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In response to the rapid development of wireless communication, enhancement of temperature stability and power durability for surface acoustic wave (SAW) devices is both scientifically and technologically important in the 5G era. This paper discusses the utilization of 5-layer electrode Ti/Cu/Ti/Cu/Ti to the development of high power and low loss temperature-compensated surface acoustic wave (TC-SAW) filters. By modulating the microstructure of 5-layer electrode, the power durability can be increased to 1.7 times that of the conventional 3-layer electrode, while the life time to failure can be enhanced by 104 times. Through the cross section analysis of devices before and after power test, it is found that the deformation mainly concentrates on the bottom edge of electrode, whose result matches well with finite element method (FEM) simulation. The enhancement of power durability can be attributed to high resistance to cyclic stress in the bottom fine grain area. Furthermore, substrate failure areas due to Ti diffusion were also observed, which may be caused by the high temperature due to the current concentration around the electrode deformation. Our results show that the 5-layer electrode configuration is a promising solution for high power TC-SAW filter without deterioration of radio frequency performance and temperature coefficient of frequency.

With the development of the radio frequency technique, the explosive growth of transmitted data in 5G era puts higher requirements on surface acoustic wave (SAW) filter bandwidth. In this work, 15°YX-LiNbO3(LN)/SiO2/Si multilayer structure was proposed, where both LN and SiO2 films possess uniform thickness and the interfaces between films are quite clear. With hierarchical cascading algorithm, the spurious resonance that resulted from Rayleigh mode was minimized through the modulation of Cu electrode thickness. One-port resonators measurement results confirm a high electromechanical coupling coefficient of shear horizontal mode ranging from 22.5% to 25.2%. Furthermore, a ladder-type filter with a center frequency of 1279 MHz and a large fractional bandwidth of 20.2% was successfully fabricated. Excellent bandpass filtering properties were achievable with minimum insertion loss of 0.8 dB and in-band fluctuation less than 0.9 dB. Multilayer structure SAW filters also exhibited a temperature coefficient of frequency of −57.7 ppm/°C and a power durability of 33 dBm, which are both significant improvements compared with that of devices built on bulk 15°YX-LN substrate. This work provides an effective solution for wideband and low-loss radio frequency filters in 5G communication systems, suitable for large-scale application and commercial promotion.

In this letter, highly (0002) oriented ZnO piezoelectric films were deposited on high acoustic velocity SiC substrates. Surface acoustic wave (SAW) devices on ZnO/SiC layered structure operating in the fundamental mode with high frequency to the 7-GHz range were successfully fabricated for the first time. The comprehensive experimental and theoretical investigations about phase velocities ${V}_{p}$ , the electromechanical coupling coefficients ${K}^{{2}}$ , and quality factors Q of one-port SAW resonators have been studied considering various ZnO normalized thicknesses ${h}/\lambda $ . The resonators with large ${K}^{{2}}$ and high Q are implemented over 5–7 GHz demonstrating ${K}^{{2}}$ of 0.47%–2.83% and Q of 146–549. Specifically, a high ${K}^{{2}}$ of 2.83% and a large Q of 549 are simultaneously achievable for the resonator at 5.19 GHz. Finally, with the high ${V}_{p}$ of ZnO/SiC structure being up to 6800 m/s at ${h}/\lambda = {0.14}$ , a 6.8-GHz SAW filter was achieved. Our work shows that the ZnO/SiC structure is of great potential for high-frequency SAW devices application.

The structural parameters of low-stepped mirror which is the core component of a light Fourier transform infrared spectrometer (FTIRS) have important influence on the performance of the instrument. A simple method of multiple deposition is proposed to fabricate a low-stepped mirror with step height of 625 nm, for its high precision, high efficiency and miniaturization. So the film stress will be introduced in the process of coating, which can lead to step deformation. We build a bending model of the low-stepped mirror and analyze the influence of its deformation. The light intensity and spectrum are changed by the step deformation. Therefore, the film stress should be reduced in order to ensure the accuracy of the spectral information. Increasing the thickness of substrate is proposed in this paper to reduce the step deformation, besides adjusting the coating temperature and adding sub-layer. Our results reveal that the basic requirements of the system are satisfied when the thickness of the substrate is 5 mm in the appropriate coating environment. An FTIRS based on stepped mirrors and grid beam splitter is assembled and corresponding experiment is carried out to obtain the spectrum curve of acetonitrile.

