Characterization and Study of Two Dimensional Material Molybdenum Disulfide Thin Film Transistors with High-k Gate Dielectric
Date Issued
2015
Date
2015
Author(s)
Huang, Zheng-Jie
Abstract
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.
Subjects
molybdenum disulfide (MoS2) thin film transistor
high-k insulator
aluminium oxide (Al2O3)
hafnium oxide (HfO2)
hysteresis effect
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-104-R02943079-1.pdf
Size
23.32 KB
Format
Adobe PDF
Checksum
(MD5):9792326d11f3d9e184420cc41901d75c