Mu-Shiang Wu

Growth of ZnO films on GaAs substrates with a SiO2 buffer layer by RF planar magnetron sputtering for surface acoustic wave applications

Abstract ZnO films were grown on GaAs substrates with or without SiO 2 buffer layers by RF planar magnetron sputtering. The as-deposited ZnO films were characterized, using X-ray diffraction (XRD) and X-ray rocking curve, scanning electron microscopy (SEM) and reflection high-energy electron diffraction (RHEED). The SiO 2 buffer layer is beneficial to the promotion of the ZnO film quality. The refractive indices of ZnO films obtained from m-line spectroscopy were 1.990 ± 0.002 and 2.004 ± 0.002, and are close to those of the ZnO single crystal. Surface acoustic wave (SAW) properties were also measured for SAW propagating along the [011] direction on (100) GaAs substrate.

Growth of ZnO thin films on interdigital transducer/Corning 7059 glass substrates by two-step fabrication methods for surface acoustic wave applications

ZnO films were grown on interdigital transducer (IDT)/Corning 7059 glass substrates by RF planar magnetron sputtering using two-step fabrication methods for surface acoustic wave (SAW) applications. The crystalline structure of the as-deposited ZnO films was characterized by x-ray diffraction (XRD) and x-ray rocking curve analysis. The SAW properties, including coupling coefficient and insertion loss, were evaluated and compared with the theoretical results. ZnO films deposited by the two-step fabrication method exhibited a lower insertion loss and a closer agreement between the experimental coupling coefficients and the corresponding theoretical values in comparison with films deposited by the one-step fabrication method. The results could be useful in the design of high-coupling low-loss SAW devices.

Theoretical investigation of the SAW properties of ferroelectric film composite structures

The characteristics of surface acoustic waves (SAW) propagating on a three-layered structure consisting of a perovskite-type ferroelectric film, a buffer layer and a semiconductor substrate have been studied theoretically. Large coupling coefficients (K(2)) can be obtained when the interdigital transducer (IDT) is on top of the perovskite-type ferroelectric film, with (type 4) and without (type 3) the floating-plane electrode at the perovskite-type ferroelectric film-buffer layer interface. In the above cases, the peak values of K (2) Of the Pb(Zr,Ti)O(3) (PZT) films (3.2%-3.8%) are higher than those of the BaTiO(3) (BT) and PbTiO(3) (PT) films. In the IDT configuration of type 4, there exists a minor peak of the coupling coefficients for the PZT and BT films, but not for the PT films when the normalized thickness (hK) of the perovskite-type ferroelectric film is about 0.3. The minor peak values of the coupling coefficients (0.62%-0.93%) for different layered structures (PZT/STO/Si, PZT/MgO/Si, and PZT/MgO/GaAs) all decrease when we increase hK value from 0 to 0.25. The results could be useful in the integration of ferroelectric devices, semiconductor devices, and SAW devices on the same substrate.

Variational analysis of single-mode graded-core W-fibers

A new trial function is proposed to obtain the propagation constant, the normalized group delay, and the modal dispersion parameter of single-mode graded-core W-type fibers. This function uses only simple elementary functions to approximate the fundamental modal fields. In many cases of study, we show that the present trial function gives a significant improvement over the existing trial functions and is very useful in the analysis of fibers and related devices.

Extended Gaussian approximation for single-mode graded-index fibers

A new trial function which extends the generalized Gaussian method for the study of weakly guiding single-mode fibers is presented. This function uses only simple elementary functions to approximate the fundamental modal fields. In many cases of study, we show that the present trial function gives a significant improvement over the existing trial functions, and it is very useful in the analysis of fibers and related devices. >

The effect of an SiO/sub 2/ buffer layer on the SAW properties of ZnO/SiO/sub 2//GaAs structure

The effect of an SiO/sub 2/ buffer layer on the surface acoustic wave (SAW) properties of ZnO/SiO/sub 2//GaAs structure is examined. Both theoretical and experimental results show that the coupling coefficient is increased appreciably by providing an SiO/sub 2/ film between the ZnO film and the GaAs substrate. Adding an SiO/sub 2/ film is also beneficial to the promotion of quality of ZnO thin film. The results could be useful for the further development of monolithic SAW devices.<<ETX>>

