Modulation of conductive property in VO 2 nano-wires through an air gap-mediated electric field Tsubasa Sasaki (Tanaka-lab) 2013/10/30

Background Metal-insulator transition(MIT) of strongly-correlated electron(Mott) materials (ex. VO 2 ) Electric control of Mott transition Previous reports Purpose of my research W side gate FET Principle PLD, Nanoimprint Fabrication Experimental result Atomosphere dependence Chemical equation expected Laser Raman spectroscopy etc Summary Contents

Strongly-correlated electron materials VO 2 Metal-insulator transition New electronic devices ex) MottFET Electron phase transition is controlled by a gate terminal. Background Insulator Metal Stimulation Temperature Electric field Magnetic field Light

Gate DrainSource VGVG Insulating layer Drain current Electric control of Mott transition Insulator EFEF EFEF U Metal EFEF Lower Hubbard Band Upper Hubbard Band Charge injection effect Charge injection effect Redox effect Redox effect O 2- H+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 Al 2 O 3 sub. Electric field effect simulation Cross-sectional view Gate Channel Vacuum 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 Al 2 O 3 VO 2 Production of thin film V 2 O 5 Pulse laser depositon(PLD)

Production of structure A optical micrograph 4mm 0.5mm Nanoimprint

A VO 2 Pt Fabrication Source Drain Gate d L W PLD ( Thin films of VO 2 ) Nanoimprint ( Pattern formation of VO 2 ) RIE (Etching) Photolithography ( Electrode pattern formation ) Sputtering ( Pt electrode ) Source Drain Gate VO 2 channel

Large resistance change was observed only under the air Air N2N2 N2N2 Dry Air Dry Air Atmosphere dependence The factor is adsorbed water (H 2 O) I tried to apply a gate voltage under various atmosphere (Air, N 2 and Dry Air) Humidity :56% Memory effect Gradual resistance change

Anode : ( ) Cathode : ( ) O O O O O O H H H H H H H H H H e e e e Chanel (Cathode) Chanel (Cathode) - - Al 2 O 3 Gate (Anode) Gate (Anode) O O H H H H H H H H V 2 O 4+x/2 H x VO2 + + H H + H H + Chemical equation expected OO HH HH O O O O O O H H H H + H H Decrease of resistivity

VO 2 resistivity change in the air Air

gate-channel current The 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 N2N2 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 Annealed in a hydrogen atmosphere Hydrogenated Peak area of 600 cm-1 near Hydrogen ions are diffused over the entire channel width(3μm) gate channel

Large resistance change by hydrogen doped Insulator EFEF U Lower Hubbard Band Upper Hubbard Band EFEF Metal EFEF

Large resistance change was observed only in the air The factor is adsorbed water (H 2 O) Hydrogenation of VO 2 by the gate electric field Summary I was fabricated W side gate type FET structure Redox-controlled Mott transistor Redox-controlled Mott transistor Future plan Summary I will perform the SIMS measurement to confirm hydrogen existence in the VO 2 channel

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