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

我博士项目的主要目的是研究量子阱霍尔效应（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由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。皮特斯拉磁强计有丰富的应用，如；磁心图，考古学，地球物理测量，身体位置跟踪，以及更多。目前，所有这些应用都是使用其他传感器完成的（体积庞大，耗电量大）。如果我的项目成功，那么QWHE传感器将可用于各种应用，从而改进各自的系统，因为QWHE传感器具有：轻，小，大范围线性，更敏感，与其他传感器相比功耗低。因此，这可能导致在这些不同的和重要的领域提高性能。动态范围下端的主要限制是电子噪声。对于QWHE传感器，这些噪声以闪烁噪声、热噪声、射散噪声和生成重组噪声的形式出现。有许多技术可以绕过噪声，如超外差混频，其工作原理是将测量频率移出闪烁噪声的范围。然而，本项目试图找到另一种方法，可以在超外差混合之前完成。这个项目提出的问题是，“QWHE传感器的并联是否可以提高传感器的性能？”这将创建一个传感器阵列，其行为就像一个具有动态范围下限的传感器。这依赖于物理学的一个非常简单的部分，平行连接。并联元件通常会使它们的电阻降低1/N，其中N是传感器的数量。这个项目接下来要问的问题是“这是否适用于QWHE传感器？”和“这对测量有什么影响？”理论很简单，如果电阻降低1/N，那么整体噪声应该降低，因为前面提到的所有4种噪声都受到电阻的影响。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种现象。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数组。将阵列从PCB尺度移动到晶体水平（将允许数千个传感器并联在一起）。对阵列应用超外差混频等降噪技术，进一步降低噪声，进入皮特斯拉范围。找到功率需求/动态范围/灵敏度之间的平衡，为实现皮特斯拉磁强计创建可用的设备。下一个问题是为什么这是小说？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的要求，传感器，如磁通门是非常大的，它很难，如果不是不可能，阵列非常多。有一些研究小组已经以类似于本项目建议的方式使用了gmr阵列，但他们只演示了N值高达几百，在尺寸和功率要求变得令人望而却步之前。与其他传感器不同，QWHE传感器本身就是一种新颖的半导体器件。这意味着它们拥有非常小的芯片尺寸（大约200微米× 200微米，传感面积低至5微米× 5微米），非常低的功率要求（毫瓦）。因此，QWHE技术可以很好地应用于大数数组的概念。综上所述，QWHE传感器的固有特性使其适合大规模并行阵列，这将大大降低其电子噪声。这将增加传感器的动态范围到皮特斯拉范围。博士打算研究这些现象。

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.