Abstract
Multilayer two-dimensional molybdenum disulfide (MoS2) field-effect transistors with Al2O3 or HfO2 as top gate dielectric and bottom passivation layer have been comparatively studied. The top-gated MoS2 transistor with Al2O3 as both top gate dielectric and bottom passivation layer exhibits excellent electrical characteristics with an on-off ratio of ∼106, a subthreshold swing of 97 mV dec−1, a low interface-trap density of 1.66×1012 cm−2eV−1, and a high field-effect mobility of 105 cm2 V−1 s−1. All these should be attributed to superior interface quality between Al2O3 top gate dielectric and MoS2, and enhanced dielectric screening effect due to Al2O3 bottom passivation layer.
Highlights
Molybdenum disulfide (MoS2) is one of the most promising two-dimensional (2-D) materials for making electronic switches due to its adjustable band gap (1.2 ∼ 2.6 eV) via film thickness and relatively high intrinsic electron mobility.1,2 MoS2-based fieldeffect transistors (FETs) have received tremendous attention because they provide an avenue to miniaturize the device into the atomic scale and reduce its power consumption.3 Xie et al.4 prepared monolayer MoS2 transistors which were free from short-channel effects and showed an on-off current ratio of > 4.5×107 and a field-effect mobility above 30 cm2V−1s−1
The electrical characteristics of the MoS2 transistors can be improved by high-κ gate dielectrics resulting from higher carrier density and stronger dielectric screening effect
Al2O3 or HfO2 grown by atomic layer deposition (ALD) has been employed as the gate dielectric of bottom-gated (BG) MoS2 FETs,8–12 or the encapsulation layer for the BG MoS2 transistors,27 or the backside passivation layer of top-gated (TG) MoS2 FETs,15,17,31 and enhanced field-effect mobility and improved subthreshold swing have been confirmed by experimental results
Summary
Molybdenum disulfide (MoS2) is one of the most promising two-dimensional (2-D) materials for making electronic switches due to its adjustable band gap (1.2 ∼ 2.6 eV) via film thickness and relatively high intrinsic electron mobility. MoS2-based fieldeffect transistors (FETs) have received tremendous attention because they provide an avenue to miniaturize the device into the atomic scale and reduce its power consumption. Xie et al. prepared monolayer MoS2 transistors which were free from short-channel effects and showed an on-off current ratio of > 4.5×107 and a field-effect mobility above 30 cm2V−1s−1. Al2O3 or HfO2 grown by atomic layer deposition (ALD) has been employed as the gate dielectric of bottom-gated (BG) MoS2 FETs, or the encapsulation layer for the BG MoS2 transistors, or the backside passivation layer of top-gated (TG) MoS2 FETs, and enhanced field-effect mobility and improved subthreshold swing have been confirmed by experimental results. Al2O3 or HfO2 applied as backside passivation layer or top-gate dielectric for the ML MoS2 transistor has not been comparatively studied. For the transistors, the MoS2 channel is fully encapsulated by 15-nm Al2O3, namely, Al2O3 acts both top gate dielectric and backside passivation, superior performance can be achieved, e.g. a subthreshold swing (SS) of 97 mV dec−1, an on-off current ratio of ∼ 106, a high field-effect mobility of 105 cm V−1 s−1, and a low interface-trap density of 1.66×1012 cm−2eV−1
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