Imec has prototyped a high-resolution short-wave-infrared (SWIR) image sensor with record small pixel pitch of 1.82 µm.

It is based on a thin-film photodetector that is monolithically integrated on a custom Si-CMOS readout circuit.
A fab-compatible process flow paves the way to high-throughput, wafer-level manufacturing.
The presented technology largely exceeds the capabilities of today’s InGaAs-based SWIR imagers in terms of pixel pitch and resolution, with disruptive cost and form factor potential.

New applications are enabled even in cost-sensitive domains, such as in industrial machine vision, smart agriculture, automotive, surveillance, life sciences and consumer electronics.
Sensing in the SWIR range (with wavelengths from around 1400 nm to above 2000 nm) offers advantages over the visible (VIS) and near-infrared (NIR) range for some applications. SWIR image sensors can, for example, see through smoke or fog, or even through silicon – which is especially relevant for inspection and industrial machine vision applications.
To date, SWIR image sensors are produced through a hybrid technology, in which a III-V-based photodetector (usually InGaAs-based) is flip-chip bonded to a silicon readout circuit.
These sensors can be made extremely sensitive, but the technology is quite expensive for mass manufacturing and limited in size of pixel and number of pixels – hindering its adoption in markets for which cost, resolution and/or form factor are crucial.
Imec introduces an alternative solution that enables record small sub-2 µm pixel pitch, by monolithically integrating a thin-film photodetector stack with a Si-CMOS readout circuit.
The photodetector pixel stack implements a thin absorber layer such as 5.5 nm PbS quantum dots – corresponding to 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 SWIR wavelength, an external quantum efficiency (EQE) of 18% is obtained (and can be upgraded towards 50% with further improvements).
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.