Implementation and application of resistive sheet boundarycondition in the finite-difference time-domain method [EM scattering]

Use of a resistive sheet boundary condition in the finite-difference-time-domain (FDTD) analysis of scattering problems involving a resistively coated dielectric object is described. An algorithm is introduced through an analysis of E-polarized scattering from a thin resistive strip. For a given resistance, numerical experiments indicate that algorithm stability is ensured for time sampling intervals chosen according to a specific criterion. Validity of the resultant FDTD method is verified in a comparison of computed E-polarized scattering data for several resistive strips with existing data. Results on the E-polarized scattering behaviour of a resistively coated dielectric strip as a function of surface resistances and angle of incidence are also presented. Extension to the H-polarized case and application of the present method to pulsed problems are briefly discussed     

膜电阻作为微波电路封装谐振模式抑制层

通常将微波电路置于金属封装之内.如果该封装波导谐振模恰好位于电路工作频率范围之内,电路与封装谐振模间的耦合将干扰电路的工作.在腔内放入覆有膜电阻的介质基片,可以有效地削弱封装谐振模,避免了放入吸波材料的传统方法给军用、宇航用毫米波电路带来的可靠性和机械加工难题.膜电阻的吸波性能取决于膜电阻方阻值和介质层厚度,使用数值方法计算得到应用该方法削弱后的最低阶封装谐振模的品质因数.     

Effects of a resistively coated dielectric strip on theTM-polarized resonant backscatter behavior of a slotted conductingrectangular shell

The performance of a resistively coated dielectric strip used to suppress the first TM-type resonant backscatter associated with a two-dimensional slotted conducting rectangular shell is analyzed using the moment method technique. Results obtained indicate that almost perfect resonance damping performances are attained when a finite-sized strip with dielectric constants ∈_r=4-j0.4 and film resistance R_s=188.5 Ω is placed: (1) at the slot (which directly faces the normally incident TM-polarized plane wave), (2) on the interior perimeter of the shell adjacent to the slot, or (3) at the center of the back wall of the shell. Poorer damping performances are observed, however, with the strip placed at other positions and/or with the same or higher film resistance. It is also shown that in general the knowledge of waveguide theory can be used advantageously in the placement of the strip for achieving best resonance damping performance     

Microwave shielding effectiveness of EC-coated dielectric slabs

Correct formulas for the microwave shielding effectiveness (SE ) of a thin metallic layer deposited on top of a dielectric slab are derived. For coatings much thinner than the skin depth, the following holds: (a) in a half-wave geometry, SE is a function of a sheet resistance only, SE (in dB)=20×log(1+188.5/R_s) if R_s is in ohms per square; (b) in a quarter-wave geometry, SE (in dB)=20×log[(1+ε_r)/(2√ε _r)+188.5/(√ε_rR_s)], where ε_r refers to the dielectric constant of the substrate. These formulas provide upper and lower limits for the effective shielding performance of an electroconductive coated dielectric slab     

A composite optical waveguide-based polarimetric interferometer forchemical and biological sensing applications

A new polarimetric interferometer has been developed on the basis of the phase difference between transverse electric (TE)₀ and transverse magnetic (TM)₀ modes in a composite optical waveguide (OWG). The composite OWG consists of a single-mode potassium ion-exchanged planar waveguide overlaid with a high-index thin film that has two tapered ends and supports only the TE₀ mode. Applying tapered velocity coupling theory, we found that the TE₀ and TM₀ modes coexisting in the potassium ion-exchanged layer were separated in the thin film region of the composite OWG: the TE₀ mode was coupled into the thin film while the TM₀ mode was confined in the potassium ion-exchanged layer. Interference occurs between TE- and TM-polarized output components when a single output beam is passed through a 45°-polarized analyzer. The phase difference φ between both orthogonal output components is very sensitive to the superstrate index n_c in the thin film region. Our experimental results indicate that a slight change of Δn_c=3.71×10^-6 results in the phase-difference variation of Δφ=1° for a 5-mm-long TiO ₂/K⁺ composite OWG with a 34-nm-thick TiO₂ film. Such a simple polarimetric interferometer can be applied to chemical or biological sensors by modifying the upper film surface of the composite OWG with a chemically or biologically active substance     

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     

A New Compact Microstrip-Fed Dual-Band Coplanar Antenna for WLAN Applications

A novel compact microstrip fed dual-band coplanar antenna for wireless local area network is presented. The antenna comprises of a rectangular center strip and two lateral strips printed on a dielectric substrate and excited using a 50 Omega microstrip transmission line. The antenna generates two separate resonant modes to cover 2.4/5.2/5.8 GHz WLAN bands. Lower resonant mode of the antenna has an impedance bandwidth (2:1 VSWR) of 330 MHz (2190-2520 MHz), which easily covers the required bandwidth of the 2.4 GHz WLAN, and the upper resonant mode has a bandwidth of 1.23 GHz (4849-6070 MHz), covering 5.2/5.8 GHz WLAN bands. The proposed antenna occupy an area of 217 mm² when printed on FR4 substrate (epsiv_r=4.7). A rigorous experimental study has been conducted to confirm the characteristics of the antenna. Design equations for the proposed antenna are also developed     

Sensitivity of Rs-measurement of HTS thin films by threeprime resonant techniques: cavity resonator, dielectric resonator, andmicrostrip resonator

