The Woodruff School

SUMMARY

Increased power density in modern microelectronics has led to thermal management challenges which can degrade performance and reliability as well as shorten device lifetime. As critical dimensions continue to decrease, the interfaces of dissimilar materials (e.g., metal/semiconductor) can limit heat removal from the device active region. Improving the thermal transport across interfaces is critical to the design process and necessitates accurate measurement of the thermal boundary conductance (TBC) and understanding of transport mechanisms.

Graphene, a two-dimensional (2D) semimetal composed of a single layer of sp2 bonded carbon atoms, has emerged as a potential candidate for next generation nanoelectronic devices because of its exceptional transport properties; however, the thermal interaction between graphene and other materials (e.g., metals) has only recently begun to be understood. Here, the TBC at metal/graphene/metal interfaces is measured at room temperature using time-domain thermoreflectance (TDTR). The metals used in this study represent two classes based on the type of bonding formed with graphene. Graphene and 2D hexagonal boron nitride (h-BN) have attracted interest as a conductor-insulator pair in next-generation devices because of their unique physical properties; however, the thermal interactions at the interface must be understood to accurately predict the performance of heterostructures composed of these materials. This work uses TDTR to estimate the TBC at the interface of h-BN and graphene. In addition, the phonon transmission and TBC at the h-BN/graphene interface is predicted by two forms of the diffuse mismatch model.

The electrical properties of 2D, semiconducting transition metal dichalcogenides (TMDs) such as molybdenum diselenide (MoSe2) have been studied extensively, including the metal/TMD electrical contact resistance, but the thermal properties have received much less attention. This work proposes to measure and analyze the TBC across the metal/MoSe2/SiO2 interface using TDTR. The results of this study will highlight the importance of the choice of metal contacts in future TMD devices. Finally, the in-plane thermal conductivity of MoSe2 will be measured using Raman spectroscopy. Overall, the findings presented in this work will improve the understanding of nanoscale thermal transport with applications to current as well as future electronic materials and devices.

SUBJECT:	Ph.D. Proposal Presentation

BY:	David Brown

TIME:	Thursday, May 10, 2018, 10:00 a.m.

PLACE:	MRDC Building, 2405

TITLE:	Experimental Characterization of Thermal Transport in Two-Dimensional Materials and Their Heterostructures

COMMITTEE:	Dr. Satish Kumar, Co-Chair (ME) Dr. Baratunde A. Cola, Co-Chair (ME) Dr. Samuel Graham (ME) Dr. Matthew McDowell (ME) Dr. Eric Vogel (MSE)

SUMMARY Increased power density in modern microelectronics has led to thermal management challenges which can degrade performance and reliability as well as shorten device lifetime. As critical dimensions continue to decrease, the interfaces of dissimilar materials (e.g., metal/semiconductor) can limit heat removal from the device active region. Improving the thermal transport across interfaces is critical to the design process and necessitates accurate measurement of the thermal boundary conductance (TBC) and understanding of transport mechanisms. Graphene, a two-dimensional (2D) semimetal composed of a single layer of sp2 bonded carbon atoms, has emerged as a potential candidate for next generation nanoelectronic devices because of its exceptional transport properties; however, the thermal interaction between graphene and other materials (e.g., metals) has only recently begun to be understood. Here, the TBC at metal/graphene/metal interfaces is measured at room temperature using time-domain thermoreflectance (TDTR). The metals used in this study represent two classes based on the type of bonding formed with graphene. Graphene and 2D hexagonal boron nitride (h-BN) have attracted interest as a conductor-insulator pair in next-generation devices because of their unique physical properties; however, the thermal interactions at the interface must be understood to accurately predict the performance of heterostructures composed of these materials. This work uses TDTR to estimate the TBC at the interface of h-BN and graphene. In addition, the phonon transmission and TBC at the h-BN/graphene interface is predicted by two forms of the diffuse mismatch model. The electrical properties of 2D, semiconducting transition metal dichalcogenides (TMDs) such as molybdenum diselenide (MoSe2) have been studied extensively, including the metal/TMD electrical contact resistance, but the thermal properties have received much less attention. This work proposes to measure and analyze the TBC across the metal/MoSe2/SiO2 interface using TDTR. The results of this study will highlight the importance of the choice of metal contacts in future TMD devices. Finally, the in-plane thermal conductivity of MoSe2 will be measured using Raman spectroscopy. Overall, the findings presented in this work will improve the understanding of nanoscale thermal transport with applications to current as well as future electronic materials and devices.