Sean Wu

The structure and properties of zinc titanate doped with strontium

Abstract Doped and undoped zinc titanate powders were prepared by a conventional solid state reaction technique using metal oxides. The characteristics of zinc titanate samples were found to depend on the heating conditions and the amounts of additions. It is shown that they are semiconductors, and the formation of SrTiO3, α-Zn2TiO4, rutile phase, morphology roughness and open porosity increase with increasing the amounts of doped Sr. The electrical resistivities of doped and undoped zinc titanate reveal a transition from semiconductor behavior to metal-like behavior as the temperature increased. All samples represent the V-type resistivity–temperature characteristic and possess the typical PTCR characteristics above room temperature.

Rayleigh surface acoustic wave modes of interdigital transducer/(100) AlN/(111) diamond

In this research, Rayleigh surface acoustic wave (SAW) modes of interdigital transducer (IDT)/(100) AlN/(111) diamond were theoretically analyzed and exhibited some excellent acoustic properties. Those Rayleigh SAW modes have smaller film thickness ratios (h/λ), higher phase velocities, and larger electromechanical coupling coefficients (K2) than the ones of IDT/(002) AlN/(111) diamond. Especially for mode 1, the phase velocity is 10 474 m/s, the K2 is 2.31%, and the film thickness ratio (h/λ) is 0.3. The research results exhibit that IDT/(100) AlN/(111) diamond has some excellent properties and provides a predictable and theoretical basis for further application in high velocity SAW devices.

Rayleigh surface acoustic wave modes of (100) ZnO films on (111) diamond

(100) zinc oxide (ZnO) films were combined with (111) diamond to be a composite high velocity surface acoustic wave (SAW) substrate. Rayleigh SAW modes of (100) ZnO films on (111) diamond were theoretically analyzed. Those Rayleigh SAW modes have smaller films thickness ratios (h/λ), higher phase velocities, and larger electromechanical coupling coefficients (K2) than the ones of (002) ZnO films on (111) diamond. The research results provide a predictable and theoretical basis for further application on the high velocity SAW devices.

Bulk acoustic wave analysis of crystalline plane oriented ZnO films

Bulk acoustic wave (BAW) properties of piezoelectric layer are very important design parameters for film bulk acoustic wave resonator devices. In this research, BAW properties of all crystalline plane oriented sputtered and epitaxial ZnO films were analyzed theoretically. The (002), (004), and (006) oriented ZnO films provided a pure longitudinal mode. The (100), (110), (200), (210), (300), and (220) oriented ZnO films provided a pure fast shear mode. The (101), (102), (103), (112), (201), (202), (104), (203), (211), (114), (212), (105), (204), (213), (302), (205), (106), and (214) oriented ZnO films provided a quasilongitudinal mode and a quasishear mode. Those bulk acoustic wave properties can be used for further device design and application.

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.

Bulk Acoustic Wave Analysis of Crystalline-Plane-Oriented Aluminum Nitride Films

Bulk acoustic wave analysis of all crystalline-plane-oriented AlN films were studied in this research. Different crystalline-plane-oriented AlN films will form different vibration modes and acoustic properties. (002)-, (004)-, and (006)-oriented AlN films provided a pure longitudinal mode. (100)-, (110)-, (200)-, (210)-, and (300)-oriented AlN films provided a pure fast shear mode. (101)-, (102)-, (103)-, (112)-, (201)-, (202)-, (104)-, (203)-, (211)-, (114)-, (212)-, (105)-, (204)-, (213)-, (302)-, (205)-, (106)-, and (214)-oriented AlN films provided a quasi-longitudinal mode and a quasi-shear mode. These bulk acoustic wave properties can be used for further device design and application.

High velocity shear horizontal surface acoustic wave modes of interdigital transducer/(100) AlN/(111) diamond

In this research, shear horizontal (SH) surface acoustic wave (SAW) modes of interdigital transducer (IDT)/(100) AlN/(111) diamond propagated along the y-axis were theoretically analyzed and they exhibited excellent SH SAW properties. This is special for mode 0 where the K2 curve shows a maximum value (1.27%) at h/λ=0.28 and the velocity is 7496 m/s. The research results provide a predictable and theoretical basis for further application on high velocity SH SAW devices.

A Novel Compact Dual-Mode Filter Using Cross-Slotted Patch Resonator for Dual-Band Applications

A novel dual-mode BPF using cross-slotted patch resonator (CSPR) combined with a square etched slot to have dual-band performances is proposed and developed for hybrid and monolithic microwave and millimeter-wave integrated-circuit. Pair of unequal crossed slot is embedded in the center of lambda/4 patch resonator to generate a passband. When the widths of the crossed slots are different, the slots are as the perturbation element to generate two transmission zeros. Meanwhile, a square slot is introduced and tilted at the angle of 45deg within the center of the CSPR to tune the second resonant frequency over a wide frequency range for application in 2.4/5.2 GHz response. The measured result is in good agreement with the full-wave simulation result.

Characterization of AlN Films on Y-128° LiNbO3 by Surface Acoustic Wave Measurement

Y-128° LiNbO3 is used extensively for the development of surface acoustic wave (SAW) devices. AlN thin films are an attractive material that have some excellent characteristics, such as high surface acoustic wave (SAW) velocity, piezoelectricity, high-temperature stability, and stable chemical properties. In this research, AlN films were sputtered on Y-128° LiNbO3 to yield a new piezoelectric substrate for SAW devices. The X-ray diffraction (XRD) method and SAW measurement were used to evaluate the material and acoustic properties of this structure. The experimental results exhibited that highly c-axis-oriented AlN films were prepared on Y-128° LiNbO3. AlN films on Y-128° LiNbO3 can effectively enhance the SAW velocity and improve the poor temperature stability, but reduce the electromechanical coupling coefficient (k2) values. As the ratio (film-thickness/acoustic-wavelength) increased, the SAW velocities and the temperature coefficient of frequency (TCF) all increased, but the electromechanical coupling coefficient (k2) values decreased.

Multiple Acoustical Matching Layer Design of Ultrasonic Transducer for Medical Application

Ultrasonic diagnostic equipment is widely used due to its merit of being a noninvasive technique as well as because it provides a clear real-time display of body tissue. Our focus is on the design of low-loss (high transmitting power) and wide-band transducers for ultrasonic diagnosis. The approach we have used consists of impedance matching the front face of the piezoelectric transducer to the propagating medium with a quarter wavelength impedance matching layer and inserting an unmatching quarter wavelength acoustical layer between the rear face and backing material. By tuning the acoustical impedance of the matching layer, transducers with wide-band characteristics and high transmitting power can be obtained. For the backing at the rear surface, a soft backing demonstrating a better impedance matching result which can improve the bandwidth, but exhibiting a longer duration impulse response should be used. A heavy backing would degrade the wide-band phenomena, but show a shorter time duration (<0.5 µS) for image application. To obtain the optimal solution to a specific design formulation, PSPICE (Personal Simulation Program with Integrated Circuit Emphasis) programming techniques can be applied. The PSPICE code of the Mason model is implemented to precisely predict the performance of the matched transducers such as impedance, insertion loss, bandwidth and duration of the impulse response. Good agreement between the simulation results and experimental results has been achieved.