Kok-Wan Tay

Highly c-axis oriented thin AlN films deposited on gold seed layer for FBAR devices

In this study, highly c-axis oriented aluminum nitride (AlN) films are deposited on gold (Au) seed layer using a rf reactive sputtering method under various rf power and sputtering pressures. The evolution of preferred orientation and surface morphologies of the deposited films was studied by x-ray diffraction, scanning electron microscope, and atomic force microscope. It was found that the AlN films prepared using the higher rf power of 400 W and sputtering pressure of 7 mTorr were shown to have the stronger c-axis orientation and exhibit smoother morphologies. The fabricated film bulk acoustic-wave resonator (FBAR) devices considered here with AlN film thickness are 2.25μm, Au and Al are used as bottom electrode and top electrode with the thickness of 0.1 and 0.18μm, respectively. The effective electromechanical coupling coefficient (keff2), quality factor (Qfx) and resonant frequency of the fabricated FBAR device were about 1.47%, 535 and 2.172 GHz, respectively. Moreover, the effect of the top electro...

Influence of Piezoelectric Film and Electrode Materials on Film Bulk Acoustic-Wave Resonator Characteristics

This study adopts the one-dimensional Mason model and basic transmission line theory to investigate the influence of different piezoelectric films and electrode materials on the characteristics of a thin film bulk acoustic-wave resonator (FBAR). The influences of different electrodes, piezoelectric films, and supporting membrane thicknesses are also explored. The results confirm that the material properties and thickness of the piezoelectric film play a significant role in determining the performance of the FBAR, and influence such characteristics as the resonant frequency, the bandwidth, and the insertion loss. Therefore, the choice of piezoelectric material has a pronounced influence upon the subsequent design of the FBAR filter. Since the results also demonstrate that the resonant frequency of the FBAR is influenced by the thickness of each of the layers within the acoustic wave path, and by the resonance area, the potential exists to tune the characteristics of the FBAR by specifying appropriate geometric parameters during the FBAR design stage.

Performance characterization of thin AlN films deposited on mo electrode for thin-film bulk acoustic-wave resonators

In this paper, we discuss the implementation and testing of a film bulk acoustic-wave resonator (FBAR) comprising an AlN piezoelectric thin film sandwiched between two metal electrodes and located on a silicon substrate with a low-stress silicon nitride (Si3N4) support membrane. In the present study, we choose molybdenum as the bottom electrode rather than the conventionally used Pt/Ti, Au/Cr or Al because it has a low acoustic attenuation and a good electrical conductivity, and provides a good adhesion between the thin AlN film and the low-stress Si3N4 membrane. We investigate the influence of AlN film thickness and top-electrode thickness on the resonance frequency of the FBAR device. 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. Furthermore, it is also determined that the resonance frequency of the device can be increased by specifying a higher RF power for the magnetron sputtering process used to deposit the AlN film. This study employs an X-ray diffraction (XRD) technique to investigate the influence of AlN film thickness and RF power on the c-axis orientation of the thin film. It is shown that increasing either the thickness of the AlN film or the power of the RF sputtering process improves c-axis orientation. However, scanning electron microscopy (SEM) and atomic force microscopy (AFM) results reveal that a thicker AlN film exhibits a rougher surface and a larger grain size, both of which decrease the coupling factor of the FBAR device.

Effect of AlN Film Thickness and Top Electrode Materials on Characteristics of Thin-Film Bulk Acoustic-Wave Resonator Devices

Highly c-axis-oriented aluminum nitride (AlN) thin films were deposited on Mo electrodes by reactive RF magnetron sputtering and their thickness effects on thin-film bulk acoustic-wave resonator (FBAR) characteristics are presented. The results obtained in this study show that thick AlN films have a strong c-axis orientation and tend to promote a small rocking curve full-width at half-maximum (FWHM), but a high grain size and a high surface roughness, hence degrading the characteristics of FBARs. The characteristics of FBARs depend not only the thickness and quality of AlN films, but also the thickness of the top electrode and the type of material used. Specifically, an increase in either AlN film or top electrode thickness increases parallel resonant quality factor (QP), but reduces effective electromechanical coupling coefficient (keff2). However, the resonance provides a maximum keff2 when AlN film thickness approaches the fundamental one-half-wavelength. The effects of the type of top-electrode material and AlN film thickness on the keff2 and quality factor of the fabricated FBARs are also discussed.

Preparation and Magnetic Properties of Ni0.36Zn0.64 Ferrite from Microwave-Induced Combustion

Ni–Zn ferrite powders were successfully synthesized using microwave induced combustion. The process took only 15 min to obtain as-received Ni–Zn ferrite powders. The resultant powders were annealed at different temperatures and were investigated by differential thermal analysis/thermogravimetry (TG/DTA), X-ray diffractometry (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and vibrating sample magnetometry (VSM). The as-received powders showed the formation of cubic ferrite with saturation magnetization (Ms) of 23 emu/g and an intrinsic coercive force (Hc) of 135 Oe, whereas upon annealing at 850°C for 2 h, the saturation magnetization increases to 58 emu/g and the intrinsic coercive force reached 197 Oe. The toroidal specimen sintered at 1200°C for 2 h presented both an optimum initial permeability (µi) and quality factor (Q). The high initial permeability and large quality factor were closely associated with effective improvement of the densification and magnetic characteristics properties of sintered specimen made from nanosized Ni–Zn ferrite powder prepared by microwave-induced combustion.

Growth of AlN thin film on Mo electrode for FBAR application

In this study, a FBAR device with four-layered composite structure is studied. In this four layer structure, an AlN piezoelectric thin film is sandwiched between two metal electrodes, all of which lied on a low stress silicon nitride (Si/sub 3/N/sub 4/) as a support membrane in silicon. Most of the researches are using Pt/Ti and Al as the bottom electrode. But in this study, molybdenum was chosen as the bottom electrode because it has low acoustic attenuation, good electrical conductivity and has a good adhesive with AlN and low stress silicon nitride. Compare to Pt/Ti bi-layer electrode, the process of Mo electrode is easier. Compare to Al, there is no evidence transition region between Mo and AlN film which is indicative of smooth interface quality to fabrication FBAR. The high quality c-axis orientation AlN thin films with different thickness are achieved by optimum sputter deposition conditions on Mo and showed quasi-single crystal piezoelectric properties assessed using XRD, SEM, AFM and electrical characterizations are reported. The experimental results indicate that the resonance frequency is mainly determined by the thickness of the AlN film layer, which reducing the AlN thickness increase the resonant frequencies. One of the devices considered here with AIN film thickness is 1.35/spl mu/m, Mo and Al is used as bottom electrode and top electrode with the thickness of 0.1/spl mu/m and 0.18/spl mu/m, respectively. The resonant frequency of the devices is 3.42 GHz and the return loss is -37.95 dB.