平面微波光子晶体表面波带隙的直线法分析

运用直线法对一种以微带基片为载体的平面微波光子晶体进行了分析.详细介绍了直线法分析过程,并对直线法中阻抗矩阵的提取方式作出了改进.在不同的周期边界条件下,通过对由直线法所得的特征方程的求解,得出所对应的本征频点,从而求得整个平面微波光子晶体的表面波色散图,标明表面波带隙所在.文中分别对矩形贴片型以及环形贴片型光子晶体进行了分析.     

Effect of bottom electrode materials on the electrical andreliability characteristics of (Ba, Sr)TiO3 capacitors

The dielectric constant and the leakage current density of (Ba, Sr)TiO₃ (BST) thin films deposited on various bottom electrode materials (Pt, Ir, IrO₂/Ir, Ru, RuO₂/Ru) before and after annealing in O₂ ambient were investigated. The improvement of crystallinity of BST films deposited on various bottom electrodes was observed after the postannealing process. The dielectric constant and leakage current of the films mere also strongly dependent on the postannealing conditions. BST thin film deposited on Ir bottom electrode at 500°C, after 700°C annealing in O₂ for 20 min, has the dielectric constant of 593, a loss tangent of 0.019 at 100 kHz, a leakage current density of 1.9×10 ^-8 A/cm² at an electric field of 200 kV/cm with a delay time of 30 s, and a charge storage density of 53 fC/μm² at an applied field of 100 kV/cm. The BST films deposited on Ir with post-annealing can obtain better dielectric properties than on other bottom electrodes in our experiments. And Ru electrode is unstable because the interdiffusion of Ru and Ti occurs at the interface between the BST and Ru after postannealing. The ten year lifetime of time-dependent dielectric breakdown (TDDB) studies indicate that BST on Pt, Ir, IrO₂/Ir, Ru, and RuO₂/Ru have long lifetimes over ten gears on operation at the voltage bias of 2 V     

Fabrication and performance of selective HSG storage cells for 256Mb and 1 Gb DRAM applications

Fabrication of rapid thermal nitrided HSG transformed crown capacitor storage cells incorporating an ultrathin low pressure chemical vapor deposition (LPCVD) Ta₂O₅ and Si₃N ₄/SiO₂(NO) dielectric is proposed. 256 Mb array with HSG crown cells of 0.3 μm diameter×0.6 μm height and 49 A T_eff showed an area enhancement factor of 1.7 (relative to untransformed crown cell). C_min/C_max ratio of >0.95, and capacitance of 16.7 fF/cell is obtained. A measured leakage current density of 0.7 nA/cm² at 1.2 V is reported. Metal-oxide-semiconductor capacitor (MOSCAP) devices with HSG electrodes for 1 Gb application are characterized using capacitance-voltage (C-V) and current-voltage (I-V) analyses. Detailed HSG grain characterization results are presented with correlation to the electrical behavior of the devices. Devices are formed using LPCVD Ta₂O₅ and/or Si₃N₄ dielectric. HSG films formed from 4×10²⁰ atoms/cc phosphorus doped amorphous silicon show depletion in C-V behavior. It is shown that phosphine doping of HSG film is required to avoid depletion. Process selectivity of the UHV/CVD HSG transformation mechanism applied to thermal oxide and nitride field dielectrics is fully explored. Selectivity limits for different types of dielectric are also presented. Effect of critical parameters such as a-Si dopant concentration, HSG incubation time, anneal conditions, and a-Si layer thickness on HSG transformation are discussed for 1 Gb crown cells     

Dual-metal gate CMOS technology with ultrathin silicon nitride gatedielectric

We report the first demonstration of a dual-metal gate complementary metal oxide semiconductor (CMOS) technology using titanium (Ti) and molybdenum (Mo) as the gate electrodes for the N-metal oxide semiconductor field effect transistors (N-MOSFETs) and P-metal oxide semiconductor field effect transistors (P-MOSFETs), respectively. The gate dielectric stack consists of a silicon oxy-nitride interfacial layer and a silicon nitride (Si₃N₄) dielectric layer formed by a rapid-thermal chemical vapor deposition (RTCVD) process. C-V characteristics show negligible gate depletion. Carrier mobilities comparable to that predicted by the universal mobility model for silicon dioxide (SiO₂) are observed     

Scattering by an infinite circular dielectric cylinder coatingeccentrically an elliptic metallic one

