Yuan-Feng Chiang

Effects of conducting layers on surface acoustic wave in AlN films on diamond

The interdigital transducer (IDT)/AlN/conducting layer/diamond structures are investigated in this study to design surface acoustic wave (SAW) devices in the super high frequency band. Simulation results using the finite element method show that a thin conducting layer can effectively increase the coupling coefficient and, thus, broaden the bandwidth of SAW devices. For the Sezawa mode, it is illustrated that using a Ti layer with a layer thickness-to-wavelength ratio of 0.02 the maximum coupling coefficient is 2.546% and the associated SAW phase velocity is 10657 m/s at the AlN films’ thickness-to-wavelength ratio of 0.14. This coupling coefficient is 105% higher than that in the IDT/AlN/diamond structure. The research results can be applied to design SAW devices using diamond based structures in the super high frequency band.

Theoretical analysis of SAW propagation characteristics in (100) oriented AlN/diamond structure

In this study, the finite element method is employed to calculate SAW characteristics in (100) AlN/diamond based structures with different electrical interfaces; i.e., IDT/ AlN/diamond, AlN/IDT/diamond, IDT/AlN/thin metal film/ diamond, and thin metal film/AlN/IDT/diamond. The effects of Cu and Al electrodes as well as the thickness of electrode on phase velocity, coupling coefficient, and reflectivity of SAWs are illustrated. Propagation characteristics of SAWs in (002) AlN/diamond-based structures are also presented for comparison. Simulation results show that to retain a large reflectivity for the design of RF filters and duplexers, the Cu IDT/(100) AlN/diamond structure possesses the highest phase velocity and largest coupling coefficient at the smallest AlN film thickness-to-wavelength ratio.

Effects of metal buffer layer on characteristics of surface acoustic waves in ZnO/metal/diamond structures

The interdigital transducer (IDT)/ZnO/metal/diamond structure is investigated for use in the design surface acoustic wave (SAW) devices in the super-high-frequency (SHF) band. Simulation results indicate that adding a metal buffer layer with a finite thickness significantly increases the coupling coefficient. In the Sezawa mode, the coupling coefficient is 4.71% when an Al interlayer is applied. This coupling coefficient is 75% and 77% larger than those in the IDT/ZnO/diamond and IDT/ZnO/shorted surface/diamond structures, respectively. The results in this study are useful in designing SAW devices using diamond-based structures with a large coupling coefficient in the SHF band.

Effect of Metal Buffer Layer on Surface Acoustic Wave in AlN/Diamond Structure

This study investigates the propagation characteristics of surface acoustic waves in interdigital transducer/AlN/Mo/diamond structures using the finite element method. Propagation characteristics in AlN/thin metal film/diamond and AlN/diamond structures are also evaluated for comparison. Results indicate that by adding the Mo layer at the AlN/diamond interface, the maximum coupling coefficient can be upgraded to 2.24%, which is 5% and 81% higher than that of AlN/thin metal film/diamond and AlN/diamond structures, with a very high phase velocity of 10745 m/s. The effects of electrodes on surface acoustic waves in interdigital transducer/AlN/Mo/diamond structures are also discussed.

Measurement of methanol solutions using love mode liquid sensor

Controlling the methanol concentration is a key factor in improving the efficiency of the direct methanol fuel cell. In this study, the immersed-type Love mode sensor based on SiO2/ST-cut Y-propagation quartz was fabricated for monitoring the methanol concentration. A temperature controlled measurement system consisting of a spectrum analyzer and an oscillator circuit was employed to characterize the methanol solutions with different weight concentrations at different temperatures. A theoretical prediction of the phase velocity shift for the methanol solutions with different weight concentrations was also performed for comparison. The results of methanol solutions with different weight concentrations at different temperatures show that the amount of the frequency shift is approximately linearly proportional to the weight concentration, and the proportional rate increases as the temperature increases. The concentration resolutions were 1.1876 and 0.2484 %/kHz by weight at 25°C and 70°C.

