Synthesis and Optimization of VO₂ Thin Films for Phase Transition Applications by Atomic Layer Deposition and RF Magnetron Sputtering

Author

Madhavi Tangirala, Old Dominion University

Date of Award

Fall 2013

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Electrical & Computer Engineering

Program/Concentration

Electrical Engineering

Committee Director

Helmut Baumgart

Committee Member

Gon Namkoong

Committee Member

Sylvain Marsillac

Call Number for Print

Special Collections LD4331.E55 T3552 2013

Abstract

Among many Vanadium oxides and suboxides, VO₂ has received considerable attention due to its remarkable metal-insulator transition (MIT) or semiconductor-metal transition (SMT) behavior, a reversible change in its electrical and optical properties that occurs due to a phase transition near a temperature of 68°C. Electrically, the resistivity of VO₂ can be changed as large as 4-5 orders of magnitude. Optically, the transmittance drops dramatically above the transition temperature in the metallic state where the VO₂ film becomes highly reflective in the infrared region. All these properties result in structural phase transformation from a low temperature monoclinic to high temperature tetragonal rutile crystal phase above the transition temperature of 68°C. VO₂ is a thermochromic material which can be employed in smart windows. Therefore, VO₂ has the potential to be used in nonvolatile resistive memories, switches in microelectronics and optical sensors.

VO₂ films have been prepared earlier using many techniques. Recently, atomic layer deposition (ALO) has been extensively investigated to deposit thin films or complex nanostructures with exceptional conformity, controlled thickness and uniformity. Tetrakis [ethylmethylamino] Vanadium was the novel metal-organic ALD precursor used to synthesize VO₂films. Vanadium oxide thin films were grown on Si (100) wafers using the Savannah 100 ALD cross flow reactor system. The technical challenge is the fact that Vanadium oxide thin films obtained by the ALD process are mostly in the V20₅ phase and the thin films are amorphous since the growth temperature is lower than the crystallizing temperature. The solution for this challenge is to employ post thermal heat treatment in a carefully controlled atmosphere in order to achieve re­ crystallization and reduction to stoichiometric polycrystalline VO₂ structure.

For benchmarking of film properties, VO₂ films were also fabricated by oxidizing RF magnetron sputtered Vanadium metal thin films. The post deposition annealing was carried out in a furnace with an accurately controlled mixture of N₂+o₂ at low pressure in order to oxidize the Vanadium metal to synthesize the desired stoichiometric VO₂ thin films. Structural characterization of the resulting Vanadium oxide films has been performed by using XRD, AFM, TEM and FE-SEM.

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DOI

10.25777/cf8v-bw56

Recommended Citation

Tangirala, Madhavi. "Synthesis and Optimization of VO₂ Thin Films for Phase Transition Applications by Atomic Layer Deposition and RF Magnetron Sputtering" (2013). Master of Science (MS), Thesis, Electrical & Computer Engineering, Old Dominion University, DOI: 10.25777/cf8v-bw56
https://digitalcommons.odu.edu/ece_etds/538