Preparation And Research Of High Frequency SAW Devices Based On AlN Thin Films

In recent years,with the rapid development of mobile communication technology and the more and more degree of integration of semiconductor devices,the demands for high frequency,high power,high stability and miniaturized surface acoustic wave?SAW?devices is increasing.Therefore,it is the key to further development of mobile communication technology that improving the central frequency of SAW devices and reducing the size of the devices.The diamond has the highest SAW velocity and higher thermal conductivity in nature,so it is the preferred material to prepare highfrequency and highpower SAW devices.The AlNpiezoelectric thin filmswith high SAW velocity,low transmission loss,outstanding thermal stability and chemical stability,while belonging to the six cubic crystal system of III-V compounds and having a similar lattice constant with diamond.Thus,it is considered to be one of the ideal piezoelectric materials for the fabrication of high frequency SAW devices.Firstly,the process parameters such as the growth power,the substrate temperature and the ratio of nitrogen?N₂?and argon?Ar?of AlN thin film were optimized,and the influence of the different process parameters for crystallinity,morphology and piezoelectric properties on AlN thin films were investidgated by XRD,AFM,PFM and so on.The preparation of AlN thin films with the best?002?orientation,more uniform surface morphology?RMS=1.53nm?,atomic ratio of N and Al is 1.06:1,close to 1:1,excellent piezoelectric properties(the highest relative coefficient d*₃₃=0.79V)and piezoelectric response consistency?the same trend for 64 butterfly curves and saturated windows for hysteresis loop?at the growth conditions of 180W,500°C substrate temperature and the15:15 ratio of nitrogen and argon,which is the optimal process.Furthermore,the 200nm interdigital width was fabricated by optimization electrion beam lithography?EBL?based on optimal AlN thin films.The center frequency is 4.47GHz for the SAW devices based on IDT/AlN/Pt/Ti/SiO₂/Si structure,the influence of different IDTs pairs?N=10,25,50?and different aperture?W=50?,100??for signal transmission were analized.It is found that the width of main peak decreases and insertion loss increases slightly with the increasing of IDTs pairs,the center frequency increases and insertion loss decreases with the increasing of aperture.Then,the devices of IDT/AlN/Diamond structure with 25 pairs IDT,400nm finger width and 50?aperture were fabricated,the center frequency is 5.77GHz with-65.57 dB insertion loss.The miniaturization high frequency SAW devices were realized by combining AlN thin films with high velocity diamond substrate and configuring submicron scale IDTs,it will be helpful to the application of AlN thin films in the preparation of high frequency SAW devices.