The strategy for fabricating bendable micro-light emitting diode arrays is presented and the mechanical properties of bent arrays are analysed in this paper. The key procedures of the fabrication process consist of grooving the wafer, welding the upside electrode with an indium tin oxide current-spreading layer, integrating the micro-pixels, removing the substrate, electroplating the backside electrode, and encapsulating the device. In order to prevent potential physical destruction and improve the reliability and fatigue of the arrays, the position of the neutral mechanical plane was calculated. Strain and stress distributions in bent LED arrays showed that strain concentrated in the polymers and the generated stress preferentially concentrated in the electrodes and semiconductor. These results indicate that physical destruction, rupture, or delamination may first occur in the electrodes or semiconductor interface. Display Omitted A strategy for fabricating polymer-integrated bendable micro-LED arrays is presented.Potential physical destructions likely occur in the regions around LED pixel edges.Bent the sample with radius of 10mm found no observable degradation.

We investigate the electrical control of the spin–orbit (SO) interaction in GaAs wells, involving both one- and two-subband electron occupations altered by a gate potential V g , over a wide range of well widths w 's. Through the self-consistent Schrodinger–Poisson calculation, we determine all the intrasubband Rashba α ν ( ν = 1 , 2 ) and Dresselhaus β ν , and also the intersubband Rashba η and Dresselhaus Γ couplings. We observe two distinct regimes marked off around w = w c = 30 − 35 nm . In the first regime with w w c , we find the usual behavior of SO couplings, i.e., the intrasubband Rashba couplings α 1 and α 2 have the same sign and both change almost linearly with V g , while the Dresselhaus couplings β 1 and β 2 obeying the relation β 1 β 2 are almost constant. In contrast, in the second regime with w > w c , we observe that α 1 and α 2 can either have the same sign or opposite signs depending on V g . In addition, even though α 1 sensitively depends on V g , we find that α 2 remains essentially constant within a certain gate voltage range. As for the Dresselhaus couplings in this second regime, the inequality β 1 β 2 (valid in the first regime) only holds near the symmetric configuration of our wells, but otherwise the inequality tends to be reversed. On the other hand, we find that both the intersubband Rashba η and Dresselhaus Γ couplings change almost linearly with V g in the first regime while in the second one a maximum of | η | occurs near the symmetric configuration. We also determined the persistent-spin-helix symmetry points of the two subbands, where the Rashba and the renormalized (due to cubic corrections) Dressehaus couplings are matched. We find that the helix symmetry for the second subband retains over a broad range of V g 's, thus possibly facilitating its locking in practice. Our results should be essential for experiments pursuing an universal electrical control of the SO interaction in semiconductor nanostructures.

A method of “slope splicing” is proposed to build a tall-stepped mirror with high precision in a stepped-mirror-based static Fourier transform infrared spectrometer. The structural parameters were designed, and their errors were analyzed. We present the test results and an analysis of the combined effect of the errors on the recovered spectrum. The spectrum-constructing error of the constructed spectrum, 5.81%, meets the requirements for the system and suitable for realization of a miniaturized spectrometer. We performed experiments with the tall-stepped mirror to obtain the interferogram and spectrum of a silicon carbide light source. Further work is needed to optimize the capability of the system.

Visible light communication offers abundant spectrum resources, which can alleviate the current shortage of wireless communication spectrum resources, and the security of the system is very reliable. In this study, a new photodiode (PD) array with micro-nano optical structure is designed and shown to effectively improve the absorption efficiency of PDs to blue, green, and red light. The absorption efficiency of blue, green, and red light at the central wavelength reached 96.8%, 97.5% and 98.6%, respectively, thus demonstrating the improved quantum efficiency of the device. Moreover, three color PDs are integrated into an ultra-thin silicon-on-insulator structure, increasing the integration and response speed of the device. The ultra-thin structure of the PD increases the response bandwidth up to the GHz level.

A type of spatial modulating micro Fourier transform spectrometer (FTS) based on micro multi-step mirrors (MMSMs) is designed and manufactured in this paper. The interference system is based on Michelson interferometer, using two MMSMs instead of plane mirrors in two arms. The recovered spectrum is simulated with different distances between MMSMs and the detector, and the influence of diffraction on the recovered spectrum is analyzed. The edge-enlarging method for the MMSMs is proposed to eliminate edge noise, and the influence of surface roughness of MMSMs on the recovered spectrum is also analyzed. Moreover, the way of manufacturing the MMSMs is investigated. 2014 Tianjin University of Technology and Springer-Verlag Berlin Heidelberg.

Plasmon and coupled plasmon–phonon modes of Dirac particles in graphene are investigated theoretically within the diagrammatic self-consistent field theory. It shows that two terahertz plasmon modes and four infrared coupled plasmon–phonon modes can be achieved via intra- and inter-band transitions in graphene. We find that with increasing q and carrier density, the plasmon modes are strongly coupled with optic-phonon modes in graphene in the infrared region. The coupled plasmon–phonon modes exhibit some interesting features which can be utilized to realize the plasmonic devices. Our results suggest that the carrier–phonon interaction should be considered to understand and explain the properties of elementary electronic excitations in graphene.

