Fabrication and Device Characterization of Omega-Shaped-Gate ZnO Nanowire Field-Effect Transistors

TLDR

Omega‑shaped‑gate nanowire FETs are expected to outperform conventional gate geometries, attracting recent interest. The authors fabricated OSG FETs on oxidized Si by photolithographically defining ZnO nanowire channels (~110 nm), coating them with Al₂O₃ as gate dielectric, and covering ~80 % of the surface with gate metal. A representative device achieved 30.2 cm² V⁻¹ s⁻¹ mobility, 0.4 µS peak transconductance at Vg = –2.2 V, and an Ion/Ioff ratio of 10⁷, surpassing prior nanowire FETs and improving mobility, transconductance, and Ion/Ioff by 3.5×, 32×, and 106× over a back‑gate counterpart.

Abstract

Omega-shaped-gate (OSG) nanowire-based field effect transistors (FETs) have attracted a great deal of attention recently, because theoretical simulations predicted that they should have a higher device performance than nanowire-based FETs with other gate geometries. OSG FETs with channels composed of ZnO nanowires were successfully fabricated in this study using photolithographic processes. In the OSG FETs fabricated on oxidized Si substrates, the channels composed of ZnO nanowires with diameters of about 110 nm are coated with Al2O3 using atomic layer deposition, which surrounds the channels and acts as a gate dielectric. About 80% of the surfaces of the nanowires coated with Al2O3 are covered with the gate metal to form OSG FETs. A representative OSG FET fabricated in this study exhibits a mobility of 30.2 cm2/ (V s), a peak transconductance of 0.4 μS (Vg = −2.2 V), and an Ion/Ioff ratio of 107. To the best of our knowledge, the value of the Ion/Ioff ratio obtained from this OSG FET is higher than that of any of the previously reported nanowire-based FETs. Its mobility, peak transconductance, and Ion/Ioff ratio are remarkably enhanced by 3.5, 32, and 106 times, respectively, compared with a back-gate FET with the same ZnO nanowire channel as utilized in the OSG FET.