Medium Frequency Of Ain Thin Films Prepared By Sputtering And Development Of Bulk Acoustic Wave Resonator

With the rapid development of wireless communications, the center frequency of data communications has raised to GHz or above. The RF filter, as an important component of signal processing in the communication systems, attracts more and more attention. FBAR is a kind of newly developing filter. Comparing with the ceramic filter and SAW filter, it has high working frequency, high Q value, high power capacity, and compatibility with semiconductor technology.The core of FBAR technology is the high quality AlN thin film and the fabrication process of FBAR device. In this dissertation, we study the effect of growth parameters on the quality of AlN film, the characterization of AlN thin films, and the FBAR fabricating process. The main results of this dissertation are listed as follows: Firstly, AlN thin films were prepared on Si substrates by Mid-Frequency Reactive Magnetron Sputtering. The effect of growth parameters,such as N₂ partial pressure, substrate-target spacing, sputtering power, etc, on the quality of AlN thin films, was systematically studied. The results reveal that sputtering power, substrate-target spacing and N₂ partial pressure affect the formation of [002] texture for AlN thin films. Under optimum deposition condition which was the baking temperature of 200 oC, the Ar gas flow of 80 sccm, the N₂ gas flow of 18 sccm, the target substrate distance of 7 cm, the power of 2000 W, highly C-axis oriented AlN films were obtained on the Si substrate and PI / Si substrate respectively.Secondly, AlN thin films were analyzed by XRD, SEM, AFM, XPS, Raman. The AlN thin film, which was prepared under optimal condition, has the only AlN (002) peak. The full width at half maximum (FWHM) of the rocking curve around (002) peak is 5.7°. From cross-section analysis of SEM, grain is fibrous. By the AFM analysis, roughness (RMS) is 8.0 nm. By EDS analysis, the ratio of aluminum to nitrogen in the AlN thin film is close to 1:1; by Raman analysis, the AlN thin film has E2 (high) phonon peak and A1 (TO) phonon peak. The FWHM of E2 (high) peak is 12.8 cm-1. The calculated stress is 2.4 GPa.Finally, FBAR devices were fabricated by Micro-fabrication technology. The electrical properties of the FBAR devices were tested: the resistivity of 5.6GΩ?cm , dielectric constant of 11, dielectric loss of 2.25%, the resonant frequency of 1.82 GHz, S₁₁ of -4.3 dB and electromechanical coupling coefficient of 5.4%.