The Research On The Fabrication Process Of Film Bulk Acoustic Resonator Based On The ZnO Piezoelectric Thin Film

In recent years, as the smart phones and tablet PCs going into people’s lives constantly, the RF filters and duplexers based on film bulk acoustic resonator(FBAR) have been used widely in wireless mobile communication systems. Meanwhile, the resonant mass sensor based on FBAR is also getting more and more attention for its small size, high sensitivity, low cost and so on.After the development status and basic theory of FBAR are described, the impedance characteristics of ideal and actual FBAR are simulated with the mason equivalent circuit model. The impact of the piezoelectric materials’ thickness, the electrode’s thickness, the resonance region’s area on the FBAR impedance characteristics is investigated. Thus, a theoretical basis for later design of FBAR structure parameters is established. Meanwhile, the layout structure and size of FBAR device are designed. Then, the making craft of FBAR device is investigated. Combining with the condition of the laboratory, bulk silicon micromachining technology is adopted to fabricate the FBAR. And a Al-ZnO-Al, air-backed FBAR is fabricated successfully.The preferred orientation of the ZnO piezoelectric film is identified by X-ray diffraction(XRD). The frequency response of longitudinal wave FBAR has been measured with a rf network analyzer, and the series resonant frequency(sf) and parallel resonant frequency(pf) of the micromachined FBAR are 1.546 GHz and 1.590 GHz, respectively, which are close to the theoretical value simulated by mason equivalent circuit model. According to the measured result, the effective electromechanical coupling coefficient(2effK) and quality Q have been calculated to be 6.83% and 350, respectively. After the FBAR packaging, its mass sensing characteristic is investigated by sputtering different thicknesses of ZnO layer on the FBAR backside surface. From the graph of the resonant frequency versus added ZnO thickness, the series and parallel resonant frequencies decrease linearly with increased thickness of ZnO layer. And the FBAR is measured to have a mass sensitivity mS of 1116.552 cm /g, which is almost agreed with the theoretical value of 1166.862 cm /g. The mass sensitivity is about 80 times of the conventional quartz crystal microbalance(QCM).