ZnO based surface acoustic wave ultraviolet photo sensor

Ultraviolet (UV) sensor based on ZnO thin film surface acoustic wave (SAW) device is reported. ZnO films were grown using an RF magnetron sputtering technique. SAW devices were made using such ZnO films exhibiting a central frequency at ～41.2 MHz. The SAW UV sensor was fabricated by depositing a 70 nm thin photoconducting ZnO overlayer on the fabricated SAW device. The SAW UV sensor was found to exhibit interesting photoresponse behavior to UV illumination, and a downshift in frequency of ～45 kHz, and a change in insertion loss ～1.1 dB were observed under UV illumination intensity of 19 mW/cm². The changes in the frequency of operation and the insertion loss have been attributed to the acoustoelectric interaction between the photogenerated charge carriers and the potential associated with the acoustic waves. Results show the promise of ZnO for the fabrication of low cost wireless SAW UV sensors.     

声表面波无源无线温度传感器产品研究进展

声表面波（SAW）温度传感器可以实现无线无源检测,满足高温、高压、强电磁辐射和强电磁干扰等恶劣环境下正常工作,属于高水平传感器。首先介绍了应用SAW技术的无源无线温度传感器谐振型和延迟线型2种结构的基本工作原理,着重描述了目前国内外高温和低温SAW无源无线温度传感器的产品性能,对各产品进行了比较和分析,提出了SAW温度传感器询问距离的优化方法。询问距离的优化研究对SAW温度传感器在更广泛领域的应用将有深远意义。     

Application of TiO<Subscript>2</Subscript> thin film with nanorods to surface acoustic wave type ultraviolet photo detection

TiO₂ thin films with nanorods grown on 128° Y?cut LiNbO₃ and 90° rotated 42°45′ ST?cut quartz were used to fabricate surface acoustic wave ultraviolet photodetectors. TiO₂ thin film was deposited by radio?frequency magnetron sputtering and TiO₂ nanorods were then synthesized on the thin film via the hydrothermal method. 128° Y?cut LiNbO₃ is a Rayleigh wave substrate with a high electromechanical coupling coefficient, whereas 90° rotated 42°45′ ST?cut quartz is a surface skimming bulk wave substrate with a high wave velocity. The effects of substrate characteristics and TiO₂ nanorod morphology on the ultraviolet sensitivity of the surface acoustic wave photodetectors were investigated. The variations of insertion loss, phase, resistance, and capacitance under ultraviolet illumination were examined. The performance of the TiO₂ thin film with nanorods deposited on 128° Y?cut LiNbO₃ is much greater than that of the film deposited on 90° rotated 42°45′ ST?cut quartz, which can be attributed to the former’s high electromechanical coupling coefficient.     

Acoustic characterization of AlN films using a High Overtone Bulk acoustic wave resonator

Abstract

Using the composite resonator with additional thick AlN film with the FWHM of rocking curve of 2.53° under investigation, the bulk acoustic wave attenuation constant and sound velocity along c-axis were directly measured. The method of High Overtone Bulk acoustic wave Resonator (HBAR) spectroscopy based on frequency, measurements of the positions of the resonator peculiarities of phase and amplitude of electromagnetic wave reflection coefficient from composite resonator structure was applied. The method provides attenuation and velocity measurement in a wide frequency band, using the same sample. For the measurements, standard and modified HBAR spectroscopy based on the analysis of only parallel resonance properties of composite resonator structures were used.     

Modelling of chemical surface acoustic wave sensors and comparative analysis of new sensing materials

Comparative analysis of different, new gas sensing materials in surface acoustic wave chemical sensors is presented. Different gas sensing materials as polyaniline (PANI), Teflon AF 2400, polyisobutylene (PIB), polyepichlorohydrin (PECH) are considered. They are chosen according to the type of gas to be detected and the desired accuracy: Teflon AF 2400 thin film for the detection of CO₂, PANI nanocomposites film that belongs to the group of conductive polymers for the detection of CO, NO₂ and phosgene (COCl₂), and PECH and PIB for the detection of dichloromethane (CH₂Cl₂, DCM). In the analysis, the simple and useful method of the complete analyses of gas chemical sensors is used. The method is based on the electrical equivalent circuit of the surface acoustic wave sensor. The method is very efficient and can be used for the optimal design of CO₂ sensors. The results are compared with those presented in public literature and good agreement is obtained, demonstrating the validity of modelling. Copyright © 2012 John Wiley & Sons, Ltd.     