The scattering of a plane electromagnetic wave by an infinite-circular dielectric cylinder, containing eccentrically an elliptic metallic one is considered. The electromagnetic field is expressed in terms of both circular and elliptical-cylindrical wave functions, connected with one another by well-known expansion formulas. Translational addition theorems for circular cylindrical wave functions are also used for the satisfaction of the boundary conditions in the dielectric cylinder. When the solution is specialized to small values of h=k₁c/2, with k₁ the wavenumber of the dielectric cylinder and c the interfocal distance of the elliptic conductor, semianalytical expressions of the form S(h)=S(0)[1+gh²+O(h ⁴)] are obtained for the scattered field and the various scattering cross sections of this configuration. Both polarizations are considered for normal incidence. Numerical results are given for various values of the parameters     

Scattering by an inhomogeneous dielectric/ferrite cylinder ofarbitrary cross-section shape-oblique incidence case

A moment method (MM) solution is developed for the fields scattered by an inhomogeneous dielectric/ferrite cylinder of arbitrary cross-section. The incident field is assumed to be a plane wave of arbitrary polarization with oblique incidence with respect to the axis of the cylinder. The total electric and magnetic fields are the unknown quantities in two coupled equations from which a system of linear equations is obtained. Once the total electric and magnetic fields within the cylinder are computed, the scattered fields at any other point in space can be calculated. It is noted that for the case of oblique incidence, the scattered field has TE_z and TM_z polarized fields regardless of the polarization of the incident field. The echo widths of cylinders and shells of circular, semicircular, and rectangular cross section are calculated for TE_z and TM_z polarized incident fields. It is shown that the results obtained for dielectric/ferrite cylinders and shells of circular cross section with the solutions developed here agree very well with the corresponding exact eigenfunction solutions     

Surface wave excitation on a microstrip ring antenna

A theoretical analysis of the excitation of surface waves on a microstrip ring antenna is presented. The problem is formulated using dyadic Green's functions in a layered medium with magnetic-type equivalent current sources. The integral equation for the fields is solved in the wave number complex plane so that the fields from space and surface waves are obtained separately. The space wave radiation efficiency is calculated for the TM₁₁, TM₁₂, and TM₁₃ modes for various values of the normalized dielectric substrate thickness, d/λ₀. It is noted that the TM₁₃ mode radiates more efficiently than the TM₁₁ and TM₁₂ modes. The results are of importance in the design of these antennas     

Analysis of microwave characteristics of coplanar traveling waveelectrodes on III-V semiconductor with an n+ doped layer

The microwave characteristics of coplanar traveling wave electrodes on III-V semiconductor with an n⁺ doped layer have been studied by using the method of lines. Such a structure is analyzed by using even mode and odd mode of microwave. The behaviors of n⁺ doped layer have been studied carefully and found that at certain doping concentration region the n⁺ doped layer behaves like a perfect conductor for electric field and like an insulator for magnetic field. The relations between microwave characteristics of the odd mode and structural dimensions of the modulator have been analyzed in order to find a low loss and velocity-matched structure. A bandwidth as large as 37 GHz is predicted for the traveling wave type directional coupler modulator     

Highly reliable, high-C DRAM storage capacitors with CVD TA2O5 films on rugged polysilicon

The authors report on a highly reliable stacked storage capacitor with ultrahigh capacitance using rapid-thermal-annealed low-pressure chemical vapor deposited (LPCVD) Ta₂O₅ films (~100 Å) deposited on NH₃-nitrided rugged poly-Si electrodes. Capacitances as high as 20.4 fF/μ² (corresponding to the thinnest t_ox.eff (16.9 Å) ever reported using LPCVD-Ta₂O₅ and poly-Si technologies) have been achieved with excellent leakage current and time-dependent dielectric breakdown (TDDB) characteristics. Extensive electrical characterization over a wide temperature range (~25-300°C) shows that Ta₂O ₅ films on rugged poly-Si electrodes have a better temperature stability in dielectric leakage and breakdown compared to the films on smooth poly-Si electrodes     

Novel polycrystalline silicon thin film transistors prepared by deposition from Si2H6 and subsequent annealing by NH3 plasma

This work investigated the channel layer of polycrystalline silicon (poly-Si) thin film transistors (TFTs) prepared by amorphous silicon (a-Si) films deposited using Si₂H₆ gas. The recrystallization of channel layers, source/drain, gate electrodes and post implant anneal were performed at the same time. Due to the larger grain size, the device has higher field effect mobility than SiH₄ deposited devices. These devices were also subsequently passivated by NH₃ plasma. The NH₃ plasma significantly improves the n-channel devices; however, the improvement of p-channel devices is limited. Especially, the threshold voltage of n-channel devices is significantly shifted toward the negative gate voltage than the shift magnitude of p-channel devices. To investigate the band gap width and Fermi level by determining the leakage activation energy, it is found that the channel film is changed slightly from p-type to n-type. These results may be attributed to the donor effect by NH₃ plasma passivation.     

