Compact intracerebral probe with yellow phosphor-based light conversion for optogenetic control

This paper reports on the use of phosphor particles to alter the emission spectrum of blue light-emitting diodes (LED) integrated in MEMS-based neural probes. For this purpose, we apply drop-casting to deposit the phosphor particles embedded in a transparent polymer matrix onto LED chips. The light emission is confined to spots as small as 100 μm in diameter by implementing micro-machined apertures in a probe stiffening structure made of silicon. Additionally, stray light emission from the probe rear through the semi-transparent polyimide substrate is effectively blocked by a metallic shielding layer. We demonstrate the optical down-conversion towards yellow wavelengths of 570-590 nm. A time-averaged output intensity of 0.679 mW/mm
²
was measured at 5 mA modulated at a duty cycle of 10%. The output intensity strongly depends on the amount of phosphor covering the LED surface.