The Hidden Life of Semiconductor Material

Substrate materials play an essential role in information processing. Using advanced imaging, a research team led by Penn State found that substrate material (also known as wafers) responds to changes in electricity, like the semiconductor sitting on top of it. 

Working with the semiconductor material vanadium dioxide, they found it has excellent potential as an electronic switch. The team was surprised that when used with titanium dioxide, an active layer in the substrate behaves similarly to the semiconductor material on top of it when the semiconductor switches between an insulator — not letting electricity flow — and a metal — letting electricity flow. This is significant for designing future materials and devices. The research is published in Advanced Materials

Given its low energy consumption, vanadium dioxide is considered promising for semiconductor technology as a metal-to-insulator transistor. Until now, the material’s properties were not fully understood. It was typically observed in isolation rather than while functioning in an actual device. 

The team investigated vanadium dioxide in a device rather than in isolation, applying a voltage to it to make it switch from insulating to conducting. They used the Advanced Photon Source (APS) at Argonne National Laboratory, which uses powerful X-ray beams to study the behavior and structure of materials on the atomic level. In this case, the researchers observed unexpected changes to the structure of the material and substrate.  

They found that the vanadium dioxide film changes to metal, and the whole film channel bulges, which is surprising since it is supposed to shrink. Instead, they found that the substrate is active, jiving and responding surprisingly as the film switches from an insulator to a metal and back when the electrical pulses arrive. 

Long-Qing Chen, Hamer Professor of Materials Science and Engineering and professor of engineering science, mechanics, and mathematics at Penn State, developed a theoretical framework to explain the process. The experimental results could be satisfactorily explained when their model incorporated naturally occurring missing oxygen atoms in this material of two types, charged and uncharged. 

The responses themselves require further investigation. The team believes that understanding them will assist in identifying previously unknown capabilities of vanadium dioxide, including potential yet-to-be-discovered phenomena in the TiO2 substrate that were considered passive before this study. 

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