Paper TF+EM-WeA11
Deposition Process for Vanadium Dioxide Thin Films for RF Applications

Wednesday, October 23, 2019, 5:40 pm, Room A122-123

Phase change materials (PCM) are attractive due their tunability, wide range of applications, and quasi-passive actuation as compared to traditional active integrated circuits. Vanadium dioxide (VO₂) is particularly appealing because of its high contrast between dielectric and conductive states and the relatively low temperature (68 °C) at which its metal-insulator transition (MIT) occurs. This work details a process for depositing high quality VO₂ thin films on C-plane sapphire wafers as well as alumina (Al₂O₃) buffer layers using atomic layer deposition (ALD) on silicon substrates. We compare resistivity vs. temperature measurements of VO₂ on sapphire with VO₂ on the Al₂O₃ buffer layers both as-deposited and after rapid thermal annealing (RTA) at temperatures ranging from 950 to 1150°C. The VO₂ thin films yielded ratios of resistivity between conductor (heated) and dielectric (room temperature) states of 9.8×10⁴ Ω-cm, 5.2×10³ Ω-cm, and 1.5×10⁴ Ω-cm when deposited on crystalline sapphire, amorphous Al₂O₃ buffer layers, and annealed Al₂O₃ buffer layers, respectively. This corresponds to an improvement by a factor of 2.9 in the annealed buffer layers over the amorphous buffer layers. Moreover, we studied various VO₂ thin films using X-ray diffraction, which showed clear indications that the films are highly pure and have a preferred crystal orientation. The deposition process we have developed will allow us to use high quality VO₂ thin films on silicon substrates, especially millimeter-wave devices such as reconfigurable antennas, sensors, and meta-surfaces.