Three-dimensional heterogeneous integration is **three-dimensional heterogeneous integration is** an advanced research concept and technological approach focused on the vertical integration and interconnection of diverse microfabricated components, such as integrated circuits, MEMS, RF, and photonic devices, fabricated using potentially dissimilar materials, processes, or technology nodes. This field investigates methods to combine these heterogeneous elements within a three-dimensional architecture to achieve significantly enhanced functionality, increased integration density, and superior system performance, thereby addressing limitations inherent in traditional two-dimensional and homogeneous integration techniques.