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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 0.35/spl mu/m 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.

This paper utilizes the concepts of equilibrium equations and minority carrier continuity to build and derive a CMOS photodiode model. By using the TSMC 1P3M 0.5 /spl mu/m CMOS technology, photodiodes with two different types of N/sub well/-P/sub Epitaxial/-P/sub substrate/ and N/sub diffusion/-P/sub well/-P/sub Epitaxial/-P/sub su/ /sub bstrate/ were fabricated. Measurements were done to test the photoresponse from 400 nm to 1000 nm. To simulate the photoresponses of N/sub well/-P/sub Epitaxial/-P/sub substrate/ and N/sub diffusion/-P/sub well/-P/sub Epitaxial/-P/sub su/ /sub bstrate/ photodiodes using the proposed model, if an inadequate value of the surface recombination velocity which is affected by the surface defects in the manufacture process is utilized, the proposed model would yield a little larger error in estimating the photoresponse in a shorter wavelength. To overcome this problem, the curve mapping scheme is applied to find the adequate boundary condition of the surface recombination velocity with the least mean squared error thus allowing the proposed model to achieve a good performance. The concept of the model proposed herein could be utilized in designing any CMOS photodiode for simulating its photo-electronic characteristics in various industrial applications.