High-density probe with integrated thin-film micro light emitting diodes (μLEDs) for optogenetic applications

We report on the design, fabrication, assembly and characterization of an innovative neural probe with optical functionality for optogenetic applications in neuroscientific research. In contrast to existing systems, thin-film micro light-emitting diodes (μLEDs) are directly integrated in probes based on silicon (Si) substrates using a wafer-level bonding process. It allows to considerably shrink the overall probe dimensions despite an increased density of the integrated light sources. Our new system approach demonstrates the integration of multiple μLEDs with a size of 112×112 μm2 at a minimal pitch of 150 μm that can be controlled individually. The all-electrical interconnection of this optical tool constitutes a distinct advantage over existing optical probes for in vivo experiments with freely behaving animals, as comparably stiff optical fibers interfacing external light sources are avoided. The optical power density of these μLEDs was measured to be up to 3.5 mW/mm2 in air, at a peak wavelength of 450 nm which fulfills the requirements for optogenetic applications.