Modulation of conductive property in VO2 nano-wires through an air

gap-mediated electric field

Tsubasa Sasaki(Tanaka-lab)2013/10/30

・ BackgroundMetal-insulator transition(MIT) of strongly-correlated electron(Mott) materials (ex. VO2)Electric control of Mott transitionPrevious reports

・ Purpose of my researchW side gate FET

・ PrinciplePLD , Nanoimprint

・ Fabrication・ Experimental result

Atomosphere dependenceChemical equation expectedLaser Raman spectroscopy etc

・ Summary

Contents

Strongly-correlated electron materials 　 VO2

Metal-insulator transition

New electronic devices　 ex) 　 MottFET ・・・ Electron phase transition is controlled by a gate terminal.

Background

Insulator Metal

Stimulation

TemperatureElectric fieldMagnetic fieldLight

GateDrainSource VG

Insulating layer

Drain current

Electric control of Mott transition

Insulator

EFEFU

Metal

EF

Lower Hubbard Band

Upper Hubbard Band

・ Charge injection effect

・ Redox effect

O2- H+

By applying an electric field,

Features of the transition metal oxide transistors Charge injection effect （ Mott-transistor ） Redox effect （ Redox-transistor: development of two-terminal ReRAM) 　　　

J. Jeong et al, Science 339,1402 (2013)

M. Nakano et al, Nature 487,459 (2012)

Previous reports

This time, I have found what using Redox effect.

Gate

Al2O3 sub.

電子相転移雪崩 電子相転移雪崩

Electric field effect simulation （ Cross-sectional view ）

Gate Channel

Vacuum

イオンマイグレーション イオンマイグレーション

W side gate type FET structure

Purpose

The physical-properties measurement which combined the probe

microscope etc. is possible.

Measurement by various gas environment is possible.

Advantage

Pulse laser deposition (PLD)

ArF （ λ=193nm ）レーザ

基板 レーザ

Al2O3

VO2

Production of thin film

基板

V2O5 焼結体

Pulse laser depositon(PLD)

Production of structure

A

optical micrograph

4mm

4mm

0.5mm

Nanoimprint

A

VO2

Pt

Fabrication

Source

Drain

GateGate d

LW

PLD (Thin films of VO2)

Nanoimprint 　　 (Pattern formation of

VO2)

RIE (Etching)

Photolithography 　 (Electrode pattern formation)

Sputtering 　　 (Pt electrode)

Source

Drain

GateGate

VO 2 channel

Large resistance change was observed only under the air

Air

N2

DryAir

Atmosphere dependence

The factor is adsorbed water 　 (H2O)

I tried to apply a gate voltage under various atmosphere 　(Air, N2 and Dry Air)

Humidity:56%

Memory effect

Gradual resistance change

V O2+𝑥2

H 2 O→ V 2 O4+

𝑥2

+𝑥H+ ¿¿Anode :( 陽極 )

Cathode :( 陰極 )

OO

OH H

H

HHe

eChanel

(Cathode)

--

Al2O3

Gate(Anode)

+++++

++----

-

OH HH

H

V2O4+x/2 HxVO2

++

H+

H+

Chemical equation expected

𝑦 H+ ¿+𝑦𝑒−→ 𝑦

2H 2¿

𝑦2

H 2O →𝑦4

O2+𝑦 H+¿+𝑦 𝑒−¿

●

●

●

●

O HH

OO

O

HH

+H

Decrease of resistivity

VO2 resistivity change in the air

Air

Mapping

0 10 20 30 40 500

20

40

60

80

I g-s

(pA

)

Vg (V)

in N2

in Air (humidity 60 )～ ％

gate-channel currentThe difference of gate-

channel current

The amount of current flowing along the water which is

adsorbed

The amount of movement of the H+ by electrolysis

N2

Air

Laser Raman spectroscopy

I believed that this is hydrogenated

Jiang Wei et al. Nature Nanotech 70, 357 (2012)

Peak of 199cm-1, 225cm-1, 618cm-1 decreased

0 100 200 300 400 500 600 700 800 900 1000

Inte

nsi

ty (a.

u.)

Raman shift (cm-1)

Hydrogenated VO2

Pure VO2

Annealed in a hydrogen atmosphere

30 35 40 45 50 55 60 65 700

200

400

600

800

Inte

nsity

(a.

u.)

distance (m)

20 25 30 35 40 45 50 55 60

0

200

400

600In

ten

sity

(a

.u.)

distance (m)

HydrogenatedPeak area of 600 cm-1 near

Hydrogen ions are diffused over the entire channel width(3μm)

gate gate gate gate

channelchannel

H 𝑥V O2

Large resistance change by hydrogen doped

Insulator

EF U

Lower Hubbard Band

Upper Hubbard Band

EF

Metal

EF

Large resistance change was observed only in the air⇒The factor is adsorbed water (H2O)⇒Hydrogenation of VO2 by the gate electric field

●

Summary

●

I was fabricated W side gate type FET structure

⇒Redox-controlled Mott transistor

Future plan

Summary

● I will perform the SIMS measurement to confirm hydrogen existence in the VO2 channel

Thank you for your attention