SWIR Sensor Utilizes Lead-Free Quantum Dot Photodiodes

As part of the Belgian research project Q-COMIRSE, researchers presented a prototype SWIR image sensor with indium arsenide quantum dot (QD) photodiodes. The sensor successfully demonstrated 1390 nm imaging results, offering an environmentally friendly alternative to first-generation QDs that contain lead, which has limited their widespread manufacturing.

Because SWIR sensors can distinguish between objects that appear identical to the human eye and are able to penetrate through fog or mist, they are useful in applications like facial recognition or eye tracking in consumer electronics and autonomous vehicle navigation. While current versions are costly and limited to high-end applications, wafer-level integration promises broader accessibility.

Researchers developed a proof-of-concept lead-free QD photodiode integrated onto a shortwave infrared optical sensor through the Q-COMIRSE project. Courtesy of imec.

QDs are nanoscale semiconductor particles that can be engineered to emit and absorb light at specific wavelengths. Tuned for SWIR, they offer compact, low-cost absorbers, as integration into CMOS circuits and existing manufacturing processes is possible. However, first-generation QDs often contain toxic heavy metals like lead and mercury.

“The first generation of QD sensors was crucial for showcasing the possibilities of this flexible platform. We are now working towards a second generation that will serve as a crucial enabler for the masses — aiming at cost-efficient manufacturing in an environmentally friendly way,” said Pawel Malinowski, imec technology manager and domain lead imaging. “With major industry players looking into quantum dots, we are committed to further refine this semiconductor technology towards accessible, compact, multifunctional image sensors with new functionalities.”

Researchers from imec and their partners within the Q-COMIRSE project — Ghent University, QustomDot BV, ChemStream BV, and ams-OSRAM — introduced a SWIR image sensor featuring a lead-free QD alternative as an absorber: Indium arsenide. The proof-of-concept sensor, tested on both glass and silicon substrates, was the first of its kind to produce successful 1390 nm imaging results, the researchers said.

While QDs are considered fragile in nature, careful selection of stack materials resulted in >300 hour air-stability, enabling fab manufacturing compatibility. The pixel architecture can be readily integrated with CMOS technology for image sensing applications, but also allows flat panel display integration.

According to Stefano Guerrieri, Engineering Fellow at ams OSRAM, the work paves the way toward a low-cost, lead-free SWIR technology that, once mature enough for industrial products, could enable unprecedented applications in robotics, automotive, AR/VR, and consumer electronics, and more.