Development of FBAR devices based on nitrogen-incorporated zno films

Abstract

The film bulk acoustic wave resonator (FBAR) has been emerging as a very promising technology, enabling the fabrication of the next-generation radio frequency filter as well as duplex components. This is mainly because the FBAR technology can be compatible fully with the current silicon process technology, eventually realizing the microwave monolithic integrated circuits. ZnO is an ideal candidate for FBAR device application due to the ease of obtaining high quality piezoelectric ZnO films and the high piezoelectric coupling coefficient. In this thesis, we present a new approach to fabricate the bulk acoustic wave resonator (FBAR) devices employing the high-quality piezoelectric ZnO films, particularly sputter-deposited in a mixture of $N_2O$ and Ar gases as the reactive and sputtering gases, respectively. The conventional FBAR device structure consists typically of a piezoelectric film layer sandwiched between top and bottom electrodes, where a resonance occurs when an RF signal is applied across the electrodes. The solidly mounted resonator (SMR), a type of FBAR, has a Bragg reflector (BR) that can act as a mirror to prevent a possible energy loss into the substrate from the resonating piezoelectric region. Since the piezoelectric property of piezoelectric material (ZnO) is the most important factor that determines the characteristics of the FBAR, considerable efforts have been made to realize the high quality ZnO films and thus to improve the FBAR device characteristics. In this study, ZnO thin films deposited in Ar and $O_2$ ambient under various sputtering deposition conditions have been investigated and characterized. Traditionally, the oxygen ($O_2$) gas has been employed as a reactive gas for the ZnO film deposition, followed by a thermal annealing processing for the further enhancement of the resonance performance. To the best of our knowledge, no studies have been reported on the high quality ZnO films deposited in an $N_2O$ ambient and their appl...