2D Arrays of Quantum Well Hall Effect Sensors for Picotesla Magnetometry of Inorganic and Organic Materials.

我的博士项目的主要目的是研究量子井霍尔效应(QWHE)传感器是否可以将其动态范围扩展到皮特斯拉范围。目前的技术和技术允许曼彻斯特大学开发的QWHE传感器达到非常低的纳米特斯拉范围。皮特斯拉磁学有着广泛的应用，如心磁图、考古学、地球物理测量、身体位置跟踪等等。目前，所有这些应用都是使用其他传感器来完成的(都是笨重和耗电的)。如果我的项目成功，那么QWHE传感器将可用于各种不同的应用，从而改进各自的系统，因为QWHE传感器具有以下特点：重量轻、体积小、在大范围内呈线性、与其他传感器相比更灵敏、功耗更低。因此，这可能会改善这些不同和重要领域的绩效。动态范围下限的主要限制是电子噪声。对于QWHE传感器，这以闪烁噪声、热噪声、散粒噪声和发电重组噪声的形式出现。有许多技术可以绕过噪声，例如超外差混频，它的工作原理是将测量频率从闪烁噪声的领域转移出来。然而，这个项目试图找到另一种方法，可以在超外差混频之前完成。这个项目提出的问题是，‘QWHE传感器的并联能提高传感器的性能吗？’这将创建一个传感器阵列，其行为就像一个动态范围具有下限的传感器。这依赖于物理学中一个非常简单的部分，即平行连接。元件的并联通常会导致它们的电阻降低1/N，其中N是传感器的数量。这个项目接着提出的问题是，这是否适用于QWHE传感器？以及‘这对测量有什么影响？’理论很简单，如果电阻下降1/N，那么总体噪声应该会减少，因为前面提到的所有四种类型的噪声都会受到电阻的影响。实现这一目标的目标如下。创建一个2x2阵列(4个传感器)的小测试电路，看看是否可以观察到这些现象。将测试电路扩展到更大的阵列。看看这种现象是否适用于更大的阵列。将阵列从印刷电路板规模移动到结晶级(将允许数千个传感器并行在一起)。将超外差混频和其他降噪技术应用于阵列，以进一步降低噪声，进入皮特斯拉范围。在功率需求/动态范围/灵敏度之间找到平衡点，从而创建适用于皮特斯拉磁力测量的设备。下一个问题是，为什么要写这部小说？为什么只有QWHE效应传感器才能做到这一点？这主要是由于尺寸和功率要求，诸如磁通门之类的传感器非常大，很难(如果不是不可能)排列非常多的传感器。有一些来源使用了与本项目建议的类似方式的GMR阵列，但在大小和功率要求变得令人望而却步之前，他们只展示了高达几百的N值。与其他传感器不同，QWHE传感器本身就是半导体器件。这意味着它们拥有非常小的芯片尺寸(大约200微米乘200微米，传感面积低至5微米乘5微米)，功耗要求非常低(毫瓦)。因此，QWHE技术非常适合大规模阵列的概念。总之，QWHE传感器的固有特性适合于大规模并行阵列，这将大大降低它们的电子噪声。这应该会将传感器的动态范围增加到皮特斯拉范围。博士打算对这些现象进行调查。

The principle aim of my PhD project is investigating whether Quantum Well Hall Effect (QWHE) sensors can have their dynamic range extended into the pico-tesla range. Current technologies and techniques allow the QWHE sensors, developed at the University of Manchester, to reach the very low nano-tesla range. There is a wealth of applications in pico-tesla magnetometry such as; Magneto cardiograms, Archaeology, Geophysical surveying, Body-position tracking, and many more. Currently all these applications are done using other sensors (all bulky and power hungy). If my project is successful, then QWHE sensors will be usable in this diverse range of applications leading to improvements in their respective systems as QWHE sensors are: light, small, linear over a large range, more sensitive, and low power when compared to other sensors. This could, therefore, lead to improved performance in these different and important fields. The main limitation on the lower end of the dynamic range is electronic noise. For QWHE sensors this comes in the form of flicker noise, thermal noise, shot noise, and generation-recombination noise. There are numerous techniques that can circumnavigate noise such as superheterodyne mixing which works by shifting the measuring frequency out of the realms of flicker noise. However, this project seeks to find another method that can be done before super-heterodyne mixing. The question this project asks is, 'can the sensor performance be improved by parallel connections of QWHE sensors?' This will create an array of sensors that behave as one with a lower limit on its dynamic range. This relies on a very simple part of physics, parallel connections. Connecting components in parallel usually causes their resistance to decrease by a factor of 1/N, where N is the number of sensors.The question this project then asks is 'Does this apply to the QWHE sensors?' and 'What effect does this have on the measurements?'. The theory then is simple, if the resistance goes down by a factor of 1/N then the overall noise should decrease, as all 4 types of noise previously mentioned are affected by the resistance. The objectives to achieve this are as follows. Create a small test circuit of a 2x2 array (4 sensors) and see if the phenomena can be observed. Extend the test circuit to a larger array. See if the phenomena hold true for larger arrays. Move the array from the PCB scale to the crystalline level (will allow several thousand sensors to be paralleled together). Apply superheterodyne mixing and other noise reduction techniques to the arrays to further reduce noise and enter the pico-tesla range. Find the balance between power demands/dynamic range/sensitivity that creates a useable device for implementation in pico-tesla magnetometry. The next question is why is this novel? Why can this only be done with QWHE effect sensors? This is mostly due to size and power requirements, sensors such as fluxgates are very large, and it difficult, if not impossible, to array very many. There are sources where groups have used arrays of GMRs in a similar fashion to what this project suggests but they only demonstrate N values up to a couple of hundred, before size and power requirements become prohibitive. QWHE sensors being novel in of themselves are, unlike other sensors, semiconductor devices. This means they boast very small die size (approximately 200 microns by 200 microns with sensing area as low as 5 microns x 5 microns), very low power requirements (milliwatts). QWHE technology therefore lends itself well to the concept of large number arraying.In conclusion the inherent properties of QWHE sensors lend themselves to large scale parallel arraying, which will greatly reduce their electronic noise. This should increase the dynamic range of the sensors into the pico-tesla range. The PhD intends to investigate these phenomena.