title: Effect of bias voltage and temperature on lifetime of wireless neural interfaces with Al ₂O₃ and parylene bilayer encapsulation.
abstract: The lifetime of neural interfaces is a critical challenge for chronic implantations, as therapeutic devices (e.g., neural prosthetics) will require decades of lifetime. We evaluated the lifetime of wireless Utah electrode array (UEA) based neural interfaces with a bilayer encapsulation scheme utilizing a combination of alumina deposited by Atomic Layer Deposition (ALD) and parylene C. Wireless integrated neural interfaces (INIs), equipped with recording version 9 (INI-R9) ASIC chips, were used to monitor the encapsulation performance through radio-frequency (RF) power and telemetry. The wireless devices were encapsulated with 52 nm of ALD Al2O3 and 6 μm of parylene C, and tested by soaking in phosphate buffered solution (PBS) at 57 °C for 4× accelerated lifetime testing. The INIs were also powered continuously through 2.765 MHz inductive power and forward telemetry link at unregulated 5 V. The bilayer encapsulated INIs were fully functional for ∼35 days (140 days at 37 °C equivalent) with consistent power-up frequencies (∼910 MHz), stable RF signal (∼-75 dBm), and 100 % command reception rate. This is ∼10 times of equivalent lifetime of INIs with parylene-only encapsulation (13 days) under same power condition at 37 °C. The bilayer coated INIs without continuous powering lasted over 1860 equivalent days (still working) at 37 °C. Those results suggest that bias stress is a significant factor to accelerate the failure of the encapsulated devices. The INIs failed completely within 5 days of the initial frequency shift of RF signal at 57 °C, which implied that the RF frequency shift is an early indicator of encapsulation/device failure.
authors: University of Utah, Salt Lake City, UT, USA, xianzongxie@gmail.com.
authors: Xianzong
authors: X
authors: Xie
authors: Loren
authors: L
authors: Rieth
authors: Ryan
authors: R
authors: Caldwell
authors: Sandeep
authors: S
authors: Negi
authors: Rajmohan
authors: R
authors: Bhandari
authors: Rohit
authors: R
authors: Sharma
authors: Prashant
authors: P
authors: Tathireddy
authors: Florian
authors: F
authors: Solzbacher
mesh_terms: D000537:Aluminum Oxide / Q000737:chemistry*; D004567:Electrodes, Implanted; D008422:Materials Testing; D011108:Polymers / Q000737:chemistry*; D059015:Wireless Technology; D014992:Xylenes / Q000737:chemistry*
chemical_list: D011108:Polymers; D014992:Xylenes; C011055:parylene; D000537:Aluminum Oxide