Improvement in Electrical Characteristics of ZnSnO/Si Bilayer TFET by W/Al₂O₃ Gate Stack

Kimihiko Kato,Hiroaki Matsui,Shinichi Takagi,Yukinori Morita,Takashi Matsukawa,Mitsuru Takenaka,Takahiro Mori,Hitoshi Tabata

doi:10.1109/jeds.2020.2982424

Abstract

We have examined impacts of gate insulator (Al2O3 or HfO2) and gate electrode (TiN or W) on electrical performance of ZnSnO/Si bilayer tunneling fieldeffect transistors (TFETs). It is found from the capacitance-voltage ( ${C}$ - ${V}$ ) characteristics that the W gate is effective to reduce the counter-clockwise hysteresis. Additionally, the optimal temperature of post-metallization annealing (PMA) is different for each gate stack, and this optimization is critically important for the high ON-state current ( ${I} _{\mathrm{ ON}}$ ) and steep ON/OFF switching. The W/Al2O3/ZnSnO/Si bilayer TFET provides the hysteresis-free steep ON/OFF switching with the minimum sub-threshold swing ( SS ) of 65.4 mV/dec. and average SS of 72.0 mV/dec. in a gate-voltage swing of 0.3 V, which are 19% and 18% lower than the control TiN/Al2O3/ZnSnO/Si bilayer TFET. When the gate stack is replaced by W/HfO2/Al2O3, the TFET exhibits less steep ON/OFF switching in spite of thinning capacitance equivalent thickness (CET) from 5.9 and 2.3 nm. These results indicate the importance of improvement in the gate stack quality on the sub-threshold characteristics of the bilayer TFETs.

Highlights

In order to increase ON-state current (ION) of tunneling field-effect transistors (TFETs) without increasing the OFFstate leakage current (IOFF), a hetero tunneling junction with type-II energy band alignment is promising because of the reduced effective tunneling barrier height [1]–[12]
We have proposed a bilayer TFET structure composed of the hetero-tunneling junction of an n-type oxide semiconductor (n-OS) and a p-type group-IV semiconductor (p-IV), which can realize the above two approaches at the same time [17]
We have experimentally demonstrated the TFET operation by utilizing ZnO/Si, ZnO/Ge [19], and ZnSnO/Si [20] bilayer TFET devices with a TiN/Al2O3 gate stack, where it has been confirmed that the source-to-drain current is dominated by tunneling current [19]

Summary

Introduction

In order to increase ON-state current (ION) of tunneling field-effect transistors (TFETs) without increasing the OFFstate leakage current (IOFF), a hetero tunneling junction with type-II energy band alignment is promising because of the reduced effective tunneling barrier height [1]–[12]. KATO et al.: IMPROVEMENT IN ELECTRICAL CHARACTERISTICS OF ZnSnO/Si BILAYER TFET BY W/Al2O3 GATE STACK

Results

Conclusion