IEDM 2021: A shortwave infrared global shutter sensor uses Quantum dots to break records

ST submitted four papers at the latest IEEE International Electron Devices Meeting (IEDM 2021). One of them resulted from an invitation by the organizers, while another is the fruit of a collaboration with Samsung. All of them aim to make industry-changing innovations more accessible. Indeed, Samsung and ST showed the first 18 nm FDSOI microcontroller thanks to new processes. Similarly, the other papers look to make sensors or memories more cost-effective in the next few years. Let us, therefore, dive into some of the papers ST showcased at the event.

“1.62μm Global Shutter Quantum Dot Image Sensor Optimized for Near and Shortwave Infrared”
What’s New at IEDM 2021?
IEDM 2021: QF technology qualification wafer showing elementary QF photodiode test structures (a), pixel matrix test chips (b), and full image sensor products (c)
QF technology qualification wafer showing elementary QF photodiode test structures (a), pixel matrix test chips (b), and full image sensor products (c)

One of the showstoppers was a paper led by Johnathan Steckel on the first 1.62 µm pixel pitch global shutter image sensor for near-infrared (NIR) and shortwave infrared (SWIR) produced on a 300 mm silicon wafer. Using lead sulfide quantum dots, the image sensor is significantly more cost-effective than indium gallium arsenide (InGaAs) alternatives. Additionally, it’s a global shutter technology with a record-breaking small pixel pitch and excellent efficiency. It is thus possible to capture more details in the infrared portion of the spectrum. As a result, the paper creates new opportunities for mobile devices, machine vision, hyperspectral imaging and spectroscopy, security, and surveillance.
Why Quantum Dots?

Quantum dots are tiny (between 2 nm to 20 nm usually) semiconductor crystals. One of their unique properties is that their optical and electrical properties change with their size. In an image sensor, using quantum dots of various sizes makes it possible to capture different wavelengths of light beyond silicon’s absorption limitations. In ST’s IEDM 2021 paper, researchers tuned quantum dots to capture 940 nm and 1400 nm light, the latter rivaling InGaAs sensors. However, InGaAs imaging devices are challenging and costly to make. Using a conventional 300 mm silicon wafer process in existing fabs, ST can produce the quantum dot sensor for shortwave infrared at a fraction of the cost.

Why IEDM 2021 and Not Years Ago?

Quantum dots are not new, and scientists were already studying their properties in the early 1980s1. However, it took years to colloidally synthesize crystals that could absorb infrared light and to create thin-film devices and fabrication processes that would yield the performance and stability necessary for real-world applications. More specifically, ST developed a manufacturing process that would not exceed 150ºC while also creating lithographic methodologies that would preserve the quantum dot’s integrity.

The IEDM 2021 paper explains in detail how ST created this image sensor technology on 300 mm wafers and describes the performance and reliability achieved to date. We plan to provide samples and evaluation kits to potential customers in 2022 and move to mass production in the coming years. Among the potential applications, mobile devices could use the new sensors to improve facial or object detection. Ultimately, a low-cost high-volume SWIR image sensor accessible to all consumers will open the door to new use-cases and applications.


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