高介電係數閘極氧化層應用於二維材料二硫化鉬薄膜電晶體特性和探討

Characterization and Study of Two Dimensional Material Molybdenum Disulfide Thin Film Transistors with High-k Gate Dielectric

黃政傑(Zheng-Jie Huang)

指導教授 ： 李嗣涔

國立臺灣大學/電機資訊學院/電子工程學研究所/碩士(2015年)

https://doi.org/10.6342/NTU.2015.01062

摘要

本論文使用機械剝離法分離出擁有奈米級厚度的二硫化鉬，並製作出薄膜電晶體。利用光學顯微鏡及原子力顯微鏡的搭配篩選出較佳厚度範圍的二硫化鉬，並搭配使用低功函數金屬鈦當作金屬電極來達成歐姆接觸。電晶體的表現可以達到電流開關比為8數量級的電晶體，場效電子遷移率可以達到約16cm2/V-sec。傳統上為了有好的光干涉條件以辨別二硫化鉬膜厚度，使用約300奈米的二氧化矽，導致閘極控制電壓過高，所以此篇論文使用更薄的高介電係數氧化層氧化鋁當作閘極介電層，發現製作出來的薄膜電晶體有很好的特性，電流開關比也可達到6×107的數量級，場效電子遷移率可以達到約23cm2/V-sec，而使用氧化鉿作閘極介電層之薄膜電晶體更可達到電子遷移率約28cm2/V-sec，次臨界擺幅可以降低至127mV/dec，閘極電壓降到±1V，達到更佳的電性。
另外在本論文中還發現在空氣中，二硫化鉬在表面會明顯的物理吸附水氣和氧分子，導致元件操作穩定度下降，以及更嚴重的遲滯效應。透過真空量測和保護層的方法，可以明顯降低此種現象。

關鍵字

二硫化鉬薄膜電晶體 ； 高介電係數氧化層 ； 氧化鋁 ； 二氧化鉿 ； 遲滯效應

並列摘要

In this thesis, the mechanically exfoliated 2D material MoS2 nanosheet was used to fabricate thin film transistor and their electrical properties were investigated as well. By checking their thickness by optical microscopy and atomic force microscopy, the nanosheet with an appropriate thickness can be selected. It was found that the ohmic contact on MoS2 can be achieved by low work function metal titanium. The performance of TFTs achieved the high on/off current ratio up to 8 th order of magnitude and the mobility of 16 cm2/V-sec. However, in order to identify MoS2 thickness on SiO2/Si substrate by means of better optical interference, the thickness of silicon dioxide was limited to 300nm thick. The thick oxide lead to very high gate control voltage. To reduce the operation voltage, the use of thinner high-k gate dielectric Al2O3 and HfO2 were used, resulting in much better performances than traditional SiO2. The on/off current ratio for Al2O3 gate insulator thin film transistor was 6×107 and mobility of 23 cm2/V-sec. HfO2 gate insulator could even boost the mobility to 28 cm2/V-sec and the sub-threshold swing to only 127mV/dec, combining with the gate operation voltage below ±1 V.
In addition, it was also found that the oxygen and water molecules were easily absorbed at the MoS2 surface in air, which would deteriorate the stability and hysteresis of devices. Finally, the high vacuum measurement method and passivation layer were used to improve the stability.

並列關鍵字

molybdenum disulfide (MoS2) thin film transistor ； high-k insulator ； aluminium oxide (Al2O3) ； hafnium oxide (HfO2) ； hysteresis effect

參考文獻

[1] Novoselov, K. S. et al. Science, 306, 666–669(2004).

[2] F. Schwierz, Nature Nanotechnology, Vol. 5, 487 (2010)

[3] Radisavljevic, B.; Radenovic, A.; Brivio, J.; Giacometti, V.; Kis, A.

Nat. Nanotechnol. 6, 147-150(2011).

[4] Wilson, J. A.; Yoffe, A. D, Adv. Phys. 1969, 18, 193–335.