Abstract
Although CMOS technology scaling has provided tremendous power and circuit density benefits for innumerable
applications, focal plane array (FPA) readouts have largely been left behind due to dynamic range and signal-to-noise
considerations. However, if an appropriate pixel front end can be constructed to interface with a mostly digital pixel, it
is possible to develop sensor architectures for which performance scales favorably with advancing technology nodes.
Although the front-end design must be optimized to interface with a particular detector, the dominant back end
architecture provides considerable potential for design reuse.
In this work, digitally dominated long wave infrared (LWIR) active pixel sensors with cutoff wavelengths
between 9 and 14.5 μm are demonstrated. Two ROIC designs are discussed, each fabricated in a 90-nm digital CMOS
process and implementing a 256 x 256 pixel array on a 30-μm pitch. In one of the implemented designs, the feasibility
of implementing a 15-μm pixel pitch FPA with a 500 million electron effective well depth, less than 0.5% non-linearity
in the target range and a measured NEdT of less than 50 mK at f/4 and 60 K is demonstrated. Simple on-FPA signal
processing allows for a much reduced readout bandwidth requirement with these architectures.
To demonstrate the potential for commonality that is offered by a digitally dominated architecture, this LWIR
sensor design is compared and contrasted with other digital focal plane architectures. Opportunities and challenges for
application of this approach to various detector technologies, optical wavelength ranges and systems are discussed.
