Promising 2D material Amorphous boron nitride as a 2D material for semiconductors: Fabrication without oxidation, promising performance leaps

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How do you protect sensitive semiconductor materials from oxidation without compromising their performance? Researchers have found a solution: amorphous boron nitride (a-BN), which not only prevents corrosion but also enhances the performance of semiconductor devices. Could a-BN optimize the electronics of the future?

Oxidation in semiconductors can be problematic as it negatively affects the properties of semiconductor materials. For instance, if metal contacts oxidize, the electrical resistance increases, which deteriorates conductivity and reduces the efficiency of components like MOSFETs or diodes. Additionally, uncontrolled oxidation layers on semiconductor surfaces can lead to unwanted insulation effects that impair the function of components. In short, oxidation leads to electrical losses, impairs durability, and can render components unusable in the long term.

In particular, oxidation is considered a problem for 2D materials for advanced semiconductors that are only one or a few atoms thick. These materials control the flow of electricity in electronic devices, and any corrosion can render the material unusable. Since their thinness offers electrons a shorter and more direct path to move quickly and with less resistance through the material, they enable faster and more efficient electronic performance. How can the issue of oxidation be addressed in this case?

Rust-free coating with additional properties—and without water

Researchers have developed a synthesis process to create a "rust-free" coating with additional properties suitable for the development of faster and more durable electronics. The team, led by researchers from Penn State University, published their work in Nature Communications.

In addition to Robinson, other authors of the study include experts from Penn State. Additional co-authors are scientists from the National Yang Ming Chiao Tung University in Taiwan, Purdue University, Intel Corporation, and the Kurt J. Lesker Company.

"One of the biggest problems in researching 2D semiconductors today is the fact that the materials oxidize quickly," says Joshua Robinson, professor of materials science and engineering and co-author of the paper. "You have to ensure their long-term reliability because they are used in transistors or sensors that are supposed to last for years. Currently, these materials don't last more than a week outdoors."

Conventional methods for protecting these materials from rust include oxide-based coatings, but these processes often involve water, which can ironically accelerate oxidation. The team therefore sought a coating material and method that completely avoids water. The choice fell on amorphous boron nitride (a-BN).

"We wanted to get away from water in this process, so we thought about what kind of 2D materials we could produce that don't use water in their processing. Amorphous boron nitride is one of those materials," said Robinson.

Amorphous boron nitride as a complement to dielectrics

This non-crystalline form of boron nitride, namely a-BN, is known for its high thermal stability and electrical insulation properties. This qualifies it for use in semiconductors to insulate components, prevent unwanted electrical currents, and improve device performance, says Robinson. He explains that a-BN has a high dielectric strength—a measure of how well a material can withstand high electric fields without breaking down. This is a crucial factor for reliable performance.

"The high strength of a-BN is comparable to the best available dielectrics, and we do not need water to produce it," said Robinson. "In the paper, we demonstrate that amorphous boron nitride improves the performance of components compared to conventional dielectrics alone." This means that a-BN could potentially be used in addition to other dielectrics to enhance the overall efficiency and reliability of the semiconductor. It is still unclear whether a-BN is used solely as a complementary material in all designs, or if it might also be employed as a primary dielectric in some cases.

Two-step method

While the coating helped to create a better 2D transistor, coating the 2D materials proved to be a challenge. Two-dimensional materials lack "free bonds," meaning they have no unpaired electrons on their surface that could react or bond with other atoms. A conventional coating process, conducted in a single step and at higher temperatures, results in uneven and incomplete coatings—and this is far from sufficient for electronics to function reliably.

To uniformly coat 2D materials with a-BN, the team developed a two-step atomic layer deposition method, where initially a thin a-BN "seed layer" is deposited at low temperatures before the chamber is heated to typical deposition temperatures between 482°F and 572°F. This approach allowed the researchers not only to create a uniform a-BN coating on the 2D semiconductors but also to improve the transistor performance by 30% to 100%, depending on the transistor design, compared to devices without a-BN.

"When you place 2D semiconductors between the amorphous boron nitride, you essentially get a flat electronic highway that enables improved electronics," says Robinson. "The electrons can move faster through the 2D material than if they were between other dielectric materials."

Despite these findings, the team is only scratching the surface of the potential of a-BN as a dielectric material for semiconductor devices. "We still have room for improvement, even though it already surpasses other dielectric materials," explains Robinson. "At the moment, we are mainly trying to improve the overall quality of the material and then integrate it into some complex structures that will be seen in future electronics."

Link: Tailoring amorphous boron nitride for high-performance two-dimensional electronics

Link: Water-free manufacturing approach could help advance 2D electronics integration