LED-based intracerebral optrode for simultaneous optical stimulation and electrophysiological recording

We present a new type of optrode based on light-emitting diodes (LED) applying a 70μm-thin multifunctional stiffening structure made of silicon (Si). By combining optical and electrical functionalities in a single implantable device, we successfully addressed the requirement of reduced tissue damage during in vivo applications. The improved stiffener comprises apertures (100 μm diameter) used for confining the illumination area of the integrated LEDs and iridium oxide (IrOx) electrodes (40 μm diameter) for electrophysiological recordings. The novel dual-sided wafer-level micromachining process applies wafer bonding and grinding to process 70-μm-thin Si substrates. The lateral dimensions of the optrodes are defined mainly by the size of the commercial LEDs resulting in a shank width and thickness of 283 μm and 80 μm, respectively. The choice of IrOx as electrode material results in a low average electrical impedance of 43.1 kΩ at 1 kHz. Despite the aperture-confined illumination area, light intensities of 7.85 μW (emittance: 1 mW/mm2) well above the stimulation threshold are achieved at sub-milliwatt electrical power.