Study On Single Crystal Lithium Niobate Thin Film Materials And FBAR Devices

The popularization of wireless communication devices such as mobile phones and wireless TVs bring much convenience to our lives and greatly improve the quality of people's lives due to the popularity of wireless communication devices.But at the same time,the competition for spectrum resources in the communications industry has also become more intense.The advent of 5G,Internet of Things and big data eras has forced the development of RF front-ends to high frequencies and miniaturization.In this wave,FBAR?Thin Film Bulk Acoustic Wave Resonator?filters have undoubtedly played an important role.In the conventional filters,the large size hinders the integration of the ceramic filter and the line width of interdigital electrode limits the resonant frequency of the SAW filter.Oppositely,the FBAR filter has attracted eyes of the world due to its integration and compatibility with the silicon process.The FBAR devices in this thesis use lithium niobate?LiNbO₃?thin film as piezoelectric layer including Y128-and Y36-cut LiNbO₃.In particular,the electromechanical coupling coefficient is up to 49%in P-wave mode for Y36-cut LiNbO₃,which is the best choice for making high performance FBAR devices.The preparation of film materials uses"Smart-cut"stripping technique taking the benzocyclobutene?BCB?as bonding layers and the specific research work and experimental results are as follows:?1?Through the BCB prebaking experiment,it was found that 100°C for 180s or more can completely volatilize organic solvents.?2?Referring to the BCB cure temperature curve and based on a large number of repeated experiments,it was found that thermal treating of boned pair was performed at T=250°C for one hour can achieve the peeling off of single crystal LiNbO₃ and the complete solidification of BCB.?3?Though ion implantation and BCB bonding technology,we have studied the stripping experiments of LiNbO₃ based on heterogeneous and homogeneous substrates.Because of heat mismatch,the LiNbO₃ film produced cracks in the heterostructure.The homogenous LiNbO₃ film has no crack and are continuous.The first order diffraction peaks of the two types of Y128 and Y36 in the XRD?X-ray diffraction?analysis are at32.77 and 23.80 degrees respectively,and the full width at half maximum?FWHM?are0.11 and 0.13 degrees,respectively.The surface topography of SEM?Scanning Electron Microscopy?proved that there is no crack on the surface of the film furtherly,TEM?Transmission electron microscope?images can clearly observe the alignment of the crystal direction and the electron diffraction pattern has not found the lattice distortion.The above results show the high quality of the LiNbO₃ thin film material stripped by the homogeneous substrate.?4?The dielectric constant of the film was about 57 measured by the LabVIEW program and the resistance value of the tested film was in the range of3.51×10⁸⁶.45×10¹⁰?indicating the high insulation of the LiNbO₃ film.?5?The influence of He ion implantation parameters on the single-crystal LiNbO₃thin film during He ion implantation was explored.Different implantation energies were matched to the corresponding implantation dose to ensure the continuity and integrity of the peeled thin film.In the experiments,four implantation doses of 1×10¹⁶,2×10¹⁶,3×10¹⁶,and 4×10¹⁶ ions/cm² were investigated.The results showed that the implantation dose of 1×10¹⁶ ions/cm² was too low,and the peeled film was severely cracked;3×10¹⁶implanted dose film could not be stripped or the implantation LiNbO₃ produced fragments;4×10¹⁶ ions/cm² was prone to produce stripe cracks,but it was known from the later experiments that this was due to the bonding mode demonstrating the crystal anisotropy.Besides,the film thicknesses corresponding to 115,150,and 285 keV implantation energy are 393.5,626.5,and 932.6 nm,respectively,which are in line with the SRIM simulation results.?6?The RMS?Root Meam Square?of the thin film surface was measured at about9 nm by AFM?Atomic Force Microscope?,which was reduced to about 4 nm by argon ion treatment and etching rate is about 9 nm/min.?7?FBAR Resonance Performance Test:S parameters S₂₁ parameter of FBAR was tested by GSG?Ground-Signal-Ground?RF probes.Since the cavity type structure and the test calibration card was not used,the test result was not ideal.The resonant frequency is⁶50MHz,and the insertion loss of the device is a little large.