Pseudologic Optical Circuit Method for Advanced Color Sensing in IGZO Phototransistor Arrays with Chlorophyll Absorption Layers

Recently, the elimination of color filters has become a key focus in photodetector research because of the potential to create more compact and cost-effective sensor systems. In this study, a novel concept of a filter-free color-discrimination photosensor using an indium gallium zinc oxide (IGZO, In/Ga/Zn = 3.1:2.6:1.0)-based phototransistor with an integrated chlorophyll absorption layer (CAL) and a solution-processed oxide absorption layer (SAL) was developed. Chlorophyll, known for its role in photosynthesis as a natural light absorber, offers distinct characteristics compared to conventional photodetectors (i.e., SAL/IGZO), whereby the photoresponsivity decreases with increasing wavelength. Using the ability of chlorophyll to absorb blue and red light, the proposed CAL/IGZO phototransistor exhibited a higher photoresponsivity to red light than to green light. The device achieved a photoresponsivity of 1570 A/W for red light and 681 A/W for green light, with a photosensitivity of 8.35 × 10⁵ and 8.96 × 10⁴ and a detectivity of 8.47 × 10¹¹ and 6.80 × 10¹⁰ Jones, respectively, under an illumination intensity of 1 mW/mm². Furthermore, by integrating the proposed CAL/IGZO phototransistor with a SAL/IGZO phototransistor, which exhibited a different order of photoresponse across RGB wavelengths, an innovative color-discrimination pixel pseudologic circuit was successfully developed. The capability of this circuit to distinguish colors across various light intensities was validated through experimental data and SPICE simulations, with the output voltage ranges confirmed as -2.61 to -3.51 V for red, 1.56 to 2.69 V for green, and -0.22 to -0.68 V for blue over light intensities from 0.1 to 3 mW/mm². This innovative approach allows effective color detection without conventional color filters, providing an advanced solution for photodetection technologies.