Interface Engineering in Piezoelectric‐on‐Insulator Platforms: Coupling of Electrons, Photons, and Phonons for Multifunctional Integration

The growing demand for higher speed, wider bandwidth, and enhanced power handling in electronic, photonic, and radio‐frequency systems drives the rapid advancement of monolithic heterogeneous integration. The piezoelectric‐on‐insulator (POI) architecture isolates high‐quality single‐crystal piezoelectric thin films from supporting substrates through engineered heterointerfaces, enabling simultaneous confinement of optical modes, acoustic waves, and electric fields within the active layer. This configuration provides a versatile platform for multifunctional devices targeting 5G/6G communications, high‐power electronics, and quantum photonics. This review systematically examines the physical mechanisms governing POI heterointerfaces, with a focus on interface engineering strategies across key material systems, including LiNbO 3 /Si, LiNbO 3 /SiC, LiNbO 3 /diamond and AlN/diamond heterostructures. The strategies discussed encompass atomic‐scale bonding optimization, interfacial nanostructuring, and the design of ultrathin phonon‐bridge interlayers. A notable emerging capability is voltage‐tunable thermal conductivity enabled by ferroelectric domain wall engineering. Furthermore, this review addresses current challenges in scalable synthesis, defect control, and thermomechanical stress management, while outlining future directions, such as monolithic multifunctional system integration, dynamic interface tuning, and quantum photonic integration. By repositioning the heterointerface as an actively tunable functional element, this review offers a systematic framework for the design of POI interfaces in next‐generation electronic–photonic integrated systems.