Effects of rapid thermal annealing in different ambients on structural, electrical, and optical properties of ZnO thin films by sol-gel method

We studied the effects of rapid thermal annealing in different ambients on the structural, electrical and optical properties of the sol-gel derived ZnO thin films. All the films after annealing showed highly degree of (002) oriented in the X-ray diffractometry (XRD) patterns. The effects of annealing ambients on electrical properties of the films were studied. Carrier concentration, resistivity and mobility were found to be distinguished after annealed in different ambients. The sample with the lowest resistivity of 0.095 ??·cm and the largest mobility of 105.1 cm²/v·s was achieved after annealing in vacuum. XPS results indicated that more oxygen vacancies existed on the ZnO surface when annealed in vacuum than that in O₂.     

Effects of O2 rapid thermal annealing on themicrostructural properties and reliability of RF-sputteredTa2O5 films

The microstructural properties and reliability of sputtered Ta₂O₅ films treated by various temperatures of rapid thermal annealing (RTA) in O₂ atmosphere have been systematically investigated. Analytical results revealed that whenever the RTA temperature was >650°C, the noncrystallinity of as-grown Ta₂O₅ film would be effectively improved from an amorphous phase to the β-Ta₂O₅ phase. Leakage current measurement indicated that leakage current decreases with increasing annealing temperature in a low RTA temperature range (⩽650°C) and, contrarily, increases with increasing annealing temperature in a high RTA temperature range (650 to 950°C). The former result was asserted in that reducing pinholes and oxygen vacancies played key factors. However, the latter result arose due to significant Si diffusion into the Ta₂O₅ film, causing a leaky transition layer distributed along the grain boundary to form the leakage path. Finally, the time-dependent dielectric-breakdown experiments revealed that 950°C O₂ RTA treated Ta₂ O₅ film possessed the superior crystallinity, creating less interfacial hole trap states at the junction of Ta₂O₅/Si and exhibiting the best long-term reliability     

Characteristics of Bi4Ti3O12 thin films on ITO/glass and Pt/Si substrates prepared by R.F. sputtering and rapid thermal annealing

Bi₄Ti₃O₁₂ thin films are deposited on ITO/glass and Pt/Ti/Si(100) substrates by R.F. magnetron sputtering at room temperature. The films are then heated by a rapid thermal annealing (RTA) process conducted in oxygen atmosphere at temperatures ranging from 550–700^∘C. X-ray diffraction examination reveals that the crystalinity of the films grown on Pt/Ti/Si is better than that of the films grown on ITO/glass under the same fabrication conditions. SEM observation shows that the films grown on Pt/Ti/Si are denser than those grown on ITO/glass substrates. Interactive diffusion between the Bi₄Ti₃O₁₂ film and the ITO film increases with the increase of annealing temperature. The optical transmittance of the thin film annealed at 650^∘C is found to be almost 100% when the effect of the ITO film is excluded. The relative dielectric constants, leakage currents and polarization characteristics of the two films are compared and discussed.     

Deposition of Europium Oxide on Si and its optical properties depending on thermal annealing conditions

We investigate the influence of the ambient gas during thermal annealing on the photoluminescence (PL) properties of europium compound thin films on Si substrates. The films were deposited by radio-frequency magnetron sputtering and subsequently annealed in N₂ or O₂ ambient gas by rapid thermal annealing (RTA). The results of X-ray diffraction indicate that the resulting europium compound annealed in N₂ ambient have several silicate phases such as EuSiO₃ and Eu₂SiO₄ compared to those annealed in O₂ ambient. The spectral results revealed that a broad luminescence associated with Eu²⁺ ions, with a maximum intensity at 600 nm and a FWHM of 110 nm, was observed from the thin film annealed at 1000 °C in N₂ ambient. However, a series of narrow PL spectra from Eu³⁺ ions were observed from the film annealed in O₂ ambient.     

