A multi-microchip retinal stimulator for in vitro / in vivo experiments

This paper describes the fabrication and in vitro/in vivo operation of a retinal stimulator based on CMOS multi-microchips. To enhance reliability and reproducibility for in vitro/in vivo with large array size, we introduce a flip-chip bonding technique and place microchips on the reverse side of a substrate. A microchip with a size of 600 mum square was fabricated using 0.35-mum standard CMOS process technology. Twelve microchips were flip-chip bonded on a polyimide substrate through Au bumps. We successfully fabricated a stimulator with 12 microchips and 118 electrodes made of Pt/Au bumps. For in vitro, we demonstrated their operation in a saline solution over two weeks. Also, for in vivo, a stimulator with one active IrO_x electrode was implanted into the scleral pocket of a rabbit and EEP signals with a threshold of 100 muA were obtained.