Preparation Of Solidly Mounted Film Bulk Acoustic Resonators And Modification Of Tunable BST Film By Doping

With the rapid development of wireless communication systems, new requirements of miniaturization, integration, high frequency for the wireless terminal filter devices were proposed. As a new device to meet these requirements, the solidly mounted thin film bulk acoustic wave resonator?abbreviated FBAR? has been investigated. Requirements for the precision of device structure and material properties of the solidly mounted FBAR are extremely strict. Study on the manufacturing process of FBAR is of great important.Barium strontium titanate?BST? thin film can be used to replace the traditional piezoelectric material to improve the tunability of FBAR devices because of it's characteristics of low dielectric loss, small size, high tunablity.Firstly, the complete preparation process of the solidly mounted and tunable FBAR was investigated. Then the preparation of its key material —— barium strontium titanate?BST? thin films and its modification by doping was investigated in detail. The main contents and conclusions are as follow:SiO₂, W and ZnO thin films were prepared by RF magnetron sputtering method, the effect of sputtering conditions?such as sputtering pressure, sputtering power, argon oxygen ratio, etc? on the morphology of these thin films was studied, and then their manufacturing parameters were optimized. The effect of different annealing temperature on the morphology of Bragg reflector was also investigated. The results show that the maximum annealing temperature at which the W/SiO₂ Bragg reflector could withstand was 650 ?.The solidly mounted FBAR devices of which the resonant frequency was 4 GHz were prepared successfully by magnetron sputtering method. ZnO was used as its piezoelectric layer. The related researches of post-annealing treatment for the whole devices were done,which made the Q value of the FBAR devices increased by two times.Applications of BST thin films on tunable FBAR devices were addressed for their lowdielectric loss and high tunability. Doping is a major means to improve its performance.The ionic radius of Rb is very close to that of Ba and Sr ions, and it has the potential to improve the dielectric properties of BST thin films as an acceptor doping. Moreover,researching on Rb-doped BST thin films have not been reported yet. In this article, sol-gel method was adopted to prepare Ba0.6Sr0.4TiO3 thin films with different Rb doping level. The effects of Rb doping on the microstructure and dielectric properties of Ba0.6Sr0.4TiO3 thin film were studied. It was found that the Ba0.6Sr0.4TiO3 thin film with 4 mol% Rb doping exhibited the smallest surface root-mean-square roughness?RMS? of 2.409 nm, the highest dielectric constant of 486 at 2 MHz. It also got the highest tunability of 63.37% when the electric field intensity was 377 KV/cm. The largest figure of merit value of 31.53 was achieved in this optimized recipe. It is proved that the proper amount of Rb doping can improve the comprehensive properties of Ba0.6Sr0.4TiO3 thin films.