| AVS 60th International Symposium and Exhibition | |
| Thin Film | Wednesday Sessions |
| Session TF+VT-WeM |
| Session: | Thin Film Permeation Barriers and Encapsulation |
| Presenter: | X. Xie, University of Utah |
| Authors: | X. Xie, University of Utah L.W. Rieth, University of Utah F. Solzbacher, University of utah |
| Correspondent: | Click to Email |
Encapsulation of three dimensional neural interfaces with complex geometries and tight gaps between components is one of the greatest challenges to achieve long-term functionality and stability. We present a novel encapsulation scheme that combines atomic layer deposited (ALD) Al2O3 and Parylene C for biomedical implantable. Our approach is composed of the highly effective moisture barrier properties of ALD alumina, and Parylene as a barrier to many ions and for preventing contact of alumina with liquid water.
Different configurations of Utah electrode array (UEA) based devices were used to test the encapsulation performance from three different aspects: long-term impedance stability, current drawing level, and long-term wireless signal strength and frequency shift.52 nm of Al2O3 was deposited by plasma-assisted (PA) ALD on assembled UEAs at 120 °C. A 6-µm thick Parylene-C layer was deposited by CVD using Gorman process on top of Al2O3 and A-174 (Momentive Performance Materials), an organosilane, was used as adhesion promoter.
Hybrid methods were used to de-insulate the tips of the UEAs in order to interact with neurons for recording and stimulation. First, 200 laser pulses with fluence of 1400 mJ/cm2 were used to remove the Parylene C layer. 3 minutes of oxygen plasma etching was added to remove the carbon residue on the tips from laser de-insulation. Then the alumina layer was removed by dipping the array into buffered oxide etch (BOE) for 10 minutes. Parylene C acted as a mask layer for BOE etching and only alumina in the area where Parylene was removed by laser was etched away. The tip exposure was ~ 35 µm. The devices were then put into saline solution for soak testing.
The median tip impedance of the bi-layer encapsulated wired Utah electrode array increased from 60 kΩ to 160 kΩ during the 960 days of equivalent soak testing at 37 °C. The loss of tip metal iridium oxide and etching of silicon in PBS solution contributed to the increase of impedance. Also bi-layer coated fully integrated Utah array based wireless neural interfaces had stable power-up frequencies at ~910 MHz and constant RF signal strength of -50 dBm during the 1044 days of equivalent soaking time at 37 °C. Bi-layer coated Utah arrays had steady current drawing of about 3 mA during 228 days of soak testing at 37 °C. The relatively stable tip impedance, constant power-up frequencies and signal strengths, and low current drawing suggested that the alumina and Parylene C bi-layer coating is very suitable for encapsulating chronic implantable devices.