Pseudologic Optical\nCircuit Method for Advanced Color\nSensing in IGZO Phototransistor Arrays with Chlorophyll Absorption\nLayers

Recently, the elimination of color filters has become\na key focus\nin photodetector research because of the potential to create more\ncompact and cost-effective sensor systems. In this study, a novel\nconcept of a filter-free color-discrimination photosensor using an\nindium gallium zinc oxide (IGZO,\nIn/Ga/Zn = 3.1:2.6:1.0)-based phototransistor with an integrated chlorophyll\nabsorption layer (CAL) and a solution-processed oxide absorption layer\n(SAL) was developed. Chlorophyll, known for its role in photosynthesis\nas a natural light absorber, offers distinct characteristics compared\nto conventional photodetectors (i.e., SAL/IGZO), whereby the photoresponsivity\ndecreases with increasing wavelength. Using the ability of chlorophyll\nto absorb blue and red light, the proposed CAL/IGZO phototransistor\nexhibited a higher photoresponsivity to red light than to green light.\nThe device achieved a photoresponsivity of 1570 A/W for red light\nand 681 A/W for green light, with a photosensitivity of 8.35 ×\n10<sup>5</sup> and 8.96 × 10<sup>4</sup> and a detectivity of\n8.47 × 10<sup>11</sup> and 6.80 × 10<sup>10</sup> Jones,\nrespectively, under an illumination intensity of 1 mW/mm<sup>2</sup>. Furthermore, by integrating the proposed CAL/IGZO phototransistor\nwith a SAL/IGZO phototransistor, which exhibited a different order\nof photoresponse across RGB wavelengths, an innovative color-discrimination\npixel pseudologic circuit was successfully developed. The capability\nof this circuit to distinguish colors across various light intensities\nwas validated through experimental data and SPICE simulations, with\nthe output voltage ranges confirmed as −2.61 to −3.51\nV for red, 1.56 to 2.69 V for green, and −0.22 to −0.68\nV for blue over light intensities from 0.1 to 3 mW/mm<sup>2</sup>.\nThis innovative approach allows effective color detection without\nconventional color filters, providing an advanced solution for photodetection\ntechnologies.