Fabrication of CMOS Based Flexible Retinal Stimulator With Bullet-shaped Platinum Electrodes

Abstract

 

Purpose:

 

A CMOS based flexible retinal stimulator for Suprachoroidal-Transretinal Stimulation (STS) configuration has been developed by our group. In this study, a stimulus current generator was integrated into the CMOS microchip and bullet-shaped stimulus electrodes were mounted in array on a flexible substrate.

 

Methods:

 

A CMOS microchip with 400 µm sq. die has stimulus current generation and operation control logic circuits. The stimulus current generator outputs current controlled pulse. Pulse current can be controlled from 50µA to 1mA. Pulse type can be selected from monophasic pulse or biphasic pulse. Chip operation is controlled by the logic circuit. Each microchip has intrinsic ID number and is controlled individually using the ID number. Thus, many microchips can be mounted on one stimulator. Bullet-shaped platinum electrodes were utilized as a stimulus electrode. The electrode has 500 µm diameter and height, respectively. The electrodes were mounted on a flexible substrate. CMOS microchips were flip-mounted on the substrate near the stimulus electrodes and connected to the electrodes by one to one. Whole device except for the stimulus electrodes was coated by parylene for improvement of bio-compatibility and waterproofness.

 

Results:

 

Newly designed CMOS microchips operated normally as the design. 3 by 3 array stimulator succeeded in fabrication and durability of the device was evaluated in phosphate-buffered saline. Stimulus pulse current generated by on-chip CMOS circuit was output from bullet-shaped electrodes. In-vivo evaluation using experimental animal was also performed.

 

Conclusions:

 

A flexible retinal stimulator with bullet-shaped platinum electrodes and a CMOS microchip that includes a stimulus current generator was developed successfully. A stimulator which has more electrodes in high density can be realized with the same device configuration.  

 

Keywords: retina