"A photosensing circuit using thin-film transistors (TFTs) for a retinal prosthesis has been developed. First, the TFTs that are low-temperature polycrystalline silicon (poly-Si) TFTs are fabricated on a transparent substrate, which enables us to build an epiretinal implantation system without using any extracorporeal cameras. Then, the photosensing circuit is fabricated by connecting a p/i/n-type phototransistor and a ring oscillator, which provides stimulating current pulses with an oscillation frequency dependent on light illuminance. In particular, the device structure of the p/i/n-type phototransistor is designed well on the basis of device physics, and the configuration of the photosensing circuit on the basis of device characteristics. Subsequently, a wireless power transfer system is architected by magnetic resonance coupling. Finally, a retinal prosthesis is produced by assembling the photosensing circuit and wireless power transfer system, and the stimulating performance is confirmed in an in vitro experiment, which suggests a future possibility of this retinal prosthesis."
