Optimization of Sputtering Condition of IrOx Thin Film Stimulation Electrode for Retinal Prosthesis Application

A fork-shaped retinal stimulator for a wide viewing angle was fabricated and demonstrated. This stimulator has two flexible fork elements, each with a stimulus head. The two fork elements can be implanted at different places in the eyeball to cover a wider area of the retina. The stimulus head has stimulus electrodes with the same shape as the electrodes utilized in a clinical trial for six weeks. Complementary metal-oxide semiconductor (CMOS) microchips were integrated into the stimulator and mounted next to the stimulus electrodes. Since stimulus current generators are integrated into the microchips, no external wires for stimulus current are required. A multiplexer, which reduces the number of wirings, was also integrated into the microchips. The fabricated stimulator was evaluated through in vivo animal experiments. The stimulator was successfully implanted in two places of the eyeball. Retinal stimulation by the device evoked nerve responses from optic chiasma and produced a specific peak of evoked potential. Experimental results demonstrate the proof of concept of a fork-shaped stimulator and suggest that the same device configuration can realize multiple forkshaped stimulators for a wider viewing angle. Moreover, increasing the number of fork elements of the multifork stimulator without additional wirings becomes possible.

Section: Discussionmentioning

confidence: 99%

Fabrication of Fork-Shaped Retinal Stimulator Integrated with CMOS Microchips for Extension of Viewing Angle

Noda

Sasagawa

Tokuda

et al. 2014

“…Our focus has been on achieving high-performance iridium oxide (IrOx) materials by optimizing the fabrication process and fundamental electrochemical properties. (11,12) The in vivo validation of neural stimulation by IrOx electrodes was also successfully achieved. (13) Moreover, we attempted another approach for enhancing the electrochemical performance by introducing a threedimensionalized electrode.…”

Section: Introductionmentioning

confidence: 93%

Electrochemical Evaluation of Geometrical Effect and Three-dimensionalized Effect of Iridium Oxide Electrodes Used for Retinal Stimulation

Noda

Chen

et al. 2018

Keywords: retinal prosthesis, neural stimulation, stimulus electrode, three-dimensionalized electrode, iridium oxideThe geometry dependence and three-dimensionalized effect of the electrochemical properties of iridium oxide electrodes used in retinal prosthesis are discussed herein. Planar electrodes with various geometries were fabricated. Three-dimensionalized electrodes with microfabricated resin cores were also fabricated. The charge storage capacity (CSC) and charge injection capacity (CIC), both of which are important properties for neural stimulation, were quantitatively evaluated. This evaluation showed the important electrode property that the surface area dominantly affects the CSC. On the other hand, the CIC was not proportionally related to the electrode area, confirming that the edge region of the electrodes is significant in the mechanism of action. Moreover, performance enhancement with a three-dimensionalized electrode was clearly confirmed. The fundamental properties of highly effective stimulus electrodes were successfully evaluated and a detailed discussion is presented.

“…(32) Since the threshold charges for successful stimulation differ for each patient, the increase in injected charge is necessary. This can be achieved by either increasing the electrode area by using bump electrodes (22)(23)(24) or increasing the stimulation voltage by using charge pump circuits. These improvements will be realized in the future.…”

Section: Electrical Test and In Vivo Testmentioning

confidence: 99%

“…It is known that electrode performance can be improved by applying a surface coating of a high-performance material, and IrOx is the leading candidate for such a material. (21)(22)(23)(24)(25) An…”

Section: Introductionmentioning

confidence: 99%

A CMOS 256-pixel Photovoltaics-powered Implantable Chip with Active Pixel Sensors and Iridium-oxide Electrodes for Subretinal Prostheses

Wu¹,

Kuo²,

Lin³

et al. 2018

Keywords: divisional power supply scheme, active pixel sensor, photovoltaic cell, CMOS image sensor, biocompatible package A CMOS implantable chip with 256 active pixel sensors (APSs), on-chip photovoltaic cells, and iridium-oxide (IrOx) electrodes is proposed and designed for subretinal prostheses. In the proposed chip, the on-chip electrode surface is deposited with IrOx by RF sputtering and photolithography patterning. The divisional power supply scheme (DPSS) is adopted to generate sufficient stimulation current whereas the APS is used to enhance the image sensitivity. The proposed chip consists of a 16 × 16 photodiode array with 8 DPSS divisions, control signal generator circuits, and photovoltaic cells. It is designed and fabricated into 180 nm CMOS image sensor (CIS) technology and postprocessed with an IrOx coating. From the electrical measurement results, the fabricated chip has a peak output stimulation current of 16.7 μA under the equivalent electrode impedance load. The stimulation frequency is 30.2 Hz and the amount of injected charges at each pixel is 3.5 nC. Both image light sensitivity and injection charges are significantly improved. The surface morphology, crystallinity, charge storage capacity, and biocompatibility of sputtering iridium oxide film (SIROF) were investigated. As a result, the SIROF has desirable physical and electrochemical properties that make it suitable for the neurostimulation electrodes on the 256-pixel implantable chip. The 7-month biocompatibility and charge delivery capability of the fabricated chip have been confirmed by electroretinography (ERG) measurement on a Lanyu minipig in in vivo animal tests.