ABSTRACT
Planar solutions for the implementation of THz systems benefit from the small form factor, low power dissipation, and possibly low cost. This aspect applies to THz sources, the topic of this book, as well. The early planar solutions for THz sources were mostly diode-based device-level approaches, such as IMPATT (IMPact ionization Avalanche Transit Time) diode, Gunn diode, and RTD (Resonant Tunneling Diode). However, the advent of modern high-frequency semiconductor transistor technologies, driven by both structural and material innovations, has enabled THz sources based on transistor-based circuit-level solutions. This can be considered as a great milestone for the development of compact THz sources (and other systems) for a couple of good reasons. First, the transistor is a general-purpose device, which would allow the integration of THz sources with other electronic circuitry, both analog and digital. Second, the system optimization can be made on the circuit level rather than the device level, which would provide a much 390higher level of design flexibility. Considered first as THz-compatible semiconductor solutions were III–V technologies, namely HBT (Heterojunction Bipolar Transistor) and HEMT (High Electron Mobility Transistor) technologies. Now, Si-based technologies, not only SiGe HBT but also Si CMOS (Complementary Metal–Oxide– Semiconductor), are regarded as viable options for the realization of THz systems. In this chapter, the device operation principles and the performance trend will be reviewed with these four major candidate technologies for THz applications.
