Thickness-Dependent Study of High- Performance WS2-FETs With Ultrascaled Channel Lengths

• Published in: IEEE transactions on electron devices 2021-04, Vol.68 (4), p.2123-2129
• Main Authors: Pang, Chin-Sheng, Wu, Peng, Appenzeller, Joerg, Chen, Zhihong
• Format: Article
• Language: English
• Subjects: Dielectrics; Distance measurement; Electrostatics; Field effect transistors; Hafnium oxide; Logic gates; n-field-effect transistor (FET); Performance evaluation; scaled effective oxide thickness (EOT); scaled LG; Thickness; Threshold voltage; WS
• ISSN: 0018-9383; 1557-9646
• DOI: 10.1109/TED.2021.3058078

Ultrascaled WS 2 field-effect transistors (FETs) fabricated on exfoliated multilayer channels with excellent ON-state and OFF-state performance are reported. Recorded high ON-state current ( {I}_{ \mathrm{\scriptscriptstyle ON}} ) and ultralow contact resistance ( {R}_{C} ) were achieved in a double-gated FET at a scaled overdrive voltage ( {V}_{OV}\boldsymbol = {V}_{GS}\boldsymbol -{V}_{TH} ), reaching >600 ( \boldsymbol \mu \text{A}/\boldsymbol \mu \text{m} ) normalized to footprint at {V}_{DS}\boldsymbol =1 V and {V}_{OV}\boldsymbol =2 V with a {R}_{C}~\sim ~500 ( \Omega \times \mu \text{m} ). We report statistics of more than 50 FETs with varying channel lengths, showing excellent OFF-state behavior with small threshold voltage ( {V}_{TH} ) variations, near-ideal subthreshold slope (SS), and small drain-induced barrier lowering (DIBL). Various channel thicknesses ( {T}_{CH} ) ranging from 2.1 to 7 nm were carefully evaluated in terms of short channel effects (SCEs) and ON-state current, and a WS 2 body thickness of 2.1 nm (three layers, the thinnest in our statistics) shows the best performance in both ON-state and OFF-state.