GaN-based micro-LED arrays on flexible substrates for optical cochlear implants

Currently available cochlear implants are based on electrical stimulation of the spiral ganglion neurons. Optical stimulation with arrays of micro-sized light-emitting diodes (mu LEDs) promises to increase the number of distinguishable frequencies. Here, the development of a flexible GaN-based micro-LED array as an optical cochlear implant is reported for application in a mouse model. The fabrication of 15 mu m thin and highly flexible devices is enabled by a laser-based layer transfer process of the GaN-LEDs from sapphire to a polyimide-on-silicon carrier wafer. The fabricated 50 x 50 mu m(2) LEDs are contacted via conducting paths on both p- and n-sides of the LEDs. Up to three separate channels could be addressed. The probes, composed of a linear array of the said mu LEDs bonded to the flexible polyimide substrate, are peeled off the carrier wafer and attached to flexible printed circuit boards. Probes with four mu LEDs and a width of 230 mu m are successfully implanted in the mouse cochlea both in vitro and in vivo. The LEDs emit 60 mu W at 1 mA after peel-off, corresponding to a radiant emittance of 6 mW mm(-2).