Design & fabrication of FBAR device and RF inductor based on bragg reflector for RFIC applications

Abstract

The rapid expansion of the wireless market has led to a huge growth of more advanced mobile communication systems. Especially, the miniaturized mobile phones have been developed that have multi-functions with higher operating frequencies. Complying with the recent trends, there has been a great demand particularly for ultra-miniaturization and monolithic integration of RF filters as one of core components in mobile communication systems. Typical filters used in RF front-end for commercial wireless handsets are ceramic or surface acoustic wave (SAW) resonators. However, neither of them is compatible fully with the standard IC-technology. Film bulk acoustic wave resonator (FBAR) devices and their related fundamentals can play an important role for the fabrication of the next generation radio-frequency (RF) filters. The FBAR devices basically utilize the acoustic resonant characteristics of piezoelectric materials such as AlN or ZnO. Compared with the so-called Surface Acoustic Wave (SAW) filters, FBAR device filters can also be realized to have smaller size and higher performance especially in power handling capability. The typical FBAR device is composed of a thin piezoelectric film sandwiched between top and bottom conductor plates (electrodes). The devices must have two acoustically reflecting surfaces in order to trap energy and produce a resonating characteristic. As the reflecting surfaces for FBAR devices, the solidly mounted-type has a Bragg reflector part which is made up of alternating thin-film layers of both low and high acoustic impedance materials. The ZnO-based FBAR devices are made up of a piezoelectric ZnO film sandwiched between top and bottom electrodes (e.g., aluminum) deposited on 5-layer W/$SiO_2$ Bragg reflectors. The 5-layer W/$SiO_2$ Bragg reflectors were fabricated by alternately depositing the tungsten (0.57 $\mum$-thick) of high acoustic impedance material and $SiO_2$ films (0.6 $\mum$-thick) of low acoustic impedance material o...