Research On Deposition Of Piezoelectrical AlN Thin Films By Magnetron Sputtering And Fabrication Of SAW Filter

The Ill-nitrides AlN, GaN and InN form an interesting class of wide bandgap materials, which are likely to be the basis of a strong development of a novel family of semiconductor device, for Optronics as well as for electronics. For example, the entire spectral region from UV to infrared can be covered with III-N optical devices. Furthermore, AlN has some outstanding physical properties that have attracted much interest. Its hardness, high thermal conductivity, resistance to high temperture and caustic chemicals, makes AlN an attractive material for electronic and optical devices. In this study, AlN thin films have been deposited on Si (111) substrates by medium frequency magnetron(MF) reaction sputtering. The influence of substrate temperture and annealing temperature is especially studied. The morphological and structural chacterizations have been determined by atomic force microsiscopy(AFM), x-ray diffraction. Optical constants and thickness have been analyzed from ultraviolet-visible spectrometry. In the mean time, we have also explored the fabrication technology of SAW filter. The mean results can be described as following:First, AlN thin films have been successfully deposited by MF magnetron reaction sputtering. In order to solve target poison and anode disppearance, MF power supply is used in our work. To prevent arc discharge, which affect deposition stability and the quality of the thin films, due to positive charge accumulation, 50v pulsed discharge supply is applied.Second, since it is very interrelated between application and quality of AlN thin films, we study influence of substrate temperture and annealing temperature for microstructure and properties of AlN thin films by MF magnetron sputter to optimize AlN thin films deposition conditions. It was shown by AFM that altering substrate temperature enables the surface roughness to be changed. The optimal substrate temperature for smooth surface of AlN films is 230℃, and the RMS is 5.751nm for the sample with substrate temperature of 230℃. The effect of the annealing process on the structure AlN film was also discussed. The result showed that the annealing temperature increase, the crystallization of the film become better, and the optimal annealing temperature is 700℃.Third, 1stOpt software is useded to attain the optical constants and physical thickness of AlN films by fitting the experimental optical reflective curve with the help of the physical model proposed by Forouhi and Bloomer. The ranges of the optical attained from the reflectivity in the spectral range of 400-800 nm are as follows: thickness d =396-698nm, refractive index n =1.94-2.2, extinction coefficient k <0.006, which show the thin film is good transpanency for light.Finally, we explored the initial fabrication technology of SAW devices. Our results show that the piezoelectric films on substrates are very easy to be damaged in SAW device fabrication, and the performance of the SAW devices is badly destroyed. So the technology for fabricating SAW devices using piezoelectric single crystal cannot be applied directly in the fabrication of SAW devices using piezoelectric thin films.