An artistic rendering of the MacEtch-produced fin array structures in a beta-gallium oxide semiconductor substrate. Image: ACS Nano.
An artistic rendering of the MacEtch-produced fin array structures in a beta-gallium oxide semiconductor substrate. Image: ACS Nano.

Electrical engineers at the University of Illinois at Urbana-Champaign have cleared another hurdle in high-power semiconductor fabrication by adding the field's hottest material – beta-gallium oxide – to their arsenal. According to the researchers, beta-gallium oxide is readily available and promises to convert power faster and more efficiently than today's leading semiconductor materials – gallium nitride and silicon. They report their findings in a paper in ACS Nano.

Flat transistors have become about as small as is physically possible, but researchers are addressing this problem by going vertical. By taking advantage of a technique called metal-assisted chemical etching – or MacEtch – University of Illinois engineers have now been able to use a chemical solution to etch a semiconductor into three-dimensional (3D) fin structures. These fins increase the surface area on a chip, allowing for more transistors or current, and can therefore handle more power while keeping the chip's footprint the same size.

Developed at the University of Illinois at Urbana-Champaign, the MacEtch method is superior to traditional ‘dry’ etching techniques because it is far less damaging to the delicate surface of semiconductors like beta-gallium oxide.

"Gallium oxide has a wider energy gap in which electrons can move freely," said the study's lead author Xiuling Li, a professor of electrical and computer engineering. "This energy gap needs to be large for electronics with higher voltages and even low-voltage ones with fast switching frequencies, so we are very interested in this type of material for use in modern devices. However, it has a more complex crystal structure than pure silicon, making it difficult to control during the etching process."

Applying MacEtch to gallium oxide crystals could benefit the semiconductor industry, Li said, but the advancement is not without hurdles.

"Right now, the etching process is very slow," she said. "Because of the slow rate and the complex crystal structure of the material, the 3D fins produced are not perfectly vertical, and vertical fins are ideal for efficient use of power."

In the new study, the beta-gallium oxide substrate produced triangular, trapezoidal and tapered fins, depending on the orientation of the metal catalyst relative to the crystals. Although these shapes are not ideal, the researchers were surprised to find that they still do a better job at conducting current than the flat, unetched beta-gallium oxide surfaces.

"We are not sure why this is the case, but we are starting to get some clues by performing atomic-level characterizations of the material," Li said. "The bottom line is that we have shown it is possible to use the MacEtch process to fabricate beta-gallium oxide, a potentially low-cost alternative to gallium nitride, with good interface quality."

Li said further research will need to address the slow etch rate, develop high performance beta-gallium oxide devices and try to get around the problem of low thermal conductivity.

"Increasing the etch rate should improve the process's ability to form more vertical fins," she said. "This is because the process will happen so quickly that it will not have time to react to all of the differences in crystal orientations."

The low thermal conductivity issue is a deeper problem, she added. "High-power electronics produce a lot of heat, and device researchers are actively seeking thermal engineering solutions. While this is a wide-open aspect in the semiconductor field right now, 3D structures like what we have demonstrated could help guide the heat out better in some device types."

This story is adapted from material from the University of Illinois at Urbana-Champaign, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.