I Introduction
Visual prosthesis capable of eliciting visual sense in a blind or visually impaired individual through electrical stimulation is mainly utilized for restoring vision of patients blinded by retinitis pigmentosa (RP) or age-related macular degeneration (AMD) [1], because of the photoreceptors in the retinal of the patients are damaged but the remaining inner retinal circuitry remains largely intact [2]. Implantable microelectrodes are needed for stimulating the remaining inner retinal cells which should be fabricated for meeting strict requirements such as biological compatibility, thin, flexible and low electrochemistry impedance to ensure safe and long-term effective stimulation.