title: Long-term bilayer encapsulation performance of atomic layer deposited Al₂O₃ and Parylene C for biomedical implantable devices.
abstract: We present an encapsulation scheme that combines atomic layer deposited (ALD) Al₂O₃ and Parylene C for the encapsulation of implantable devices. The encapsulation performances of combining alumina and Parylene C was compared to individual layers of Parylene C or alumina and the bilayer coating had superior encapsulation properties. The alumina-Parylene coated interdigitated electrodes (IDEs) soaked in PBS for up to nine months at temperatures from 37 to 80 °C for accelerated lifetime testing. For 52-nm alumina and 6-μm Parylene C, leakage current was ∼20 pA at 5 VDC, and the impedance was about 3.5 MΩ at 1 kHz with a phase near -87° from electrochemical impedance spectroscopy for samples soaked at 67 °C for equivalent lifetime of 72 months at 37 °C. The change of impedance during the whole soaking period (up to 70 months of equivalent soaking time at 37 °C) over 1 to 10⁶ Hz was within 5%. The stability of impedance indicated almost no degradation of the encapsulation. Bias voltage effect was studied by continuously applying 5 VDC, and it reduced the lifetime of Parylene coating by ∼75% while it showed no measurable effect on the bilayer coating. Lifetime of encapsulation of IDEs with topography generated by attaching a coil and surface mount device (SMD) capacitor was about half of that of planer IDEs. The stable long-term insulation impedance, low leakage current, and better lifetime under bias voltage and topography made this double-layer encapsulation very promising for chronic implantable devices.
authors.forename: Xianzong
authors.initials: X
authors.lastname: Xie
authors.forename: Loren
authors.initials: L
authors.lastname: Rieth
authors.forename: Ryan
authors.initials: R
authors.lastname: Caldwell
authors.forename: Mohit
authors.initials: M
authors.lastname: Diwekar
authors.forename: Prashant
authors.initials: P
authors.lastname: Tathireddy
authors.forename: Rohit
authors.initials: R
authors.lastname: Sharma
authors.forename: Florian
authors.initials: F
authors.lastname: Solzbacher
mesh_terms: D000537:Aluminum Oxide / Q000737:chemistry*; D001826:Body Fluids / Q000737:chemistry*; D020099:Coated Materials, Biocompatible / Q000138:chemical synthesis*; D017097:Electric Impedance; D019544:Equipment Failure Analysis; D008422:Materials Testing; D011108:Polymers / Q000737:chemistry*; D019736:Prostheses and Implants; D011474:Prosthesis Design; D013499:Surface Properties; D014992:Xylenes / Q000737:chemistry*
chemical_list: D020099:Coated Materials, Biocompatible; D011108:Polymers; D014992:Xylenes; C011055:parylene; D000537:Aluminum Oxide