Techniques for sensing the current distribution and charge storage of high-density neuroelectrodes

High-density neural-stimulation depends on miniaturized electrodes with high charge-injection capability. This dissertation proposes a novel electrode surface that incorporates electroplated microposts to provide additional surface area and charge injection capability. Such an approach has been discouraged because traditional simulations that were based on steady-state resistive-only models have shown severe current crowding at sharp electrode topologies. In contrast, this study uses an improved time-stepping simulation method that can properly reflect the capacitive behavior of the 3-D microelectrodes. The simulations performed with SPICE and ANSYS show that even with the sharp features, the variation in the electrode-surface current that is less than 5%. While the simulations do show current crowding in the solution adjacent to edges of the microposts, the ionic current in the solution at these sites is found to be parallel to the electrode surface.;The uniform current distribution is confirmed with a dissolution study of electrodes with gold surface and polyimide substrate. At a low charge density setting of 50 muC/cm2, uniform corrosion and redeposition pattern is observed on all the surfaces. However, when the average charge density is increased to 200 muC/cm2, the corrosion pattern reflects current crowding at the edge of the electrode and the edges of the microposts. Additionally, a 1-mm-diameter electrode is designed and fabricated that incorporate pixels for measuring current distribution. The measured current profile shows a uniform trend.;A pulse-clamp circuit is designed and employed to characterize the electrode charge-storage capability that will allow different electrodes to be quickly and accurately compared. Pulse-clamp measurements are performed on flat platinum electrodes in 0.15 M saline solution in air with 1-ms pulses at a charge density of up to 1 mC/cm2. Results indicate a safe charge-injection limit of 0.1 mC/cm2, and a hydrolysis-dominated regime above 0.5 mC/cm2. Comparing different electrode sizes indicates that the charge-storage capability of an electrode is proportional to its surface area. The scalability of the pulse-clamp technique allows it to be used to accurately quantify the roughness of a surface modification.