This paper reports an LNO surface acoustic wave (SAW) resonator based on a shear horizontal mode with high operating frequency over 3 GHz, large electromechanical coupling of 33.54%, Q factor of 380, and a relatively good figure of merit (FOM) of 127. Combing crystal-ion-slicing (CIS) technology with a room temperature bonding method, a 4-inch single crystalline LNO thin film on silicon is prepared successfully. The influence of damaged LNO film on crystalline quality and SAW performance is comprehensively analyzed. After totally removing the damaged layer, the electromechanical coupling and Q factor is significantly improved. The high-performance SAW resonator possesses the potential to meet the requirements of SAW filters for the fifth-generation (5G) communication in terms of high frequency, large bandwidth, and a high-quality factor.

Bulk acoustic wave (BAW) filter with large bandwidth is an urgent need in fifth-generation (5G) communication systems. In the present work, 43° Y-cut lithium niobate (LN) single-crystal film is prepared on multilayer oxide film, and bulk acoustic filter with oxide Bragg reflector (BR) is successfully achieved. The design method of the filter and the fabrication process are presented. Atomic force microscope (AFM) and scanning electron microscope (SEM) are used to characterize the quality of thin films. The results demonstrate the feasibility of transferring single-crystal film onto multilayer oxide, which is efficient for the confinement of acoustic energy. The resonator has effective electromechanical coupling coefficient of 14.6% and figure of merit (FOM) of 32.94. The filter with a compact size of 600 $\mu \text{m}\,\,\times 400\,\,\mu \text{m}$ has a relative bandwidth of 10.3% at a center frequency of 3.128 GHz, which is promising for the application of 5G systems.

In the present work, a lithium niobate (LN) 43°Y cut LN film is transferred onto a substrate with 11 layers of SiO₂/Ta₂O₅ and solidly mounted resonators with a reflector are successfully fabricated with the multilayer structure. The design method and fabrication process are demonstrated. The finite element model and the Mason model are used. Scanning electron microscopy and atomic force microscopy are used to characterize film quality. An optimized design of a Bragg reflector to suppress the leakage of acoustic energy by thickness shear mode is proven to be effective. The influence of the reflector on parasitic modes and filter out-of-band suppression is analyzed. The resonator for 3.5 GHz shows an effective electromechanical coupling coefficient of 17.9%, and the figure of merit is 40.4, which is suitable for band pass filter on the N78 band with high rejection.

To solve the problem of filter bandwidth in 5G communication, it is urgent to develop an acoustic resonator with a large effective electromechanical coupling coefficient (K_eff²). In this paper, the dependence between the resonance area and the performance of the bulk acoustic wave (BAW) resonator is studied. The solidly mounted resonators (SMRs) based on 43° Y cut lithium niobate (LN) were fabricated by the wafer transfer technique. The on-chip inductor was integrated with the BAW resonator through a pad electrode. Resonators with different resonant areas were fabricated and tested. Finite element modeling (FEM) simulation of acoustic resonators and electromagnetic (EM) simulation of layout were carried out, respectively. The Modified Butterworth Van Dyke (MBVD) model was used to analyze the results, and simulation of the Mason model was adopted. The results show that the dependency relationship between the resonant area and the effective electromechanical coupling coefficient can be induced by on-chip inductance. In the resonant area range of 20 × 20 μm²~160 × 160 μm², the K_eff² increases from 11.97% to 43.28%.

Flexible single crystal 0°YX LNO thin film is fabricated on polyimide substrate combining Crystal-Ion-Slicing (CIS) technology and benzocyclobutene (BCB) bonding method. By finite element method (FEM) simulation, surface acoustic wave resonator (SAWR) with Q factor of 493 is demonstrated by increasing the thickness of BCB layer. While applying compressively strain and tensile strain, the SAWR strain sensors show good performance with strain sensitivity of 587 Hz/με and wider strain range from -2231 με or 2241 με compared with our previous work in solidly mounted resonators (SMR) and memristor. The repeatability testing while applying compressively strain and tensile strain is performed at two strain states of 0 με and -1594 με, and 0με and 1599 με, respectively. As changing the strain value, the resonance frequency shows great consistency and displays good repeatability and high stability, indicating that the flexible LNO SAWR strain sensor has potentially applicable in flexible electronics system.