Quantum dot SWIR sensor has sub-2µm pixel pitch
imec in Belgium has developed a prototype high-resolution short-wave-infrared (SWIR) image sensor on a CMOS process with record small pixel pitch of 1.82 µm.
It is based on a thin film photodetector that is monolithically integrated on a custom CMOS readout circuit. Unlike the current InGaAs-based SWIR imagers, the process is compatible with CMOS fabs, opening up high-throughput, wafer-level manufacturing.
The details are being presented at the IEDM conference this week.
The photodetector pixel stack implements a thin absorber layer with 5.5nm PbS quantum dots, giving peak absorption at 1400 nm wavelength. The peak absorption wavelength can be tuned by adjusting the nanocrystal size and is extendable to wavelengths even above 2000 nm.
At the peak wavelength, the external quantum efficiency (EQE) is 18 percent, but further enhancements currently being tested development see this rising to 50 percent. The photodetector stack is monolithically integrated with a custom readout circuit, processed in 130 nm CMOS technology. In this readout circuit, the 3-transistor pixel design was optimized for the scaling of pixel size in the accessible 130 nm technology node, resulting in record small pitch of 1.82 µm for the prototype SWIR imager.
“With our compact, high resolution SWIR image sensor technology, we offer our customers a path to affordable low-volume manufacturing within imec’s 200 mm facility,” said Pawel Malinowski, thin-film imagers program manager at imec. “These image sensors can be deployed in industrial machine vision, smart agriculture, automotive, surveillance and life sciences with lens-free imaging and many more. Due to their small form factor, they can potentially be integrated in small cameras, such as in smartphones or AR/VR glasses – with eye-safe SWIR light sources. Some of exciting future developments include increasing of the EQE, reducing the sensor noise and introducing multispectral arrays with customized patterning approach.”
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