A color image sensor using adaptive color pixels

A color image sensor using adaptive color pixels is proposed where the adaptive color pixel is based on three PN junctions to sense color spectrum (RGB : Red, Blue and Green). The three PN junctions from four layers of which junctions are selected by two control signals to get RGB photo responses on the same pixel. Simulation results show that by controlling the process parameters of each layer, RGB photo responses with peak wavelengths on 650nm, 550nm and 460nm can be derived at on the same pixel, respectively. In actuality, such approach could effectively replace the color filter process commonly used today in color image sensors. For demonstration, we used the three-layer photodiode with Pdiffusion-Nwell-Psubstrate junction currently available from the TSMC 1P4M 0.35μm CMOS standard process. As the measurement results show, by using the two PN junctions formed by the three layers of such photodiode, we have successfully obtained photo responses with peak wavelengths close to 460nm and above 650nm on the same pixel. This proves the feasibility of the proposed photodiodes without color filters to reduce their manufacturing costs.