The scaling of CMOS has enabled the implementation of mm-wave and THz circuits in standard CMOS technologies, which promises a wide variety of new applications. While f max poses a challenge to generate fundamental signals at THz frequencies, non-linear circuit techniques enable the generation of above-f max signals by utilizing harmonics of below-f max signals. This work describes the fundamental issue of f max when designing mm-wave and THz circuits, and discusses the implementation of a 0.49THz SIW-based harmonic signal source. Some of the many application opportunities for the mm-wave/THz spectrum are shown: THz imaging using signal generators fabricated in 40nm and 28nm CMOS is demonstrated, as well as high-speed data links through plastic polymer fibers utilizing 40nm CMOS transceiver chips.