Ferroelectric gating for agile and reconfigurable 2D electronics

Smart technologies are infiltrating our daily lives. From healthcare to transport to entertainment, electronics that adapt to our desires are becoming ubiquitous. For electronics hardware, this is creating a pull for the design of responsive and agile next generation technologies that can provide rapid, flexible and multifunctional devices.

To realise electronic functionality, voltages are used to control the electrical properties of materials, changing the conductivity of a channel to create transistors, diodes, memory elements and more, with the function tied to the device geometry. The performance of the electrical device depends on both the material used for the conducting channel and the way the voltage is coupled to it. Similar devices are also used to probe the fundamental Physics of electronic interactions in materials, where a voltage can be used to control the number of charge carriers in the material in order to study the effect of interactions between them. These interactions can lead to novel phases, such as unconventional superconductivity or reversible transitions from metallic to insulating behaviour, that offer new opportunities for advanced electronics. The functionality of the devices is thus tied to the design and integration of advanced functional materials to engender the optimal physical properties to the conducting channel and its most efficient coupling to the applied control voltage.

For the conducting channel, two-dimensional materials (2DMs) are one of the most exciting areas of research and are an area in which the UK is truly world-leading. There are now large and diverse families of 2DMs, with metallic, semiconducting, insulating, magnetic, superconducting and more properties. As they are atomically thin, the external voltage effects all of the atoms in the 2DM equally, giving more defined control over the conductivity than in conventional three-dimensional materials. Coupling to external voltages, with spatial control over the pattern of applied voltages, can be used to create highly efficient light-emitting diodes, transistors, and memory elements. What is achievable is usually limited by the coupling to the external voltage.

Ferroelectrics offer the potential to dynamically control this coupling, with nanoscale spatial resolution and fast switching. A ferroelectric has a spontaneous polarisation, with a large net surface charge, organised in nanoscale domains of positive or of negative surface charge. If a 2DM is placed on a ferroelectric, with a clean interface between them, this surface charge can dramatically alter the electronic properties of the 2DM by changing the number of charge carriers in the 2DM. By dynamically controlling the domain structure in the ferroelectric, fast and agile 2D electronics can be formed. Unfortunately, although proof-of-principle devices have been made, efficient coupling between ferroelectrics and 2DM has not yet been achieved.

Our team is uniquely suited to address this challenge, developing optimised processes for integrating 2DMs and ferroelectrics and demonstrating new agile electronics based on moving and switching the domains in the ferroelectric. By doing this, we will bring together two important fields, taking the potential of each to create a new area that will give new opportunities for probing fundamental Physics and developing new electronics.

The combination of ferroelectrics and two-dimensional materials is an exciting one for potential long-term impact. With their comparatively long history, ferroelectrics are already ubiquitous in consumer electronics in both high-cost and low-cost products. By contrast, two-dimensional materials are still predominately at the fundamental research stage, with the promise of future technological impact in the areas of electronics and optoelectronics. Combining these two fields brings new opportunities that will have both fundamental and applied impact in areas as diverse as energy storage and generation, quantum technologies, and healthcare.

To exploit these emergent technologies, a people pipeline of skilled researchers is required. Our project will deliver training in growth, device fabrication, characterisation, and high-resolution microscopy of ferroelectrics and 2DMs, and their hybrid heterostructures for researchers across the development spectrum from undergraduates, through postgraduates and postdoctoral researchers, to academics. These skills will be developed by focussed training, and supplemented by transferrable skills as part of the professional development of each researcher, overseen by the project leader and making the most of the University of Warwick's many professional development courses. We expect the researchers trained through this project to be highly desirable in both academia and industry, in the UK and worldwide.