Novel Study of Strain-Induced Piezoelectricity in VO2

Recent Advances of VO2 in Sensors and Actuators

Vanadium dioxide (VO2) stands out for its versatility in numerous applications, thanks to its unique reversible insulator-to-metal phase transition. This transition can be initiated by various stimuli, leading to significant alterations in the material's characteristics, including its resistivity and optical properties. As the interest in the material is growing year by year, the purpose of this review is to explore the trends and current state of progress on some of the applications proposed for VO2 in the field of sensors and actuators using literature review methods. Some key applications identified are resistive sensors such as strain, temperature, light, gas concentration, and thermal fluid flow sensors for microfluidics and mechanical microactuators. Several critical challenges have been recognized in the field, including the expanded investigation of VO2-based applications across multiple domains, exploring various methods to enhance device performance such as modifying the phase transition temperature, advancing the fabrication techniques for VO2 structures, and developing innovative modelling approaches. Current research in the field shows a variety of different sensors, actuators, and material combinations, leading to different sensor and actuator performance input ranges and output sensitivities.

Reversible Entropy-Driven Defect Migration and Insulator-Metal Transition Suppression in VO2 Nanostructures for Phase-Change Electronic Switching

Oxygen defects are among essential issues and required to be manipulated in correlated electronic oxides with insulator-metal transition (IMT). Besides, surface and interface control are necessary but challenging in field-induced electronic switching towards advanced IMT-triggered transistors and optical modulators. Herein, we demonstrated reversible entropy-driven oxygen defect migrations and reversible IMT suppression in vanadium dioxide (VO₂ ) phase-change electronic switching. The initial IMT was suppressed with oxygen defects, which is caused by the entropy change during reversed surface oxygen ionosorption on the VO₂ nanostructures. This IMT suppression is reversible and reverts when the adsorbed oxygen extracts electrons from the surface and heals defects again. The reversible IMT suppression observed in the VO₂ nanobeam with M2 phase is accompanied by large variations in the IMT temperature. We also achieved irreversible and stable IMT by exploiting an Al₂ O₃ partition layer prepared by atomic layer deposition (ALD) to disrupt the entropy-driven defect migration. We expected that such reversible modulations would be helpful for understanding the origin of surface-driven IMT in correlated vanadium oxides, and constructing functional phase-change electronic and optical devices.