Browsing by Author "Ohta, Jun"

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A CMOS 256-pixel Photovoltaics-powered Implantable Chip with Active Pixel Sensors and Iridium-oxide Electrodes for Subretinal Prostheses
(2018-01-01)
Wu, Chung-Yu
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Kuo, Po-Han
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Lin, Po-Kang
;
Chen, Po-Chun
;
Sung, Wei-Jie
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 x 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 mu A 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.
A CMOS 256-Pixel Self-Photovoltaics-Powered Subretinal Prosthetic Chip with Wide Image Dynamic Range and Shared Electrodes and Its In Vitro Experimental Results on Rd1 Mice
(2019-01-01)
Wu, Chung-Yu
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Tzeng, Chi-Kuan
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Huang, Shih-Yun
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Chu, Fang-Liang
;
Chiao, Chuan-Chin
A self-photovoltaics-powered CMOS 256-pixel implantable chip with wide image dynamic range and shared electrodes is proposed and fabricated for subretinal prostheses. The infra-red (IR) light is incident only on photovoltaic cells of the chip whereas the visible light is mainly incident on pixels. The proposed adaptive background cancellation circuit (ABCC) is adopted to increase the image dynamic range so that the subretinal chip can adapt for different surrounding illuminances. Moreover, the bi-directional sharing electrodes (BDSEs) is used to increase electrode size under the same chip area and boost the stimulation charges to 11.4 nC. The functions of the chip have been successfully validated with both electrical measurement and in vitro patch clamp experiments with the retinas of Rd1 mice.
Electrochemical Evaluation of Geometrical Effect and Three-dimensionalized Effect of Iridium Oxide Electrodes Used for Retinal Stimulation
(2018-01-01)
Noda, Toshihiko
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Noda, Yoshiko
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Chen, Po-Chun
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Haruta, Makito
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Sasagawa, Kiyotaka
The 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.
Emerging Technologies for Biomedical Applications: Artificial Vision Systems and Brain Machine Interface
(2017-01-01)
Imai, Masaharu
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Takeuchi, Yoshinori
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Ohta, Jun
;
Suaning, Gregg Jorgen
;
Wu, Chung-Yu
Improved Charge Pump Design and Ex Vivo Experimental Validation of CMOS 256-Pixel Photovoltaic-Powered Subretinal Prosthetic Chip
(2020-05-01)
Kuo, Po-Han
;
Wong, Oi-Ying
;
Tzeng, Chi-Kuan
;
Wu, Pu-Wei
;
Chiao, Chuan-Chin
An improved design of CMOS 256-pixel photovoltaic-powered implantable chip for subretinal prostheses is presented. In the proposed subretinal chip, a high-efficiency fully-integrated 4x charge pump is designed and integrated with on-chip photovoltaic (PV) cells and a 256-pixel array with active pixel sensors (APS) for image light sensing, biphasic constant current stimulators, and electrodes. Thus the PV voltage generated by infrared (IR) light can be boosted to above 1V so that the charge injection is increased. The proposed chip adopts the 32-phase divisional power supply scheme (DPSS) to reduce the required supply current and thus the required area of the PV cells. The proposed chip is designed and fabricated in 180-nm CMOS image sensor (CIS) technology and post-processed with biocompatible IrOx electrodes and silicone packaging. From the electrical measurement results, the measured stimulation frequency is 28.3 Hz under the equivalent electrode impedance load. The measured maximum output stimulation current is 7.1 mu A and the amount of injected charges per pixel is 7.36 nC under image light intensity of 3200 lux and IR light intensity of 100 mW/cm(2). The function of the proposed chip has been further validated successfully with the ex vivo experimental results by recording the electrophysiological responses of retinal ganglion cells (RGCs) of retinas from retinal degeneration (rd1) mice with a multi-electrode array (MEA). The measured average threshold injected charge is about 3.97 nC which is consistent with that obtained from the patch clamp recording on retinas from wild type (C57BL/6) mice with a single electrode pair.
Performance Improvement of a Micro-stimulus Electrode for Retinal Prosthesis by Introducing a High-Performance Material and a Three-Dimensional Structure
(2016-01-01)
Fujisawa, Takumi
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Noda, Toshihiko
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Hayashi, Megumi
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Kobe, Ryo
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Tashiro, Hiroyuki
High-performance electrodes intended for retinal prosthesis were fabricated and evaluated. Iridium oxide (IrOx) was introduced as a high-performance material. A three-dimensional (3D) structure was also introduced to enlarge the electrode's surface area. We tried to improve the electrode performance by combining these approaches, even if the electrode was miniaturized. The effectiveness of IrOx was demonstrated through electrochemical evaluation by comparing it with Pt. IrOx showed 1.6-6 times higher performance for the injection of stimulus pulse current than Pt. The performance of the 3D electrode compared with a planar electrode was also evaluated. Accordingly, the 3D electrode showed 2-4 times higher performance than the planar electrode by surface area enlargement. An ex vivo validation of the stimulus performance was conducted to demonstrate its practical use. A fabricated electrode was implanted in an extracted pig eyeball and the electrochemical performance was evaluated. The fabricated electrode showed sufficient performance of the retinal stimulation, with a high margin of safety. The proposed approach was successfully demonstrated as a stimulus electrode candidate for use in next-generation retinal prosthesis.