Naser Pour Aryan, Christian Brendler, Viola Rieger, Steffen Kibbel, Alex Harscher, Gerhard Heusel, Albrecht Rothermel
TiN, Iridium, Iridium Oxide, Electrode, Electrode activation
In some applications of neural stimulation, high amounts of charge should be transferred into tissue. Iridium oxide (IrOx), showing high stability during charge injection, is one main candidate for these applications. According to our study, iridium oxide shows a much higher charge injection capacity compared to titanium nitride TiN (4 times more than TiN in ±1V window), which is also widely used in many medical applications such as cardiac pacemakers. Our evaluation of charge injection capacity of IrOx shows somewhat smaller values compared to the previous reports [1][2][4][5]. According to our investigations, IrOx electrodes are able to deliver at most 0.6mC/cm2 charge density for square shaped electrodes with 50µm x 50µm dimensions. The waveforms’ timing, 0.3ms cathodic and 0.5ms anodic signals, was similar to previous reports. We used the slow cyclic ramp voltage method originally developed by [Robblee & Rose, 1990] to activate the iridium electrodes. We showed that the activation process needs slow activation signals. Activation is not possible by using 2Hz or faster, 50% duty cycle square waves, for different amplitude parameters, even after several days of activation process. With slower square waves (as slow as 1Hz or slower), activation is possible.
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