Improved Gate Dielectric Deposition and Enhanced Electrical Stability for Single-Layer MoS2 MOSFET with an AlN Interfacial Layer.

Qingkai Qian,Zhaofu Zhang,Mengyuan Hua,Yongkuan Xu,Kevin J Chen,Feifei Lan,Baikui Li,Ruyue Yan

doi:10.1038/srep27676

Abstract

Transistors based on MoS2 and other TMDs have been widely studied. The dangling-bond free surface of MoS2 has made the deposition of high-quality high-k dielectrics on MoS2 a challenge. The resulted transistors often suffer from the threshold voltage instability induced by the high density traps near MoS2/dielectric interface or inside the gate dielectric, which is detrimental for the practical applications of MoS2 metal-oxide-semiconductor field-effect transistor (MOSFET). In this work, by using AlN deposited by plasma enhanced atomic layer deposition (PEALD) as an interfacial layer, top-gate dielectrics as thin as 6 nm for single-layer MoS2 transistors are demonstrated. The AlN interfacial layer not only promotes the conformal deposition of high-quality Al2O3 on the dangling-bond free MoS2, but also greatly enhances the electrical stability of the MoS2 transistors. Very small hysteresis (ΔVth) is observed even at large gate biases and high temperatures. The transistor also exhibits a low level of flicker noise, which clearly originates from the Hooge mobility fluctuation instead of the carrier number fluctuation. The observed superior electrical stability of MoS2 transistor is attributed to the low border trap density of the AlN interfacial layer, as well as the small gate leakage and high dielectric strength of AlN/Al2O3 dielectric stack.

Highlights

Molybdenum disulfide (MoS2), as a layered material from the transition metal dichalcogenide (TMD) family, has been widely studied in recent years[1,2,3], for its intriguing properties such as atomic-layer thickness, tunable bandgap[4], high mobility[3] and good thermal stability[1]
We report the experimental demonstration of single-layer MoS2 MOSFETs with aluminum nitride (AlN)/Al2O3 as top-gate dielectric
Gate dielectrics scaling down to 6 nm on the dangling-bond free MoS2 are realized by the insertion of AlN interfacial layer

Summary

Introduction

Molybdenum disulfide (MoS2), as a layered material from the transition metal dichalcogenide (TMD) family, has been widely studied in recent years[1,2,3], for its intriguing properties such as atomic-layer thickness, tunable bandgap[4], high mobility[3] and good thermal stability[1]. As reported previously, when exposed to air, the MoS2 MOSFETs could exhibit large performance variation in terms of large shift in threshold voltage (i.e. hysteresis), due to the water or oxygen adsorbates[18,19]. This threshold voltage instability (ΔVth) is detrimental to both logic and analog circuit applications. MoS2 MOSFETs still exhibit significant hysteresis problem[7,26], due to high-density traps at MoS2/dielectric interface or in the gate dielectric. The observed excellent threshold voltage stability is contributed by the low border trap density of AlN near the MoS2 interface, as well as the small gate leakage and high dielectric strength of AlN/Al2O3

Methods

Results

Conclusion