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J. Ohta, T. Tokuda, K. Kagawa, A. Uehara, Y. Terasawa, K. Shodo, T. Fujikado, Y. Tano; Large–scale Electrode Array Based On Distributed Microchip Architecture For Suprachoroidal Transretinal Stimulation . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3182.
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For suprachoroidal–transretinal stimulation (STS), we have proposed a flexible and extendible microchip–based stimulator in which a number of microchips are distributed on a flexible polyimide substrate. Each microchip accommodates several stimulus electrodes with switching circuits, which can be externally controlled to turn on and off through an external control circuit. This report aims to explore the microchip–based stimulator with large number of stimulus electrodes such as over 100 electrodes for STS.
To enhance extendibility of the stimulator for large array size, we have developed a new stimulator design, in which the microchips are placed on the backside of the flexible substrate, that is, flip–chip bonding. The stimulus electrodes are electrically connected with the microchips through micro via–holes. The microchips are connected to each other such that the column can be extended vertically, so that the stimulator can increase the number of microchip placed on it. All of the connection wires are placed on the backside of the substrate; no wire bonding is needed in the configuration and thus the new stimulator is more reliable. The microchip is fabricated in 0.35 µm standard CMOS technology with a high voltage option.
We have successfully fabricated a micro via–hole less than 50 µm in diameter and a connect between the stimulus electrode and the bonding pad on the microchip. The fabricated stimulator has 12 microchips with 600 µm square, each of which controls 9 electrodes as shown in the figure.
We have proposed and fabricated a flip–chip type stimulator for a large number of stimulation in STS. The fabricated microchip is now under testing. The fabricated stimulator will be tested to operate in a saline solution.
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