Towards High-Precision Control of Transformation Characteristics in VO2 through Dopant Modulation of Hysteresis

Abstract

As we approach the limits of what traditional computer architecture is capable of, a new system is needed to continue growth in computational power. One solution lies in neuromorphic systems and, specifically, those that utilize specialized materials capable of inherently mimicking brain functions. Due to its metal-insulator transition (MIT) at ~68C and the accompanying magnitude change in electronic resistance, VO2 is one such material. Previous studies have shown that the transition temperature can be tuned through chemical doping, but little is known about how these dopants affect the microscopic progression of the phase transformation through a volume. This is critical as changes to the MIT directly affect the functionality of VO2 in these devices and could enable control over various aspects of the transition such as degree of volatility. Therefore, a more mechanistic understanding of how dopants affect transformation behavior is needed. Here we utilize an optical technique to investigate the effects of substitutional tungsten, and interstitial boron dopants on the MIT behavior in VO2 compared to its undoped state. Tungsten demonstrates the ability to depress the transition temperature, reduce hysteresis and increase the width of transformation. Boron also induces a small increase in transformation width but maintains a hysteresis similar to undoped while exhibiting unique relaxation behavior. In addition, both dopants negate size effects observed in undoped particles. Likely due to their ability to enhance or suppress point defect concentrations and thereby improve the consistency of hysteresis. Both effects are vital for practical application of VO2 in neuromorphic devices which require precise control of transformation characteristics.