Modulation of Electric Field in Metal Insulator Transition(MIT) of VO₂ Thin Film by Manipulating the Interface

Metal to insulator transition (MIT) in VO₂ is a notable phenomenon which makes it a versatile material to be utilized for infrared detection, electronic and resistive switches, smart windows, etc [1]. Temperature is one stimulus which triggers the MIT, while electric field is also other stimuli which can trigger the transition but at a much lower temperature [2]. However, at room temperature alone VO₂ requires higher electric field for transition which restricts its application in low power electronic devices. TiO₂ in rutile phase plays a major role in interfacial strain engineering for VO₂/TiO₂heterostructures and facilitates the modulation of transition electric field, transition temperature, magnitude of resistance change and potentially lowers the required electric field of transition [3]. In this work, attempt has been made to reduce the MIT electric field using TiO₂ as an interfacial layer. Studies were conducted on two different systems, namely VO₂/Al₂O₃and VO₂/TiO₂/Al₂O₃. Here, the VO₂ and TiO₂ were deposited on sapphire substrate (0001) using the pulse laser deposition (PLD) technique [4]. X-ray diffraction (XRD) was performed in order to observe the phase formation and growth direction in both systems. Additionally, temperature dependent in situ XRD was performed to analyse the structural phase transition from monoclinic (M1) phase (at room temperature) to tetragonal (T) phase above 68^oC [5] . Further electrical characterization was also carried out for both the samples in two different configurations i.e. with in-plane and out of plane contacts. Temperature dependent resistance measurement was done to observe the order of change in resistance at MIT for both the systems. Out of all four configurations, the VO₂/TiO₂/Al₂O₃in plane contact configuration showed the highest change in magnitude of resistance. Subsequently, the effect of TiO₂ was observed on transition voltage from I-V measurements at temperatures ranged between 20^oC to 80^oC. Further, the VO₂/TiO₂/Al₂O₃in-plane contact configuration showed transition at the lowest electric field i.e. 1.4MV/m. This indicates that VO₂/TiO₂/Al₂O₃in plane contact configuration is superior to the VO₂/TiO₂/Al₂O₃out of plane configuration and VO₂/Al₂O₃system in terms electric field and magnitude of resistance change. Lowering in electric field may be attributed to Poole–Frenkel effect or the joule heating at the VO₂-TiO₂ junction. Therefore, the VO₂ deposited on TiO₂ interface of sapphire can be used in resistive memory devices and other low powered sensors.<br/>References:<br/>[1] S. A. Bukhari, S. Kumar, P. Kumar, S.P. Gumfekar, H.J. Chung, T. Thundat, A. Goswami, “The effect of oxygen flow rate on metal–insulator transition (MIT) characteristics of vanadium dioxide (VO₂) thin films by pulsed laser deposition (PLD),” <i>Appl. Surf. Sci.</i>, vol. 529, no. April, p. 146995, 2020.<br/>[2] S. Jessadaluk, N. Khemasiri, P. Rattanawarinchai, S. Rahong, A. Rangkasikorn, N. Kayunkid, S. Wirunchit, A. Klamchuen, J. Nukeaw, “A tunable thermal switching device based on Joule heating-induced metal-insulator transition in VO₂ thin films via an external electric field,” <i>Jpn. J. Appl. Phys.</i>, vol. 58, no. SD, 2019.<br/>[3] E. Breckenfeld, H. Kim, K. Burgess, N. Charipar, S.F. Cheng, R. Stroud, A. Pique, “Strain effects in epitaxial VO2 thin films on columnar buffer-layer TiO2/Al2O3 virtual substrates,” <i>ACS Appl. Mater. Interfaces</i>, vol. 9, no. 2, pp. 1577–1584, 2017.<br/>[4] D. Bhardwaj, A. Goswami, and A. M. Umarji, “Synthesis of phase pure vanadium dioxide (VO2) thin film by reactive pulsed laser deposition,” <i>J. Appl. Phys.</i>, vol. 124, no. 13, 2018.<br/>[5] R. McGee, A. Goswami, S. Pal, K. Schofield, S. A. M. Bukhari, and T. Thundat, “Sharpness and intensity modulation of the metal-insulator transition in ultrathin VO2 films by interfacial structure manipulation,” <i>Phys. Rev. Mater.</i>, vol. 2, no. 3, pp. 1–10, 2018.