(19) Chronic Performance of Sputtered Ruthenium Oxide Electrode coating on Amorphous SiC Microelectrode Arrays in Rodent

Introduction: Implantable microelectrode arrays (MEAs) are essential for Brain-Machine Interfaces (BMI), enabling neural recording and stimulation [1]. A critical factor in the long-term success of these devices is the stability and performance of electrode materials. Low-impedance electrode films are particularly important for chronic applications, as they facilitate reliable action potential recording while ensuring stability in the tissue environment without inducing adverse reactions that could lead to neuronal damage [2,3].

Methods: In this study, we evaluate the chronic recording performance of an electrode coating, Ruthenium Oxide (RuOx) [4,5], on ultra-thin amorphous silicon carbide (a-SiC) MEAs [6]. RuOx films were sputtered using DC magnetron deposition with H₂O gas introduced to optimize film porosity and enhance electrochemical properties. We hypothesized that RuOx coated a-SiC MEAs provide stable, low-impedance neural recording performance over 16 weeks in a rat cortical model. To test this hypothesis, we fabricated four-shank a-SiC MEAs and implanted them into the motor cortex of three female Sprague Dawley rats. Each shank (8 µm thick, 20 µm wide, 2 mm long) contained four RuOx-coated electrodes (200 µm2), totaling 16 electrodes per array. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (50 mV/s and 50,000 mV/s) were conducted weekly to assess electrode stability, while neural recordings were analyzed for single-unit activity.

Results: Our findings are summarized in Table 1 with data presented as median and interquartile range (1st quartile, 3rd quartile). The results demonstrate a significant decrease from week 1 to 16 post implantation in impedance values in the mid-frequency range at 1 kHz (p < 0.0001). Cyclic voltammetry (CV) was used as a key measure of chronic electrode stability. While 50 mV/s charge storage capacity (CSCc) showed no significant difference over 16 weeks (p = 0.7), 50,000 mV/s CSCC exhibited a slight but significant increase (p < 0.0001). These minor changes are not expected to compromise recording performance. Overall, electrochemical data suggest that RuOx electrode coatings remain stable during chronic implantation. Neural recordings confirmed stable functionality, with 78% of channels detecting unit activity at week 1, decreasing to 57% by week 16. The average peak-to-peak voltage (Vpp) showed a modest but significant reduction over time (p = 0.009).

Conclusion: These findings confirm that RuOx-coated a-SiC UMEAs maintain stable electrochemical properties and neural recording capabilities over 16 weeks, highlighting their potential for chronic neural interface applications.