Journal
NANOTECHNOLOGY
Volume 29, Issue 34, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/1361-6528/aac853
Keywords
few-layered MoS2; field-effect transistors (FET); high-k dielectric screening; high-k encapsulation
Funding
- National Natural Science Foundation of China [61774064]
- Fundamental Research Funds for the Central Universities [2015TS042]
- RGC of HKSAR, China [PolyU 252013/14E]
- University Development Fund of the Hong Kong Polytechnic University [1-ZVB1]
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The carrier mobility of MoS2 transistors can be greatly improved by the screening role of high-k gate dielectric. In this work, atomic-layer deposited (ALD) HfO2 annealed in NH3 is used to replace SiO2 as the gate dielectric to fabricate back-gated few-layered MoS2 transistors, and good electrical properties are achieved with field-effect mobility (mu) of 19.1 cm(2) V-1 s(-1), subthreshold swing (SS) of 123.6 mV dec(-1) and on/off ratio of 3.76 x 10(5). Furthermore, enhanced device performance is obtained when the surface of the MoS2 channel is coated by an ALD HfO2 layer with different thicknesses (10, 15 and 20 nm), where the transistor with a 15 nm HfO2 encapsulation layer exhibits the best overall electrical properties: it = 42.1 cm(2) V-1 s(-1), SS = 87.9 mV dec(-1) and on/off ratio of 2.72 x 10(6). These improvements should be associated with the enhanced screening effect on charged-impurity scattering and protection from absorption of environmental gas molecules by the high-k encapsulation. The capacitance equivalent thickness of the back-gate dielectric (HfO2) is only 6.58 nm, which is conducive to scaling of the MoS2 transistors.
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