Autozeroed bias circuit to enhance gain and uniformity of THz FET detectors for imaging

Terahertz focal plane arrays (THz FPAs) based on field-effect transistor (FET) detectors enable compact imaging within monolithic complementary metal-oxide-semiconductor (CMOS) chips. However, pixel uniformity is difficult to achieve due to the near-threshold optimal operation of the device, leading to strong pixel-to-pixel variations caused by CMOS manufacturing process and operating temperature. Additionally, imager readouts must meet stringent noise requirements as a result of the extremely low amplitude of the FET output signal. The article describes the design, realization, and characterization of a low-noise, high-homogeneity technique for THz FPAs with FET detectors. This technique is implemented by utilizing an autozeroed current bias circuit to achieve simultaneously a signal amplification, resulting in a lower noise equivalent power (NEP), and a self-biasing operation to reduce the nonuniformity of FPAs. The THz pixel and the bias circuit have been realized using 65 nm CMOS technology, achieving a minimum NEP of 10 pW/Hz−−−√ and an improvement of responsivity and noise nonuniformity of 3× and 2.5×, respectively.