Growth of c-Axis-Oriented LiNbO3 Films on ZnO/SiO2/Si Substrate by Pulsed Laser Deposition for Surface Acoustic Wave Applications

Highly c-axis-oriented LiNbO3(006) thin films were successfully grown on SiO2/Si substrates with a ZnO buffer layer by XeCl excimer pulsed laser deposition (PLD). The as-deposited films were characterized by X-ray diffraction, scanning electron microscopy, and atomic force microscopy to analyze their crystalline structure and surface morphology. The results show that the highly c-axis-oriented LiNbO3 thin films of 2.5 µm thickness were successfully grown on SiO2/Si substrates with a ZnO buffer layer by PLD. The full width at half maximum intensity of the LiNbO3(006) peak of the sample fabricated under the optimum deposition conditions is only 0.18°. The center frequency of the LiNbO3/ZnO/SiO2/Si substrate with line width of 4 µm is 188 MHz, and the phase velocity is 3010 m/s, which is slightly lower than that of the 36° Y–X LiNbO3 substrate.

Effect of a Buffer Layer on the Surface Acoustic Wave Characteristics of Pb(Zr, Ti)O3 Film/Buffer Layer/Semiconductor Substrate Structures.

The effect of a buffer layer on the surface acoustic wave properties of Pb(Zr, Ti)O3 (PZT) film/buffer layer/ semiconductor substrate structures was examined theoretically. Large coupling coefficients (2.8–3.4%) can be obtained when the interdigital transducer (IDT) is on top of the PZT film, with (type 4) and without (type 3) the floating-plane electrode at the PZT film-buffer layer interface. In the type 4 IDT configuration, there exists a minor peak of the coupling coefficient when the hK value of the PZT film is about 0.3. The minor peak values of the coupling coefficient (0.62–0.93%) decrease when we increase the thickness of the buffer layer from 0 to 0.25. These results could be useful for the further development of ferroelectric devices, semiconductor devices and SAW devices on the same substrate.

Growth of C-Axis Oriented LiNbO3 Film on Sapphire by Pulsed Laser Deposition for Surface Acoustic Wave Applications

Highly c-axis oriented LiNbO3(006) thin films have been successfully grown on sapphire substrates by XeCl excimer pulsed laser deposition (PLD). The as-deposited films were characterized by X-ray diffraction, scanning electron microscope and atomic force microscopy to analyze their crystalline structure and surface morphology. The results show that highly c-axis oriented LiNbO3 thin films of 1 μm thickness were successfully grown on sapphire substrates by PLD. The full width at half maximum intensity of LiNbO3(006) peak of the sample fabricated under the optimum deposition parameters is only 0.15°. The center frequency of the LiNbO3/sapphire substrate with electrode width of 10 μm is 137 MHz, and phase velocities is 5480 m/s, which is much larger than that of the 36° Y-X LiNbO3 substrate (3632 m/s).

Preparation of BaTiO3 Films on Si Substrate with MgO Buffer Layer by RF Magnetron Sputtering

Highly (002)- or (200)-oriented BaTiO3 thin films were successfully grown on a Si substrate with a MgO buffer layer by RF magnetron sputtering. The deposition parameters need to be stringently controlled in order to grow BaTiO3 films with good crystallinity. The sputtering parameters such as substrate temperature, RF power, gas flow ratio, and deposition pressure were varied to obtain the optimum deposition conditions for the BaTiO3 films. The as-deposited films were characterized by X-ray diffraction analysis and atomic force microscopy to analyze their crystalline structure and surface morphology. The full width at half maximum intensity of the BaTiO3 (002) or (200) peak of the sample fabricated under the optimum deposition parameters was only 0.28°. The surface roughness of the BaTiO3 films was about 3.2 nm. The results could be useful in the integration of ferroelectric and semiconductor devices on the same Si substrate.