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G.Y. McLean; Optoelectronic and Electrochemical Characteristics of Subretinal Photodiode Arrays . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3183.
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To characterize the optoelectronic and electrochemical behavior of implantable photodiode arrays produced by Optobionics Corporation. We characterize the responsivity, electrode impedance, electrode charge injection characteristics, and other properties of the devices that are relevant to the conversion of light into electrical charge, and the injection of charge into retinal tissue.
The methods we employ include (a) measurement of electronic and optoelectronic test structures built on the same silicon wafer substrate as ASR devices, using conventional electronic microprobing techniques, and (b) electrochemical measurements of ASR devices under conditions similar to those the device experiences when implanted into the subretinal space of the eye. Through the former we characterize the photodiode junctions and their electrical interface to the electrodes, and through the latter we investigate the behavior of the electrodes and the system as a whole in an aqueous medium.
ASR devices achieve an effective responsivity in excess of 0.3 A/W over the range of wavelengths from 400 nm to 900 nm, with a peak sensitivity of about 0.5 A/W near 750 nm. The devices generate photocurrents in proportion to the incident light intensity over a wide range, extending from less than 10 nW/cm2 to greater than 1 mW/cm2. The instantaneous stimulus currents reflect an interplay between the diode characteristics and the electrode polarization and impedance characteristics.
We discuss several properties of ASR devices that are relevant to the conversion of light into electrical charge, and the injection of charge into retinal tissue, and discuss the relationship between various lighting conditions and electrical stimuli.
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