Properties of AlN films grown by two-step deposition and characteristics of AlN-FBAR devices

摘要

A two-step deposition method using RF reactive magnetron sputtering is proposed to obtain AlN thin films of high quality for film bulk acoustic resonators (FBARs). The 1st step deposition is focused on lowering the surface roughness of AlN films. This is accompanied by the 2nd step deposition where the RF power and the working pressure are controlled to enhance the c-axis preferred growth of AlN films. It is seen by monitoring the x-ray diffraction (XRD) spectra that the films deposited by two-step method reveal the improved c-axis preferred orientation. The atomic force microscope (AFM) images show that the surface roughness of the films is drastically reduced by adopting the two-step deposition. It is also found from the measurement of frequency response characteristics for AlN-FBARs that the devices based on the AlN films prepared using the two-step method reveal the better device performance in return loss and electro-mechanical coupling coefficient ((k{sub}t){sup}2).