High-contrast, highly textured VO2 thin films integrated on silicon substrates using annealed Al2O3 buffer layers

Abstract

We present vanadium dioxide (VO2) thin films having high resistivity contrast with silicon substrates through use of crystallized alumina (Al2O3) buffer layers, engineered for this purpose. We first optimized the process by depositing VO2 onto C-plane sapphire substrates prior to alumina thin films. The latter of which were grown via atomic layer deposition on silicon substrates. We then applied rapid thermal annealing (RTA) to crystallize the alumina films. Scanning electron microscopy results indicated a thickness of 107 nm for each VO2 film, which yielded hot–cold resistivity contrast ratios of 9.76 × 104, 1.46 × 104, and 3.66 × 103, when deposited on the C-plane sapphire, the annealed buffers, and the as-deposited alumina buffers, respectively. Atomic force microscopy of the film surface roughness of the VO2 films indicated root mean squared roughness (Rq) of 4.56 nm, 6.79 nm, and 3.30 nm, respectively, for the films grown on the C-plane sapphire, annealed buffers, and as-deposited buffers. Finally, x-ray diffraction (XRD) of the VO2 films indicated the desired composition and strong (0h0)/(00h) texturing, when deposited on both the C-plane sapphire and the annealed alumina buffer layers. XRD results indicated a series of peaks corresponding to the α-Al2O3/C-plane sapphire, and an XRD analysis of the buffers alone confirmed crystallization of the buffer layer via RTA. The process defined in this paper produced a series of highly textured VO2 films making them most valuable for the integration of VO2 with silicon-based devices.

Exploiting Nonlinear Properties of Vo2 in a Mmwave Antenna-Coupled Sensor

“…Thus, VO2 thin film whose electricity exhibiting a sharp change in the metal-insulator-transition (MIT) is appealing for a microbolometer to improve the responsivity. Especially, the TCR of VO2 in the MIT region in our previous study can reach up to 171%/K [8,9]. However, there are few studies demonstrating improved properties of microbolometer utilizing nonlinear properties of VO2.…”

“…Our previous studies analytically demonstrated the approaches to enhance the responsivity of the microbolometer by the utilization of VO2's nonlinearity in the MIT region and air suspension [9,13,14]. Also, the architecture of VO2 thin film on alumina (Al2O3) buffer layer by the atomic layer (ALD) technique is adopted in this report to design and fabricate the sensor [8]. The VO2 microbolometer is coupled with a dipole antenna and coplanar waveguide (CPW) designed to operate at 30 -60 GHz.…”

“…Vanadium dioxide (VO2) is an electrical phase change material that adopts insulating monoclinic (M1) phase (space group P21/c) below the transition temperature (~68 C) and metallic tetragonal rutile (R) phase (space group P42/mnm) above the transition temperature [5][6][7][8]. Thus, VO2 thin film whose electricity exhibiting a sharp change in the metal-insulator-transition (MIT) is appealing for a microbolometer to improve the responsivity.…”

Fabrication and Optical Characterization of VO2-Based Thin Films Deposited on Practical Float Glass by Magnetron Sputtering and Professional Annealing

“…This two-step technique was beneficial to improve the reproducibility and protect the sputtering equipment, but they did no further works in studies of substrates, visible transmittance improvement, doping, oxygen vacancies, and so on. Silicon [21], quartz [10,22], sapphire [10,23], and other materials are often used as substrates for depositing VO 2 film to achieve better phase transition performance. However, these substrates are expensive, difficult to obtain, and inconsistent with the actual glass used in windows and doors.…”

Local structure elucidation of tungsten-substituted vanadium dioxide (V$$_{1-x}$$W$$_x$$O$$_2$$)

“…Vanadium dioxide (VO ) undergoes a fully reversible metal-insulator transition (MIT) that drastically changes the structure and properties despite slight compositional 1 , thermal 2 , 3 , electrical 4 , 5 , or optical 6 , 7 perturbations. Across the MIT ( °C), VO ’s paramagnetic moment increases by nearly an order of magnitude 3 , the electrical conductivity increases by 4–5 orders of magnitude 8 , 9 depending on oxygen-vacancy concentration instigating V reduction 10 , and infrared transmittance decreases by almost an order of magnitude 11 , 12 . The MIT is concomitant with a structural phase transformation (SPT) from the low-temperature monoclinic structure 13 , , to the high-temperature tetragonal structure 14 , (Fig.…”