2PFCTM Image Sensors: Better Image Quality at Lower Cost

SLA has developed a low cost alternative to the standard Bayer CFA and photodiode structure for CMOS imagers. The "Two-Pixel, Full Color" (2PFCTM) imager represents a new direction in imager technology. The blue and red filters of the Bayer pattern are replaced by magneta filters. Under each magenta filter are two stacked, pinned photodiodes; the diode nearest the surface absorbs mostly blue light and the deeper diode absorbs mostly red light. The magenta filter absorbs green light, improving color separation between the resulting blue and red diodes. The dopant implant defining the bottom of the red-absorbing region can be made the same as the green diodes, simplifying the fabrication. SInce the spatial resolution for the red,green, and blue channels are identical, color aliasing is greatly reduced. Luminance resolution can also be improved, the thinnner diodes lead to higher well capacity with resulting better dynamic range, and fabrication costs can be similar to or less than standard Bayer CMOS imagers. Demosaiced images look better with 2PFCTM than with Bayer. Also the geometry of the layout lends itself naturally to frequency based demosaicing.