Nanoscale thermal transport

Overview

Thermal transport and self-heating have become some of the most important limiting factors to increasing density, performance and reliability of many scaled devices for logic, storage and energy conversion.

Specifically future transistors, which will be characterized by low-dimensionality structures and numerous interfaces, are expected to be subject to serious self-heating problems. In these devices, heat generated in so-called hot spots has to be dissipated across many interfaces of dissimilar materials (semiconductors, metals, oxides). As thermal impedance mismatches between adjacent materials and confined geometries (thin films, nanowires) limit thermal transport, device-level thermal design has become necessary.

Whereas the reduction of thermal transport can degrade the performance and reliability of transistors, it can be beneficial in other devices. In particular, thermoelectrics are well known to show increased conversion efficiencies due to reduced thermal conductivities of nanostructures. In yet other devices, such as certain data storage systems, local heating is exploited to induce local switching of the storage materials properties [1].

For these applications, it is crucial to understand thermal phenomena at nanoscopic levels. Our work focuses on spatially resolved temperature sensing in nanoscale devices (e.g single nanowire devices) [2] and the study of thermal transport in nanostructures and nanoscopic contacts [3,4,5,6].

Scanning thermal microscopy

Scanning thermal microscopy

We use home-built scanning thermal microscopes and tips to determine thermal conductivity of nanostructures [3,4] and to measure temperature distributions [2]. In contrast to conventional thermometry, scanning thermal microscopy is based on nanoscale measurements. We find that the temperature sensor does not equilibrate with the sampled interaction volume under the scanning tip. In order to perform a quantitative analysis, the thermal conductance of the tip–surface contact needs to be quantified along with the temperature rise in the sensor [2].

Collaboration partners include the groups of Prof. A. Stemmer (ETH Zurich, Switzerland). Funding from the Swiss Science Foundation (SNF grant 134777) and the EU project Nanoheat is gratefully acknowledged.

Quantized thermal transport across mechanical contacts with atomic-scale roughness

In a recent study [5], heat transport was measured across nanoscale polished contacts exhibiting roughness only on the atomic scale. From the data on the pressure dependence of thermal conductance across such contacts it was possible to find evidence for the contribution of individual atoms to heat transport. A model was derived in which each contacting atom contributes a quantum of thermal conductance, thereby relating the atomistic nature of contacting surfaces to thermal transport.

References

[1] B. Gotsmann, U. Duerig,
“Nano-Thermomechanics: Fundamentals and Application in Data Storage Devices,”
in “Applied Scanning Probe Methods IV: Industrial Applications,”
B. Bushan and H. Fuchs (Eds.) (Springer, Berlin, Heidelberg, 2006) 215-250.
DOI.

[2] F. Menges, H. Riel, A. Stemmer, and B. Gotsmann,
“Quantitative thermometry of nanoscale hot spots,”
Nanoletters 12, 596-601 (2012).
DOI.

[3] B. Gotsmann, M.A. Lantz, A. Knoll, U. Duerig,
“Nanoscale Thermal and Mechanical Interactions Studied Using Heatable Probes,”
in “Nanotechnology vol. 6: Nanoprobes,”
Edited by H. Fuchs (Wiley-VCH, Weinheim, 2009) 121-169.
DOI.

[4] M. Hinz, O. Marti, B. Gotsmann, M. A. Lantz, U. D. Duerig,
”High resolution vacuum thermal microscopy of HfO2 and SiO2,”
Applied Physics Letters 92, 043122, 2008.
DOI.

[5] B. Gotsmann, M. A. Lantz,
“Quantized thermal transport across contacts of rough surfaces,”
Nature Materials 12, 59-65, 2012.
DOI.

[6] S. Karg, P. Mensch, B. Gotsmann, H. Schmid, P. Das Kanungo, H. Ghoneim, V. Schmidt, M. T. Björk, V. Troncale, H. Riel,
“Measurement of Thermoelectric Properties of Single Semiconductor Nanowires,”
Journal of Electronic Materials 42(7), 2409-2414, 2013.
DOI.

[7] F. Menges, H. Riel, A. Stemmer, C. Dimitrakopoulos, and B. Gotsmann,
“Thermal Transport into Graphene through Nanoscopic Contacts,”
Physical Review Letters 111, 205901 (2013).
DOI.

[8] B. Gotsmann, F. Menges, S. Karg, V. Troncale, M. Lantz, P. Mensch, H. Schmid, P. Das Kanungo, U. Drechsler, V. Schmidt, M. Tschudy, A. Stemmer, H. Riel,
“Heat dissipation and thermometry in nanosystems: When interfaces dominate,”
71st Annual Device Research Conference (DRC), pp. 231-232, 2013.
DOI.