Atomic layer deposited Al2O3 and parylene C dual-layer encapsulation for biomedical implantable devices

We present a novel bi-layer encapsulation method combining atomic layer deposited Al₂O₃ and Parylene C to extend the lifetime of biomedical implantable devices. The atomic layer deposited alumina and Parylene C bi-layer coated interdigitated electrodes had leakage current of about 20 pA and impedance of 3.5 MΩ after 260 days of soaking in phosphate buffered solution at 67°C (roughly 6 years of equivalent lifetime at 37°C). Also 5 VDC continuous bias had no measurable effect on the lifetime of bi-layer coating while it shortened the lifetime of Parylene coating by 75%. The long-term low leakage current and high insulation performance under continuous bias demonstrated its suitability for encapsulation of chronic implantable devices.