Propagation of lower-order modes in a radially anisotropiccylindrical waveguide with liquid crystal cladding

The propagation behavior of the four lower-order modes, HE₁₁ , TE₀₁, TM₀₁, and HE₂₁, in a radially anisotropic cylindrical waveguide with liquid crystal cladding is studied both theoretically and experimentally. The cylindrical waveguide is a doubly-clad fiber with an isotropic core and inner cladding and a radially anisotropic outer cladding made of nematic liquid crystal. Theoretically, the propagation and decay constants for the TE₀₁ and TM₀₁ modes are obtained by solving the wave equations exactly, while those for the HE₁₁ and HE ₂₁ modes are derived using perturbation techniques under the weakly guiding approximation. It is predicted that in such a structure the guided TE₀₁ mode can be separated from the leaky HE₁₁, TM₀₁, and HE₂₁ modes. The theoretical results show good agreement with the experimental observations for a 3 cm long fiber cell with a 5 μm inner cladding radius     

Improved coupled-mode theory for anisotropic waveguide modulators

An improved coupled-mode theory for the propagation of modulated light waves in anisotropic dielectric waveguides is presented. Starting from Maxwell's equations, a partial differential equation is derived to describe mode-coupling between two normal modes which may propagate in anisotropic waveguide systems under modulation. The theory is applied to the analysis of typical waveguide modulators; examples for LiNbO₃ phase modulator, Mach-Zehnder, and directional coupler modulator are presented. The theory is applicable to both bulk and waveguide modulators/switches from DC to the high-frequency band. The only limitation is that the modulating wave has to propagate collinearly to the light waves     

三种典型化学物质释放变态电离层的数值模拟研究

电离层人工变态会影响短波通信及卫星通信,对空间物理研究具有重要意义.基于中性气体扩散方程、离子化学反应方程及等离子体扩散方程,模拟了三种典型化学物质（氢气H₂、二氧化碳CO₂和三氟溴甲烷CF₃Br）经点源和多源释放后导致的电离层三维扰动变化,并利用自适应变步长的三维数字射线追踪技术讨论了化学释放变态电离层对不同频率短波传播的影响.结果表明:点源释放时产生的"空洞"在水平面上沿磁场线方向的轴长略大于其垂直方向;在释放量及释放高度相同的前提下,H₂扩散最快,CF₃Br扩散最慢,但就t=100 s时电子密度最大相对变化率而言,CF₃Br最大,CO₂次之,H₂最小;CF₃Br释放形成的"空洞"垂直范围最小,开始发生穿透现象所需的短波频率最高;H₂扰动下"空洞"边界的电子密度梯度最小,射线聚焦点明显偏高,聚焦效应最弱;多源释放产生类抛物线管状的电离层"空洞"结构,射线的传播路径更加多样,此时仍有聚焦效应出现,且聚焦点随射线频率增加而升高,聚焦效应减弱.     

LiNbO3晶体纳秒级光开关的研究

LiNbO3晶体由于其透光范围广，响应速度快，不易潮解等特点而广泛用于高精度和高速光开关快门。为了将LiNbO3光开关曝光时间拓宽到纳秒领域从而弥补现有的高速光开关的不足，文章阐述了LiNbO3作为光开关理论原理，对多波段通光的晶体长宽比进行了优化设计，并对LiNbO3纳秒级光开关的可行性进行了实验验证。实验半波电压与理论符合很好，实验光信号和电信号在纳秒级范围内能实现同步响应。研究结果证实了LiNbO3光开关在纳秒级范围内的可行性，并为LiNbO3纳秒级光开关的制作提供了理论和实验依据。     

Remote sensing of water salinity at decameter wavelengths

The possibility of remote sensing of surface water salinity in the decametric wave range is studied. The theoretical consideration of sensitivities to salinity variations proves the decametric range to be best for measuring small water salinities [0.3-5 parts per thousand ( ⁰/₀₀) at 30 MHz]. The conclusion is confirmed by 30 MHz radar experiments, which show a good agreement with the in situ data in the range 0.3-30 ⁰/₀₀. Radar contrasts of about 0.35 db and 1.6 db are observed when salinity changes from 0.3 ⁰/₀₀ to 1.2 ⁰/₀₀ and to 30 ⁰/₀₀, correspondingly     

