Narrow Results

This study focuses on the characteristics of film bulk acoustic-wave resonator (FBAR) on Pt electrodes for high frequency wireless applications, and the critical parameters of the sputtering process such as RF power, deposition pressure, substrate temperature and Ar/N2 flow rate ratio were studied to clarify the effects on the Pt electrodes characteristic of the zinc oxide (ZnO) films using reactive RF magnetron sputter system.

Measurements of X-ray diffraction (XRD) and scanning electron microscopy (SEM) show that the ZnO film deposited on the Pt electrode exhibits highly c-axis orientation with well-aligned columnar and smoother surface. The fabricated two-port FBAR consisted of 1.5μm thick ZnO film with 0.2μm thick Pt top and bottom electrodes was characterized with a network analyzer have a resonant frequency of 1.5 GHz and the return loss is -24.76dB. Furthermore, the effects of varying ZnO thickness on the performance of of the fabricated FBAR devices are also discussed.

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 (Si3N4) support membrane for high frequency wireless applications, and analysis the optimization of the thin AlN film deposition parameters on Mo electrodes using reactive RF magnetron sputter system.

Several critical parameters of the sputtering process such as RF power and Ar/N2 flow rate ratio were studied to clarify their effects on the different electrodes characteristic of the AlN films. The experiment indicated that the process for Mo electrode is easier compared with the Pt/Ti or Au/Cr bi-layer electrode as it entails only one photo resist and metal deposition step. Besides, Pt/Ti or Au/Cr electrodes reduced the resonance frequency due to it high mass density and low bulk acoustic velocity. Compared with the case of an Al bottom electrode, there is no evident amorphous layer between 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 the carefully controlling AlN film thickness. Besides, increasing either the thickness of the AlN film or higher RF power have improves a stronger c-axis orientation and tend 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 and the quality factor (Q_fx) were about 1.5% and 332, respectively.

A focused ion beam (FIB) was successfully applied to prepare cross-sectional samples for transmission electron microscopy (TEM), scanning TEM (STEM), scanning electron microscopy (SEM), and scanning ion microscopy (SIM). The FIB milling has been prospectively applied also to nanofabrication. The FIB allows to mill with high accuracy in positioning, being in contrast with a broad ion beam with poor accuracy. Controlling beam conditions of ion pixel-dose (or pixel dwell time) and FIB scanning direction/velocity, and sample tilt/rotation, we can extend the FIB milling from cross-sectioning to three-dimensional (3D) fabrication. We review inherent characteristics of the FIB milling such as positioning accuracy, milling speed, uniformity of cross-section, beam damage, and secondary electron emission. Discussions are mainly held from a viewpoint of interaction of ion beam with solids.

Lithium niobate (LiNbO3, LN) thin films have been extensively studied for applications in acoustic and photonic devices, due to their outstanding piezoelectric, ferroelectric and electro-optical properties. With the increasing demand for high speed and low latency wireless communication, LN thin films with high electromechanical coupling coefficients are very attractive to improve the performance of acoustic resonators for radio frequency filters. The current bottleneck for LN-based devices is the synthesis of high-quality LN thin films, which is typically fabricated by expensive and inefficient process of ion slicing and layer transfer from bulk single crystals. This review paper focuses on the direct growth of high-quality LN thin films, which has the potential to scale up and lower the cost of LN thin films. We first introduce the crystal structure and piezoelectric properties of LN, followed by an overview of the state-of-the-art LN acoustic resonators. After a summary of the challenges in the fabrication of LN thin films, we review the direct growth of LN thin films by sputtering, pulsed laser deposition, metalorganic chemical vapor deposition and molecular beam epitaxy. With the progress in optimizing the crystallinity and surface roughness, the quality of the LN thin films synthesized by direct growth has been greatly improved. As a result of the fast-growing industrial interests, we believe that the research works in direct growth of LN thin films will increase exponentially to achieve the same quality of the LN thin films as the bulk single crystals.