Papers by Author: Chien Chuan Cheng

Abstract: We had investigated the electromechanical coupling coefficient (K²) of surface acoustic wave (SAW) on proton-exchanged (PE) and annealed PE (APE) z-cut LiNbO₃ waveguides using octanoic acid. The penetration depth of hydrogen assumed to be equal to the waveguide depth (d) was measured by secondary-ion mass spectrometry (SIMS). The frequency response of SAW was measured with a network analyzer. The annealing process was carried out in a horizontal furnace kept at 400°C for 2 h under a dry O₂ gas flow. The change of K² in PE and APE samples fabricated under different conditions was dependent on kd, where k was the wavenumber. The experimental results showed that the variation of K² in PE samples was significantly decreased with the increase of kd. The reduction of K² may be due to the reduced piezoelectric coefficients in the PE layer. On the other hand, the variation of K² in APE samples also exhibited the decreased tendency after annealing. It indicated that the annealing process could not restore the reduction of K² caused by the PE process.

Abstract: This study provides a simple and low cost method to deposit TiO2 nanoporous thin films onto the titanium mesh substrate. The flexible titanium mesh is adopted as electrodes where a novel structure of dye-sensitized solar cell (DSSC) is fabricated. The titanium mesh owns many advantages such as low resistance, cheap and high temperature tolerance. The photoanode is fabricated while the Ti mesh immersed into the alcohol solution of nanopowder of TiO2 (P25). For a better adhesion, several treatments against the titanium mesh are carried out. The photovoltaic parameters of various DSSC are discussed through the observations of TiO2 nanoporous thin films. The alcohol solution of N719 dye is used to sensitized the photovoltaic and the electrolyte is a mixture of 0.5 M LiI, 0.05 M I2 and 0.5 M 4-tert-butyl-pyridine in 3-methoxypropionitrile. With a Xenon illuminating, a flexible cell with Jsc=2.9 mA, Voc=0.5 V and F.F =0.68, η=1.02 % is obtained.

Abstract: This paper describes the design and fabrication of dual-mode film bulk acoustic resonator (TFBAR) devices to construct wafer level dual-band T-ladder type filters. The T-ladder type filters is selected in this study for its high quality and simple fabrication processes. The c-axis-tilted ZnO thin films to obtain dual-mode TFBAR devices have been investigated. The characteristics of dual-mode TFBAR devices appeared by off-axis deposition of ZnO thin films with the RF magnetron sputtering. The top and bottom electrodes consisted of titanium (Ti) and platinum (Pt) layers are deposited by dual-gun DC sputtering system. The pass-band width of filters is controlled by the mass loading on the dual-mode. The frequency response is measured using an HP8720 network analyzer and a CASCADE probe station.

Abstract: This paper reports a dual-mode film bulk acoustic resonator (FBAR) device combined with Au/Cr layer to construct a liquid sensor. In order to obtain a liquid sensor with high sensitivity, the dual-mode FBAR with piezoelectric layer of ZnO thin film has been investigated. The dual-mode characteristics of FBAR appeared by off-axis deposition of ZnO thin film with the RF magnetron sputtering. The top and bottom electrodes consisted of a titanium (Ti) and a platinum (Pt) layers were deposited by dual-gun DC sputtering system. Owing to the chemical stability, the Pt layer is not only a perfect bottom electrode but also an etching stop layer. The gold layer (Au) is adopted for the formation of sensory area. In order to improve the adhesion between the Au layer and the Pt layer, a chromium (Cr) layer was deposited onto the backside cavity of the FBAR device before the Au layer was deposited by a DC sputter. The Au/Cr layer is used as the binding layer with analytes of DI water because of its hydrophile. The frequency response is measured using an HP8720 network analyzer and a CASCADE probe station. The resonant frequencies of longitude and shear modes in air appear at 2262.5 MHz and 1012.5MHz, whereas the resonant frequencies of longitude and shear modes in DI water are 2062.5 MHz and 955MHz, respectively.

Abstract: Electrochromic properties of transition metal oxides had much attention in recent years. The electrochromic thin films can be assembly as electrochromic devices (ECDs) and then used for applications in devices such as mirrors, panels and smart windows. A kind of complementary ECD is popular in resent years. Therefore, a specific investigation on nickel oxide (NiO) electrochromic properties is completed in this study. The crystalline structure of the NiO films was analyzed using XRD (PANalytical X’Pert PRO) with Cu-Kα radiation. The atmosphere of oxygen concentration increasing has changed the NiO films crystalline from (200) to (111). The thicknesses and surface microstructures of the NiO films were investigated using a scanning electron microscope (SEM, Philips/FEI XL40 FEG). It is observed that films are relatively smooth deposited without oxygen. The characterization of the electrochromic properties was carried out in a two-electrode cell with an electrochemical analyzer (CHI 611B). The NiOx changes the transmittance of NiO films in the wavelength range of 300-1500 nm and the color of the film changes from transparent to brown. The nano-crack exhibits in the NiO film did enhance the electrochromic properties.

Abstract: In this study, an SMR-based filter was fabricated by dc/rf magnetron sputtering and photolithography, and a thermal annealing treatment was adopted to improve the frequency response. The SMR-based filter is composed of a ZnO piezoelectric thin film onto SiO2/W Bragg reflector. ZnO thin films were prepared by two-step sputtering with various deposition temperatures to obtain good piezoelectric properties. ZnO layers deposited at the temperature of 200 °C exhibit a highly c-axis preferred orientation, good crystalline characteristics and low surface roughness. The filter is thermal treated by a rapid thermal annealing (RTA) technique. The thermal annealing treatment has improved the film properties of ZnO layers, resulting in a higher c-axis preferred orientation and a lower surface roughness of ZnO films than those of as-deposited ZnO films. The atomic ratio of Zn to O in ZnO film approaches one at the annealing temperature of 400 °C, which results in a comparatively oxidized stoichiometric ZnO film. Finally, the frequency response of the annealed filter is improved, and a lower insertion loss is obtained.

Abstract: Aluminum nitride (AlN) is one of the most popular piezoelectric materials for high frequency resonators, filters and sensors. The piezoelectric property, i.e. electromechanical coupling coefficient, of AlN thin film is highly related to its crystalline orientation. AlN thin films with various c-axis-tilted angles can be fabricated by the RF sputtering technique. The crystallization and grain growth orientations of AlN thin film are examined by XRD, SEM, and TEM, while the bonding condition and nano-mechanical properties are investigated by a raman system and a nano-indentation technique.

Abstract: In this study, ferroelectric thin films of Ba(Zr0.1Ti0.9)O3 were successfully deposited on Pt/Ti/SiO2/Si substrate under the optimal rf magnetron sputtering parameters, and their electrical and ferroelectric characteristics were investigated. The MFMIS structure of Al/Ba(Zr0.1Ti0.9)O3/ Pt/Ti/SiO2/Si was proposed in order to be applied as NDRO FRAM applications. From the experimental results obtained, the dielectric constant and the leakage current density of BZT films were about 200 and 1×10-9A/cm2, respectively, under the electrical field of 1 MV/cm. Besides, the saturation polarization and coercive field of Ba(Zr0.1Ti0.9)O3 films were found to be 4 μC/cm2 and 25 kV/cm, respectively, as the frequency of 103 Hz was applied. The variations of saturation polarization and coercive filed of films under various frequencies ranging form 102 to 106 Hz were also discussed.