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

Abstract

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.

Sputtered Iridium Oxide as Electrode Material for Subretinal Stimulation

“…Compared with the SIROF electrodes reported in the literature, the presented sputtering process results in similar CSC values at comparable sweep rates. (10)(11)(12)(19)(20)(21) The high CSC can be attributed to the previously described morphology of the sputtered iridium oxide that represents a greatly increased and, in slow-sweep CV, accessible electrochemical surface.…”

“…In contrast, iridium oxide offers outstanding CIC and CSC as well as low impedance. (10,11) Different routes for the fabrication of iridium oxide are known. (4,12) Sputtered iridium oxide films (SIROFs) are typically deposited by reactive sputtering from an iridium target.…”

Emerging Implantable Energy Harvesters and Self-Powered Implantable Medical Electronics

“…In 2018, Wu et al . designed an implantable chip integrated with photovoltaic cells as the 256-pixel subretinal prostheses that were placed in the posterior pole of the eyeball of a pig …”

Autocharging Techniques for Implantable Medical Applications

“…Song et al documented solar cell arrays in a hairless mouse's transcutaneous site ( Figure 4 ) and harvested electrical power up to 647 μ W [ 43 ]. In 2018, Wu et al developed an implanted chip comprising photovoltaic panels as a 256-pixel artificial subretina that was mounted in the subsequent pole of a pig's eyeball with maximum output converted current up to 16.7 μ A [ 44 ].…”