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Imec unveils monolithic thin-film image sensor for the SWIR range with record pixel density

Wafer with image sensors for the SWIR range. These thin-film imagers can be produced with increased throughput and cost compared to today’s conventional IR imagers, while at the same time enabling multi-megapixel resolution

Imec, a research and innovation hub in nanoelectronics and digital technology, has presented a new thin-film monolithic image sensor that captures light in the near-infrared (NIR) and short-wavelength infrared (SWIR).

Based on a monolithic approach, the process will deliver increased fabrication throughput and cost compared to today’s conventional IR imagers, while at the same time enabling multi-megapixel resolution. IR imagers are used in a wide variety of applications, and imec says this new technology will extend possibilities into surveillance, biometric identification, virtual reality, machine vision, and industrial automation.

“We are excited to present this outstanding thin-film imager, a collaborative result of several teams with expertise ranging from chemistry, device engineering, readout design through integration and fab manufacturing. This result opens up many new applications for thin-film imagers,” commented Pawel Malinowski, imec’s thin-film imagers program manager.

“Our imagers could be integrated in next generation world-facing smartphone cameras coupled with eye-safe light sources, enabling compact sensing modules for augmented reality. In inspection, they could be used for food or plastics sorting, and in surveillance for low-light cameras with better contrast. Additionally, by enabling feature distinction in bad weather or smoke conditions, one can envision firefighting applications and, in the future, Advanced Driver Assistance Systems.”

Infrared image sensors are commonly produced with the crystalline semiconductor detector and the electronic readout being fabricated separately, and then interconnected at pixel or chip periphery level. This is an expensive and time-consuming process with a low throughput, resulting in sensors with a restricted resolution, as well as preventing widespread use of IR imagers in consumer applications. With this approach, Imec will look to pave the way to high-resolution, low-cost, wafer-based SWIR imagers.

Imec's IR imagers consist of a thin-film photodetector pixel stack based on quantum dots deposited directly on top of an electronic readout. They are manufactured in a monolithic process compatible with wafer-based mass production. The pixels embed newly developed high-performance low bandgap quantum dot materials that match or even surpass the performance of inorganic light absorbers.

The stacks have been engineered so they can be tuned to target a spectrum from visible light all the way up to 2µm wavelength. Test photodiodes on silicon substrate achieve an external quantum efficiency above 60 percent at 940nm wavelength, exceeding the state-of-the-art, and above 20 percent at 1450nm, allowing for uncooled operation with dark current comparable to commercial InGaAs photodetectors. The prototype imager has resolution of 758x512 pixels and 5um pixel pitch.

The company aims to develop a wafer-level NIR and SWIR image sensor technology and develop technologies for companies with a roadmap in innovative image sensors, cameras and smart imaging applications. The current SWIR photodetector is the result of several collaborations, including the Flemish VLAIO-SBO project MIRIS (IWT/150029) with academic partners Ghent University and University of Hasselt, and Flanders based companies active in imaging technology.

Author
Charlotte Hathway

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