Development of 3DIC/TSV Technology and Its Application to Artificial Retina for Visual Sensory Recovery

3DIC using TSVs is one of the most promising candidates for high-performance computing systems since 3DICs have many advantages, such as high memory bandwidth and low power consumption due to short wiring length, small pin capacitances, and ultra-parallel operation. Until now, several kinds of 3DICs, including 3D-memory and 3D-CIS, have been fabricated successfully. Among several types of 3DIC technologies, multiple chips-to-wafer (MCtW) stacking can stack known-good chips fabricated with different technologies and sizes, leading to a true 3D heterogeneous system. A fully implantable retinal prosthesis with a 3D-stacked artificial retina (AR) chip has been developed at Tohoku University using MCtW stacking. In the 3D-stacked AR chip, the photoreceptor chip and stimulus current generator with image processing circuits are vertically stacked and electrically connected by many TSVs. The 3D-stacked AR chip has a layered structure similar to the human retina, so the AR chip of approximately 1,500 pixels can be fabricated. By implanting the 3Dstacked AR chip into the eyeball, the patients can employ their lens and cornea and shift a gaze point by moving the eyeball. The 3D-stacked AR chip leads to a small chip size, lightweight, large fill factor, high resolution, and a high quality of life for the patients.