Dielectrophersis Control of InAs based Nanowires for bio sensing

半导体器件越来越多地用于基于医疗保健的传感器应用中，这是由于它们通过其电学和光学特性的改变来检测其周围环境的微小变化的优异能力。最近，人们对半导体纳米线产生了很大的兴趣，这些线从半导体表面垂直向上生长，其中纳米线已经从一系列化合物半导体中得到证明，所述化合物半导体包括砷化镓、磷化镓、砷化铟和锑化铟。这些线的生长要么通过最初在表面上沉积微小的金属液滴，要么通过在氧化物掩模中形成纳米级的孔来启动。这些纳米线在生物传感和医疗保健应用中具有特殊的意义，首先，它们的小尺寸使它们成为集成分子和其他光学和电学元件的理想材料。其次，由于金属丝的圆柱形形状，大部分电荷驻留在表面上，使它们对环境的变化特别敏感，例如由不同生物标记物的存在引起的变化。然而，生长的垂直性质和所得的器件几何形状严重限制了这些纳米线的开发，因为纳米线通常被平面化并封装在聚合物层下。这导致相对较大的最终器件，并且还抑制了大部分表面电荷。本论文的工作为利用介电电泳技术开发纳米线传感器和器件提供了一个新的突破。这是一个过程，其中施加的非均匀电场的结果在带电粒子上的力。通过适当地控制电场，可以利用该过程来精确地移动和定位颗粒。为了实现这一点，将纳米线从其天然生长基底上移除，然后分散在溶剂中，然后进行介电泳以将纳米线定位在预定位置。由于能够将纳米线直接与微流体和其他光学或电气系统集成，从而利用该技术提供的准确和可靠的定位，这为进行纳米线生物传感和监测提供了有吸引力的途径。另一个优点是，通过该技术形成的纳米线器件可以以水平而不是垂直配置实现。这将使与其他组件的集成更加简单，也使纳米线的整个表面与其环境相互作用，大大提高了导线对环境变化的敏感性。这些潜在的好处提供了可能性，大大提高纳米线传感器和器件的性能，以及使制造更有效，以降低成本。具体而言，本项目旨在通过介电电泳制造纳米线器件，建立工艺参数和最终器件的电，光学和物理特性之间的关系，为可预测的器件制造开辟了一条路线。最后，纳米线设备将与微流体系统集成，以演示离子流传感器，允许在紧凑的芯片设备实验室中监测液体的浓度和流速。

Semiconductor devices are increasingly being utilized in healthcare based sensor applications due their excellent ability to detect minute changes in their surroundings due via alterations in their electrical and optical properties. Recently there has been much interest in semiconductor nanowires, these wires are grown vertically upwards from a semiconductor surface, with nanowires having been demonstrated from a range of compound semiconductors including, Gallium Arsenide, Gallium Phosphide, Indium Arsenide and Indium Antimony. Growth of these wires is initiated either by initially depositing tiny metal droplets on the surface or by forming nanoscale holes in an oxide mask. The resultant nanowires can have lengths in excess of 1um and diameters below 100nm.These nanowires are of particular interest for bio-sensing and healthcare applications for a number of reasons, firstly their small size makes them ideal to integrate molecules and other optical and electrical components. Secondly due to the cylindrical shape of the wires the majority of the charge resides on the surface making them especially sensitive to changes in their environment, for example arising from the presence of differing bio-markers. However the vertical nature of the growth and resultant device geometry severely limits the exploitation of these nanowires as the nanowires are routinely planarised and encapsulated under a polymer layer. This results in a relatively large final device and also supresses much of the surface charge. The proposed work here offers a step-change in the development of nanowire based sensors and devices by utilizing the process of dielectrophoresis. This is a process whereby the application of a non-uniform electric field results in a force upon a charged particle. By appropriately controlling the electric field it is possible to utilize this process to accurately move and position particles. To achieve this the nanowires will be removed from their native growth substrate and then dispersed in solvent before undergoing dielectrophoresis to position the wires at pre determined positions. This offers an attractive route to undertake nanowire bio-sensing and monitoring due to the ability to integrate the nanowires directly with microfluidics and other optical or electrical systems thus exploiting the accurate and reliable positioning offered by this technique.A further advantage is that nanowire devices formed via this technique can be achieved in a horizontal rather than vertical configuration. This will make integration with other components much more straightforward and also enable the whole surface of the nanowire to interact with its environment, greatly enhancing the sensitivity of the wires to any changes in their environment. These potential benefits offer the possibility to greatly enhance the performance of nanowire based sensors and devices as well as enabling to be fabricated more efficiently and at a reduced cost.Specifically this project aims to fabricate nanowire devices via dielectrophoresis, establishing relationships between the process parameters and the final devices electrical, optical and physical characteristics, opening a route for predictable device fabrication. Finally nanowire devices will be integrated with microfluidic systems to demonstrate an ionic flow sensor, allowing both the concentration and flow rate of liquids to be monitored in a compact lab on a chip device.