Quantum Dot-based Sensor Captures More Light in Less Space

Researchers from Chung-Ang University introduced a photodetector integrated into a dense sensor array for high-resolution multispectral (color) imaging. The technology uses quantum dots to overcome the space-consuming design of current sensors.

In most image sensors, the red, green, and blue components of a given pixel are captured independently using a dedicated photodetector cell for each color. Although the three cells of each pixel are arranged laterally and as close to each other as possible, the design takes at least three times as much space as each individual cell. Additionally, the manufacture and processing costs for these photodetectors can be high due to their complexity.

Quantum dots, nanoparticles tailored to be sensitive to specific frequencies, owe their quantum effects mainly to their small size. Their durability, sensitivity, and ease of use in manufacturing processes make them uniquely attractive for developing revolutionary color image sensors. Courtesy of Chung-Ang University.

Quantum dots present an advantage over the traditional lateral pixel arrangement because they can be stacked vertically in each pixel, thereby reducing the surface area required to create a sensor. The quantum dots in lower positions are still able to receive photons that are not absorbed by the upper levels of quantum dots, enabling photodetectors for each color in each pixel to be accommodated in a much tighter area.

Using a low-temperature fabrication procedure, the scientists managed to squeeze in an astoundingly high number of pixels in a small area. “The device density of our photodetector array is 5500 devices per square centimeter, which is remarkably larger than that reported for previous solution-processed flexible photodetectors, which reaches up to 1600 devices,” said Sung Kyu Park, a professor at Chung-Ang University.

The device demonstrated excellent color selectivity and photosensitivity. In the long term, the team believes that future improvements could enable vertically stacked quantum dots to replace existing CMOS sensors in many applications due to their simple fabrication, low power consumption, durability, and capabilities. “It should be widely applicable in fields such as wearable sensory systems, biomedicine, and autonomous driving,” Park said.

The research was published in Advanced Materials (www.doi.org/10.1002/adma.202106215).