Thermal imaging with ultrafine spatial resolution in the scanning electron microscope

从手机到笔记本电脑再到物联网，现代微电子的决定性趋势是在更小的区域内封装更多处理能力的不懈努力。一个必然的结果是，单位面积的散热也呈指数级增长，这对热管理提出了严峻的挑战，以防止设备过热。一些尖端技术利用纳米级热现象，如热辅助磁记录和电阻随机存取存储器，它们依赖于在~10纳米及以下的非常小的长度尺度上精确的热产生和耗散。显然，这种先进的纳米级器件的合理设计需要测量它们的温度，但在如此小的长度尺度上直接实验测量温度仍然是非常具有挑战性的。理想的测量技术的空间分辨率为10纳米或更小，无需与样品进行物理接触，可以在许多材料上工作，并使用广泛可用的硬件。开发这样一种度量技术是这个项目的首要目标。在初步概念验证研究的基础上，该项目的目标是开发一种新的扫描电子显微镜测温技术，使其成为一种强大的温度测绘工具。该团队专注于无处不在的二次电子信号，这已经是超高分辨率（~1 - 10纳米）结构和几何映射的标准。该提案设想了三个主要的推力：(i)通过实验澄清温度如何影响二次电子信号的基本物理学。（ii）严格测量和理解该技术在温度、空间和时间上的极限分辨率。（iii）证明这种新的实验工具对纳米级热现象的创新研究以及在器件表征中的应用的有用性。这个项目的智力价值首先在于将扫描电子显微镜测温技术发展成为一种强大的实用工具，可以使用广泛可用的信号和硬件，实现~10纳米空间分辨率的温度测绘。另一个贡献是将严格量化空间分辨率的概念从光学引入到热学界，特别是热点扩散函数。最后，该团队将应用该工具，通过绘制完整的温度场，对温度逆转和定位等弹道现象进行首次直接观察。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.