Flexible, Monolithic, High-Density µLED Neural Probes for Simultaneous Optogenetics Stimulation and Recording*

Abstract

Modern optogenetic experiments require high spatio-temporal resolution stimulation deep in brain tissue. Implantable optoelectrical neural probes with integrated recording electrodes and photonic devices offer unique opportunities for simultaneous electrical recording and optical stimulation of neural activity. Micro-light-emitting diodes (µLEDs) have been used for optical stimulation. However, such µLEDs are mostly fabricated on rigid substrates such as silicon and sapphire. Flexible, polymer substrates are preferred for realizing neural probes that reduce damage to brain tissue. Commercial off-the-shelf LED chips have been packaged in polymer substrates; however, the prohibitively large sizes of such LED chips limit the density of the probes and process scalability. Here, we demonstrate a novel monolithic design in which recording electrodes and GaN µLEDs (30 µm x 30 µm) are realized directly in a flexible, biocompatible Parylene C substrate. Due to its biocompatibility and compliance, Parylene C is widely used as insulation or substrate in neural probes. We demonstrate one-dimensional and two-dimensional individually-addressable µLED arrays that emit blue light at the wavelength of 453 nm for stimulation of Channelrhodopsin-2 (ChR2), with output intensities greater than 15 mW/mm2, well above the threshold for stimulation of ChR2. High-density (400 µLEDs/mm2) two-dimensional electrode arrays are realized on a 3.5 cm x 920 µm flexible probe shank.