3D integration technology for 3D stacked retinal chip

To recover visual sensation of blind patients, we have proposed a novel three dimensionally (3D) stacked retinal prosthesis chip in which several LSI chips such as consisting of photodetector, signal processing circuit and stimulus current generator are vertically stacked and electrically connected using 3D integration technology. In this work, we developed several key process for realizing 3D stacked retinal prosthesis chip. Fine sized Cu TSV of 10 mum width and 30 mum depth was successfully formed from the back side of the thinned prosthesis chip. The prosthesis chip with the back side Cu TSVs was flip-chip bonded to Si substrate/flexible substrate through Cu/Sn micro-bumps for evaluating the feasibility of 3D integration technology.