A 128-Pixel System-on-a-Chip for Real-Time Super-Resolution Terahertz Near-Field Imaging

Abstract

This paper presents a fully integrated system-on-a-chip for real-time terahertz super-resolution near-field imaging. The chip consists of 128 sensing pixels with individual cross-bridged double 3-D split-ring resonators arranged in a 3.2 mm long $2\times 64$ 1-D array. It is implemented in 0.13- $\mu \text{m}$ SiGe bipolar complementary metal–oxide–semiconductor technology and operated at around 550 GHz. All the functions, including sensor illumination, near-field sensing, and detection, are co-integrated with a readout integrated circuit for real-time image acquisition. The pixels exhibit a permittivity-based imaging contrast with a worst case estimated relative permittivity uncertainty of 0.33 and 10–12- $\mu \text{m}$ spatial resolution. The sensor illumination is provided with on-chip oscillators feeding four-way equal power divider networks to enable an effective pixel pitch of 25 $\mu \text{m}$ and a dense fill factor of 48% for the 1-D sensing area. The oscillators are equipped with electronic chopping to avoid $1/f$ -noise-related desensitization for the SiGe-heterojunction bipolar transistor power detectors integrated at each pixel. The chip features both an analog readout mode and a lock-in-amplifier-based digital readout mode. In the analog readout mode, the measured dynamic range (DR) is 63.8 dB for a 1-ms integration time at an external lock-in amplifier. The digital readout mode achieves a DR of 38.5 dB at 28 f/s. The chip consumes 37–104 mW of power and is packaged into a compact imaging module. This paper further demonstrates real-time acquisition of 2-D terahertz super-resolution images of a nickel mesh with 50- $\mu \text{m}$ feature size, as well as a biometric human fingerprint.