Reseach On Preparation And Properties Of Scandium-Doped Aluminum Nitride Thin Films

Presently, the industrial demand for new SAW devices with higher-frequency, larger-bandwidth, higher-power and intergratability with complementary metal oxide semiconductor (CMOS) is drastically increasing because of the rapid development of modern communication system and equipment. As the key component of SAW device, research on the choice and preparation of piezoelectric thin film is necessary to ensure high performance of SAW device. Scandium-doped aluminum nitride (ScAIN) piezoelectric thin film is very attractive in the field of SAW applications because of its unique combination of remarkable properties, such as high acoustic velocity, high thermal conductivity, compatibility with conventional silicon technology, and above all, the higher piezoelectric response compared with pure aluminum nitride.This dissertation mainly concentrates on the preparation of ScAIN films with high crystal quality and good electrical properties. The effects of sputtering parameters, pressure, on ScAIN films’crystal orientation, surface morphology, deposition rate and electrical properties were investigated systemically. The internal mechanism of the experimental phenomena was explored theoretically. In addition, the differences between ScAIN film and pure AlN film were also studied. The main contents and conclusions are as follows.Ⅰ. Four serieses of ScAIN samples were prepared under different conditions, varying one sputtering parameter each series. The samples were investigated by XRD, AFM, SEM, Stylus Profiler, a standard ferroelectric test system to clear the influence of sputtering parameters on crystal quality, deposition rate, leakage current and resistivity of ScAIN films. The crystal quality and electrical properties of samples change obviously with varyinging sputtering parameters. The influence rules were obtained.Ⅱ. The optimized sputtering parameters of depositing ScAIN films using DC reactive magnetron sputtering were achieved, that is, a N2/Ar-flow ratio of 3.3:7, a sputtering power of 130W, a substrate temperature of 650℃ and a sputtering pressure of 0.5Pa. It’s demonstrated that highly c-axis oriented ScAIN thin films, with low RMS roughness of 4.08nm and good electrical performance, can be obtained with the optimized parameter, which finally meet the demand of new SAW devices.Ⅲ. ScAIN films and pure AlN films with excellent crystal quality were prepared with the optimized sputtering parameters to study the differences between ScAIN film and pure AIN film, especially for electrical properties. Results indicate that Sc-doped AIN thin film allows for an improvement of surface quality, insulating property and dielectric property, which is meaningful to the research on new SAW devices.