A new image sensor using quantum dots could replace CMOS

Quantum dots are nanoparticles most commonly found in screens today, but researchers have managed to leverage the technology to detect wavelengths of light on a sensor. The team argues that the technology is capable of replacing CMOS sensors.

Quantum dot technology

Quantum dot technology, or QLED, uses a panel of phosphorescent crystals that react to light and electricity to improve picture quality on televisions. These quantum dots are, individually, extremely small – less than 500 nanometers – and can glow in a range of colors that is determined by the atoms within each. As Viewsonic explainsinstead of using pure white backlights, a TV with QLED technology will instead emit red or green when hit with blue light, which means more saturated and accurate colors than a screen LEDs without quantum dots.

“Each pixel on the screen emits red, green or blue light, or sometimes a combination of the three,” says Viewsonic. “The color accuracy of each pixel is defined by the wavelengths. And quantum dots can be easily tuned to their determined size to unleash different specific wavelengths for the best color production.

The image below shows how the quantum dots are arranged in a QLED display:

quantum dots arranged in a display

Quantum dots are extremely useful for dramatically improving the quality of a display. The researchers succeeded in using these exact principles but in reverse: instead of using quantum dots to display colors, the technology is used to record them.

The quantum dot sensor

CMOS sensors are great, but there are limitations to their implementation and the way they record data is also limited by their size.

“Many growing application areas, such as self-driving cars, flexible electronics, healthcare and medical imaging, require even higher resolutions and levels of integration. This is difficult to achieve due to the way each pixel in a color image is captured,” the researchers explain.

“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. While the three cells of each pixel are arranged laterally and as close together as possible to efficiently use the available area, this design takes up at least three times the space of each individual cell. In addition, the manufacturing and processing costs of these photodetector arrays can be high due to their complexity. »

The researchers, led by Professor Sung Kyu Park of Chung-Ang University in Korea, explain that they have developed a new type of sensor that exploits quantum dot technology.

The sensor uses vertically stacked quantum dots which, as mentioned above, are each sensitive to specific light frequencies. When light passes through the layers of differently tuned dots, only light that would react with the dot of a specific frequency would be triggered, so the sensor knows what color to record that information.

The researchers say the pixel structure uses far less area per pixel than conventional image sensors, meaning more of them can be placed in a space than with current CMOS technology.

“The device density of our photodetector array is 5,500 devices per square centimeter, which is remarkably larger than that reported for previous solution-treated flexible photodetectors, which reach up to 1,600 devices.”

Basically, using a low-temperature fabrication method, the researchers were able to fit a significantly higher number of pixels into the same small area than is currently possible with conventional methods.

Additionally, the researchers claim that manufacturing the sensors is much simpler and the resulting sensor has high photosensitivity and durability, meaning the design could be used for high-resolution sensors in a wide variety of applications. .

“We believe our design is a great step towards establishing a high-resolution, low-cost integrated image sensor system that goes beyond conventional systems,” Park says.

The full research paper can be read in the January issue of Advanced materials.

Picture credits: Header image courtesy of the research team depicting quantum dots as a tool for next-generation color image sensors.

Michael C. Garrison