Effects of Ag nanoparticles decorated on ZnO nanorods under visible light illumination on flexible acetylene gas sensing properties

In this work, piezoelectric and plasmonic effects on a flexible acetylene (C₂H₂) gas sensor based on silver (Ag) nanparticles (NPs)-coated ZnO nanorods (Ag-ZnO) were realized. Using visible light illumination, the sensing properties can be modulated and the power consumption can be reduced significantly. Upon exposure to 1000 ppm C₂H₂ under 8.36 mW cm^?2 light illumination, the power consumption of the sensor noticeably reduced from 3.48 W (in dark) to 1.64 W. A large number of light-induced chemisorbed oxygen ions were generated in the Ag-ZnO forest due to the strong coupling effect between the plasmonic Ag NPs and the ZnO NRs. This resulted in increased surface charge densities, which facilitated the sensor to react with the C₂H₂ molecules at lower operating temperature, hence reduced the power requirement. Moreover, the sensor exhibited reliable detection of C₂H₂ gas within the concentration of 3–1000 ppm including a maximum sensor response of 26.2, response-recovery time of 66/68 s, the excellent mechanical stability at a bending angle up to 90^o, and 10⁴ cycles of repeated deformation processes. These results might facilitate research in developing a low power C₂H₂ gas sensor and will open up new approaches for future light modulated gas sensors.     

Enhancement of the surface and structural properties of ZnO epitaxial films grown on Al2O3 substrates utilizing annealed ZnO buffer layers

ZnO films were grown on Al₂O₃ (1000) substrates without and with ZnO buffer layers by using radio-frequency magnetron sputtering. Atomic force microscopy images showed that the surface roughness of the ZnO films grown on ZnO buffer layers annealed in a vacuum was decreased, indicative of an improvement in the ZnO surfaces. X-ray diffraction patterns showed that the crystallinity of the ZnO thin films was enhanced by using the annealed ZnO buffer layer in comparison with the film grown on without a buffer layer. The improvement of the surface and structural properties of the ZnO films might be attributed to the formation of the Zn-face ZnO buffers due to annealing in a vacuum. These results indicate that the surface and structural properties of ZnO films grown on Al₂O₃ substrates are improved by using ZnO buffer layers annealed in a vacuum.     

基于ICA盲源分离的声表面波无线传感器信号抗干扰方法

针对声表面波传感器无线信号易受环境中同频信号干扰的问题,设计了基于独立分量分析(ICA)盲源分离的抗干扰算法.该算法对传感器和同频干扰的混合信号进行分离,然后基于分离信号波形的衰减和等幅特征对信号进行判别.MATLAB仿真结果表明,算法能够有效分离混合信号并且保留了源信号的时域波形特征和频域信息.将抗干扰算法在基于数字...     

Influence of rapid thermal annealing on pyrochlore/perovskite phase formation in laser ablated Pb(Zr,Ti)O3 thin films

Abstract

Pb(Zr,Ti)O₃ thin films were prepared by ArF excimer laser deposition on silicon and Pt-coated silicon substrates, and then were treated by rapid thermal annealing. The dependence of perovskite/pyrochlore phase formation on annealing conditions was investigated. The results show that the formation of perovskite phase or pyrochlore phase in the films was not only dependent on the heat treatment temperature, but also dependent on the heat treatment time. A wide range operational window of heat treatment time and temperature for obtaining single phase perovskite Pb(Zr,Ti)O₃ thin films was given, and the films were analyzed by Rutherford backscattering spectroscopy to explain this phase transition.     

The annealing effect on properties of ZnO thin film transistors with Ti/Pt source-drain contact

ZnO-based thin film transistors (TFTs) with Ti/Pt contacts were fabricated on SiO₂/Si substrates. The as-deposited ZnO TFT did not work well as a TFT device but the annealed ZnO TFT showed acceptable characteristics with a mobility (μ_sat), threshold voltage (V_th), on/off ratio and subthreshold swing (SS) of 0.8 cm²/V.s, 2.5 V, over 10⁶ and 0.84 V/dec, respectively. Complete oxygen loss was observed in ZnO after annealing at 300°C under a N₂ atmosphere. The annealing process altered the crystallinity, density and composition of the ZnO active layers due to the formation of oxygen vacancies as shallow donors. This process is expected to play an important role in controlling the TFT performance of ZnO. In addition, it is expected to form the basis of the future electronic devices applications, such as transparent displays and active matrix organic lighting emitted displays (AMOLED).     