In this study, the insertion of both Al and Cr atoms into SiC matrix has been experimentally evidenced by X-ray diffraction, Raman scattering, elements analysis and magnetic measurements. Structure analysis showed that (Al, Cr)-codoped SiC has a single-phase 4H-crystal structure and no trace of any other impurity phases were detected. Raman scattering showed that several new features appeared in (Al, Cr)-codoped 4H-SiC: (1) the vanishing of the folded longitudinal-optical phonons modes-plasmon coupling (FLOPC) modes with x=(q/q(B))=0; (2) an obvious absorbing peak was found in Si(1-x-y)Al(x)Cr(y)C with y=0.0203 at%; (3) folded transverse-optical (FTO) mode shifts to high frequency and linewidths [full widths at half maximum (FWHM)] decrease with increase in Cr content. Magnetic properties characterizations showed that weak ferromagnetism order is established. With increase in Cr content, the magnetization decreased. No clear influence of Al doping on the magnetic properties of codoped 4H-SiC is evidenced while the magnetic origin should be ascribed to be induced by Cr. It is speculated that doping Cr elements at Si sites destroy the effective coupling of the spins induced by Al doping. The major role of Al is to stabilize the codoped crystal structure as 4H-single-phase. (C) 2011 Elsevier B.V. All rights reserved.

A gated nanowire model was proposed to estimate the field-emission performance of a conductive nanowire in gated structure. The actual electric fields around the nanowire top and the field-enhancement factor were calculated analytically based on an electrostatic theory. The influence of the device parameters such as the gate and anode voltages, the gate-hole radius, and the radius and length of the nanowire on the field-enhancement factor, the current and apex current density were discussed in detail. The results show that the field enhancement increases rapidly with the decrease of the gate-hole and nanowire radius, but the former almost increases linearly with the nanowire length. In addition, it was found that the current and current density at the edge of the nanowire increases exponentially with the gate and anode voltages.

Carbon submicrotubes were synthesized on carbon microfibers by floating catalyst method, and carbon nanotubes were also observed to grow on the rough surface of carbon submicrotubes. The morphology, microstructure and composition of the obtained products were characterized by field emission scanning electron microscopy, high-resolution transmission electron microscopy, Raman spectroscopy and energy dispersive X-ray spectroscopy. The growth of carbon submicrotubes on carbon microfibers was attributed to the pretreatment of carbon microfibers, which gave rise to catalyst areas, while the secondary growth of carbon nanotubes could be related to the defects of hexagonal graphite on the surface of carbon submicrotubes.

Carbon nanotubes with uniform density were synthesized on carbon fiber substrate by the floating catalyst method. The morphology and microstructure were characterized by scanning electron microscopy and Raman spectroscopy. The results of field emission showed that the emission current density of carbon nanotubes/carbon fibers was 10 μA/cm2 and 1 mA/cm2 at the field of 1.25 and 2.25 V/μm, respectively, and the emission current density could be 10 and 81.2 mA/cm2 with the field of 4.5 and 7 V/μm, respectively. Using uniform and sparse density distribution of carbon nanotubes on carbon fiber substrate, the tip predominance of carbon nanotubes can be exerted, and simultaneously the effect of screening between adjacent carbon nanotubes on field emission performance can also be effectively decreased. Therefore, the carbon nanotubes/carbon fibers composite should be a good candidate for a cold cathode material.

Nanocrystalline graphite films were synthesized on carbon fibers by the direct current discharge plasma chemical vapor deposition method. The morphology and microstructure of the obtained products were characterized by scanning electron microscopy, Raman spectroscopy, and transmission and high-resolution transmission electron microscopy. The results showed that the size and thickness of graphite nanosheets were about 0.3−2 μm and 5−20 nm, respectively, and the purity and graphitization degree of the films can be improved by increasing the deposition time of graphite nanosheets. The down-shift of the G peak in Raman spectra can be attributed to the temperature differences of samples heating by laser radiation. In comparison with the products grown on silicon substrate under similar experimental parameters, carbon fiber substrate is more favorable for the deposition of graphite structure.

