From cell phones to laptops to the internet of things, the defining trend of modern microelectronics is the relentless drive towards packing more processing power in smaller areas. A corollary is that the heat dissipation per unit area also increases exponentially, posing serious challenges in thermal management to keep the devices from overheating. Some cutting-edge technologies exploit nanoscale thermal phenomena such as heat-assisted magnetic recording and resistive random access memory, which rely on precise heat generation and dissipation at extraordinarily small length scales of ~10 nm and below. Clearly the rational design of such advanced nanoscale devices requires measuring their temperatures, yet direct experimental measurement of temperature at such small length scales remains extraordinarily challenging. An ideal measurement technique would have spatial resolution of 10 nm or less, operate without physical contact to the sample, work on many materials, and use widely available hardware. Developing such a measurement technique is the overarching vision of this project.
Building on a preliminary proof-of-concept study, the goal of this project is to develop a novel scanning electron microscopy thermometry technique into a robust tool for temperature mapping. The team focuses on the ubiquitous secondary electron signal, which is already the standard for ultrahigh resolution (~1 - 10 nm) mapping of structure and geometry. The proposal envisions three major thrusts: (i) Experimentally clarify the underlying physics of how temperature affects the secondary electron signal. (ii) Rigorously measure and understand the limiting resolutions of this technique, in temperature, space, and time. (iii) Demonstrate the usefulness of this new experimental tool for innovative studies of nanoscale thermal phenomena as well as applications in device characterization. The intellectual merit of this project is firstly in developing scanning electron microscopy thermometry into a robust, practical tool for temperature mapping with ~10 nm spatial resolution, using signals and hardware which are widely available. Another contribution will be bringing concepts for rigorously quantifying spatial resolution from optics into the thermal community, specifically the thermal point spread function. Finally, the team will apply the tool to pursue the first ever direct observations of ballistic phenomena such as temperature reversal and localization via mapping their full temperature fields.
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.
