2-Dimensional Magnetoresistance Imager

1988年，磁性多层材料中巨磁电阻（GMR）的发现，将磁电阻的典型值从1-2%提高到10-100%，激发了自旋电子学领域的广泛研究。这是对高灵敏度磁流变体传感器的需求，在15年内，磁流变体传感器被引入到硬盘的读头中。他们的表现是如此成功，该技术现在被转移到其他部门，如运动，位置，旋转和现场传感；例如在汽车和生物系统中。这些传感器的纳米级特性使它们与纳米技术高度兼容。虽然制造这种复杂传感器的能力已经被磁记录工业证明，但这些材料在纳米尺度上工作，层的厚度通常是纳米。质量控制至关重要。理想情况下，应该测试设备的功能特性，在这种情况下，其MR的电气测量需要电流通过触点通过样品，导致表面损坏和污染。更重要的是，电测量无法提供空间分辨率，无法提供晶圆片上的变化信息。此外，在光刻图案之后测试晶圆片的性能是不切实际的，因此传感器的特性要经过后续昂贵的复杂阶段才能确定。因此，明确需要一种非接触式、非破坏性的mr表征方法，使用红外电磁辐射提供了所有这些优点。我们率先使用红外反射和透射作为mr探针，基于这一经验，我们最近提出了一种使用热发射率的替代方案。与反射相比，这与MR的关系更大，更直接，并且易于在数十微米的尺度上实现空间分辨率。这项技术依赖于电阻和辐射率之间的联系，辐射率是材料根据其温度发射辐射的效率。发射率取决于材料的表面特性，在长红外波长（bbb50微米）与电阻的平方根成正比。我们探测到由于电阻的变化而引起的辐射强度的变化。用红外探测器测量辐射，并将其转换为表观温度。当磁场作用于GMR薄膜时，其电阻降低，因此其发射率降低。较低的发射率导致较少的辐射被发射，这被探测器解释为温度的降低。因此，GMR表现为外加磁场中温度的明显变化。当探测器被CCD相机取代时，这种技术的力量就实现了，CCD相机可以产生二维的视温度图像。通过对不同磁场下的温度图像进行相减，产生由电阻变化引起的温度变化图像，从而独特地提供了空间分辨的磁电阻图像。我们建议开发一种能够进行二维磁共振成像的仪器，用于进行GMR晶圆的质量控制。成功的开发将引领晶圆在生长腔内的原位测量，在光刻图像化过程的不同阶段对材料进行评估，并开辟新的应用，例如在MR中故意引入空间变化用于模式识别。

The discovery of Giant Magnetoresistance (GMR) in magnetic multilayers in 1988, which increased typical values of magnetoresistance (MR) from 1-2% to 10-100%, stimulated extensive research leading to the field of spintronics. Such was the demand for highly sensitive MR sensors, that within 15 years, GMR sensors had been introduced into the read head of magnetic hard disks. Their performance has been so successful that the technology is now being transferred to other sectors such as motion, position, rotation and field sensing; for example in automotive and biological systems. The nanoscale nature of these sensors makes them highly compatible with nanotechnology. Although the ability to manufacture such complex sensors has been proven by the magnetic recording industry, these materials operate on the nanoscale, and layer thicknesses are typically a nanometre. Quality control is crucial. Ideally, the functional property of the device should be tested, in this case, its MR. Electrical measurements of MR require an electric current to be passed through the sample via contacts, resulting in surface damage and contamination. More importantly, electrical measurements offer no spatial resolution, providing no information about variations across the wafer. Furthermore, it is impractical to test the performance of the wafer following lithographic patterning and so sensor characteristics cannot be determined until after subsequent costly intricate stages. There is therefore a clear requirement for a contactless, non-destructive method for characterising MR. Using electromagnetic radiation in the infrared provides all these advantages. We have pioneered the use of reflection and transmission of infrared as a probe of MR. Based on this experience, we recently proposed an alternative using thermal emissivity. This presents a larger and more direct relationship with MR than reflection, and additionally lends itself readily to spatial resolution on the scale of tens of microns. The technique relies on the connection between electrical resistance and emissivity, the efficiency with which a material emits radiation according to its temperature. Emissivity depends on the surface properties of a material and at long infrared wavelengths (> 5 microns) is directly proportional to the square root of resistance. We detect the change in the intensity of the emitted radiation due to a change in resistance. The radiation is measured using an infrared detector and converted into an apparent temperature. When a magnetic field is applied to a GMR thin film, its resistance and consequently its emissivity reduces. The lower emissivity results in less radiation being emitted and this is interpreted by the detector as a reduction in temperature. The GMR therefore manifests itself as an apparent change in temperature in an applied magnetic field. The power of this technique is realised when the detector is replaced by a CCD camera generating a 2D image of the apparent temperature. By subtracting temperature images in different magnetic fields, an image is produced of the change in temperature resulting from the change in resistance, uniquely providing a spatially resolved image of the magnetoresistance.We propose the development of an instrument capable of 2D imaging of MR designed to carry out the quality control of GMR wafers. Successful development will lead the way for insitu measurement of wafers whilst still inside a growth chamber, the evaluation of material at different stages of the lithographic patterning process and open up new applications such as the deliberate introduction of spatial variations in MR for use in of pattern recognition.