With the increasing demand for channel capacity, higher data rate, and wider bandwidth for wireless communication and sensing, the focus of millimeter-wave (mmWave) technology development is moving toward higher frequencies. For example, the 5G standard maps the frequency range 2 (FR2) bands into 24.25–52.6 GHz to satisfy the need for higher bandwidth, while the upcoming 6G communications is considering W-band (75–110 GHz), D-band (110–170 GHz), and even G-band (110–300 GHz) as the targeted operating frequencies. This evolution is driving mmWave systems toward the miniaturization of devices and components. This trend advocates the need for integrating compact passive and active components into the package, leading to complex heterogeneous integration platforms.