Large area synthesis and multilayer hBN transfer for fabrication of 2D . electronics

Researchers at Kyushu University, the National Institute of Advanced Industrial Science and Technology (AIST) and Osaka University in Japan recently introduced a new strategy for synthesizing multilayer hexagonal boron nitrides. hBN), a material that can be used to integrate different 2D materials. materials in electronic devices, while preserving their unique properties. Their proposed approach, outlined in a paper published in nature electronicscould facilitate the fabrication of new high-performance graphene-based devices.

“The atomic planar 2D insulator hBN is the main material for integrating 2D materials into electric devices“, Hiroki Ago, one of the researchers who carried out the study, told Tech Xplore. “For example, carrier mobility is the highest in the world. monolayer graphene is achieved only when it is clamped by the multilayer hBN. Superconductivity observed in torsion two layers of graphene also need multilayer hBN to isolate from the environment.”

Beyond the value to craft graphene-based on the device, hBN can also be used for integration transition metal dichalcogenide (TMD) in devices, achieving strong luminescence and high carrier mobility. It may also be valuable to conduct studies that focus on moiré physics.

Despite many possible applications, the synthesis of high-quality hBN has been challenging so far, especially compared with the synthesis of other 2D materials. hBNs generated using existing methods are often too thin or heterogeneous.

“Although promising results have been achieved with use chemical vapor deposition (CVD), it is limited to monolayer hBN, but monolayer hBN is not thick enough to screen for environmental effects,” Ago said. complex interactions between B and N species and catalytic substrates.”

The main goal of the recent study by Ago and his colleagues was to determine a strategy to produce hBN of uniform thickness at different scales to meet the needs of different devices. The team also aspires to enable the successful integration of the synthesized hBN with graphene, achieving reliable and high-performance devices at the slice scale.

The strategy they devised was based on CVD, a chemical process commonly used to grow hBN and other 2D materials. Although this procedure has been applied in previous studies, it has not always produced homogenous and good quality hBN.

“The process involves exposing a metal substrate (in our case, a polycrystalline Fe-Ni foil) to a gas containing precursors of hBN (B and N), which undergoes reactions. high-temperature chemical reaction to produce hBN layers on the surface of Fe-Ni,” explains Ago. “By adjusting the relative amounts of Fe and Ni, a uniform hBN cleavage can be obtained. In addition to CVD growth, the transition from the metal catalyst is also important, as it strongly influences the physical properties.”

To transfer the hBN they developed onto graphene, Ago and his colleagues used a material transfer technique called electrochemical delamination, which utilizes H₂ bubbles form at the interface of the Fe-Ni and hBN layers. Although this process is known to be cleaner and more efficient than other methods of material transfer, they found that the interface between the hBN and the graphene layer was not as clean as they had hoped and would therefore not produce devices. homogenized by graphene at the slice scale.

“To address this issue, we systematically investigated the impact of different cleaning and treatment procedures on the transfected hBN and on the subsequent graphene,” Ago said. “We found that sequential annealing in H₂ the high-temperature environment ensures relatively clean interfaces between hBN and graphene.”

Using their proposed hBN transfer and synthesis method, the researchers were able to fabricate high-performance devices in which graphene is enclosed by hBN. These devices were found to perform better than others where graphene was placed directly on SiO .₂ class.

“This Improve the performancepreviously observed for devices carefully molded at specific clean and uniform locations, observed here for the first time for devices manufactured at the wafer scale using processes compatible with mass production,” said Ago. “We have demonstrated the successful synthesis of high-quality hBN on a large scale using Fe- foils. Ni is relatively inexpensive and the development of scalable transfer processes enables the fabrication of graphene devices with improved performance at the slice scale.”

Recent work by Ago and his colleagues demonstrates the potential of CVD-grown 2D materials for the mass production of high-performance and homogeneous electronic devices. In the future, the strategy they have developed could be used to reliably produce uniform hBN on a large scale and then integrate it in different devices.

Ago and his colleagues now plan to further improve their synthesis and transfer processes, to facilitate their introduction in both research and industrial settings. For example, the hBN produced in their experiments showed uniform thicknesses ranging from 5–10 nm on a wafer, which may not satisfy the requirements of particularly complex and demanding electronic applications. rigorously asked.

“The ability to create thicker hBN films would provide better isolation than other 2D materials, but it has proven to be a challenge to increase thickness while maintaining uniformity,” Ago adds. . “As a result, we are currently working to improve our synthesis methods. Additionally, our current transfer process relies on using the PMMA sacrificial layer, so we are currently working on it. investigate alternative methods that lead to cleaner delivered hBN and are more suitable for industrial-scale processing, allowing for increased processing throughput while maintaining instrument quality.”

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