Abstract: A high-Q diaphragm-structure film bulk acoustic resonator (FBAR) with a flat support diaphragm,made of Si3N4/SiO2/Si3N4 composite films,is proposed.The N/O/N composite diaphragm overcomes the wrinkling in the released support diaphragm caused by the residual stress of a single Si3N4 or SiO2 diaphragm.ZnO piezoelectric film deposited employing a DC reactive magnetron sputtering method is used as the piezoelectric material for the FBAR device.The XRD θ-2θ scan indicates that the ZnO film has the preferred c-axis orientation growth,implying good piezoelectric properties.The S parameter measurement shows that there are three primary resonances in the frequency range from 0.4 to 2.6GHz.The series resonant frequency,parallel resonant frequency,K2eff,and quality factors of the three resonances are calculated.The third one,with a frequency of about 2.4GHz,has the highest quality factor about 500.Thus,it is expected to be a candidate to form a 2.4GHz low-phase-noise oscillator.

Key words: film bulk acoustic resonator, oscillator, filter, composite diaphragm, ZnO