This application note starts with a motivation for vertical stacking of integrated circuits, focusing on the benefits for electronic image sensors. Next, it considers general principles in the design of vertically-integrated (VI) CMOS image sensors that are fabricated by flip-chip bonding. These sensors are composed of a silicon die with CMOS circuits and a transparent die with photodetectors. As a specific example, the note presents a VI-CMOS image sensor that was designed at the University of Alberta, and fabricated with the help of CMC Microsystems and Micralyne Inc. Finally, recommendations are made for future projects of a similar nature.
