The Fabrication And Study Of HBAR Based On AlN Piezoelectric Film

High overtone bulk acoustic resonator(HBAR) is used in the multiple frequencies microwave sources or low phase noise oscillators, which utilizes the multimode and high Q properties. Besides, HBAR is also used in sensors.In this paper, preferred c-axis AlN film was deposited by pulsed laser deposition(PLD). We fabricated HBAR with the wide spacing of the parallel resonance frequency based on AlN film, and developed its theoretical model, simulation design, fabrication process and test analysis.Firstly, we deduced the Mason equivalent circuit models of piezoelectric film, ordinary acoustic layer and HBAR based on the piezoelectric equations and kinematics equations. Then, we built the simulation model of piezoelectric film, ordinary acoustic layer and HBAR based on Mason model by RF simulation software ADS. According to ADS simulation model, we designed HBAR with the structure of 0.1 ?m Mo/ 0.9 ?m AlN/ 0.1 ?m Mo/ 60.3 ?m sapphire and wide spacing of the parallel resonance frequency, which had the value of 0.91 GHz.Secondly, we deposited AlN film by PLD and studied the influence of laser energy density, substrate temperature and substrate material on the orientation and surface roughness of AlN film. It turns out that with the increasement of the laser energy density(1.5~3.0 J/cm2) and substrate temperature(500~700 ?), AlN film is inclined to be the preferential(002) growth, but the surface roughness increases. Based on the research of these process parameters, we deposited the preferred c-axis AlN film on the patterned Mo/sapphire substrate with laser energy density of 3.0 J/cm2 and substrate temperature of 700 ?, whose full width at half maximum was measured to be 1.6°.Finally, we studied the fabrication process of HBAR, fabricated two kinds of HBARs by micro-nano fabrication process and tested them. The experimental results show the multi-mode resonant characteristics of HBARs from 0.7 to 5.0 GHz and the strongest resonance in close half wavelength of piezoelectric film transfer. The spacing of the parallel resonance frequency(?f) reaches 0.91 GHz, which is wide and has never been reported. Compared the magnitude of impedance of HBAR 1, the magnitude of impedance of HBAR 2 decreased with the increasement of effective areas. The test results also show that parallel resonance frequency(fp) and series resonant frequency(fs) conform to the theoretical value well.