Flexible Vanadium Dioxide Films and Devices on Kapton Fabricated With Low-Temperature Atmospheric Oxidation of Vanadium

Vanadium dioxide (VO2) is a functional material, attractive for many optical and electronic applications due to its reversible insulator to metal phase transition. The synthesis of VO2 often involves high-temperature processes originating from the complex nature of the V-O system. In this work, we report the synthesis of VO2 on a flexible Kapton substrate using a low-temperature atmospheric thermal oxidation process. The synthesized VO2 film shows ~3 orders of reversible resistance switching, which is among the highest reported on polyimide substrates without any buffer. Structural and surface properties of the peak resistance switching sample are characterized by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). We also characterize the VO2 films under different bending radii and find stable resistance switching over 500 bending cycles. Long-wave infrared (LWIR) imaging of flexible VO2 film reveals emissivity variation due to VO2 phase transition. Using this flexible VO2, we fabricate two-terminal devices, which show stable voltage-induced reversible transition over 250 cycles. We observe stochastic variation in threshold voltages similar to VO2 films reported on rigid substrates and with potential applications in true-random number generators. By coupling these flexible VO2 devices to a MOSFET, we demonstrate a steep switching phase-field effect transistor (Phase-FET) with a sub-Boltzmann subthreshold slope (SS) of 29 mV/decade at room temperature. This demonstration of flexible VO2 synthesis and devices can open possibilities for several flexible VO2-based device applications.