The Fbar Using Aln Thin Films By Mocvd Preparation

Thin film bulk acoustic wave resonators (FBAR) show considerable promise as an integrable solution for RF bandpass filters with center frequencies at GHz. It can replace conventional microwave ceramic filters and surface wave filters (SAW) because it provides several prominent advantages such as small size, high Q, high power handling capability, high operating frequency, good temperature stability, and the possibility of being integrated into semiconductor technology.Piezoelectric thin films are an essential component of FBAR. Aluminum Nitride (AlN) is one of the most attractive piezoelectric materials for FBAR application because of its low dielectric loss, high electromechanical coupling coefficient and similar thermal expansion coefficient with Si and GaAs. The quality of AlN thin films will strongly influence the performance of FBAR, and thus the bandwidth as well as the insertion loss of FBAR-based filters. So far, lots of researches have been done in order to obtain highly c-axis oriented AlN thin films.In this dissertation, the AlN thin films were grown on hexagonalα-Al2O3 (0001) substrates, Mo/Si substrates and ZrN/Si substrates by metalorganic chemical vapor deposition (MOCVD), respectively. The crystal microstructure, dielectric properties, and piezielectric properties of the deposited AlN thin films were systematically studied through the study on the effect of growth parameters, such as the substrate temperature, the flux flow of TMA and NH3, the total pressure in the reactor, and the kinds of substrates.The dissertation is mainly focous on the follows:Firstly, AlN thin films were grown on hexagonal Al2O3 (0001) substrates by MOCVD. The effect of growth parameters, such as the substrate temperature, the flux flow of TMA and NH3, and the total pressure in the reactor, on the crystallinestructure, texture, and microstructure, was systematically studied. It had been found that the AlN thin films were highly c axis oriented and extension films with hexagonal spiauterite structure. The full width at half maximum (FWHM) of the rocking curve around (0002) diffraction peak is only 0.10°and the inplane relation between AlN and Al2O3 was AlN[30 1?3]//Al2O3[33 2? 9]. The refractive index of the AlN thin films measured by elliptical polarimeter was between 2.0 and 2.4.Secondly, we deposited molybdenum (Mo) thin films on Si (111) substrates by DC magnetron sputtering. It showed that Mo thin films with (110) preferential orientation can be obtained after optimizing the deposition conditions. Then AlN thin films were grown on such Mo/Si substrates by MOCVD from the 950℃to 1050℃. It had been found that the AlN thin films were highly c axis oriented. The dielectric constant of the AlN thin films was between 8.9 and 11.8. The dielectric loss of the AlN thin films was between 1.0% and 2.0%. The piezoelectric coefficient of the AlN thin films was between 2.1 and 2.9.Finally, in order to decrease the high dielectric loss of AlN thin films prepared on Si substrates with Mo electrodes. So, we prepared zirconium nitride (ZrN) thin films on Si (111) substrates by reactive RF magnetron sputtering. It indicated the ZrN thin films with a (111) preferential orientation under optimized depositon condition. Then the AlN thin films were prepared on ZrN/Si substrates by MOCVD from the 1000℃to 1050℃. It had been found that the AlN thin films were highly c-axis oriented in this condition. The best microstructure and electrical properties can be obtained at 1025℃. In addition, the properties of dielectric loss and the piezoelectric properties of AlN thin films were enhanced on the ZrN/Si substrates, which can be interpreted by better crystal lattice match between AlN and ZrN compared to AlN and Mo. The dielectric constant of the AlN thin films on ZrN electrode was ranging from 8.3 to 8.6. The dielectric loss of the AlN thin films was between 0.1% and 0.6%. The piezoelectric coefficient of the AlN thin films was between 2.8 and 3.1.