Preparation And Study Of SAW Characterization Of LiNbO₃ Film On Diamond Substrate

As the processing information amount of modern electronics increases rapidly, the carrier wave in communication must move to higher frequency band. Surface acoustic wave (SAW) devices are one of the most necessary devices in communication system. The central operating frequency of SAW filter (f) is defined as f=V/L, among which V means the SAW speed of the used material, and L is the period of its inter-digital transducer (IDT). At present, it is difficult for SAW devices operating under GHz frequency because of the limitation of materials and fabrication technology. Diamond has a very high acoustic speed, and it is possible to fabricate GHz SAW devices using piezoelectric films on diamond substrates based on the present technology. However, diamond is not piezoelectric, and it need be layered with other materials such as lithium niobate (LiNbO3) to permit the electrical generation and detection of acoustic waves. Thus, it is competition to fabricate higher frequency SAW devices using diamond substrates.As an important ferroelectric material for fabrication of SAW devices, LiNbO3 exhibits excellent electro-optical, piezoelectric and nonlinear optical properties. Buffer layer is an important aspect in film growing. In this dissertation, the buffer layer is amorphous SiO2 layer or c-axis oriented ZnO layer, and the structure of multilayer is LiNbO3/SiO2/diamond/Si or LiNbO3/ZnO/diamond/Si. The function of the buffer layer and the method of depositing buffer layer are introduced. We studied the influence of different experimental parameters of PLD on the film growth and obtained the following results:1. Using PLD technology, we prepared completely c-axis oriented LiNbO3 thin films on diamond/Si substrate with amorphous SiO2 buffer layer without the application of induced electrical field. Through systematically study of the influence of experimental parameters of PLD on the films growth, the optimal process conditions were determined:substrate temperature 650℃, oxygen pressure is 40 Pa, laser energy density is 3.6J/cm2, laser frequency is 3 Hz, and target-substrate distance is 4.0 cm.2. We also prepared highly c-axis oriented LiNbO3 thin films on diamond/Si substrate with highly c-axis oriented ZnO buffer layer by the pulsed laser deposition technique. The optimal growth conditions were determined:substrate temperature 600℃, oxygen pressure is 40 Pa, laser energy density is 3.0J/cm2, laser frequency is 3 Hz, and target-substrate distance is 4.0 cm.3. The frequency characteristics of the fabricated SAW filters were measured with RF-network analyzer. Diamond SAW filters have rather good performance with high acoustic speed of 8664m/s, twice more than that of in single crystal LiNbO3.