Thinned and Back-side Illuminated Photodiodes
Wireless Retina Implant Electrostimulates Ganglion Cells
Wafers with PREMA photodiodes consisting of pn-junctions close to the upper surface have been back-grinded to 20 µm, 35 µm, 60 µm and 100 µm. The spectral sensitivity of singulated photodiodes has been measured with back-side illumination. The spectral sensitivity is increased up to 0,18 A/W by a metal cap above the photodiodes. Here, photons that have not been absorbed are reflected. The retina implant consists of thinned photodiodes embedded in a foil substrate. While the light enters the photodiode at the back-side, the contact pads at the front-side can be utilized to electro-stimulate the ganglion cells.