Integrating 2D materials into devices, such as computer chips, has long been a challenging endeavor. The ultrathin nature of these materials makes them susceptible to damage from traditional fabrication techniques, often involving chemicals, high temperatures, or destructive processes like etching.
To address this difficulty, a team of researchers from MIT and other institutions has devised a novel technique for seamlessly integrating 2D materials into devices in a single step. This method ensures that both the surfaces of the materials and the resulting interfaces remain pristine and free from defects.
The approach leverages nanoscale surface forces to enable the physical stacking of 2D materials onto other prebuilt layers of a device. By preserving the integrity of the 2D material, the researchers can fully exploit its unique optical and electrical properties.
The team applied this method to create arrays of 2D transistors, demonstrating enhanced functionalities compared to devices produced using conventional fabrication techniques. The versatility of this approach, applicable to various materials, opens up possibilities for diverse applications in high-performance computing, sensing, and flexible electronics.
Crucial to unlocking these new functionalities is the ability to form clean interfaces, bound by van der Waals forces—special forces existing between all forms of matter. Despite the challenges, the researchers believe that van der Waals integration of materials into fully functional devices holds significant potential.
Farnaz Niroui, assistant professor of electrical engineering and computer science at MIT and senior author of the study, highlights a fundamental limit associated with van der Waals integration. She explains that these forces, relying on intrinsic material properties, lack the flexibility for easy tuning. Consequently, certain materials cannot be directly integrated using van der Waals interactions alone. To overcome this limitation and enhance the versatility of van der Waals integration, the researchers have developed a platform. This platform aims to facilitate the creation of 2D-materials-based devices with novel functionalities and improved performance. The research detailing this advancement will be published in Nature Electronics.
Beneficial allure
Creating complex systems, such as computer chips, using traditional fabrication techniques can be a messy process. Typically, rigid materials like silicon are carved down to the nanoscale and then combined with other components like metal electrodes and insulating layers to form an active device. This method can result in damage to the materials.
In contrast, recent efforts have focused on constructing devices and systems from the ground up using 2D materials and a sequential physical stacking process. Rather than relying on chemical adhesives or high temperatures to attach a delicate 2D material to a conventional surface like silicon, researchers utilize van der Waals forces to physically integrate a layer of 2D material onto a device.
Van der Waals forces represent natural forces of attraction present between all forms of matter. For instance, a gecko’s feet can temporarily stick to a wall due to van der Waals forces.
While all materials exhibit van der Waals interaction, the strength of these forces varies depending on the material. For example, a widely used semiconducting 2D material like molybdenum disulfide may adhere to gold (a metal) but may not directly transfer to insulators like silicon dioxide through mere physical contact.
In the construction of electronic devices, heterostructures—integrating semiconductor and insulating layers—are fundamental building blocks. Traditionally, achieving this integration involved bonding the 2D material to an intermediate layer like gold, utilizing this intermediate layer to transfer the 2D material onto the insulator, and subsequently removing the intermediate layer using chemicals or high temperatures.
In contrast, the MIT researchers have devised an innovative approach. Instead of relying on a sacrificial layer, they embed the low-adhesion insulator within a high-adhesion matrix. This adhesive matrix is the crucial element that enables the 2D material to adhere to the embedded low-adhesion surface, generating the necessary forces to establish a van der Waals interface between the 2D material and the insulator.
Creating the matrix
The process of creating electronic devices involves the formation of a hybrid surface comprising metals and insulators on a carrier substrate. This surface is then detached and flipped over, unveiling a perfectly smooth top surface that encompasses the essential components for constructing the desired device.
The emphasis on achieving smoothness is crucial because any gaps between the surface and the 2D material can impede van der Waals interactions. Subsequently, the researchers undertake the preparation of the 2D material separately in an impeccably clean environment. The final step involves bringing the prepared 2D material into direct contact with the meticulously crafted device stack.
Satterthwaite explains that the hybrid surface, when in direct contact with the 2D layer, can seamlessly acquire and integrate the 2D layer without the necessity for high temperatures, solvents, or sacrificial layers. This innovative approach enables van der Waals integration, which would conventionally be deemed impossible. Now, with this method, it becomes feasible, allowing for the creation of fully functioning devices in a single, streamlined step.
The single-step process maintains a completely clean interface for the 2D material, allowing it to achieve its fundamental performance limits without being hindered by defects or contamination.
The pristine surfaces also enable researchers to engineer the 2D material’s surface to create features or connections to other components. For instance, the technique was utilized to produce p-type transistors, a challenging task with 2D materials. The resulting transistors exhibit improvements over previous studies and provide a platform for exploring the performance required for practical electronics.
This approach is scalable, facilitating the production of larger arrays of devices. Additionally, the adhesive matrix technique is versatile and compatible with various materials, offering the potential to enhance the platform’s flexibility. For example, the researchers successfully integrated graphene into a device, establishing the desired van der Waals interfaces using a matrix composed of a polymer. In this case, adhesion relies on chemical interactions rather than van der Waals forces alone.
Looking ahead, the researchers aim to expand this platform to integrate a diverse array of 2D materials, enabling the study of their intrinsic properties without the influence of processing damage. They also plan to develop new device platforms that capitalize on these superior functionalities.
Resources
- ONLINE NEWS Zewe, A. & Massachusetts Institute of Technology. (2023, December 8). Researchers safely integrate fragile 2D materials into devices, opening a path to unique electronic properties. Phys.org. [Phys.org]
- JOURNAL Satterthwaite, P.F., Zhu, W., Jastrzebska-Perfect, P. et al. (2023). Van der Waals device integration beyond the limits of van der Waals forces using adhesive matrix transfer. Nature Electronics. [Nature Electronics]
Cite this page:
APA 7: TWs Editor. (2023, December 8). Novel Electronic Features from Delicate 2D Materials Integrated into Devices Safely. PerEXP Teamworks. [News Link]
