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Si-based CMOS imagers to detect SWIR wavelengths above 1µm

Nov 15, 2019 | Allgemein, Topstory

Figure 2 | Schematic illustration of the design choices targeting Imec’s progressive application roadmap. Left: basic IR-detector; Middle: IR detection integrated in visible-light imager; Right: multispectral IR detection thanks to tunable TFPD layers. (Image: Imec)

Progressive application roadmap

In a first instance, monochrome infrared imagers based on a single TFPD stack are created and integrated as a separate die/functionality on the system level. This first implementation is the simplest, as it uses a plain, unpatterned layer of the thin-film photodetector stack. In this scenario, all pixels have the same absorption spectrum, unless you use specific filters. Potential application could be wavelength extension of the face scanner in smartphone cameras, allowing to move to the 1450nm spectrum without adding too much cost or complexity at the system level. Especially for Augmented Reality, this could become a valuable option to enable room-size scanning and applications.

In a second implementation, Imec targets monolithically integrated TFPD stacks into the RGB pixel composition on the CMOS imager itself. In this design, an infrared subpixel can be added next to the conventional red, green and blue photodiodes. This means a separate sensor for IR detection would not be required, reducing both the system footprint and power consumption. Also, it would add an additional layer of information to visible cameras. Think for example about very accessible cameras with depth sensing capability.

The third implementation builds further on the monolithic pixelated design concept, combining multiple TFPD stacks with different active materials. Such configuration would enable pixel-level multispectral sensors in NIR and SWIR ranges, at a very compact form factor and a price point in the range of silicon image sensors. Application potential could be in autonomous vehicles needing long-range scanning capabilities (enabled by 1450nm-sensitive TFPD) as well as visibility in bad weather or low-light conditions (enabled by 1550nm-sensitive TFPD). Another application example could be in material sorting applications, where tuning pixels to characteristic wavelengths would add material-determination capabilities (e.g. discrimination of vegetation vs. buildings or real vs. fake plants).

For the first concept – the monochromatic IR sensor – Imec has built a complete end-to-end prototype integrated into a camera. Starting with a 200mm ROIC wafer processing in the foundry. Post-processing and TFPD integration (on die or wafer level) was executed in the Imec fab, as well as chip packaging and buildup of the camera module. For the two monolithic designs, who are still in an earlier stage of research, the ambitions and roadmap are similar.

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Ph.D. Paweł E. Malinowski, Program Manager User Interfaces & Imagers; Ph.D. David Cheyns, Team Leader Future Interactive Thin-Film Technology; Ph.D. Pierre Boulenc, Leader Pixel Devices Team, Imec


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