Nano-structured RC Networks - A Pathway To Artificial Skin

这项雄心勃勃的研究计划将开发一种位置敏感的触摸传感器，该传感器在制造后可以适应灵活的不规则表面，因此可以作为人造皮肤移植物中的传感元件。该传感器的愿景是其低功耗、大面积和简单的器件架构将有助于其适应医疗保健应用的能力。“随机阻抗网络传感器”（RINS）的概念源于人工合成的原子级薄材料的形态，这些材料几乎完全以多晶形式生长。在高端应用中通常避免半导体中的多晶性，因为i）它们的电阻率高于它们的单晶（MC）等效物，以及ii）每对微晶（或晶粒）被非晶和富含缺陷的界面（晶界）分开，这是电阻率的额外来源。少数例外情况，如简并掺杂多晶硅（PC），用作MOSFET的栅极金属，或在低端消费级产品中销售的PC-Si光伏电池，突出了PC材料在全球微电子行业中的边缘地位。第一个假设是，PC薄膜是固有的自由电荷载流子耗尽，由于介电失配与他们的环境。更少的电荷载流子意味着静电屏蔽效率降低，并且表现为非常长的屏蔽长度和宽的捕获横截面。这转化为对静电事件的长距离敏感性，例如手指的触摸。第二个假设是，晶粒和晶界的复杂网络形成了电阻器（晶粒）和压控电容器（边界）的随机定向网络，其显示直流电阻和交流电抗。所得到的膜阻抗是偏置相关的、非线性的，并且关键地是位置相关的，因为沿着材料的每个电流路径携带签名阻抗特性。这些假设的结合使得能够通过三角测量其在表面上的位置来定位任何静电事件，例如手指触摸，使得PC薄膜成为位置敏感应用的理想基底。为了实现位置敏感触摸传感中的这种新范例，需要知道晶粒-晶粒边界系统的完整电子结构，并且需要很好地理解电荷载流子穿过它的传输机制。研究方法将包括功能探针显微镜与宏观运输测量相结合，这将为RINS探测器的设计提供信息。最后，我们的目标是开发传感器本身，并设计的方法，其表面上的静电“事件”被映射到他们的确切位置使用阅读从几个低功耗的外围probes.The提出的传感机制和传感器之间的鲜明区别，今天转化为令人兴奋的新应用的机会。目前，电容式触摸传感器（诸如在移动的电话和平板设备中使用的那些）由稀土材料制成的透明电极的正交网格组成。这限制了它们在刚性表面上的应用，或者在大的预定义曲率半径上是柔性的表面上的应用。这里提出的传感器通过仅使用外围电极克服了这种限制，从而减轻了对刚性网格图案化的需要。此外，在电流传感器中，通过两个正交电极之间的重叠节点处的电容变化以及它们附近的节点来推断位置。这意味着节点需要顺序寻址和读取，使得响应时间很长，特别是在大表面上。使用很少的外围探头，所有连续读取，意味着处理信息可以快速完成，并在一个更大的规模。

The ambitious research programme will see the development of a location sensitive touch sensor that can conform, after its fabrication, to flexible irregular surfaces and thus, can function as the sensing element in an artificial skin graft. The vision for the sensor is that its low power consumption, large area and simple device architecture will contribute to its ability to adapt to use in healthcare applications.The concept for the 'random impedance network sensors', or RINS, stems from the morphology of artificially synthesised atomically thin materials, that are grown almost exclusively as polycrystalline. Polycrystallinity in semiconductors is usually avoided in high-end applications because i) their resistivity is higher than their monocrystalline (MC) equivalents, and ii) each pair of crystallites (or grains) is separated by an amorphous and defect-rich interface (grain boundary) which is an additional source of resistivity. The few exceptions to the rule, such as degenerately doped polycrystalline (PC) silicon, which is used as gate metal in MOSFETs, or PC-Si photovoltaic cells marketed at the low-end of consumer-grade products, highlight the marginal position PC materials occupy in the global microelectronics industry. The first hypothesis is that PC thin films are inherently depleted of free charge carriers due to dielectric mismatch with their environment. Fewer charge carriers mean that the electrostatic screening efficiency is diminished and is manifested in extraordinarily long screening lengths and wide capture cross sections. This translates to a long-distance sensitivity to electrostatic events, such as the touch of a finger. The second hypothesis is that the intricate network of grains and grain boundaries forms a randomly oriented network of resistors (grains) and voltage-controlled capacitors (boundaries), which display both DC resistance and AC reactance. The resulting film impedance is bias-dependent, non-linear, and, crucially, position dependent, as each current pathway along the material carries a signature impedance characteristic. The combination of these hypotheses enables positioning of any electrostatic event, such as a finger touch, by triangulation of its position on the surface, making PC thin films the ideal substrates for position sensitive applications.To realise this new paradigm in location sensitive touch sensing, the full electronic structure of the grain-grain boundary system needs to be known, and the transport mechanism of traversing charge carriers across it needs to be well understood. The research methodology will include a combination of functional probe microscopy with macroscopic transport measurements, which will inform the design of the RINS detector. Finally, we aim to develop the sensor itself, and design the methodology by which electrostatic 'events' on its surface are mapped to their exact location using the reading from few low power peripheral probes.The stark difference between the proposed sensing mechanism and the sensors available today translate to exciting opportunities for new applications. Currently, capacitive touch sensors, such as those used in mobile phones and tablet devices, consist of orthogonal grid of transparent electrodes made of rare earth materials. This limits their use to applications on rigid surfaces, or surfaces that are flexible on a large, pre-defined radius of curvature. The sensor proposed here overcomes this limitations by using only peripheral electrodes, alleviating the need of rigid grid patterning. Furthermore, in current sensors location is inferred through capacitive changes at an overlap node between two orthogonal electrodes, and their nearby nodes. This means that nodes need to be sequentially addressed and read, making the response time long, especially on large surfaces. The use of few peripheral probes, all continuously read, means that processing the information can be done quickly, and on a much larger scale.