact resistance (Rc) limits the electrical performance of MoS2 FETs and the achievement of Ohmic contacts for MoS2 stays a challenge so far. Recent studies reveals that the MoS2 FETs are basically a Schottky barrier transistor whose transistor characteristics is controlled by varying the Schottky barrier height. Therefore, a lot of research has focused on the contact metal. Furthermore, most of these reports still showed a non-negligible Schottky barrier height which result from fermi-level pinning. A stable and effective method to reduce the contact resistance is quite essential in fabricating a functional MoS2 FETs. In this study, a stable fabrication process of exfoliated 2D material FETs was established, and it could be an important foundation of our 2D material research. Also, this thesis demonstrates our attempts to achieve a good performance MoS2 FETs. First, the Argon treatment is used to increase the sulfur vacancies to lead to n-type behavior of the MoS2 FET. The on-current is enhanced from 25 nA/µm to 250 nA/µm. Second, the chloride doping method is also adopted to increase the electron densities which induce the Schottky barrier thinning to raise the possibility of electron tunneling. The on-current is enhanced from 0.1 µA/µm to 13 µA/µm which owns 2 order improvement. Finally, the PMMA is used to passivate our device from ambient environment to avoid the MoS2 oxidizing and dopant escaping.