Fabrication and characterization of co-planar type MEMS structures on SiO2 /Si 3 N 4 membrane for gas sensors with dispensing method guided by micromachined wells

MEMS structures for micro gas sensors had advantage for lower power consumption, reducing size, and easily making cavity structures. Also, co-planar type MEMS structures (CPMS) for gas sensors with low power consumption heater and dispensed sensing materials were newly proposed and investigated. CPMS, which were formed with micro heater and sensing electrodes at the same layer, to reduce process steps, diffusions between upper layer and lower layer, and thermal differences between the center and the periphery of the sensing layer compared with stacked structure. Dispensing method guided by back-side etched well was good for forming sensing material on sensing electrode and had advantage that various sensing materials could be applied for array type sensors. CPMS were fabricated on four-inch diameter and double side polished (100) silicon wafers and using anisotropic bulk silicon micromachining for membrane formation and etched well. A size of chips with 1.15 mm × 1.15 mm membrane was 4.8 mm × 4.8 mm. And co-planar type sensing electrodes were located in the middle of low stress SiO₂/Si₃N₄ (400 nm /1 μm) membranes. Membranes are thermally isolated from the chip frame because they have low thermal conductivity, generally. Temperatures were measured using IR thermometer with linearly increasing applied power. Power consumption at 400^∘C was 150 mW. Membranes of CPMS were withstood up to 730^∘C at the power of 350 mW. Characteristics of micro heaters for various heater widths of 50 μm, 75 μm, 100 μm and ratios of membrane dimension to heater dimension were measured. Sensing materials guided by micromachined well were dispensed on sensing electrodes. CPMS were mounted on a TO-8 package. From these results, fabricated and characterized CPMS could be used for applications in portable gas sensors for detection of CO, NO_x, CH_x, H₂S, and so on.     

Growth and characterization of device quality ZnO on Si(111) and c-sapphire using a conventional rf magnetron sputtering

In this article, it is shown that high quality ZnO films were grown on Si(111) and Al₂O₃(0001) substrates using a conventional rf magnetron sputtering. High-resolution X-ray diffractometry (HR-XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and photoluminescence (PL) investigations clearly confirmed that the ZnO films grown on Al₂O₃ (0001) at substrate temperatures above 650^∘C are single crystal as well as high optical quality. It is also estimated in both cases grown on Si and Al₂O₃ that an introduction of template pre-grown at 500^∘C can induce a homogeneous interface and improvement of emission characteristic by relaxing the strain caused by large lattice and thermal mismatch between the film and substrate and by reducing defect density in interface region.     

锌粉退火处理对碱锰电池性能的影响

分析退火温度及时间对碱锰电池性能的影响。SEM分析结果表明:退火处理可使锌粉表面趋于光滑。当退火温度为200℃时,电池的防漏性能和电性能最佳。随着退火时间的延长,电池的析气量和高温漏液率逐渐降低,电性能逐渐提高。当退火温度为200℃、时间为2 h时,电池的析气量降低33.4%,高温漏液率降低90%,1 000 m A脉冲放电性能提高6.5%,1.5 W/0.65 W脉冲放电性能提高23.1%。     

Effects of oxygen partial pressure on the preferential orientation and surface morphology of ITO films grown by RF magnetron sputtering

In this study, effects of oxygen pressure in the sputtering ambient on the preferential orientation and resultant surface morphology of ITO films grown by RF magnetron sputtering were investigated. ITO film grown with pure Ar gas shows a preferential (400) plane orientation parallel to the substrate surface and a sawteeth-shaped rough surface. ITO film grown in the sputtering ambient of Ar and oxygen mixtures shows a preferential (222) plane orientation and a flat and smooth surface. The differences in the growth rate, surface morphology, and roughness between the preferentially orientated films were discussed in terms of the surface energy of planes. The electrical and optical properties of the films were examined.     

固化程度对氰酸酯-酚醛环氧树脂共混物热/湿热性能的影响

论文研究了具有不同固化程度的双酚A二氰酸酯-酚醛环氧树脂共混物的Ts转变和后固化过程中Ts转变的变化以及共混物的吸湿规律和湿热老化对共混物结构的影响。结果表明，固化程度可显著影响固化物的Ts和后固化过程中剩余反应的温度。表观转化率提高，则吸湿性降低；固化程度越大，湿热老化对化学结构影响越小，但当固化转化率不高时(例如小于90％)，湿热老化可能对共混物结构产生显著影响。