Heterogeneous Integration Of Lithium Niobate Ferroelectric Single Crystal On A Silicon Substrate And Its Thin-film Preparation

In-situ accurate measurement of spatial environmental parameters requires the micro-electromechanical system（MEMS）sensor to be placed in the area to be tested,and to directly contact the test object to output electrical response signals.Traditional silicon-based MEMS sensors need to be treated with anti-irradiation reinforcement,the volume and mass cost are higher,and the improvement of sensing test sensitivity is limited.Compared with traditional silicon-based functional materials,lithium niobate（Li Nb O₃,LN）ferroelectric single crystals have shown broad application prospects in the aerospace field due to their excellent corrosion resistance,low temperature resistance and intrinsic radiation resistance.Focusing on the application requirements of space-level sensors for miniaturization,integration,low power consumption and high reliability,the completion of the heterogeneous integration of silicon-based lithium niobate ferroelectric single crystal thin films is gradually becoming a research focus to solve the problem of compatible manufacturing of silicon-based ferroelectric materials.The thesis focuses on the three aspects of LN and Si wafer-level bonding process,wafer bonding mechanism and LN single crystal thin film technology:（1）Based on the spin-coating process,the surface of LN wafer and silicon substrate is grown to obtain resistance Irradiation,low temperature resistance and high mechanical stability polyimide adhesive,combined with the pre-baking process to remove the solvent of the polyimide adhesive layer,to obtain a uniform and complete bonding interface with a certain degree of curing,with the help of O₂plasma activation technology,Solve the problems of weak pre-bonding strength and small area of the polyimide adhesive layer after pre-baking.The pre-bonded samples are kept at the atmosphere and normal temperature for 24 hours after the saturated pre-bonding strength,and then annealed at low temperature to complete the bonding of LN wafer and Si wafer;（2）The physical and chemical properties of the bonding surface and interface were analyzed in the whole process by XPS,SEM,EDX and other characterization methods.The LN-Si wafer-level bonding mechanism was explored,and the low-temperature bonding model combining the plasma-activated pre-bonding and the polyimide bonding was constructed;（3）A large-area,high-quality silicon-based lithium niobate single crystal film is prepared by the film preparation technology combining mechanical grinding and chemical mechanical polishing.This thesis uses polyimide bonding technology to successfully bond 4-inch Z-cut LN single crystal wafers and 4-inch Z-cut LN single crystal wafers with Cr/Au bottom electrodes to a silicon substrate.The tight and defect-free bonding interface was confirmed by SEM.The bond strength tested by the tensile tester is 6.582Mpa.The paper conducts bonding strength test on bonded samples after low temperature treatment,in order to evaluate the stability of bonded samples.The bonding strength of samples after ultra-low temperature（-263.15℃）treatment for 24 hours is 3.339Mpa,which meets the bonding strength requirements of aerospace applications.Based on the analysis of the bonding interface,water molecules diffuse along the interface during the annealing process,forming a stable C-O-C covalent bond at the interface,which promotes intermolecular cross-linking.After the annealing is completed,a 4-inch,high-crystalline silicon-based lithium niobate single crystal film is prepared by the film preparation technology combining mechanical grinding and chemical mechanical polishing.