Oxide Materials Enable Faster, Thinner Electronic Devices, Graphene Sandwich Technique Penn State Study Finds

An international team of researchers has suggested that a new method for producing 2D oxide materials could be the key to enabling high-speed electronics in the future. The ability to create increasingly small transistors has historically driven advances in computing power, but the limits of commonly used silicon materials have almost been reached.

Joshua Robinson, who is a professor of materials science and engineering at Penn State, has explained that shrinking the distance electrons need to travel between two points can speed up the performance of electronic devices like transistors. However, the properties of 3D materials such as silicon change when they are reduced to nanometer size, so there is a need to explore new materials like 2D materials.

The research team, led by Furkan Turker, a graduate student in the Department of Materials Sciences, used confinement heteroepitaxy (CHet) to produce 2D oxides, which have unique properties that can function as an extremely thin insulating layer between electrically conducting materials.

Faster, Thinner Electronic Devices,

Furkan Turker, the lead researcher of the team, has stated that they have been able to produce extremely thin oxides, just a few atoms thick, using confinement heteroepitaxy. This allows for the creation of an ultrathin insulating barrier between conducting layers, which is critical for the development of advanced electronic devices such as diodes or transistors. By bringing conducting layers closer together than ever before, without letting them touch, they have created the thinnest oxides in the world. Laboratory tests have shown that these oxides have excellent properties for use in heterostructures - 2D/3D stacked materials that allow for vertical electron transport through the structure, rather than the conventional horizontal transport.

The researchers highlighted that shortening the distance that electrons must travel to generate an electric current is a crucial factor in developing high-speed devices that operate at gigahertz and terahertz frequencies. Their findings, which were published in the journal Advanced Functional Materials, show that it is possible to create a few-atoms-thick insulator that can control the electronic properties of an entire stack. According to Robinson, this is the primary motivation behind the research - enabling electrons to travel from point A to B more quickly, without requiring an increase in their speed.

The research builds upon previous work at Penn State, where confinement heteroepitaxy was utilized to produce metals that were only a few atoms thick. This technique is now being explored as part of the Center for Nanoscale Science at Penn State, which is a National Science Foundation Materials Research, Science and Engineering Center (MRSEC). To produce these metals, silicon carbide is heated to high temperatures, causing a layer of silicon to evaporate from the surface. This leaves behind carbon, which rearranges itself to form graphene - a 2D form of carbon that essentially acts as a protective layer over the material.

(Photo : Penn State)
Furkan Turker, graduate student in the Department of Materials Sciences, works on a silicon carbide chip in the laboratory.

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Using the Graphene Sandwich Technique

The interface between graphene and silicon carbide is only partially stable, which is a crucial characteristic. This instability allows the scientists to poke holes in the graphene and evaporate pure metal powders onto the surface at high temperatures. Through a process similar to capillary action, the metals are then pulled into the holes. These metals are conductive, and some are even superconductive, but they can be converted into insulators through oxidation, which is the same process that causes metals to rust when they are exposed to air. In their new study, the scientists introduced additional holes or patterns in the material and heated it again. This enabled gas to interact with the metal layer inside.

To Robinson, the process is similar to playing with Lego blocks. The researchers create a stack of blocks with different colors and then modify the color of the block in the center by adding a small amount of oxygen without removing anything else. This approach enables the stabilization of materials that are typically 3D, such as gallium oxide, in a 2D form. When gallium oxide is grown using traditional methods, the material clumps together initially and does not form a uniform film until it is several nanometers thick. However, the new method allows for the creation of uniform films of the material, even when they are only a few atoms thick, as reported by Phys.

According to scientists, the CHet technique uses a graphene layer to sandwich the materials and create extremely thin layers on a molecular level. The properties of the graphene layer control the properties of the layers underneath it, allowing scientists to manipulate the electronic properties of the 2D/3D heterostructure. The next step of the research involves growing materials on top of the graphene layer to create the device structure and investigating the junctions between the layers and potential defects in the materials.