Fabrication and Electrical Characteristics of ZnSnO/Si Bilayer Tunneling Filed-Effect Transistors

Kimihiko Kato,Hitoshi Tabata,Mitsuru Takenaka,Hiroaki Matsui,Shinichi Takagi

doi:10.1109/jeds.2019.2933848

Abstract

We demonstrate improvement of electrical characteristics of a bilayer tunneling field effect transistor (TFET) composed of an n-type zinc-tin-oxide (ZnSnO) channel with superior thickness uniformity and a p-type Si source. Careful optimization of the deposition condition of the ZnSnO layer leads to the significant improvement of the thickness uniformity thanks to its amorphous structure. It is promising to reduce the average sub-threshold swing ( ${S}$ . ${S}$ .) of the bilayer TFET. The average ${S}$ . ${S}$ . of the amorphous ZnSnO/Si TFET is 87 mV/dec. in a gate voltage swing of 0.3 V, which is lower by 30% than that of the poly-crystalline ZnO/Si TFET with the rough surface. The minimum ${S}$ . ${S}$ . value of 80 mV/dec. in the ZnSnO/Si TFET is similar to that in the ZnO/Si TFET. Additionally, the ZnSnO/Si TFET has realized the increase in on-state current ( ${I} _{\mathrm{ on}}$ ) and the achieved ${I} _{\mathrm{ on}}$ of 1.7 $\mu \text{A}/\mu \text{m}$ is approximately 8 times higher than that of the ZnO/Si TFET. We also found that the ZnSnO/Si TFET shows the stronger temperature dependence of both ${I} _{\mathrm{ on}}$ and ${S}$ . ${S}$ . than the ZnO/Si TFET. These differences in the electrical characteristics between ZnSnO and ZnO TFETs are discussed in terms of the amorphous and ploy-crystalline natures of the OS channels.

Highlights

Tunneling field effect transistors (TFETs) attract much attention as a steep switching transistor in order to effectively reduce power consumption by reducing operating voltage
In order to combine these structural and material approaches, we have recently proposed a bilayer TFET structure which is composed of an n-type oxide semiconductor (n-OS) channel and a p-type group-IV semiconductor (p-IV) source [10]
Type-II energy band alignment is realized at this hetero tunneling junction, because the OS channel materials such as zinc-oxide (ZnO), tin-oxide (SnO2) and titaniumoxide (TiO2) generally have lower Ec compared to Si or Ge [11]–[13]

Summary

Introduction

Tunneling field effect transistors (TFETs) attract much attention as a steep switching transistor in order to effectively reduce power consumption by reducing operating voltage. MEASUREMENT TEMPERATURE DEPENDENCE OF ZN(SN)O/SI TFETS In order to understand the physical origin to limit the subthreshold characteristics of the Zn(Sn)O/Si bilayer TFETs, we evaluated the measurement temperature (Tmeas) dependence of the electrical characteristics of the fabricated TFETs. Figure 7 shows the Id-Vg characteristics of (a) the poly-crystalline ZnO/Si TFET (sample (A)) and (b) the amorphous ZnSnO/Si TFET (sample (C)), measured in the range from 25 ◦C to about 100 ◦C.

Results

Conclusion