Projects per year
The objective of this work is to develop and test a photovoltaic retinal prosthesis for restoring sight to patients blinded by degenerative retinal diseases. A silicon photodiode array for subretinal stimulation has been fabricated by a silicon-integrated-circuit/MEMS process. Each pixel in the two-dimensional array contains three series-connected photodiodes, which photovoltaically convert pulsed near-infrared light into bi-phasic current to stimulate nearby retinal neurons without wired power connections. The device thickness is chosen to be 30 µm to absorb a significant portion of light while still being thin enough for subretinal implantation. Active and return electrodes confine current near each pixel and are sputter coated with iridium oxide to enhance charge injection levels and provide a stable neural interface. Pixels are separated by 5 µm wide trenches to electrically isolate them and to allow nutrient diffusion through the device. Three sizes of pixels (280, 140 and 70 µm) with active electrodes of 80, 40 and 20 µm diameter were fabricated. The turn-on voltages of the one-diode, two-series-connected diode and three-series-connected diode structures are approximately 0.6, 1.2 and 1.8 V, respectively. The measured photo-responsivity per diode at 880 nm wavelength is ~0.36 A W−1, at zero voltage bias and scales with the exposed silicon area. For all three pixel sizes, the reverse-bias dark current is sufficiently low (<100 pA) for our application. Pixels of all three sizes reliably elicit retinal responses at safe near-infrared light irradiances, with good acceptance of the photodiode array in the subretinal space. The fabricated device delivers efficient retinal stimulation at safe near-infrared light irradiances without any wired power connections, which greatly simplifies the implantation procedure. Presence of the return electrodes in each pixel helps to localize the current, and thereby improves resolution.
|Number of pages||12|
|Journal||Journal of Neural Engineering|
|Early online date||12 Jul 2012|
|Publication status||Published - Aug 2012|
- medical physics
- biophysical techniques
FingerprintDive into the research topics of 'Photovoltaic retinal prosthesis: implant fabrication and performance'. Together they form a unique fingerprint.
- 1 Finished
SU2P: Stanford-Scotland Photonics Innovation Collaboration (Science Bridges)
Ferguson, A., Ackemann, T., Burns, D., Dawson, M., McConnell, G. & Riis, E.
EPSRC (Engineering and Physical Sciences Research Council)
1/09/09 → 28/02/13
- 1 Visiting an external academic institution
University of Stanford
Keith Mathieson (Visiting researcher)Sep 2009 → Sep 2011
Activity: Visiting an external institution types › Visiting an external academic institution