Abstract

The Terahertz (THz) band of the electromagnetic spectrum, also defined as sub-millimeter waves, covers the frequency range from 300 GHz to 10 THz. There are several unique characteristics of the radiation in this frequency range such as the non-ionizing nature, since the associated power is low and therefore it is considered as safe technology in many applications. THz waves have the capability of penetrating through several materials such as plastics, paper, and wood. Moreover, it provides a higher resolution compared to conventional mmWave technologies thanks to its shorter wavelengths. The most promising applications of the THz technology are medical imaging, security/surveillance imaging, quality control, non-destructive materials testing and spectroscopy. The potential advantages in these fields provide the motivation to develop room-temperature THz detectors. In terms of low cost, high volume, and high integration capabilities, standard CMOS technology has been considered as an excellent platform to achieve fully integrated THz imaging systems. In this Ph.D. thesis, we report on the design and development of field effect transistor (FET) THz direct detectors operating at low THz frequency (e.g. 300 GHz), as well as at higher THz frequencies (e.g. 800 GHz – 1 THz). In addition, we investigated the implementation issues that limit the power coupling efficiency with the integrated antenna, as well as the antenna-detector impedance-matching condition. The implemented antenna-coupled FET detector structures aim to improve the detection behavior in terms of responsivity and noise equivalent power (NEP) for CMOS based imaging applications. Since the detected THz signals by using this approach are extremely weak with limited bandwidth, the next section of this work presents a pixel-level readout chain containing a cascade of a pre-amplification and noise reduction stage based on a parametric chopper amplifier and a direct analog-to-digital conversion by means of an incremental Sigma-Delta converter. The readout circuit aims to perform a lock-in operation with modulated sources. The in-pixel readout chain provides simultaneous signal integration and noise filtering for the multi-pixel FET detector arrays and hence achieving similar sensitivity by the external lock-in amplifier. Next, based on the experimental THz characterization and measurement results of a single pixel (antenna-coupled FET detector + readout circuit), the design and implementation of a multispectral imager containing 10 x 10 THz focal plane array (FPA) as well as 50 x 50 (3T-APS) visible pixels is presented. Moreover, the readout circuit for the visible pixel is realized as a column-level correlated double sampler. All of the designed chips have been implemented and fabricated in 0.15-µm standard CMOS technology. The physical implementation, fabrication and electrical testing preparation are discussed.