CMOS-compatible aluminum pairs with silicon for on-chip color detection
Researchers at Rice University's Laboratory for Nanophotonics (LANP; Houston, TX) have created a CMOS-compatible color photodetector that selectively responds to red, green, and blue (RGB) light.
|An imaging sensor based on CMOS-compatible aluminum (Al) and silicon (Si) integrates light amplifiers and color filters directly into pixels. (Credit: B. Zheng/Rice)|
Researchers at Rice University's Laboratory for Nanophotonics (LANP; Houston, TX) have created a CMOS-compatible color photodetector that selectively responds to red, green, and blue (RGB) light.1 The new device uses two Schottky junctions to accumulate charge and a plasmonic aluminum grating that enhances photocurrent and provides the RGB selectivity.
Conventional photodetectors require added color filters to measure RGB color components, commonly done using off-chip dielectric or dye color filters, which degrade under exposure to sunlight and can also be difficult to align with the imaging sensor array.
"Today's color filtering mechanisms often involve materials that are not CMOS-compatible, but this new approach has advantages beyond on-chip integration," says LANP Director Naomi Halas, the lead scientist on the study. "It's also more compact and simple and more closely mimics the way living organisms 'see' colors." The Rice color photodetector benefited from a $6 million research program funded by the Office of Naval Research that aimed to mimic cephalopod skin using optical metamaterials.
Cephalopods like octopus and squid are masters of camouflage, but they are also color-blind. Halas say the "squid skin" research team, which includes marine biologists Roger Hanlon of the Marine Biological Laboratory (Woods Hole, MA) and Thomas Cronin of the University of Maryland, Baltimore County, suspect that cephalopods may detect color directly through their skin. Based on that hypothesis, LANP graduate student Bob Zheng, the lead author of the new Advanced Materials study, set out to design a photonic system that could detect RGB light.
Zheng's color photodetector uses a combination of band engineering and plasmonic gratings. Color selection is performed by using interference effects between the plasmonic grating and the photodetector's surface. Tuning the oxide thickness and the width and spacing of the slits allows color selection. The plasmonic grating also results in near-field enhancement, which increases the proportion of light that passes through the metallic slits to the detector.
1. Ruibin Jiang et al., Advanced Materials (2014); doi: 10.1002/adma.201400203