Different methods to alter surface morphology of high aspect ratio structures.
Different methods to alter surface morphology of high aspect ratio structures.
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DOI：
10.1016/j.apsusc.2016.01.008
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发表时间：
2016-03-01
影响因子：
6.7
通讯作者：
Negi S
中科院分区：
文献类型：
--
作者：
Leber M;Shandhi MM;Hogan A;Solzbacher F;Bhandari R;Negi S
在诸如神经假体或太阳能电池的各种应用中，需要改变高纵横比结构的表面形态，使得真实的表面积大于几何面积。表面形态的变化增强了器件的功能。改变表面形态的应用之一是神经植入物，例如犹他州电极阵列（UEA），其通过电荷注入诱导的刺激或通过记录电神经信号与单个神经元通信。为了在神经系统的单个细胞之间实现高选择性，需要电极表面积尽可能小，同时需要阻抗尽可能低以在神经记录期间实现良好的信噪比（SNR）。为了刺激，需要电极的高电荷注入和电荷转移能力，其随着电极表面而增加。传统上，研究人员一直致力于增加现有金属化（铂灰色，黑色）或其他材料（如氧化铱和PEDOT）的粗糙度。所有这些先前研究的方法导致更复杂的金属沉积过程，其难以控制并且通常对金属膜的机械性能具有关键影响。因此，电极涂层下方的表面的改性将增加其表面积，同时保持标准和良好控制的金属沉积过程。在这项工作中，硅微针的表面是通过使用几种方法，如激光烧蚀，聚焦离子束，溅射蚀刻，反应离子蚀刻（RIE）和深反应离子蚀刻（DRIE）在电极表面上创建一个定义的微结构来设计的。针对UEA的高深宽比硅结构，优化了表面改性工艺。使用扫描电子显微镜（SEM）和电化学阻抗谱（EIS）验证了在保持几何表面积的同时真实的表面积的增加。DRIE诱导的表面形貌得到了最好的结果。电极的阻抗值降低高达76%，表明高深宽比硅结构的成功表面工程。
In various applications such as neural prostheses or solar cells, there is a need to alter the surface morphology of high aspect ratio structures so that the real surface area is greater than geometrical area. The change in surface morphology enhances the devices functionality. One of the applications of altering the surface morphology is of neural implants such as the Utah electrode array (UEA) that communicate with single neurons by charge injection induced stimulation or by recording electrical neural signals. For high selectivity between single cells of the nervous system, the electrode surface area is required to be as small as possible, while the impedance is required to be as low as possible for good signal to noise ratios (SNR) during neural recording. For stimulation, high charge injection and charge transfer capacities of the electrodes are required, which increase with the electrode surface. Traditionally, researchers have worked with either increasing the roughness of the existing metallization (Platinum grey, black) or other materials such as Iridium Oxide and PEDOT. All of these previously investigated methods lead to more complicated metal deposition processes that are difficult to control and often have a critical impact on the mechanical properties of the metal films. Therefore, a modification of the surface underneath the electrode’s coating will increase its surface area while maintaining the standard and well controlled metal deposition process. In this work, the surfaces of the Silicon micro-needles were engineered by creating a defined microstructure on the electrodes surface using several methods such as Laser ablation, focused ion beam, sputter etching, reactive ion etching (RIE) and deep reactive ion etching (DRIE). The surface modification processes were optimized for the high aspect ratio Silicon structures of the UEA. The increase in real surface area while maintaining the geometrical surface area was verified using scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The best results were obtained by DRIE induced surface morphology. Decreases in impedance values of electrodes up to 76 % indicate the successful surface engineering of the high aspect ratio Silicon structures.