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Proceedings Paper

Photovoltaic retinal prosthesis for restoring sight to the blind: implant design and fabrication
Author(s): Lele Wang; Keith Mathieson; Theodore I. Kamins; James Loudin; Ludwig Galambos; James S. Harris; Daniel Palanker
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Paper Abstract

We have designed and fabricated a silicon photodiode array for use as a subretinal prosthesis aimed at restoring sight to patients who lost photoreceptors due to retinal degeneration. The device operates in photovoltaic mode. Each pixel in the two-dimensional array independently converts pulsed infrared light into biphasic electric current to stimulate remaining retinal neurons without a wired power connection. To enhance the maximum voltage and charge injection levels, each pixel contains three photodiodes connected in series. An active and return electrode in each pixel ensure localized current flow and are sputter coated with iridium oxide to provide high charge injection. The fabrication process consists of eight mask layers and includes deep reactive ion etching, oxidation, and a polysilicon trench refill for in-pixel photodiode separation and isolation of adjacent pixels. Simulation of design parameters included TSUPREM4 computation of doping profiles for n+ and p+ doped regions and MATLAB computation of the anti-reflection coating layers thicknesses. The main process steps are illustrated in detail, and problems encountered are discussed. The IV characterization of the device shows that the dark reverse current is on the order of 10-100 pA-negligible compared to the stimulation current; the reverse breakdown voltage is higher than 20 V. The measured photo-responsivity per photodiode is about 0.33A/W at 880 nm.

Paper Details

Date Published: 6 February 2012
PDF: 8 pages
Proc. SPIE 8248, Micromachining and Microfabrication Process Technology XVII, 824805 (6 February 2012); doi: 10.1117/12.909104
Show Author Affiliations
Lele Wang, Stanford Univ. (United States)
Keith Mathieson, Stanford Univ. (United States)
Univ. of California, Santa Cruz (United States)
Theodore I. Kamins, Stanford Univ. (United States)
James Loudin, Stanford Univ. (United States)
Ludwig Galambos, Stanford Univ. (United States)
James S. Harris, Stanford Univ. (United States)
Daniel Palanker, Stanford Univ. (United States)

Published in SPIE Proceedings Vol. 8248:
Micromachining and Microfabrication Process Technology XVII
Mary Ann Maher; Paul J. Resnick, Editor(s)

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