Ultrafast Scanning Thermal Microscope Probes

热是一个普适量.由于所有的能量都转化为热，所以对热现象的研究适用于整个科学和工程领域。例如，许多现代半导体器件的性能受到其热性能的限制，例如RF功率晶体管、激光器、功率开关和微处理器。在宏观尺度上，热效应通常是缓慢的，因为热传输是扩散性的。扩散现象的一个特点是，它们的速度随着尺寸的变化而呈二次方增加：如果一个设备或温度计被做得小十倍，它的热响应就会快一百倍。在普通材料中，这种效应可以变得非常迅速，对于现代设备来说，在GHz范围内，这是一个与其工作频率相当的速率。在纳米尺度上，现代设备和材料的制造，热的传输不再是经典的和扩散的。热可以“弹道式”传播，而不会在小距离上散射，从而导致在小型设备中甚至更快的热传输，并且窄导线的热导率可以通过热导体的尺寸来量化，使得热导率的经典值不适用，并且预测这种系统的热性能变得不可能：它只能被测量。由于热通常通过被称为横向声学声子的声波传输，该声波可以具有接近材料中的原子间距的波长，因此材料之间的界面及其在原子尺度上的粗糙度的影响对结构良好的材料可以传导热的程度具有巨大的影响。这可以用于热电材料或热绝缘材料，或者当试图从诸如激光器或微处理器的设备中提取操作热时，这可能是一个巨大的问题。同样，由于原子尺度界面的技术控制是困难的，这使得界面之间的热传导无法预测，所以我们被迫测量它。扫描热显微镜是一种使用传感器探针在表面上进行机械扫描以在纳米尺度上测量局部温度的技术。这是非常有效的，但目前使用的传感器的响应时间非常慢，因为它们相对较大（约10微米），并且由大量的绝热材料支撑。该项目涉及对探头进行完全重新设计，使其更小，并且在制造时不使用厚的支撑结构。这将使传感器能够快速响应样品的温度变化，并允许在空间和时间域中以30nm x 30nm x 1ns的分辨率进行热测量。这种探头的重要性在于，它将首次能够在设备操作规模上测量设备和材料中的局部温升。至关重要的是，这将使我们能够通过热容区分热量被传导出去和热量被局部“储存”。该信息允许确定通过设备的热流路径，使设计人员能够控制它，并且还确定所达到的最高温度。由于器件的热降解受到“热激活能”的限制，因此器件的损坏率和寿命随温度呈指数变化：器件寿命由峰值温度而不是平均温度决定。由于材料的性质不简单地与尺寸成比例，并且由于设备的工作频率由设备尺寸固定，因此峰值温度的热测量只能在实际设备的空间和时间尺度上进行。所提出的工具独特地满足了现代技术成就核心的测量要求。

Heat is a universal quantity. Since all energy turns to heat, the study of thermal phenomena is applicable over the whole range of science and engineering. For example, the performance of many modern semiconductor devices are limited by their thermal performance e.g. RF power transistors, lasers, power switches and microprocessors. At the macroscopic scale thermal effects are generally slow, because heat transport is diffusive. A characteristic of diffusive phenomena is that they speed up quadratically with changes in dimension: If a device or thermometer is made ten times smaller it will have a thermal response which is a hundred times faster. In a normal material the effects can become enormously rapid, in the GHz range for modern devices which is a rate with is comparable to their operating frequency.At the nanometre scale, where modern devices and materials are fabricated, the transport of heat ceases to be classical and diffusive. Heat may travel "ballistically" without scattering across a small distance leading to even more rapid thermal transport in a small device and the thermal conductivity of narrow wires may be quantised by the dimensions of the thermal conductor so that classical values of thermal conductivity do not apply and prediction of the thermal performance of such systems becomes impossible: it can only be measured. Since heat is often transported by sound waves known as transverse acoustic phonons which may have a wavelength which approaches the atomic spacing in the material the influence of interfaces between materials and their roughness on the atomic scale has a huge effect on how well structured materials may conduct heat. This might be used to advantage in thermoelectric materials or thermally insulating materials, or it may be an enormous problem when trying to extract the heat of operation from a device such as a laser or microprocessor. Again, since the technological control of atomic scale interfaces is hard this makes thermal conduction across interfaces impossible to predict, so we are forced to measure it.Scanning Thermal Microscopy is a technique using the mechanical scanning of a sensor probe over a surface to make measurements of local temperature at the nanometre scale. This is very effective but currently the sensors used are very slow in response time, because they are relatively large (about ten micrometres) and are supported by large volumes of thermally insulating material. This project is concerned with the complete re-engineering of the probe to make it much smaller and to fabricate it without the use of thick support structures. This will allow the sensor to respond rapidly to the temperature variation of the sample and permit thermal measurements with a resolution of 30nm x 30nm x 1ns in the spatial and temporal domains.The importance of such a probe is that it will, for the first time, enable the measurement of local temperature rise in devices and materials on the scale of device operation. Crucially, this will allow us to distinguish between heat being conducted away and heat being locally "stored" by heat capacity. This information allows the path of flow of heat to be determined through a device, enabling the designer to control it, and also determines the maximum temperature achieved. Since the thermal degradation of devices is limited by "thermal activation energy" the rate of damage and hence the lifetime of a device varies exponentially with temperature: The device lifetime is determined by the peak temperature, not the average. Since the properties of a material do not scale simply with size, and since the operating frequency of devices is fixed by device size, thermal measurements of the peak temperature can only be made at the spatial and temporal scales of the actual device. The proposed tools uniquely fulfil this requirement for measurements at the very heart of modern technological achievements.