Insulator–metal transition in substrate-independent VO2 thin film for phase-change devices

Abstract

Vanadium has 11 oxide phases, with the binary VO2 presenting stimuli-dependent phase transitions that manifest as switchable electronic and optical features. An elevated temperature induces an insulator–to–metal transition (IMT) as the crystal reorients from a monoclinic state (insulator) to a tetragonal arrangement (metallic). This transition is accompanied by a simultaneous change in optical properties making VO2 a versatile optoelectronic material. However, its deployment in scalable devices suffers because of the requirement of specialised substrates to retain the functionality of the material. Sensitivity to oxygen concentration and larger-scale VO2 synthesis have also been standing issues in VO2 fabrication. Here, we address these major challenges in harnessing the functionality in VO2 by demonstrating an approach that enables crystalline, switchable VO2 on any substrate. Glass, silicon, and quartz are used as model platforms to show the effectiveness of the process. Temperature-dependent electrical and optical characterisation is used demonstrating three to four orders of magnitude in resistive switching, >60% chromic discrimination at infrared wavelengths, and terahertz property extraction. This capability will significantly broaden the horizon of applications that have been envisioned but remained unrealised due to the lack of ability to realise VO2 on any substrate, thereby exploiting its untapped potential.

In Situ Nanostructural Analysis of Volatile Threshold Switching and Non‐Volatile Bipolar Resistive Switching in Mixed‐Phased a‐VOx Asymmetric Crossbars

“…After a couple of biasing cycles, a minor crystalline region is observed in the functional oxide. [19] This, to the best of our knowledge, is the first demonstration of a-VO 2 thin film crystallizing into localized c-VO 2 with electric bias. Here, the separation between fringes is 0.35 nm as shown in high resolution TEM (HRTEM) and FFT insets which corresponds to the (011) plane of VO 2 -M1 phase.…”

“…[19] X-ray Photoelectron Spectroscopy: XPS spectra of a-VO x thinfilms were collected with Thermo Scientific K-alpha instrument. Primary target used was vanadium (V), with a substrate of thermally-grown silicon dioxide (300 nm) on silicon (SiO 2 /Si).…”

“…In situ electrical biasing is performed with controlled voltages starting from 25 mV in the steps of 20 mV with bottom electrode (BE) positively biased and top electrode (TE) grounded. [19,20] to show temperature-dependent IMT at 68 °C. At 4 V clear localized crystalline region is observed as shown in Figure 4b.…”

Selective IR response of highly textured phase change VO2 nanostructures obtained via oxidation of electron beam deposited metallic V films

“…VO 2 can be synthesized both in bulk powder form as well as in thin film form. As the latter is more suitable option for a variety of applications pertaining to device design and surfaces, many groups have investigated the growth of VO 2 films using pulsed laser deposition (PLD) [16,17], magnetron sputtering [18][19][20][21][22], molecular beam epitaxy (MBE) [23], e-beam deposition [24][25][26], sol-gel [27][28][29][30][31][32] and CVD [33][34][35][36][37][38] methods. Some of these attempts also focused on the effect of strain via the choice of the substrate on the phase transition characteristics of this system [39][40][41][42][43][44], while there was at least one work attempting to utilize the MBE method that is known for small scale film growth to obtain high quality VO 2 films on large area substrate [45].…”

A Photonic Switch Based on a Hybrid Combination of Metallic Nanoholes and Phase-change Vanadium Dioxide

“…Post-deposition annealing at low pressure enhances the level of control over oxygen vacancies and limits oxygen loss, which happens at a rapid rate in VO 2 thin films. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and micro-Raman spectroscopy were conducted to characterize the VO 2 thin films 57 . The thin films showed good insulator–metal transition, as expected at ~68 °C for the VO 2 phase of vanadium oxide 57 .…”