用于重金属离子电化学传感器的TiO2NT/AuNP纳米复合材料

采用水热合成法将金纳米颗粒(AuNP)修饰到TiO₂纳米管(TiO₂NT)表面。用X射线衍射仪(XRD)和场发射扫描电子显微镜(FESEM)对制备的纳米复合材料进行表征。采用电化学阻抗谱(EIS)和循环伏安法分析了TiO₂NT/AuNP纳米复合材料修饰的玻碳电极(GCE)。通过方波阳极溶出伏安法(SWASV)分析了纳米复合材料检测重金属离子的可行性。纳米复合材料对Pb(Ⅱ)、Cd(Ⅱ)、Hg(Ⅱ)和Cu(Ⅱ)具有较高的电分析活性和灵敏度,对Pb(Ⅱ)、Cd(Ⅱ)、Hg(Ⅱ)和Cu(Ⅱ)的灵敏度分别为15.63、213.19、287.86和72.75μA·μM^-1(1 M=1 mol/L),检出限分别为0.052、0.004、0.003和0.011μmol/L。采用TiO₂NT/AuNP纳米复合材料对多种重金属离子进行了检测。此外,TiO₂NT/AuNP/GCE具有抗干扰性能和稳定性。因此,TiO₂NT/AuNP纳米复合材料可适用于电化学传感器来检测多种重金属离子。     

Fractional superlattices and their device applications

(AlAs)_1/2(GaAs)_1/2 fractional-layer superlattices (FLSs) are grown on a (001) vicinal substrate by metalorganic chemical vapor deposition (MOCVD). FLSs are new types of lateral superlattice with a period of 4–20 nm. The uniform superlattice period is observed over a large surface area by bright field transmission electron microscopy (TEM). The results suggest the ideal growth from a kink site occurs during MOCVD growth, and the distances between kink sites are equal.

Polarization-dependent photoluminescence and optical absorption spectra of FLSs are also observed. Electron wave interference devices with a lateral periodic potential have been fabricated.     

Conduction mechanisms in barium tantalates films and modificationof interfacial barrier height

The leakage current-voltage characteristics of rf-magnetron sputtered BaTa₂O₆ film in a capacitor with the top aluminum and the bottom indium-tin-oxide electrodes have been investigated as a function of applied field and temperature. In order to study the effect of the surface treatment on the electrical characteristics of as-deposited film we performed an oxygen plasma treatment on BaTa₂O₆ surface. The dc current-voltage, bipolar pulse charge-voltage, dc current-time, and small ac signal capacitance-frequency characteristics were measured to study the electrical and the dielectric properties of BaTa₂O ₆ thin film. All of the BaTa₂O₆ films in this study exhibited a low leakage current, a high breakdown field strength (3-4.5 MV/cm), and a high dielectric constant (20-30). From the temperature dependence of the leakage current, we could conclude that the dominant conduction mechanism under high electrical fields (>1 MV/cm) is ascribed to the Schottky emission while the ohmic conduction is dominant at low electrical fields (<1 MV/cm). Furthermore, the oxygen plasma treatment on the surface of as-deposited BaTa₂O ₆ resulted in a lowering of the interface barrier height and thus, a reduction of the leakage current at Al under a negative bias. This can be explained by the formation of Ba-rich metallic layer by surface etching effect and by filling the oxygen vacancies in the bulk     

High-efficiency nonadiabatic trapping of electrons in theponderomotive potential wells of laser beats

Experimental results are reported for nonlinear interactions between a nonrelativistic electron beam and the ponderomotive field (beat wave) of two counterpropagating pulsed CO₂ laser beams, operating at different frequencies in a stimulated Compton scheme. Very high electron trapping efficiencies were obtained by introducing a nonadiabatic shift in the energy of the electrons in order to bring them into resonance with the ponderomotive wave. With an axial decelerating electric field applied along an interaction path of 12 cm, trapping efficiencies of above 60% with energy transfer of 6 eV between the electrons and the radiation field were obtained     

Low Weibull slope of breakdown distributions in high-k layers

The reliability of various Al₂O₃, ZrO₂ and Al₂O₃/ZrO₂ double layers with a physical oxide thickness from 3 nm to 15 nm and TiN gate electrodes was studied by measuring time-to-breakdown using gate injection and constant voltage stress. The extracted Weibull slope β of the breakdown distribution is found to be below 2 and shows no obvious thickness dependence. These findings deviate from previous results on intrinsic breakdown in SiO₂, where a strong thickness dependence was explained by the percolation model. Although promising performance on devices with high-k layers as dielectric can be obtained, it is argued that gate oxide reliability is likely limited by extrinsic factors