Flexible polyimide-based hybrid optoelectric neural interface with 16 channels of micro-LEDs and electrodes

In this paper, a polyimide-based flexible device that integrates 16 micro-LEDs and 16 IrOx-modified microelectrodes for synchronous photostimulation and neural signal recording is presented. The 4 x 4 micro-LEDs (dimensions of 220 x 270 x 50 mu m(3), 700 mu m pitch) are fixed in the SU-8 fence structure on a polyimide substrate and connected to the leads via a wire-bonding method. The recording electrodes share a similar fabrication process on the polyimide with 16 microelectrode sites (200 mu m in diameter and 700 mu m in pitch) modified by iridium oxide (IrOx). These two subparts can be aligned with alignment holes and glued back-to-back by epoxy, which ensures that the light from the LEDs passes through the corresponding holes that are evenly distributed around the recording sites. The long-term electrical and optical stabilities of the device are verified using a soaking test for 3 months, and the thermal property is specifically studied with different duty cycles, voltages, and frequencies. Additionally, the electrochemical results prove the reliability of the IrOx-modified microelectrodes after repeated pressing or friction. To evaluate the tradeoff between flexibility and strength, two microelectrode arrays with thicknesses of 5 and 10 mu m are evaluated through simulation and experiment. The proposed device can be a useful mapping optogenetics tool for neuroscience studies in small (rats and mice) and large animal subjects and ultimately in nonhuman primates.