Design and Characterization of a 10 × 10 Pixel Array THz Camera in 350 nm CMOS Technology

Abstract

In this paper, a $10\times 10$ pixel array camera for room-temperature THz imaging application in 350 nm CMOS technology is presented. The camera consists of a $10\times 10$ focal-plane array (FPA) of THz detectors, on-chip column amplifiers, digital-to-analog converter (DAC) and on-chip memory for per-pixel calibration. High performance THz detectors are realized by integrating on-chip antennas and sub-threshold Si MOSFETs. The detectors are biased with a current source for increased responsivity and improved NEP. Our designed detector improves responsivity and NEP by a factor of 900 and 7, respectively, compared to conventional photo-voltaic (cold) FET-based detector in the same technology node and detection settings. Additionally, we proposed a successive-approximation (SA) calibration scheme to adjust the operating point of the pixels to maximize the THz response and improve uniformity, in the presence of pixel-to-pixel process variation. At 200 GHz illunimation frequency, the average responsivity and NEP of the 2D imager are measured as 16.4 kV/W and $216~\frac {nW}{\sqrt {Hz}}$ , respectively, with an image acquisition rate of 2 Hz. The responsivity and NEP of a representative pixel are extrapolated to 10 KHz (where 1/f noise has substantially decreased) for comparison with literature. The extrapolated values are 19 kV/W and $535~\frac {pW}{\sqrt {Hz}}$ , respectively. By placing the THz camera in an optical setup, we were able to acquire images of concealed metal objects in a cardboard box at 200 GHz illumination frequency.