Atomic Layer Deposited Al 2 O 3 and Parylene C Bi-layer Encapsulation for Utah Electrode Array Based Neural Interfaces
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Atomic Layer Deposited Al2O3 and Parylene C Bi-layer Encapsulation for Utah Electrode Array Based Neural Interfaces Xianzong Xie1, Loren W. Rieth1, Rohit Sharma1, Sandeep Negi1, Rajmohan Bhandari2, Ryan Caldwell3, Prashant Tathireddy1, and Florian Solzbacher1,3 1 Electrical and Computer Engineering, University of Utah, Salt Lake City, UT, 84112 U.S.A 2 Blackrock microsystems, Salt Lake City, UT, 84108 U.S.A 3 Department of Bioengineering, University of Utah, Salt Lake City, UT, 84112 U.S.A ABSTRACT Long-term functionality and stability of neural interfaces with complex geometries is one of the major challenges for chronic clinic applications due to lack of effective encapsulation. We present an encapsulation method that combines atomic layer deposited Al2O3 and Parylene C for encapsulation of biomedical implantable devices, focusing on its application on Utah electrode array based neural interfaces. The alumina and Parylene C bi-layer encapsulated wired Utah electrode array showed relatively stable impedance during the 960 equivalent soaking days at 37 °C in phosphate buffered solution. For the bi-layer coated wireless neural interfaces, the powerup frequency was constantly ~ 910 MHz and the RF signal strength was stably around -73 dBm during equivalent soaking time of 1044 days at 37 °C (still under soak testing). INTRODUCTION Implantable systems for long-term clinic trials require chronic implantations able to perform their intended functionalities for years or decades, in order to reduce surgical risks and generate levels of efficacy that justifies the risks associated with the implantation. Hermetic and thin-film based encapsulation are the commonly used methods to protect the device from physiological environment. Device miniaturization and electromagnetic power raise new challenges for traditional hermetic encapsulation. Thus, thin film based encapsulation have been widely employed. Compared with metal cans and lids based hermetic encapsulation, thin film based encapsulation takes less space, can handle feedthroughs easily, and is more economic and easier for mass production. Implantable neural interfaces have been widely developed and also used to diagnose and treat neural disorders in both research and clinical applications. The Utah electrode array (UEA) is a well-developed and FDA-cleared example of this technology for stimulating and recording multiple neurons simultaneously with good selectivity[1]. Parylene C has been widely used as coating material for biomedical devices [2, 3] due to attractive properties including chemically inertness, low dielectric constant (İr=3.15), high resistivity ( 1015 ·cm) and relative low water vapor transmission rate (WVTR) 0.2 g·mm/m2·day. Failure of Parylene encapsulation has also been reported [4] due to moisture diffusion and interface contamination. To overcome the condensation of moisture around interface contaminants, a highly effective moisture barrier can be introduced between the neural interface and Parylene film. Atomic layer deposited (ALD) Al2O3 has WVTR at
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