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，现代微电子的定义趋势是坚持不懈地在更小的区域中封装更多的处理能力。一个必然结果是，单位面积的散热也呈指数级增长，这给热管理带来了严峻的挑战，以防止设备过热。一些前沿技术利用了纳米级的热现象，如热辅助磁记录和阻性随机存取存储器，这些现象依赖于在~10 nm及以下的极小长度尺度上精确的热产生和散热。显然，这种先进的纳米设备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进行温度实验测量仍然具有极大的挑战性。理想的测量技术应该具有10纳米或更低的空间分辨率，操作时不需要与样品进行物理接触，可以处理多种材料，并使用广泛可用的硬件。开发这样的测量技术是该项目的总体愿景。该项目的目标是在初步概念验证研究的基础上，将一种新的扫描电子显微镜测温技术开发成一种强大的温度映射工具。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 nm)结构和几何图形绘制的标准。该提案设想了三个主要方面：(I)通过实验阐明温度如何影响二次电子信号的潜在物理学。(Ii)严格测量和理解这项技术在温度、空间和时间上的极限分辨率。(3)展示这一新的实验工具对纳米尺度热现象的创新研究以及在设备表征中的应用的有用性。该项目的智能优点是首先利用广泛可用的信号和硬件，将扫描电子显微镜测温技术发展成为一种强大的、实用的温度映射工具，空间分辨率为~10 nm。另一项贡献将是将严格量化空间分辨率的概念从光学引入热学领域，特别是热点扩散函数。最后，该团队将应用该工具，通过绘制弹道现象的完整温度场图，对弹道现象进行首次直接观测，如温度反转和局部化。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.