9 March 2015

US-Ireland UNITE initiative developing 2D transition metal dichalcogenide materials

Ireland's Tyndall National Institute (based at University College Cork) says it is participating in a three-year US-Ireland collaborative project that aims to reduce power consumption and increase battery life in mobile devices. Under the auspices of the US-Ireland Research and Development Partnership (launched in 2006), researchers will explore new semiconducting materials enabling the further miniaturization of transistors.

Researchers in the Republic of Ireland (Tyndall National Institute & Dublin City University), Northern Ireland (Queens University Belfast) and the US (University of Texas at Dallas) - funded by €343,000 from Science Foundation Ireland (SFI), £319,859 from Invest Northern Ireland (InvestNI) and $420,000 from the US National Science Foundation (NSF) government agencies respectively - are collaborating to develop ultra-efficient electronic materials through the UNITE project 'Understanding the Nature of Interfaces in Two-Dimensional Electronic Devices'.

UNITE's principal investigators are professor Robert Wallace at the University of Texas at Dallas, professor Greg Hughes at Dublin City University, Dr David McNeill at Queens University Belfast and Dr Paul Hurley at Tyndall National Institute.

UNITE will create and test the properties of atomically thin, two-dimensional layers of transition metal dichalcogenide (TMD) semiconductors. The properties these materials have displayed to date suggest that they could facilitate extremely efficient power usage and high-performance computing.

"Materials that we are currently reliant on, such as silicon, are soon expected to reach the limit of their performance," says Hurley. "If we want to continue to increase performance, while maintaining or even reducing power consumption, it is important to explore these new TMD materials."

Specifically, UNITE is investigating the synthesis, device fabrication and characterization of 2D TMDs for applications in low-voltage tunnel field-effect transistors. The researchers will explore two separate routes to large-area synthesis through van der Waals epitaxy and atomic layer deposition (ALD). In parallel, characterization and understanding of the surfaces and interfacial regions between commercially available bulk crystals and technologically relevant contacts and insulators will be conducted. This will be accomplished using a combination of in-situ and ex-situ characterization covering questions such as: how can 2D semiconductor surfaces be functionalized to allow uniform and continuous oxide thin films to be formed by ALD; can capacitance-voltage based metrology be applied to metal-oxide-semiconductor systems on 2D semiconductor surfaces; what is the nature of conduction for metal contacts on 2D semiconductors; and how are the atomic-scale electrical properties related to larger-area contacts. The development of growth methods for large-area substrates will not only demonstrate the potential to move 2D semiconductor-based transistors from research to production, but will also provide a source of technologically interesting 2D semiconductor materials for basic study that are not commonly available through geological sources. Finally, the growth and characterization studies will be applied to the fabrication of a tunnel field-effect transistor based on 2D heterostructures.

It is reckoned that, if the UNITE team can understand the issues relating to large-area 2D synthesis, uniform insulator deposition, ohmic contact formation, and charge transport in single- or few-layer 2D semiconductors, then this knowledge will be relevant to a range of potential device architectures.

The application of such 2D TMD materials in transistors could hence not only prolong the battery charge life of portable devices and phones, but also have applications in larger more power-intensive operations such as data storage and server centres. This will have environmental benefits through the reduction of electrical energy consumed by information and communication technologies as well as benefitting consumers.

UNITE builds on the previous US-Ireland collaborative project 'FOCUS' between these academic research partners. The success of this project played a role in demonstrating why funders should back the new project, including training five graduate students in the USA and Ireland, as well as student exchanges between the institutes.

Tags: Tyndall Metal dichalcogenide heterostructure ALD

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