Researchers safely integrate fragile 2D materials into devices, opening a path to unique electronic properties




Only a few atoms thick, two-dimensional materials can have amazing qualities including incredibly efficient electric charge transport, which could improve the functionality of electronic gadgets of the future.

Nevertheless, there is a well-known difficulty in integrating 2D materials into systems and equipment like computer chips. Conventional manufacturing methods, which sometimes include the use of chemicals, high temperatures, or damaging procedures like etching, might harm these very thin structures.

To address this issue, scientists at MIT and other institutions have created a novel method that allows for the one-step integration of 2D materials into devices without compromising the quality or defect-free appearance of the materials' surfaces or the ensuing interfaces.

Their technique is based on manipulating surface forces that exist at the nanoscale to enable the actual stacking of the 2D material onto further layers of prefabricated devices. The rare optical and electrical capabilities of the 2D material may be fully utilized by the researchers since it is unaltered.

By employing this method, they were able to create arrays of 2D transistors that were capable of novel functions as compared to devices made with more traditional fabrication methods. Their approach might have a wide range of uses in flexible electronics, sensing, and high-performance computing since it is adaptable enough to work with a variety of materials.

The capacity to create clean interfaces, bound together by unique forces known as van der Waals forces that exist between all matter, is essential to opening up these new functions.

Farnaz Niroui, an assistant professor of electrical engineering and computer science (EECS), a member of the Research Laboratory of Electronics (RLE), and the senior author of a recent paper detailing the work, notes that such van der Waals integration of materials into fully functional devices is not always simple.

She says, "Van der Waals integration has a fundamental limit." These forces cannot be easily adjusted since they rely on the inherent characteristics of the materials. Because of this, certain materials cannot be directly merged with one another through their van der Waals interactions. In order to assist make van der Waals integration more flexible and to encourage the creation of 2D-materials-based devices with fresh and enhanced features, we have created a platform to overcome this constraint."

Nature Electronics will publish the research.

favorable attraction

Using traditional manufacturing methods to create complicated systems, like computer chips, may be messy. To create an active device, a stiff material like silicon is often chiseled down to the nanoscale and interfaced with other parts like metal electrodes and insulating layers. Materials may get damaged as a result of this technique.

Lately, scientists have concentrated on creating systems and gadgets from the bottom up by employing 2D materials and a method that necessitates physical stacking in sequence. With this method, researchers physically integrate a layer of 2D material into a device by employing van der Waals forces instead of chemical glues or high temperatures to connect a fragile 2D material to a traditional surface like silicon.

All matter is naturally attracted to one another by Van der Waals forces. For instance, van der Waals forces allow a gecko's foot to momentarily adhere to a wall.

Despite the van der Waals interaction present in all materials, the forces may not always be sufficient to keep them together depending on the substance. For example, molybdenum disulfide, a well-known semiconducting 2D substance, will adhere to metals like gold but will not transfer straight to insulators such as silicon dioxide just by touching that surface.

Nonetheless, the essential components of an electronic device are heterostructures, which are created by combining semiconductor and insulating layers. The 2D material was previously bonded to an intermediate layer, such as gold, and then used to transfer the 2D material onto the insulator. The intermediate layer was then removed using chemicals or high temperatures. This allowed for the integration of the two materials.

The MIT researchers embed the low-adhesion insulator in a high-adhesion matrix as an alternative to employing this sacrificial layer. The 2D material adheres to the embedded low-adhesion surface because of this adhesive matrix, which also provides the forces required to form a van der Waals contact between the 2D material and the insulator.

constructing the matrix

They create a hybrid surface of insulators and metals on a carrier substrate to create electrical devices. The required device's construction pieces are then contained on the perfectly smooth top surface that is revealed once this surface is peeled off and turned over.

Van der Waals interactions can be hampered by gaps between the surface and 2D substance, hence this smoothness is crucial. Next, in an entirely sterile setting, the researchers manufacture the 2D material independently and place it in close proximity to the device stack that has been ready.

"The hybrid surface can take up the 2D layer and integrate it with the surface once it comes into touch with it, without the requirement for high temperatures, solvents, or sacrificial layers. By doing this, we are permitting a van der Waals integration that was previously prohibited but is now feasible and enables the creation of completely functional devices in a single step, according to Satterthwaite.

This one-step procedure maintains the 2D material contact entirely clean, allowing the material to realize its fundamental performance limitations free from impurities or flaws.

Additionally, because the surfaces stay immaculate, scientists may manipulate the 2D material's surface to create features or linkages with other elements. They employed this method, for instance, to produce p-type transistors, which are often difficult to fabricate from 2D materials. Their transistors are a step above from those studied in the past and can offer a platform for research and development toward the performance required for real-world electronics applications.

Their method can produce bigger arrays of devices at scale. To further the adaptability of this platform, the adhesive matrix technology may also be used to a variety of materials and even to other forces. For example, the scientists incorporated graphene onto a device and used a polymer matrix to produce the required van der Waals interactions. Here, van der Waals forces are not the only means of adhesion; chemical interactions also play a role.

In order to explore the inherent characteristics of 2D materials without being impacted by processing damage, the researchers hope to expand on this platform in the future. They also hope to create new device platforms that take use of these enhanced functions.