Implanted Devices Group, Department of Medical Physics and Biomedical Engineering, University College London, Gower Street, London, United Kingdom.
Department of Microelectronics, Faculty of Electrical Engineering, Mathematics and Computer Science, Delft University of Technology, Delft, The Netherlands.
J Neural Eng. 2021 Apr 6;18(5):055003. doi: 10.1088/1741-2552/abf0d6.
Ensuring the longevity of implantable devices is critical for their clinical usefulness. This is commonly achieved by hermetically sealing the sensitive electronics in a water impermeable housing, however, this method limits miniaturisation. Alternatively, silicone encapsulation has demonstrated long-term protection of implanted thick-film electronic devices. However, much of the current conformal packaging research is focused on more rigid coatings, such as parylene, liquid crystal polymers and novel inorganic layers. Here, we consider the potential of silicone to protect implants using thin-film technology with features 33 times smaller than thick-film counterparts.Aluminium interdigitated comb structures under plasma-enhanced chemical vapour deposited passivation (SiO, SiON, SiON+ SiC) were encapsulated in medical grade silicones, with a total of six passivation/silicone combinations. Samples were aged in phosphate-buffered saline at 67 C for up to 694 days under a continuous ±5 V biphasic waveform. Periodic electrochemical impedance spectroscopy measurements monitored for leakage currents and degradation of the metal traces. Fourier-transform infrared spectroscopy, x-ray photoelectron spectroscopy, focused-ion-beam and scanning-electron- microscopy were employed to determine any encapsulation material changes.No silicone delamination, passivation dissolution, or metal corrosion was observed during ageing. Impedances greater than 100 GΩ were maintained between the aluminium tracks for silicone encapsulation over SiONand SiC passivations. For these samples the only observed failure mode was open-circuit wire bonds. In contrast, progressive hydration of the SiOcaused its resistance to decrease by an order of magnitude.These results demonstrate silicone encapsulation offers excellent protection to thin-film conducting tracks when combined with appropriate inorganic thin films. This conclusion corresponds to previous reliability studies of silicone encapsulation in aqueous environments, but with a larger sample size. Therefore, we believe silicone encapsulation to be a realistic means of providing long-term protection for the circuits of implanted electronic medical devices.
确保植入设备的寿命对于其临床应用至关重要。这通常通过将敏感电子设备密封在不透水的外壳中来实现，然而，这种方法限制了设备的微型化。另一种方法是使用硅橡胶对植入式厚膜电子设备进行长期保护。然而，目前大部分的保形封装研究都集中在更刚性的涂层上，如派瑞林、液晶聚合物和新型无机层。在这里，我们考虑使用薄膜技术的硅橡胶的潜力，其特征尺寸比厚膜对应物小 33 倍。在等离子体增强化学气相沉积钝化（SiO、SiON、SiON+SiC）下的铝叉指梳状结构被封装在医用级硅橡胶中，总共使用了六种钝化/硅橡胶组合。将样品在磷酸盐缓冲盐水（67°C）中老化，在连续的±5V 双相波形下最多老化 694 天。周期性的电化学阻抗谱测量监测漏电流和金属迹线的降解情况。傅里叶变换红外光谱、X 射线光电子能谱、聚焦离子束和扫描电子显微镜被用来确定任何封装材料的变化。在老化过程中，没有观察到硅橡胶分层、钝化层溶解或金属腐蚀。在 SiON 和 SiC 钝化下，用于硅橡胶封装的铝轨道之间保持的阻抗大于 100GΩ。对于这些样品，唯一观察到的失效模式是开路线键合。相比之下，SiC 的逐渐水合使其电阻降低了一个数量级。这些结果表明，当与适当的无机薄膜结合使用时，硅橡胶封装可为薄膜导电轨道提供出色的保护。这一结论与硅橡胶在水介质中的可靠性研究结果相符，但样本数量更大。因此，我们认为硅橡胶封装是为植入式电子医疗设备的电路提供长期保护的一种现实手段。
