Figure 6. Benchmark of VO₂ thin films.

(a) Temperature-dependent resistivity of VO₂ films grown under optimized condition on a 3-inch r plane Al₂O₃. Measurement was taken at the wafer center. (b) Benchmark of resistivity ratios Δρ/ρ=(ρ_50 °C−ρ_80 °C)/ρ_80 °C for VO₂ across the metal-to-insulator transition. Note that the low temperature resistivity was taken at 50 °C. For a direct comparison, all films were grown on Al₂O₃ substrates above the critical films thickness. The blue-shaded area indicates the highest values reported for VO₂ films on sapphire and typical values obtained in bulk single crystals. A dotted line was added as guide to the eye. Note the two PLD samples with resistivity ratios higher than Δρ/ρ=10³ at film thicknesses <25 nm, from ref. 21. A thickness much >200 nm was estimated for the VO₂ films grown by PLD in ref. 57 and the data were added as ‘bulk' value. Data for bulk VO₂ were taken from refs 47, 48, 49, 50, 51, 52, 53. Properties of VO₂ films on Al₂O₃ substrate grown by PLD were taken from refs 21, 42, 52, 53, 54, 55, 56, 57, MOCVD from refs 58, 59, MBE from ref. 27 and sputtering from refs 8, 23, 25, 60, 61, 62, 63.