Lithium niobate (LiNbO₃) has remarkable ferroelectric properties, and its unique crystal structure allows it to undergo significant spontaneous polarization. Lithium niobate plays an important role in the fields of electro-optic modulation, sensing and acoustics due to its excellent electro-optic and piezoelectric properties. Thin-film LiNbO₃ (TFLN) has attracted much attention due to its unique physical properties, stable properties and easy processing. This review introduces several main preparation methods for TFLN, including chemical vapor deposition (CVD), molecular beam epitaxy (MBE), pulsed laser deposition (PLD), magnetron sputtering and Smartcut technology. The development of TFLN devices, especially the recent research on sensors, memories, optical waveguides and EO modulators, is introduced. With the continuous advancement of manufacturing technology and integration technology, TFLN devices are expected to occupy a more important position in future photonic integrated circuits.

This study introduces shear horizontal (SH) surface acoustic wave (SAW) resonators based on a multilayered structure of lithium tantalate (LiTaO3 or LT)/silicon dioxide (SiO2)/4H-silicon carbide (4H SiC). SiC exhibits high resistivity (HR) ( $\rho \gt 10^{{10}}~\Omega \cdot $ cm), effectively suppressing the parasitic surface conduction (PSC) effect. The suppression of the PSC effect by 4H-SiC substrates is demonstrated by extracting the substrate loss of SiO2/4H-SiC and SiO2/Si substrates in a coplanar waveguide (CPW) structure. Consequently, SAW resonators based on 4H-SiC substrates demonstrate a superior quality factor (Q) compared to the conventional SH SAW resonators based on Si substrates. The fabricated resonators with 4H-SiC and Si substrates achieved Bode- ${Q} _{\max }$ of 3916 and 1836, ${Q} _{\text {p}}$ of 3402 and 590, and admittance ratios ( ${Y} _{\text {r}}$ ) of 92 and 74 dB, respectively. The ${Q} _{\text {p}}$ of the 4H-SiC-based resonator is 5.7 times higher than that of the Si-based resonator. Substituting the Si substrate with the 4H-SiC substrate increases Q without compromising the effective electromechanical coupling ( ${k} ^{{2}}_{\text {eff}}$ ) and temperature coefficient of frequency (TCF). To suppress the transverse mode of the SAW resonators, tilted interdigital transducers (IDTs) at various titled angles were fabricated. A 12° tilt angle IDT demonstrated the most effective transverse mode suppression. When the tilted IDT was employed, the ${Q} _{\text {p}}$ of the SAW resonator based on the 4H-SiC substrate surpassed that of Si substrate. Compared to the Si substrate, the 4H-SiC substrate resulted in a higher ${Q} _{\text {p}}$ , making this technique promising for application in filters, oscillators, and sensors.

In this article, we studied the effect of radio frequency (RF) loss caused by parasitic surface conductivity (PSC) to surface acoustic wave (SAW) devices through a physical-model-based and universal method. First, through technology computer-aided design (TCAD) tools, the phenomenon of PSC attracting minority carriers to top part of Si to form an inversion layer was clearly displayed. Then, this influence was transformed into the reduction in the effective resistivity ( ${R}_{\text {eff}}{)}$ of homogeneous Si substrate using equivalent circuit model. Finally, ${R}_{\text {eff}}$ was converted into the dielectric loss tangent, which can be conveniently introduced to ANSYS electromagnetics (EM) models. This method is first used for coplanar waveguide (CPW), which is an excellent device for characterizing substrate RF loss. Using a similar method, the specific impact of PSC on SAW resonators based on 42°YX-LiTaO3 (LT)/SiO2/PSi/Si and 42°YX-LT/SiO2/Si substrate was also studied. It has been verified that PSC causes a decrease in Bode-Q of SAW resonators and deterioration in insertion loss (IL). And by calculating the changes in Bode-Q, we successfully separated substrate RF loss from other losses, such as acoustic loss. Simulations for both CPW and SAW devices have achieved good agreement with measured results. This method provides a convenient approach for analyzing the impact of PSC that exist in all similar structures on the performance of RF devices.

Lithium niobate, as an important piezoelectric substrate material, is widely used in various acoustic and microwave devices. When lithium niobate crystals are grown from a melt at high temperatures, they typically contain a high concentration of intrinsic point defects. These point defects (either intrinsic or related to impurities or external fields) often alter the material's physical constants and increase acoustic losses. In this study, in order to study the effect of defects on the performance of SAW devices, we prepared black lithium niobate crystals with different concentrations of bipolarons, lithium vacancies, niobium anti-sites and other defects in an argon–hydrogen atmosphere. The types and concentrations of defects in the blackened lithium niobate wafers at different reduction temperatures were analyzed using UV-vis and IR spectroscopy. The chemical state of oxygen on the surface of the sample was analyzed by XPS. Dual-port electrodes were fabricated on the samples using micro-nano processing technology, and the relationship between the substrate dielectric loss and defects in lithium niobate was established through S-parameter testing. The results indicate that the chemical reduction treatment increases the defects in lithium niobate, leading to lattice distortion and the formation of defect dipoles, thereby increasing the dielectric loss of the devices. These findings provide profound insights into defect engineering for the application of lithium niobate in acoustic devices.

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.

This work proposes a zero-th shear horizontal (SH 0 ) plate acoustic wave (PAW) resonator based on 36° Y-cut lithium tantalate (LT) / silicon dioxide (SiO 2 ) thin film. By using multi-physics finite-element-analysis (FEA) simulations, the rotation angle of LT and the layer thicknesses are optimized for obtaining large effective electromechanical coupling coefficient $\left( {{k^2}_{{\text{eff}}}} \right)$ and low temperature coefficient of frequency (TCF). The fabricated resonators yield a ${k^2}_{{\text{eff}}}$ of 11.8% and a Bode-Q max of 1795. Moreover, the measured temperature coefficient of frequency at anti-resonant frequency (TCF fp ) is -4.9 ppm/°C, indicating that a near-zero TCF is realized in this study. The demonstrated resonators are promising for low loss and temperature-stable acoustic devices in wireless communication system.