Microelectrode array with integrated nanowire FET switches for high-resolution retinal prosthetic systems

Abstract

In this paper, a novel microelectrode array integrated with nanowire field-effect transistor (FET) switches is developed for retinal prosthetic systems. Retinal prosthetic systems require many electrodes (generally more than several hundreds) and this paper presents a novel method of integrating silicon nanowire-FET switches with microelectrodes that can significantly reduce wiring complexity. Also, in order to fit the curvature of an eyeball, the silicon nanowire FETs are transferred to a flexible substrate. In order to demonstrate the concept of using FETs for switching collocated retinal microelectrodes, a microelectrode array with 32 × 32 pixels is fabricated, which has 1,024 microelectrodes. Using the FET switches in a two-dimensional array addressing configuration, 1,024 microelectrodes are addressed by only 64 lines (32 for scan and 32 for data), as compared to requiring 1,024 lines in the conventional one-to-one configuration. With the gate voltage of −5 V, the threshold voltage, current on/off ratio, and on-resistance of the fabricated silicon nanowire-FET switch are −0.4 V, 1 × 107, and 37–47 kΩ, respectively. The maximum allowable current injection limit of the silicon nanowire-FET switch integrated microelectrode is 44 μA with a pulse duration of 1 ms. These results show an excellent potential for high-resolution retinal prosthetic systems.