Investigation On High-quality AlN Films For High-frequency SAWD

With high-speed development of communications system and other related systems,Application frequency of surface acoustic wave (SAW) has entered the high-frequency (morethan5GHz) Times, traditional piezoelectric materials such as ZnO、LiNbO3with a soundvelocity under6000m/s are used to designed high frequency SAW devices, the speed of soundof AlN is the highest among all piezoelectric materials，about11354m/s, which is closest to thesound velocity of diamond(about18000m/s). This paper has research the preparation ofnano-AlN films with uniform crystal lattice arrangement. This paper has also researchlarge-area uniform and flat nanometer AlN films in order to volume production SAWD.There are series of defects and problems during deposition of AlN films on the diamond.1. Because of the different coefficient of thermal expansion of AlN and Si, anisotropiccoefficient of thermal expansion of AlN makes the problem of thermal mismatch of (100)AlN/(100) Si system more complicated.2. During the deposition of AlN films, there exists a rare phenomenon that Al-Al bondand N-N bond may be appeared because the surfaces of Si may be existed single atomic step,the kind of structural defect is anti-phase.In order to solve these problems, this paper puts forward two steps and annealingtreatment growth method, and the main experimental results are as follows:1. In this paper, AlN (100) thin films are deposited on N-(100) Si substrate by a radiofrequency sputtering. The growth parameters, such as N2: Ar, sputtering power, and sputteringpressure are studied.2. This paper puts forward two steps growth method and annealing treatment method fordeposition of high-quality and low-defect (100)AlN thin films. The results show that thesurface roughness (Rms) of AlN by Two step method compare with that of common process,which has decreased from6.4nm to2.1nm.3. On the basis of the above-mentioned of two-step method, high-quality and large area(100) preferred orientation of the AlN thin films are deposited by RF magnetron sputtering,The results show that the average value of the surface roughness of (4inch)AlN thin films is2.22nm, and the relative deviation of surface roughness is less than5%.4. On the basis of the above-mentioned of two-step method,(100) preferred orientation ofthe A1N films are deposited on the diamond substrate.