Magnetization reversal process of ferromagnetic granular thin films probed by magnetization-induced second harmonic generation

We propose to use magnetization-induced second harmonic generation (MSHG) technique to explore the magnetization reversal process of cobalt granular thin films. The three-dimensional magnetization reversal process can be visualized by analyzing the polarization dependent MSHG hysteresis curves. It is found that the magnetization reversal process involves not only the in-plane but also the out-plane magnetization rotation because of the uniaxial anisotropy of cobalt granular thin films. This study demonstrates that MSHG can be a versatile optical technique to investigate the magnetic property of not only ferromagnetic epitaxial thin films but also ferromagnetic granular thin films.

Design of IF Two-Track Surface Acoustic Wave Filters Using (100) AlN/Diamond Structures

In this paper, characteristics of two-track surface acoustic wave (SAW) filters based on Cu electrode/(100) AlN/diamond structures were analyzed using the finite element method (FEM) and the transmission matrix method. To achieve optimum performance, the Chebyshev window function was used to modify the reflectivity distributions of reflectors. The SAW parameters for weighted reflectors with various electrode thicknesses and different metallization ratios are retrieved using the FEM. The transmission matrix method was then employed to calculate the scattering parameters of weighted reflectors and two-track SAW filters. Simulation results show a two-track SAW filter with low insertion loss, good shape factor, good sidelobe suppression, small group delay, and flat passband can be tailored and applicable to the code division multiple access (CDMA) system.

Design of Double Mode SAW Filters Using IDT/(100) ZnO/(111) Diamond Structure

Propagation characteristics of surface acoustic waves (SAWs) in interdigital transducers (IDT)/(100) ZnO/diamond structures are investigated in this study using the finite element method. The effects of electrodes on phase velocity, coupling coefficient, and reflectivity of SAWs in the layered structures are illustrated. The extracted coupling-of-mode parameters are then applied to calculate frequency responses of double mode SAW filters using the transmission matrix method. Simulation results show a tailored filter applicable for wideband code division multiple access systems can be achieved.

Design of IF two-track filters using IDT/(100) AlN/diamond structure

Propagation characteristics of surface acoustic waves (SAWs) in IDT/(100) AlN/diamond structures are analyzed in this study using the finite element method (FEM). The extracted coupling-of-mode (COM) parameters are employed to calculate the frequency responses of two-track SAW filters using the transmission matrix method. To enhance the sideband suppression, Chebyshev function is adopted to modify the reflectivity distributions of reflectors, which can be realized using width-modulated reflectors. The copper electrode is used to retain a sufficiently high reflectivity. Simulation results show that a two-track SAW filter applicable for the CDMA system can be tailored using IDT/(100) AlN/diamond structures.

Surface acoustic wave reflection characteristics of electrodes in ZnO/diamond Structures

Zinc oxide (ZnO) films were combined with diamond to be a composite surface acoustic wave (SAW) substrate showing high velocity and high coupling coefficient. In this study, Rayleigh SAW reflection characteristics of Cu or Al electrodes in (100) or (002) ZnO films on (111) diamond structures were analyzed using the finite element method (FEM). The resonance and anti-resonance frequencies obtained using the FEM are used to compute the effective phase velocity, coupling coefficient, and reflectivity of SAWs in IDT/ZnO/diamond structures with optimized films thickness-to-wavelength ratio and different electrode thickness-to-wavelength ratios. The extracted coupling-of-mode (COM) parameters are substituted into the transmission matrix method for the design of the dual mode SAW (DMS) filter for wideband code division multiple access (WCDMA) applications. With the optimized films thickness ratio (hF/λ = 0.42) and Cu electrode thickness ratio (hE/λ) of 0.025, Sezawa mode in the IDT/(100) ZnO/(111) diamond structure possesses the phase velocity of 5209 m/s, coupling coefficient of 3.33%, and reflectivity of 0.15. The tailored DMS filter using these COM parameters yields a RF filter operating at 2140 MHz with 3 dB bandwidth of 60 MHz, insertion loss of 1.36 dB, shape factor of 1.27, and sideband suppression of 39.7 dB.