A Hybrid THz Imaging System With a 100-Pixel CMOS Imager and a 3.25–3.50 THz Quantum Cascade Laser Frequency Comb

The terahertz frequency range beyond 3 THz has exciting potential to have a transformative impact in a wide range of applications, including chemical and biomedical sensing, spectroscopy, imaging, and short-distance wireless communication. While there have been significant advancements in silicon-based THz imagers in the frequency ranges below 1 THz, technological development beyond 3 THz has been impeded by the lack of solid-state sources in this frequency range. In addition, the design space beyond 3 THz opens up fundamentally new challenges across electronics and the electromagnetic interface. In this spectral range, the wavelength is small enough (λ
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≈ 50 μm at 3 THz) that a vertical via from the top antenna layer to the detector is a distributed element (transmission line or radiator). In this letter, we follow a careful circuits-electromagnetics co-design approach toward a hybrid imaging system with a 100-pixel CMOS imager that interfaces with a THz quantum cascade laser frequency comb that spans 3.25-3.5 THz with mode spacing of 17 GHz. The array chip, while designed for an optimal operation across 2.7-2.9 THz, demonstrates an average noise equivalent power (NEP) (across pixels) of 1260 pW/ √(Hz) between 3.25-3.5 THz and a projected NEP of 284 pW/ √(Hz) across the design range of 2.7-2.9 THz. To the best of our knowledge, we demonstrate for the first time full THz imaging in a hybrid quantum cascade laser (QCL)-CMOS fashion. This approach allows future works to leverage both QCL and CMOS technologies to demonstrate new technological advances for systems in the 1-10 THz range.