Microstructure and electrochemical properties of Cr– Si–C–N coatings as biological dry electrode

Abstract

Bio-electrode Cr–Si–C–N coatings were fabricated on glass and Si wafer substrates via unbalanced magnetron sputtering. Their microstructure and mechanical properties were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and nano-indentation, respectively. The Cr–Si–C–N coatings exhibited a composite structure consisting of Cr(C, N) nanocrystals embedded in an amorphous matrix of a-SiNx, a-SiCN and a-C/a-CN. The nano-hardness of the coatings decreases with an increase in graphite target current or Si target power due to the formation of more amorphous phase. CrSiCN-3A deposited under high N2 flow (25sccm) and graphite target current (3A) exhibited the lowest open-circuit voltage (OCP, 0.119V) due to its more amorphous phase. CrSiCN–800W demonstrated maximum potential drift of 7 mV, current drift of 0.01 μA and minimum noise resistance, indicating poor corrosion resistance attributed to its low silicon content (1.9 at%) and high crystallinity (70.7%). The grain size of the coatings was not significantly affected by increasing Si target power from 1000W to 1200W, but only resulted in a reduction in crystallinity. The OCP and contact resistance exhibited an initial decrease followed by an increase with increasing Si target power. Notably, CrSiCN–1000W demonstrated the lowest potential and current drift (0.19 mV, 0.0001 μA) as well as contact impedance due to its large grain size and distinct columnar microstructure.