Improvement of Reproducibility and Durability in a Microelectronics-Based Stimulator for Suprachoroidal Transretinal Stimulation (STS)

Abstract

Purpose:: We have proposed a flexible and extendible silicon microchip-based stimulator for STS, in which a number of microchips are distributed on a flexible polyimide substrate. The stimulator has already demonstrated fundamental operation. Higher reproducibility of the fabrication process is, however, required to realize a large-scale stimulator. Also for clinical applications, we need to ensure the durability and biocompatibility of the stimulator. The aim of this research is to improve the reproducibility and durability of the microchip-based simulator.

Methods:: To improve the reproducibility and controllability of the fabrication process, we introduced a DRIE (Deep Reactive Ion Etching) to make a precisely aligned microchip array on a substrate. SF₆ was used for the etching gas. Previously, we used mechanical dicing combined with back-grinding to divide microchips instead of using the DRIE. The DRIE formed deep grooves in a mother chip with good controllability so as to divide into microchips with the area of 600 µm x 600 µm. To ensure the connectivity between the microchip and the substrate, special composite metal bump technology is developed. This is a combination of Au and Pt bumps in both side of the chip and substrate. The stimulus electrode is made of Pt with a diameter of 80 µm. The fabricated stimulator was tested in a saline solution.

Results:: The groove made with DRIE was over 200 µm in depth with an aspect ratio of over 20. The twelve microchips can be aligned precisely on the substrate. In addition, by using the composite bump technology, the fabricated stimulator shows more flexible than the stimulator that was fabricated without using DIRE. It can be bent with a radius of over 12 mm easily. The fabricated stimulator can work in a saline solution with a biphasic stimulation current pulse of about 0.5 mC/cm².

Conclusions:: We have developed a microchip-based stimulator using DRIE and composite bump technology. For ensuring further durability and biocompatibility, we are planning to cover the stimulator with palyrene.

Keywords: retina