Vertical Field Effect Transistor based on Graphene-WS2 Heterostructures for flexible and transparent electronics

Abstract: The celebrated electronic properties of graphene have opened way for materials just one-atom-thick to be used in the post-silicon electronic era. An important milestone was the creation of heterostructures based on graphene and other two-dimensional (2D) crystals, which can be assembled in 3D stacks with atomic layer precision. These layered structures have already led to a range of fascinating physical phenomena, and also have been used in demonstrating a prototype field effect tunnelling transistor - a candidate for post-CMOS technology. The range of possible materials which could be incorporated into such stacks is very large. Indeed, there are many other materials where layers are linked by weak van der Waals forces, which can be exfoliated and combined together to create novel highly-tailored heterostructures. Here we describe a new generation of field effect vertical tunnelling transistors where 2D tungsten disulphide serves as an atomically thin barrier between two layers of either mechanically exfoliated or CVD-grown graphene. Our devices have unprecedented current modulation exceeding one million at room temperature and can also operate on transparent and flexible substrates.

• The paper demonstrates a graphene-WS2 VFET achieving an ON/OFF ratio over one million at room temperature.
• It employs a layered architecture enabling a seamless transition between thermionic and tunneling currents.
• The study validates device flexibility on PET substrates, underscoring potential for wearable, transparent electronics.

Graphene-WS$_2$ Based Vertical Field Effect Transistors for Advanced Electronics

The paper under examination presents a comprehensive study on the development of vertical field effect transistors (VFETs) utilizing graphene-WS$_2$ heterostructures, proposing innovations in the field of flexible and transparent electronics. The authors explore the integration of graphene—a material with superior electronic properties—into heterostructures with tungsten disulfide (WS$_2$), exploiting its unique characteristics when reduced to a monolayer. This research presents a multifaceted investigation, from device fabrication to performance characterization, demonstrating the potential for significant advancements in semiconductor technology.

Technical Overview

The VFET developed herein is founded on a layered architecture where WS$_2$ acts as an atomically thin barrier between two graphene layers. The use of WS$_2$ is pivotal due to its transition from an indirect band gap semiconductor to a direct band gap material at the monolayer scale, allowing efficient modulation of device characteristics through tunable electronic properties. The devices exhibit a superior current modulation capability, achieving an ON/OFF ratio exceeding one million at ambient conditions. This level of performance is critical for next-generation electronic devices, which require both high efficiency and scalability.

Key Findings

Several experimental findings underscore the technological potential of the proposed devices:

• Current Modulation: The reported ON/OFF current modulation exceeds one million at room temperature. This is a considerable enhancement compared to conventional graphene-transistor devices, signifying the efficacy of the WS$_2$ barrier.
• Thermionic and Tunneling Currents: The authors highlight the interplay between these two mechanisms, suggesting that the WS$_2$-based architecture enables a seamless transition between tunneling and thermionic currents. This duality is crucial for achieving high performance under varying operational conditions.
• Flexible and Transparent Substrates: The application of these devices on flexible substrates, such as PET films, demonstrates minimal impact from mechanical deformation. This attribute suggests broad applicability in wearable and transparent electronics.

Implications and Future Prospects

The implications of integrating WS$_2$ in the graphene heterostructure extend beyond the demonstrated performance benefits. The ability to fabricate flexible and transparent electronic devices opens new avenues in consumer electronics, aligning with trends towards lightweight and adaptable technologies. Additionally, the work provides a template for further exploration into other 2D materials that may offer synergistic benefits in devices requiring nanoscale modulation.

The study also sets the stage for ongoing research into reproducible and scalable fabrication techniques, a necessity for transitioning these findings into commercially viable solutions. Future investigations may explore optimizing the layer thickness and exploring alternative top contact materials to further enhance device performance.

Conclusion

The paper delivers a substantial contribution to the field of advanced materials for semiconductor applications, particularly within the context of VFETs. It demonstrates the viability of graphene-WS$_2$ heterostructures as a pathway toward realizing high-performance, flexible, and transparent electronics. These findings not only validate the approach but also prompt further research into the optimization and application of 2D heterostructures in various domains. As the electronics industry continues its shift beyond traditional silicon-based technologies, such research heralds exciting possibilities for the future landscape of semiconductor devices.