Walter Water

Physical and structural properties of ZnO sputtered films

Abstract In this paper, poly-crystal zinc oxide (ZnO) films with c -axis (002) orientation have been successfully grown on the silicon substrate by r.f. magnetron sputtering technique. The deposited films were characterized as a function of deposition temperature, argon–oxygen gas flow ratio, and r.f. power. Crystalline structures, stress and roughness characteristics of the films were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM) measurement. By controlling deposition parameters and annealing temperature, we could improve intrinsic stress and surface roughness of ZnO film. Preferred deposition condition was found to show good film quality for SAW device applications.

Li2CO3-doped ZnO films prepared by RF magnetron sputtering technique for acoustic device application

Abstract It is necessary for zinc oxide film to have high resistivity for piezoelectric applications. The ZnO films have been deposited by RF sputtering deposition system using Li-doped ZnO ceramics as the target and high oxygen ratio (100% oxygen) for high film resistivity. The maximum resistivity of ZnO film measured was 10 8 Ω cm in our experiments, and stronger intensity of c -axis orientation was grown at 50% oxygen ratio. Postdeposition annealing ZnO films in vacuum circumstance were found to relieve stress, avoid the electrode oxidation and increase resistivity one order. The preferred deposition conditions and annealing condition were obtained for piezoelectric application. Then, an over-mode resonator was made and showed a large return loss of 42 dB at the center frequency of about 2 GHz after annealing for 1 h in vacuum circumstance at 400 °C.

Properties of (Na, K)NbO 3 and (Li, Na, K)NbO 3 Ceramic Mixed Systems

In this paper, samples of (Na x K 1 m x )NbO 3 where x = 0.1 m 1 and Li y (Na 0.5 K 0.5 ) 1 m y NbO 3 where y = 0.01 m 0.05 have been prepared by conventional ceramic technique. The prepared Sodium Potassium Niobate (Na x K 1 m x NbO 3 ) and Lithium Sodium Potassium Niobate (Li y (Na 0.5 K 0.5 ) 1 m y NbO 3 ) samples are characterized using X-ray diffraction method and grain size have been calculated using SEM photographs; the phase transitions have been observed from DSC experiments. Finally, the piezoelectric and dielectric characteristics of these ceramic systems are also investigated. Lithium dopants in (Na, K)NbO 3 ceramics play an important role on the ferroelectric curie temperature, dielectric constant, grain size as well as the planar mechanical coupling coefficient ( k p ) value.

Piezoelectric and dielectric characteristics of Lithium Potassium Niobate ceramic system

In this paper, xLi2O-yK2O-(1-x-y)Nb2O5, x = 0 − 1 and y = 0 − 1, system was partially studied using Lithium and Potassium Niobate as sintering materials in order to reduce the sintering temperature. The prepared lithium potassium niobate ceramics are characterized using X-ray diffraction method and grain size have been calculated using SEM photographs; the phase transitions have been observed from DSC experiment. Finally, the piezoelectric and dielectric characteristics of these mixed ceramic systems are also investigated. The planar mode electromechanical coupling coefficient kp reaches 33.5% and two phase transitions (orthorhombic—tetragonal; tetragonal—cubic) have been observed.

An investigation of the dependence of ZnO film on the sensitivity of Love mode sensor in ZnO/quartz structure.

Love mode acoustic devices are very promising as biosensors in liquid environments because of their high sensitivity. An experimental study of Love mode sensors based on ZnO/90 degrees rotated ST-cut quartz structure with different sputtering conditions to deposit ZnO films is presented. In order to achieve sensor with higher sensitivity, the effects of sputtering substrate temperatures to deposit ZnO films on the sensitivity of viscosity and conductivity were investigated. Phase velocity, sensitivity and temperature coefficient of frequency (TCF) of Love wave devices have been studied. The Love wave sensor has higher sensitivity as sputtering ZnO films on the unheated substrate than that of on the heated substrate. The maximum sensitivity up to -18.77 x 10(-8) m(2) s kg(-1) of ZnO film with thickness of 1.8 microm for a wavelength of 40 microm is much bigger than SiO(2)/quartz structure. In this research, we report ZnO/90 degrees rotated ST-cut quartz structure of Love wave sensors with high sensitivity of viscosity and conductivity in liquid circumstance and TCF of quartz is compensated by ZnO film.

