3D-IC: New Perspectives for a Digital Pixel Sensor

Digital Pixel Sensors (DPS) are often unsuitable in the standard market due to large pixel size and low Fill-Factor (FF) in spite of several advantages like an early conversion. Nevertheless, the digital pixel represents presages of the ``smart'' pixel integrating maximum of processing in pixel level. It's for this reason that a special attention should be paid in this one. An elegant solution to compensate for the disadvantages of the DPS is to use an emergent three-dimension integration technology. So in this paper, an explanation of the sensitivity of image sensor is done highlighting the role of the fill-factor on this characteristic. Then a description of a particular digital pixel is described as well as a brief overview of different three-dimension integration methods. The digital pixel includes a photodiode, a Delta-Sigma Modulation (DSM) and a digital decimation filter. Finally, this paper presents an approach which combines a 3D technology, the CMOS (Complementary Metal Oxide Semi-conductor) 130nm 3D-IC FaStack Tezzaron technology, and the Multi-Channel-Bit-Serial (MCBS) method allowing the presented pixel to obtain a high fill-factor about 80% and a pixel pitch of 32.5 mu m