(111) diamond microcrystals and (100) diamond microcrystals and nanorods were synthesized on Si substrate by hot cathode direct current plasma chemical vapor deposition method. The morphology, structure, and optical properties of the diamond films were characterized by scanning electron microscopy, X-ray diffraction, Raman spectra, and Fourier transform infrared spectra. The results showed that (111) and (100) diamond films can be grown under the condition of high-temperature (1223 K), low CH4 concentration (4/300 sccm) and low temperature (1098 K), high CH4 concentration (6/300 sccm), respectively. The (100) diamond film has lower purity and quality but higher optical transmittance than the (111) diamond film. Thus, the reactor temperature and CH4 concentration are responsible for the growth of diamond films.

Nanocrystalline diamond films with different grain sizes were synthesized on Si substrate by the hot cathode direct current plasma chemical vapor deposition method with different compositions of CH4/Ar/H2 gas mixture. The morphology and microstructure of the obtained products were characterized by scanning electron microscopy, atomic force microscopy, high-resolution transmission electron microscopy, X-ray diffraction, and Raman spectroscopy. The results showed that the composition of the CH4/Ar/H2 gas mixture affected greatly the grain sizes, surface smoothness, and crystal quality of the nanocrystalline diamond films. With the increase of CH4 concentration, the grain sizes got smaller and the surface of the films got smoother. However, the grain sizes got smaller and the crystal quality was weakened with the increase of Ar concentration. In the process of deposition, SiC was formed at the substrate before the growth of nanocrystalline diamond films, which increased the secondary nucleation of nanocrystalline diamonds. To obtain the nanocrystalline diamond films with uniform small grain sizes, good surface smoothness, and little non-diamond phase, the optimal composition of the CH4/Ar/H2 gas mixture is 6/70/30 and 7/70/30.

Eye-protection glasses against YAG laser injury based on band gap reflection of one-dimensional photonic crystal (PC) is designed and manufactured in this paper. The laser beam (wavelength 1.06 μm) is reflected by the one-dimensional PC (with the transmission 10−7) and absorbed by the phosphatic glass substrate (with the transmission 1% for 1.06 μm), so the transmission of the device for wavelengths of1.06 μm can reach 10−9. The glasses have enough capabilities to protect the eyes from injury of ns-YAG lasers whose energy density is 1 J/cm2 for all incident angles, and also to avoid a second injury to others from the reflected laser beams. The transmission of the glasses is beyond 70% for the visible lights. The testing data of the eye-protection glasses agree well with the theoretical predictions.

Optical bistability occurs when the effects of nonlinear behavior of materials cause hysteresis in the transmission and the reflection of a device. An optical bistable device based on one-dimensional photonic crystal waveguide is designed and fabricated. Doped semiconductor CdS x Se 1 − x glass, which has large nonlinear refractive index coefficient and fast nonlinear responding time, is used. The threshold light intensity of the optical bistability is 1.65 × 10 5 W/cm 2 and the optical switching time is 63 ps.

A dynamical addressing device for optical interconnection based on one-dimensional nonlinear photonic crystal made on the planar waveguide was designed and fabricated. The dynamical interconnection is performed by controlling the power density of the control light. In our device, when increasing the power density of the control light from 0 to 2.60 × 105 W/cm2, the angle of the signal beam can be changed by about 2°. This kind of devices is promising for use in all-optical interconnection, optical information processing and optical communication.

Optical bistability device based on nonlinear one-dimensional photonic crystals is designed and manufactured. The device has 20 periods and is made from ZnS and ZnSe layers alternately. When the incident power density reach threshold power density 1.0 × 105 W/cm2, the Ar ion laser, whose wavelength is 514.5 nm, is shifted out of the optical band gap of the one-dimensional nonlinear photonic crystals, so an optical switch is made. It also can be made into an optical bistability device. The threshold power density of the optical bistability is 1.38 × 105 W/cm2 and its switching time is about 100 ps in experiment. The experimental results are in good accordance with the theoretical ones.

The Fe-incorporated ZnO thin films prepared by magnetron sputtering at different deposition temperatures were investigated by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). The XRD patterns show the Films exhibit [001] preferred orientation which is perpendicular to the surface plane of the substrates. The growth direction tends to be along the [101]-axis when the deposition temperature is increased. Numerous defects have been observed in the present thin films. In the thin film deposited at 600 degreesC, a large number of stacking faults and domain lamellae were discovered at the bottom and the middle of the thin film, respectively. Polycrystallization occurred at the top of the thin films. It is suggested that Fe elements could have been incorporated into the ZnO thin films and these incorporated Fe ions, together with the deposition temperature, are responsible for the microstructural modifications in the microstructures of the thin films. (C) 2002 Elsevier Science B.V All rights reserved.

