Department of Bioengineering and Robotics, Graduate School of Engineering
The number of patients suffering from retinitis pigmentosa and age-related macular degeneration, which is also caused by diabetes mellitus, is increasing dramatically as society ages. More than 10 million patients worldwide are blind because of these diseases, which result from the impairment of the photoreceptor cells (called rods and cones) that convert light signals to electric signals. By contrast, other cells, such as ganglion cells, fail to develop in these diseases. Currently, studies of retinal prostheses for blind patients are in progress all over the world.
For blind patients, we hope to develop a 3D-stacked retinal prosthesis that has stimulus electrodes on its rear. In a conventional retinal prosthesis, the stimulus electrodes for stimulating the optic nerve and photosensor/circuit are separate. Therefore, we must transplant these two chips and a connecting cable into the eye socket, which is a very difficult procedure. We propose a high performance 3D-stacked retinal prosthesis using 3D-integration technology. This chip is made by thinning and stacking several LSI chips with photosensors and image processing circuits. Furthermore, the chip has stimulus electrodes on the back. First, the photosensors on the top layer convert the optical signal into an electrical signal. The lower layers receive the electrical signal via vertical interconnections that connect the LSI chips. After signal processing in image-processing circuits, such as edge detection circuits, the circuit in the bottom layer then stimulates the retina electrically. In this way, a high-performance retinal prosthesis that reduces the surgical load of implantation can be realized by miniaturizing and thinning the chips.
SEM Cross Sectional View of 3D LSI for Retinal Prosthesis