Department of Electrical Engineering, Stanford University, Stanford, CA 94305, USA.
J Neural Eng. 2012 Aug;9(4):046014. doi: 10.1088/1741-2560/9/4/046014. Epub 2012 Jul 12.
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.
这项工作的目的是开发和测试一种用于恢复因退行性视网膜疾病而失明的患者视力的光电池视网膜假体。已经通过硅集成电路/MEMS 工艺制造了用于视网膜下刺激的硅光电二极管阵列。二维阵列中的每个像素都包含三个串联的光电二极管，这些光电二极管将脉冲近红外光光转换成双相电流，无需有线电源连接即可刺激附近的视网膜神经元。该器件的厚度选择为 30 µm，以吸收大部分光，同时仍足够薄，可用于视网膜下植入。有源和返回电极将电流限制在每个像素附近，并溅射涂覆氧化铱以提高电荷注入水平并提供稳定的神经接口。像素之间的间隔为 5 µm 宽的沟槽，以实现电隔离并允许营养物质通过器件扩散。制造了三种尺寸的像素（280、140 和 70 µm），其有源电极的直径分别为 80、40 和 20 µm。单二极管、两个串联二极管和三个串联二极管结构的开启电压分别约为 0.6、1.2 和 1.8 V。在 880nm 波长下，零电压偏置时每个二极管的光电响应度约为 0.36 A W(-1)，并与暴露的硅面积成正比。对于所有三种像素尺寸，反向偏置暗电流都足够低（<100 pA），适用于我们的应用。所有三种尺寸的像素都能在安全的近红外光辐照度下可靠地引发视网膜反应，并且在视网膜下空间中对光电二极管阵列的接受度良好。该制造的器件在安全的近红外光辐照度下提供有效的视网膜刺激，无需任何有线电源连接，大大简化了植入程序。每个像素中的返回电极有助于使电流本地化，从而提高分辨率。