Diamond films with different crystal structures, morphologies and surface characteristics were synthesized under various deposition parameters and annealing conditions by the microwave plasma chemical vapor deposition (MWPCVD) method using gas mixtures of CH4, CO and H2. The effects of CH4 concentrations, grain sizes, grain orientations, film thicknesses and annealing technologies in various ambient gases on planar electron emission of diamond films were studied. The results show that small-grained and (011)-oriented diamond films deposited under the condition of high CH4 concentration present the properties of high emission current and low threshold voltage; the emission current increases with decreasing the film thickness. There are largest current density and lowest threshold voltage at the film thickness of 1.5 μm. The annealing in H2 after deposition appears to be more beneficial in lowering the threshold voltage, increasing emission current and improving stability for electron emission of films than annealing in N2 or Ar. These results indicate that diamond thin films with high emission current, low threshold voltage and high stability can be obtained by selecting suitable deposition parameters of diamond films.

In this study, we design micro, flexible light-emitting diode (LED) array devices. Using theoretical calculations and finite element simulations, we analyze the deformation of the conventional single electrode bar. Through structure optimization, we obtain a three-dimensional (3D), chain-shaped electrode structure, which has a greater bending degree. The optimized electrodes not only have a bigger bend but can also be made to spin. When the supporting body is made of polydimethylsiloxane (PDMS), the maximum bending degree of the micro, flexible LED arrays (4 × 1 arrays) was approximately 230 µm; this was obtained using the finite element method. The device (4 × 1 arrays) can stretch to 15%. This paper describes the fabrication of micro, flexible LED arrays using microelectromechancial (MEMS) technology combined with electroplating technology. Specifically, the isolated grooves are made by dry etching which can isolate and protect the light-emitting units. A combination of MEMS technology and wet etching is used to fabricate the large size spacing.

Ti films were deposited on liquid nitrogen-cooled substrates by ion-beam sputtering. The X-ray diffraction pattern of the as-deposited Ti films clearly shows Ti amorphous diffused scattering maxima. The image of the Ti films was observed by high-resolution electron microscopy and the electron diffraction pattern of the film demonstrates again the amorphous structure by its diffused halo. Energy dispersive analysis of X-ray and Auger depth profiling were used to examine the ingredients of the film. The results show that the film can be considered as Ti amorphous film. (C) 1997 Elsevier Science S.A.

An erratum is presented to correct the mistakes in the equation of a previous publication. We apologize for any inconvenience this error may have caused.

A new approach to achieve efficient coupling between photonic crystals and a nanometer waveguide via an asymmetric resonator is proposed. The asymmetric resonator was composed of the photonic crystal and the nanometer waveguide was constructed by elongating a rod of the photonic crystal resonator horizontally. By introducing the asymmetric resonator, the nanometer waveguide served as a part of the resonator, and the coupling between the photonic crystal waveguide and the nanometer waveguide was converted to internal coupling between the photonic crystal devices. The 3D theoretical coupling efficiency reached 91.31%. Such compact, efficient coupling shows great promise for applications in molecular imaging, nanoprobes, integrated photonic circuits and on-chip optical interconnects.

In this study, as a first attempt, we choose Al and transition metals (TMs), Fe, as codoping atoms to synthesize (Al, TM)-codoped SiC. X-ray diffraction and Raman analysis showed that a series of single-phase codoped 4H-SiC samples were obtained and no trace of any other impurity phases, such as Fe3Si and polytypes of other types of SiC, was found. Measurement of magnetic properties showed that codoping by Al and Fe elements changed the original glassy ferromagnetism (FM) features in Al-doped SiC and induced a robust room temperature FM order that gradually dominated (Al, Fe)-codoped 4H-SiC with increase in Fe content. The contribution of Al elements to the magnetic properties of (Al, Fe)-codoped 4H-SiC can be neglected and the magnetic origin should be ascribed to be induced by Fe doping. The only major role of Al is to stabilize the codoped crystal structure as 4H- single phase. As the first investigation on (Al, TM)-codoped SiC, this study opens a new pathway to obtain TM-doped SiC-based diluted magnetic semiconductors with a high T c via the codoping strategy.

The influences of dc bias on complex impedance, complex module and dielectric response of CaCu3Ti4O12 for different sintering durations have been investigated to elucidate the origin of its dielectric properties. It is found that both the electrode contact response and grain boundary response contribute to the dielectric constant of CaCu3Ti4O12. The origins of the semicircles in complex impedance plots of CaCu3Ti4O12 have also been investigated. At 120 °C, the mid-frequency semicircle in complex impedance plots represents the electrode contact response and the low-frequency semicircle may correspond to the oxygen-vacancy relevant response. The semicircle of the grain boundary response in the complex impedance plot is covered by the semicircle of the electrode contact response at this temperature.