Fabrication of piezoelectric AlN thin film for FBARs

Abstract

This paper focuses on the fabrication of film bulk acoustic-wave resonator (FBAR) comprising an aluminum nitride (AlN) piezoelectric thin film sandwiched between two metal electrodes and located on a silicon substrate with a low-stress silicon nitride (Si 3 N 4 ) support membrane for high frequency wireless applications, and analyzes the optimization of the thin AlN film deposition parameters on Mo electrodes using the reactive RF magnetron sputter system. Several critical parameters of the sputtering process such as RF power and Ar/N 2 flow rate ratio were studied to clarify their effects on different electrodes characteristics of the AlN films. The experiment indicated that the process for Mo electrode was easier compared with that of the Pt/Ti or Au/Cr bi-layer electrode as it entailed only one photo resist and metal deposition step. Besides, Pt/Ti or Au/Cr electrodes reduced the resonance frequency due to their high mass density and low bulk acoustic velocity. Compared with the case of the Al bottom electrode, there is no evident amorphous layer between the Mo bottom electrode and the deposited AlN film. The characteristics of the FBAR devices depend not only upon the thickness and quality of the AlN film, but also upon the thickness of the top electrode and the materials used. The results indicate that decreasing the thickness of either the AlN film or the top electrode increases the resonance frequency. This suggests the potential of tuning the performance of the FBAR device by carefully controlling AlN film thickness. Besides, increasing either the thickness of the AlN film or higher RF power has improved a stronger c-axis orientation and tended to promote a narrower rocking curve full-width at half-maximum (FWHM), but increased both the grain size and the surface roughness. An FBAR device fabricated under optimal AlN deposition parameters has demonstrated the effective electromechanical coupling coefficient (k 2 eff ) and the quality factor (Q f x ) are about 1.5% and 332, respectively. sputtering, thin film, piezoelectricThe rapid growth of wireless mobile telecommunication systems has led to an increasing demand for high-frequency oscillators, filters and duplexers capable of operating in the 0.5 to 5 GHz frequency range. Conventionally, microwave ceramic resonators and surface acoustic wave (SAW) resonators have been applied in this frequency range. However, microwave ceramic resonators tend to be physically bulky, while SAW resonators demonstrate a relatively poor sensitivity to temperature and have high insertion losses and limited power handling characteristics. Moreover, SAW devices must be generally interfaced at the board level rather than directly at the chip level. Micromachined thin film bulk acoustic-wave resonators (FBARs) have been developed to address the limitations of these conventional devices. Compared with microwave ceramic resonators and SAW resonators, FBAR devices have the advantages of low cost and enhanced electrical performance, and are characterized by low insertion losses, hig...

The influence of design parameters on the performance of FBAR in 10–14 GHz

“…FBARs operating in the frequency range of 5 GHz to 20 GHz have been reported to show a very high quality (Q) factor, good power handling and small size. The most common piezoelectric materials used for development of FBAR are aluminum nitride (AlN) and zinc oxide (ZnO) [1][2][3][4]. FBARs based on lead zirconate titanate (PZT) and cadmium sulphide (CdS) are also found in the literature [5][6].…”

Modeling and characterization of piezoelectric beams based on an aluminum nitride thin‐film layer

“…The proposed piezoelectric microcantilevers and microbeams were basically fabricated by micromachining technologies . Several bottom layers, such as Ti/Mo, Ti/TiN, Cr/Pt, Ti/Pt were deposited by a sputtering process in order to find the lower mismatch between the piezoelectric AlN lattice parameter and the lattice parameter of the as‐deposited bottom layer. Residual stress and Young's modulus in thin films are important to match the mechanical frequency and reliability of MEMS .…”