Abstract
The integration of ultra-thin gate oxide, especially at sub-10 nm region, is one of the principle problems in MoS2 based transistors. In this work, we demonstrate sub-10 nm uniform deposition of Al2O3 on MoS2 basal plane by applying ultra-low energy remote oxygen plasma pretreatment prior to atomic layer deposition. It is demonstrated that oxygen species in ultra-low energy plasma are physically adsorbed on MoS2 surfaces without making the flakes oxidized, and is capable of benefiting the mobility of MoS2 flake. Based on this method, top-gated MoS2 transistor with ultrathin Al2O3 dielectric is fabricated. With 6.6 nm Al2O3 as gate dielectric, the device shows gate leakage about 0.1 pA/μm2 at 4.5 MV/cm which is much lower than previous reports. Besides, the top-gated device shows great on/off ratio of over 108, subthreshold swing (SS) of 101 mV/dec and a mobility of 28 cm2/Vs. With further investigations and careful optimizations, this method can play an important role in future nanoelectronics.
Highlights
The integration of ultra-thin gate oxide, especially at sub-10 nm region, is one of the principle problems in MoS2 based transistors
Because of its ultrathin nature, single-layer MoS2 transistors are advantageous in nanometer-scale metal oxide semiconductor field-effect transistors (MOSFETs) as they are immune to short-channel effects[8]
To achieve uniform atomic layer deposition (ALD) Al2O3 growth on pristine MoS2, functionalization of the MoS2 surface is required to introduce uniform surface groups that serve as active nucleation sites for the ALD process[21,23]
Summary
The integration of ultra-thin gate oxide, especially at sub-10 nm region, is one of the principle problems in MoS2 based transistors. It is demonstrated that oxygen species in ultra-low energy plasma are physically adsorbed on MoS2 surfaces without making the flakes oxidized, and is capable of benefiting the mobility of MoS2 flake Based on this method, top-gated MoS2 transistor with ultrathin Al2O3 dielectric is fabricated. Even though uniform atomic layer deposition (ALD) process of Al2O3 on MoS2 at 200 °C has been reported by Liu et al.[19], leading to the suggestion that direct nucleation of precursors on MoS2 may be feasible, other works have shown that with pristine MoS2 flakes the direct deposition of high-κ dielectrics form island-like clusters, owing to the absence of dangling bonds on MoS2 basal plane[20,21]. Most of the work just stopped at the early stage of realizing uniform growth without exploring the impacts of surface functionalization on devices performance, especially on gate leakage
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