Active Terahertz Imaging Using Schottky Diodes in CMOS: Array and 860-GHz Pixel

Schottky-barrier diodes (SBD´s) fabricated in CMOS without process modification are shown to be suitable for active THz imaging applications. Using a compact passive-pixel array architecture, a fully-integrated 280-GHz 4 × 4 imager is demonstrated. At 1-MHz input modulation frequency, the measured peak responsivity is 5.1 kV/W with ±20% variation among the pixels. The measured minimum NEP is 29 pW/Hz^1/2. Additionally, an 860-GHz SBD detector is implemented by reducing the number of unit cells in the diode, and by exploiting the efficiency improvement of patch antenna with frequency. The measured NEP is 42 pW/Hz^1/2 at 1-MHz modulation frequency. This is competitive to the best reported performance of MOSFET-based pixel measured without attaching an external silicon lens (66 pW/Hz^1/2 at 1 THz and 40 pW/Hz^1/2 at 650 GHz). Given that incorporating the 280-GHz detector into an array increased the NEP by ~ 20%, the 860-GHz imager array should also have the similar NEP as that for an individual detector. The circuits were utilized in a setup that requires neither mirrors nor lenses to form THz images. These suggest that an affordable and portable fully-integrated CMOS THz imager is possible.