TiO2-Based Thin Film Transistors with Amorphous and Anatase Channel Layer

In this study, TiO 2 films were deposited on FTO (fluorine-doped tin oxide)/glass substrate by radio frequency magnetron sputtering. Amorphous and anatase structure of TiO 2 were achieved without and with thermal process, respectively. Further, TiO 2 -based thin-film transistors (TFTs) with different structure were fabricated. After the electrical characteristics measurement, it was found that the amorphous TiO 2 TFTs can be operated in the enhancement mode with a threshold voltage of 3.8 V. It was also found that the field-effect mobility and on/off current of the TiO 2 TFT with amorphous channel layer were 0.087 cm 2 V ―1 s ―1 and 10 3 , respectively. On the other hand, the TiO 2 TFTs with anatase structure were also tested. It was found that the anatase TiO 2 TFTs have the lower threshold voltage of 2.3 V than amorphous one. Besides, it was also found that the field effect mobility and on/off current ratio of the anatase TiO 2 TFTs were both increased to 10.7 cm 2 V ―1 s ―1 and 10 4 , respectively. In other words, the performance of TiO 2 TFTs was related to the structure of the channel layer.

Deposition of preferred-orientation ZnO films on the ceramic substrates and its application for surface acoustic wave filters

Polycrystal ZnO films with c-axis (002) orientation have been successfully grown on the lead-based ceramic substrates by rf magnetron sputtering technique. The deposited films were characterized as a function argon-oxygen gas flow ratio and rf power. Crystalline structures of the films were investigated by x-ray diffraction, scanning electron microscopy, and atomic force microscopy. Highly oriented films with c-axis normal to the substrates can be obtained by depositing under a total pressure of 10 mTorr containing 50% argon and 50% oxygen and rf power of 70 W. The phase velocity, electromechanical coupling coefficient, and temperature coefficient of frequency of surface acoustic wave (SAW) device with ZnO/IDT/PT (IDT: interdigital transducer; PT:PbTiO3 ceramics) structure were investigated. It shows that the preferred oriented ZnO film is beneficial for improving the electromechanical coupling coefficient of SAW device.

Surface plasma resonant effect of gold nanoparticles on the photoelectrodes of dye-sensitized solar cells

In this study, we prepared different shapes of gold nanoparticles by seed-mediated growth method and applied them on the photoelectrodes of dye-sensitized solar cells (DSSCs) to study the surface plasma resonant (SPR) effect of gold nanoparticles on the photoelectrodes of dye-sensitized solar cells. The analyses of field emission scanning electron microscopy show that the average diameter of the spherical gold nanoparticles is 45 nm, the average length and width of the short gold nanorods were 55 and 22 nm, respectively, and the average length and width of the long gold nanorods were 55 and 14 nm, respectively. The aspect ratio of the short and long gold nanorods was about 2.5 and 4, respectively. The results of ultraviolet–visible absorption spectra show that the absorption wavelength is about 540 nm for spherical gold nanoparticles, and the absorption of the gold nanorods reveals two peaks. One is about 510 to 520 nm, and the other is about 670 and 710 nm for the short and long gold nanorods, respectively. The best conversion efficiency of the dye-sensitized solar cells with spherical gold nanoparticles and short and long gold nanorods added in is 6.77%, 7.08%, and 7.29%, respectively, and is higher than that of the cells without gold nanoparticles, which is 6.21%. This result indicates that the effect of gold nanoparticles on the photoelectrodes can increase the conductivity and reduce the recombination of charges in the photoelectrodes, resulting in the increase of conversion efficiency for DSSCs. In addition, the long gold nanorods have stronger SPR effect than the spherical gold nanoparticles and short gold nanorods at long wavelength. This may be the reason for the higher conversion efficiency of DSSCs with long gold nanorods than those of the cells with spherical gold nanoparticles and short gold nanorods.

Visible-Blind Photodetectors With Mg-Doped ZnO Nanorods

In this letter, Mg-doped ZnO nanorods were fabricated successfully on a glass substrate at 80°C by hydrothermal method. The visible-blind photodetectors show good stability properties in ultraviolet (UV) illumination. The resulting Mg-doped ZnO nanorods have excellent potential for application in a UV photodetector because of Mg-doped ZnO nanorods UV photodetector has a high UV-to-visible ratio, fast rise/fall time. The dynamic response of the Mg-doped ZnO nanorods photodetector with Au electrodes was stable and reproducible with an on/off current contrast ratio of ~ 5.2×103.

Characteristics of Flexible Thin-Film Transistors With ZnO Channels

In this paper, we demonstrate the fabrication of ZnO-based thin-film transistors (TFTs) on flexible substrates (polyethylene terephthalate) through radio-frequency sputtering and low-temperature procedure. The device structure belongs to bottom-gate type TFTs where ZnO and HfO2 are used as channel and gate dielectric layer, respectively. XRD results show that the ZnO channel layers are hexagonal wurtzite structure with (002) orientation. The properties of the fabricated devices are also characterized within several environmental and physics conditions. It can be found that the flexible TFT device is with a low operating voltage and high current ON/OFF ratio; the gate leakage current and transparency are found to be ~12 nA and 75%, respectively. The gate leakage current (IG), drain-source current (IDS), ON/OFF current ratio (ION/OFF), threshold voltage (Vth), and field-effect mobility (μFE) are measured under different bending modes.