Researchers from the University of Exeter have devised a unique fabrication method that could lead to the next generation of flexible electronics. The quest to develop microelectronic devices of ever smaller sizes underpins the progress of the global semiconductor industry. At this tiny scale, quantum mechanical effects have stumped numerous companies including the communication and tech giants Toshiba and Samsung.
The thickness of conventional insulators has to be reduced to continue making devices smaller. So, researchers are looking into replacing conventional insulators with high-dielectric-constant (high-k) oxides. However, commonly used high-k oxide deposition techniques are not directly compatible with 2D materials.
A team of engineering researchers established a new way to ease the production of van der Waals heterostructures with high-K dielectrics- arrangements of atomically thin two-dimensional (2-D) crystalline materials such as graphene. Graphene is comprised of a honeycomb-shaped structure of carbon atoms just one atom thick.
While the advantages of van der Waals heterostructures are well documented, their development has been restricted because of their complex fabrication methods.
Now, the research team at the University of Exter has devised a new technique that lets these structures achieve voltage scaling, improved performance and the potential for new functionalities by embedding a high-K oxide dielectric. Specifically, this research describes a new method to embed a multi-functional, nanoscaled high-K oxide within van der Waals devices without degrading the properties of the neighboring 2D materials.
The research could lead to a new generation of flexible fundamental electronic components. The research is published in the journal Science Advances.
Dr Freddie Withers, co-author of the paper and from the University of Exeter said, "Our method to embed a laser writable high-K dielectric into various van der Waals heterostructure devices without damaging the neighbouring 2D monolayer materials opens doors for future practical flexible van der Waals devices such as, field effect transistors, memories, photodetectors and LED's which operate in the 1-2 Volt range"
This new technique allows for the creation of a host of fundamental nano-electronic and opto-electronic devices including dual gated graphene transistors, and vertical light emitting and detecting tunnelling transistors.
Dr Withers added, "The fact we start with a layered 2D semiconductor and convert it chemically to its oxide using laser irradiation allows for high-quality interfaces, which improve device performance.
"What's especially interesting for me is we found this oxidation process of the parent HfS2 to take place under laser irradiation even when its sandwiched between 2 neighbouring 2D materials. This indicates that water needs to travel between the interfaces for the reaction to occur."
The researchers demonstrated that ultrathin few-layer hafnium sulfide (HfS2) can be incorporated into a variety of van der Waals heterostructures. Then, laser irradiation can selectively transform these layers into an amorphous high-k oxide. They noted, that unlike ALD or sputtering, the use of photo-oxidized (in this case laser oxidized) HfS2 allows for clean interfaces without damaging the underlying 2D materials.
