In this paper, we investigate the frequency band-gap features of micromachined air/silicon phononic band structures using layered slanted finger interdigital transducers (SFIT). In order to achieve the applications of phononic crystals on the microelectromechanical system related components, the frequency band-gap widths of surface waves are studied both theoretically and experimentally in micrometer scale phononic crystals. For further integration with the complementary metal-oxide semiconductor processing techniques, silicon is chosen as the base material of the two-dimensional phononic crystals in this study. To cover the frequency band-gap width of the phononic crystal, the wideband SFIT- and the SFIT∕ZnO∕Si-layered structures in the measurement are analyzed and discussed. For layered structures, the dispersive relation is calculated by the effective permittivity approach, and the frequency response of the layered SFIT is then simulated by the coupling-of-modes model. The frequency band-gap width and ...

Frequency band-gap measurement of two-dimensional air/silicon phononic crystals using layered slanted finger interdigital transducers

Surface-Wave Devices for Signal Processing

Ag-doped ZnO films were prepared by direct current reactive magnetron sputtering using a zinc target with various Ag-chips attached. The influence of Ag doping on the microstructure, photoluminescence and Raman scattering of ZnO films were systematically investigated. The results indicate that ZnO films doped with Ag can still retain a wurtzite structure, although the c-axis as preferred orientation is decreased by Ag doping. The near band edge emission of ZnO film can be enhanced by Ag doping with a concentration of 1.6–2.8 at.% and quench with a further increase in the Ag concentration. A local vibrational mode at 411 cm−1 induced by Ag dopant can be observed in the Raman spectra of the Ag-doped ZnO films, which might be used as an indication of Ag incorporation into the ZnO lattice.

http://iopscience.iop.org/article/10.1088/0022-3727/39/23/014/pdf

Luminescence and Raman scattering properties of Ag-doped ZnO films

Highly c-axis oriented heteroepitaxial aluminum nitride (AlN) films were grown on epitaxial cubic silicon carbide (3C–SiC) layers on Si (100) substrates using alternating current reactive magnetron sputtering at temperatures between approximately 300–450 °C. The AlN films were characterized by x-ray diffraction, scanning electron microscope, and transmission electron microscopy. A two-port surface acoustic wave device was fabricated on the AlN/3C–SiC/Si composite structure, and an expected Rayleigh mode exhibited a high acoustic velocity of 5200 m/s. The results demonstrate the potential of utilizing AlN films on epitaxial 3C–SiC layers to create piezoelectric resonant devices.

AlN thin films grown on epitaxial 3C–SiC (100) for piezoelectric resonant devices

This paper provides a detailed study on surface acoustic wave (SAW) induced acoustic streaming and pumping, focusing on the effects of the wave mode and surface modification. SAW devices with wavelengths of 32 and 64 µm were fabricated on 128° Y-cut lithium niobate substrates with aluminium interdigitated transducers. A higher order harmonic mode wave appears in addition to the fundamental Rayleigh wave for samples with metallization ratios less than 0.6. Both waves have demonstrated the ability to induce acoustic streaming and to pump liquid. A high streaming velocity, and hence a high mixing efficiency and a higher acoustic force, can be obtained using the fundamental Rayleigh wave as the high harmonic waves have large propagation losses. A linear relationship between the streaming velocity and RF signal voltage has been obtained, and effective mixing can be achieved. An acoustic wave has also been utilized to manipulate and pump droplets with sizes up to 5 µl, and a moving speed of ~1.4 cm s−1 has been obtained on an octadecyltrichlorosilane-treated SAW device using a signal voltage of 40 V.

https://iopscience.iop.org/article/10.1088/0960-1317/19/3/035016/pdf

Surface acoustic wave induced streaming and pumping in 128° Y-cut LiNbO3 for microfluidic applications

In this paper, we propose a modified coupling of modes (COM) approach, which can be used in the practical design of a layered surface acoustic wave (SAW) filter. Unlike the half-space SAW filter, frequency dependences of the COM parameters are included by using the effective permittivity approach of surface waves. Owing to the introduction of the COM model, the effects of propagation loss, electrode reflections, electrical transduction, acoustic reception, thin film loss and the distributed finger capacitance can be taken into accounts in the frequency analysis of the layered SAW filter. The frequency response of a two-port 440 MHz IDT/ZnO/R-plane sapphire layered SAW filter is analysed and compared with the existing experimental results. Results have shown good agreement between the calculated and experimental frequency responses.

https://iopscience.iop.org/article/10.1088/0022-3727/37/1/020/pdf

Tsung-Tai Chou

Papers

Analysis of the frequency response of a dispersive IDT/ZnO/sapphire SAW filter using effective permittivity and the coupling of modes model