I. Introduction
Owing to the considerably wide bandwidth resource in millimeter-wave and terahertz (THz) frequency ranges, various applications including high-data-rate wireless communication, medical imaging, bio-sensing, and spectroscopy have drawn great attention in recent years [1]–[6]. Rapid development of silicon-based technology has led to impressive performance and provided a new low-cost solution to these applications. However, there are still challenges to be addressed in designing silicon-based THz systems due to the low supply voltage and inferior ft/fmax compared with their III–V semiconductor counterparts.