モハメッド シュルズ ミヤ

Self-sustained electrical oscillations (SEOs) in VO2 films have attracted considerable attention owing to their potential to emulate spiking pulses in neuromorphic circuits. However, triggering stable SEOs and the controlling oscillation frequency remain challenging because the details of circuit operation with VO2-based devices are not yet well understood. In this study, we propose a method to observe SEOs stably in a VO2-based planar device with Au/Ti facing electrodes by introducing a 50 Hz sinusoidal voltage from a curve tracer. The transient aspects, including the onset and collapse of the SEO, were captured, providing clarity on the oscillation frequency range and circuit conditions for the SEOs, which are closely correlated with the device temperature. It became clear that the parallel capacitance not only determined the oscillation frequency but also controlled the current through VO2 just after the insulator–metal transition of VO2, playing a role in triggering stable oscillations. We also successfully observed the transient aspects from in-phase to anti-phase synchronized oscillations in the coupled oscillations. This study advances the experimental procedures and applications of SEOs in VO2-based planar devices.

Amorphous tungsten oxide films are prepared on indium tin oxide/glass substrates using reactive magnetron sputtering and their electrochromic (EC) properties are investigated. To achieve the densely colored films, samples of 500 and 1000 nm thickness are deposited with different pumping speeds and oxygen flow rates at Ar 3 Pa atmosphere. The as‐deposited films are similarly transparent (≈80%), but their EC properties vary depending on the deposition conditions and strongly on film thickness. The 500 nm‐thick samples have a transmittance of 4–8% in the colored state, which recover well in the bleached state. In contrast, the 1000 nm‐thick films have very low transmittance (<1%) in the colored state but are not completely recovered. Among 1000 nm‐thick films, large pumping speed and a large oxygen flow rate condition result in comparatively better recoverability. The cyclic voltammograms of 500 nm films show small and balanced charge transfer, while those of 1000 nm films reveal large and unbalanced charge transfer. These indicate that more ions are intercalated into the 1000 nm samples but are not completely deintercalated. These findings contribute to the development of EC applications for light shielding.