NSF-SNSF: Uncovering the Thermal Implications of Contact Scaling and Structure in 2D Semiconductors

This NSF project is a collaboration between researchers from Duke University and ETH-Zürich (their portion funded by the Swiss National Science Foundation) and aims to explore the thermal impacts of shrinking down the size of metal contacts to two-dimensional (2D) semiconductors. There is ongoing interest in using 2D semiconductors to enable the continuation of Moore’s law beyond the physical limits of silicon-based technology.

While transistors from 2D materials show great promise, there is very little known about how thermal effects will impact their performance and the nature of electrical transport at small dimensions. Because heating will be of great importance for a fully integrated technology, it is imperative that such effects are well understood. Hence, this project will combine experimental (Duke) and theoretical (ETH-Zürich) exploration of different 2D semiconductor device structures with emphasis on the role of thermal effects.

In addition to the scientific advancements, this project will also make an intentional impact on the broader community through outreach and recruitment efforts. One way will consist of bringing hands-on lab experiences to the classrooms: Duke’s portable scanning electron microscope will be brought to local high schools in the Durham area, which has a high population of students from underrepresented backgrounds.

New material will also be developed and integrated into relevant graduate courses at both Duke and ETH-Zürich based on findings in this project.

The thermal implications of distinct contact structures to transition metal dichalcogenides (TMDCs), including the impact of scaling, will be examined in this project. As testbed, tungsten disulfide, one of the most prominent members of the TMDC family, will be used because it can act both as n- and p-type transistor. The contact issue will be addressed from an experimental and theoretical point-of-view by combining the expertise of two researchers, Prof.

Aaron D. Franklin at Duke University (USA) and Prof. Mathieu Luisier at ETH Zürich (Switzerland).

Goals for the project include: 1) Developing an apparatus for performing nanoscale thermal mapping of 2D contact structures; 2) Fabricating tungsten disulfide transistors with top, edge, and mixed contact structures; 3) Ab initio electrical and thermal quantum transport modeling of contacts validated with experimental data; 4) Characterization, electrical and thermal, of tungsten disulfide transistors with different elemental metals; 5) Moment-tensor potential force-field materials combined with tungsten disulfide for modeling contacts; and 6) Experimental and theoretical demonstration of tungsten disulfide transistors with enhanced performance. Principal investigator (PI) Franklin will concentrate on the fabrication of tungsten disulfide transistors with advanced contact structures relying on different metals and geometries and on their electrical and thermal characterization.

International partner Luisier, who has pioneered nanoscale device modeling techniques, will provide theoretical insights into the contact physics through ab initio simulations based on electron and phonon quantum transport and will deliver design guidelines to the experimental partner at Duke University. Targeted as part of this project are scalable contact configurations to mono-, bi-, and trilayer tungsten disulfide with relatively low electrical resistances, high thermal boundary conductance, and little device-to-device variability.

Satisfying these requirements is essential to enable the deployment of the 2D technology into mainstream integrated circuit applications.

This collaborative U.S.-Swiss project is supported by the U.S. National Science Foundation (NSF) and the Swiss National Science Foundation (SNSF), where NSF funds the U.S. investigator and SNSF funds the partners in Switzerland.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.