Polycrystalline ZnO thin films were for the first time deposited on SiO2/Si (100) substrate using 2-step deposition; atomic layer deposition (ALD) and RF magnetron sputtering, for Film Bulk Acoustic Resonator (FBAR) applications. The film deposition performed in this study was composed of following two procedures; the l(st) deposition was using ALD method and 2(nd) deposition was using RF magnetron sputtering. The ZnO buffer layer ALD films were deposited using alternating diethylzinc (DEZn)/H2O exposures and ultrahigh purity argon gas for purging. Exposure time of 1 sec and purge time of 23 sec yielded an ALD cycle time. Two-step deposited ZnO films revealed stronger c-axis preferred-orientation than one-step deposited. Therefore, this method could be applied to the FBAR applications, since FBAR devices require high quality of thin films.