Phase Change Material VO₂/Iridium/Yttria-Stabilized Zirconia Heterostructures on Silicon

External parameters like temperature, strain and electric fields can be employed to control the metal-insulator phase transition (MIT) of the strongly electron-correlated material vanadium dioxide (VO₂). This MIT is accompanied by an enormous decrease in electrical resistivity and optical transmittance in the infrared spectral region and especially the telecom window. VO₂ is thus a very promising material for hybrid optoelectronic integrated circuits [1,2]. In order to use its properties for introducing new functionality in integrated circuits based on silicon, high quality thin VO₂ films on dielectric and metallic layers are of importance.<br/>In this work, we demonstrate epitaxial growth of VO₂ on yttria-stabilized zirconia (YSZ) and a layer stack of iridium/YSZ epitaxially grown on (001)-silicon, where the iridium layer forms a backside metallization that is used as a capacitor plate and areal contact to the VO₂ layer on top. The heterostuctures were fabricated in the following way: at first, a dielectric and electrically insulating YSZ template-layer was grown epitaxially on a (001)-silicon substrate [3], followed by the growth of the VO₂ thin film, both deposited by pulsed laser deposition. Similarly, the VO₂/Iridium/YSZ heterostructure was grown, except that the iridium layer was grown ex-situ by e-beam evaporation [4,5]. The iridium layer provides a highly electrically conducting electrode allowing building capacitor structures with VO₂ to control the MIT by electric fields and to build vertical electronic switching devices for very fast sensing applications and current control.<br/>The YSZ template-layer inhibits silicide formation by blocking diffusion of the cations to the YSZ/Si interface. Pole figures, reciprocal space maps and temperature dependent µ-Raman spectroscopy measurements reveal (010)-oriented VO₂ layers with 30° in-plane rotated crystallites and high symmetry grain boundaries on both the (001) iridium/YSZ double layer and YSZ template-layer.<br/>Based on these multilayers metal/VO₂/iridium capacitor structures on silicon were fabricated and the effect of an electric field on the MIT were studied by µ-Raman spectroscopy and spectral reflectivity measurements.<br/><br/>[1] Jostmeier Th., et al., Optically imprinted reconfigurable photonic elements in a VO₂ nanocomposite. Applied Physics Letters 105, (2014).<br/>[2] John J., et al., Multipolar resonances with designer tunability using VO₂ phase-change materials. Physical Review Applied 13, 044053 (2020).<br/>[3] Karl H., Hartmann J. and Stritzker B., Inplane lattice-constant relaxation during laser-ablation of YBCO and yttria-stabilized zirconia. Thin Solid Films 241, 84–87 (1994).<br/>[4] Fischer, et al., Preparation of 4-Inch Ir/YSZ/Si(001) substrates for the large-area deposition of single-crystal diamond. Diamond and Related Materials 17, 1035–1038 (2008).<br/>[5] Kraus T., et al., Yttria-stabilized zirconia buffered silicon to optimize in-plane electrical conductivity of [Ca₂CoO₃]_0.62[CoO₂] thin films. Appl. Phys. Lett. 104, 183104 (2014).