Plasma-assisted atomic layer deposition of Al₂O₃ and parylene C bi-layer encapsulation for chronic implantable electronics

Abstract

Encapsulation of biomedical implants with complex three dimensional geometries is one of the greatest challenges achieving long-term functionality and stability. This report presents an encapsulation scheme that combines Al(2)O(3) by atomic layer deposition with parylene C for implantable electronic systems. The Al(2)O(3)-parylene C bi-layer was used to encapsulate interdigitated electrodes, which were tested invitro by soak testing in phosphate buffered saline solution at body temperature (37 °C) and elevated temperatures (57 °C and 67 °C) for accelerated lifetime testing up to 5 months. Leakage current and electrochemical impedance spectroscopy were measured for evaluating the integrity and insulation performance of the coating. Leakage current was stably about 15 pA at 5 V dc, and impedance was constantly about 3.5 MΩ at 1 kHz by using electrochemical impedance spectroscopy for samples under 67 °C about 5 months (approximately equivalent to 40 months at 37 °C). Alumina and parylene coating lasted at least 3 times longer than parylene coated samples tested at 80 °C. The excellent insulation performance of the encapsulation shows its potential usefulness for chronic implants.

Ultrathin, transferred layers of thermally grown silicon dioxide as biofluid barriers for biointegrated flexible electronic systems

“…This option is, however, not suitable for capacitive, biosensing applications, and it has only limited value in other possible biointerface measurements, such as those based on thermal or optical interfaces. Barrier layers formed by other deposition techniques, such as plasma-assisted atomic layer deposition (ALD), O 3 -assisted ALD, and anodization show pinhole-like defects as well (39)(40)(41)(42). For example, although plasma-assisted ALD-deposited SiN x has a low intrinsic water vapor transmission rate, pinholes lead to extrinsic effects that limit the encapsulation performance of the entire barrier (40).…”

Recent advances in materials and flexible electronics for peripheral nerve interfaces

“…Therefore, chronic implants packaged with some types of metal oxides must be co-encapsulated in other inert materials that limit water uptake into components. Flexible bilayers of nanometer-scale Al 2 O 3 films and micron-scale parylene-C can greatly extend the in vitro stability of neural probes compared to devices encapsulated with parylene alone (Xie et al, 2012;Xie et al, 2014a).…”

Bi-layer encapsulation of utah array based nerual interfaces by atomic layer deposited Al<inf>2</inf>O<inf>3</inf> and parylene C

“…The alumina-Parylene C bi-layer encapsulation has been demonstrated with excellent insulation performance on interdigitated electrode test structures [15]. By applying this new bi-layer coating method, longer lifetime is expected for UEA based neural interfaces.…”