The microwave surface resistance, R_s measurement of YBa ₂Cu₃0_{7 -δ} (YBCO) thin film deposited on 10 mm × 10 mm LaAlO₃ substrate using three prime resonating techniques, namely, cavity end plate substitution technique (20 GHz), dielectric resonator technique (18 GHz), and microstrip resonator technique (5 GHz), is reported. In addition, theoretical analysis for each technique has been performed to calculate the relative percentage error in the measured R_s -value of the YBCO thin film as a function of temperature. It has been found that the shielded dielectric resonator provides far better sensitivity for R.-measurement of the YBCO thin film with minimum relative percentage error (<4%) in the temperature range from 20 K to transition temperature of YBCO thin film compared to the other two techniques     

Dielectric ring-gap resonator for application in MMIC's

A dielectric resonator, the dielectric ring-gap resonator, is introduced and analyzed. The dielectric ring-gap resonator is obtained by sawing a narrow gap into a dielectric resonator. Resonant frequencies and unloaded Q-factors of quasi-TE_0pq mode in the ring-gap resonator have been calculated by an appropriate equivalent circuit starting from the resonant frequencies and the field distributions of the TE_0pq modes in the ring resonator. The calculated resonant frequencies of the fundamental quasi-TE₀₁₁ mode show an accuracy of <1% compared with the experimental results. Coupling techniques to couple the ring-gap resonator to a microstrip line on a thin substrate, using the electric fringing field near the gap, have been experimentally investigated. A rigorous method for determining resonant frequencies and field distributions of TE modes in a multicomposite multilayered cylindrical resonator is presented. This resonator consists of numbers of cylinders that are arbitrarily layered in the axial direction     

Study of TE0 and TM0 modes in dielectricresonators by a finite difference time-domain method coupled with thediscrete Fourier transform

An application of a numerical method of finite differences in the time domain (FDTD) coupled with the discrete Fourier transform is presented to determine the resonant frequencies of the TE₀ and TM₀ modes of axially symmetric dielectric resonators closed in a cavity. The technique is conceptually and computationally simple, and it allows access at once to information on the entire modal spectrum by means of the fast Fourier transform (FFT) applied to the time series. The cylindrical cavity dielectrically loaded at the base and the resonant frequency of the TE_01δ mode are analyzed in two systems: a cylindrical cavity with a cylindrical dielectric resonator of variable radius, and the shielded dielectric resonator on a microstrip substrate. The results obtained are compared with the rigorous (exact) theoretical solutions and with experimental results     

Novel Microwave Network for the Leaky-Wave Analysis of Evanescent Fields in Stub-Loaded Structures

In this paper, a new transverse equivalent network for the modal analysis of stub-loaded leaky-wave antennas is developed. The derived network is useful for the study of the radiation of evanescent fields that occurs when they reach the top aperture of the parallel-plate stub. This transverse network is based, for the first time, on a nonhybrid formulation of the constituent parallel-plates modes of order 1 (TE₁ ^Z and TE₁ ^Z ). The obtained network is an alternative to the one based on hybrid TE₁ ^Vand TE₁ ^V modes, and leads to a simpler transverse resonance equation. The new equivalent network is validated by obtaining leaky-mode dispersion curves for a previously studied leaky-wave antenna in non- radiative dielectric guide technology.     

Slot excitation of the dielectric disk radiator

Dielectric disk radiators which are excited by a narrow slot in the ground plane of a microstrip line are investigated. The resonance frequencies of the dielectric disk for the HEM₁₁ mode are computed numerically in the complex frequency plane. From the later results, the actual resonance frequency and the Q-factor are obtained. The dielectric disk is made of a high dielectric constant ceramic material with ϵ_r=22. The radiation patterns and reflection coefficients are measured and presented for several slot lengths and dielectric disk dimensions. The radiation patterns are also computed assuming a magnetic current element, which models the slot and excites the HEM₁₁ mode. Good agreement is obtained between the computed and measured results. The results presented here also demonstrate the viability of this type of antenna, which has high dielectric constants an efficient radiator provided the proper mode is excited     

A numerical study of a dielectric disk antenna above groundeddielectric substrate

An antenna made of a dielectric disk with a high permittivity mounted on top of a grounded dielectric substrate of low permittivity is analyzed. A numerical procedure based on surface integral equations, derived from the equivalence principle, is used to compute the natural resonant frequencies for the HEM₁₁ mode from which the radiation Q factor of the antenna is obtained. Then the radiation pattern of the antenna, operating at the resonant frequency evaluated previously, is computed with an electric dipole excitation located within the dielectric substrate under the dielectric disk. The effect of various parameters on the radiation characteristics of the antenna is studied, and presented in the form of diagrams. The low values of the radiation Q, combined with the high values of the dielectric Q and conductor Q, indicate that this antenna promises to be more efficient then the microstrip antenna     

Dielectric deposition process for Cu/SiO2 integration in a dual damascene interconnection architecture

A challenge to integrate Cu in device interconnections is to avoid Cu diffusion into silicon active zone that could seriously damage device performance, and into interlevel dielectric that could induce shorts or degrade dielectric performance. This paper relates the integration of Cu-CVD with SiO₂. Structures studied are SiO₂ deposited on Cu-CVD, and SiO₂/SiN/Cu structure: a thin SiN layer is deposited on Cu before SiO₂ to act as diffusion barrier and as an etch stop during the interconnect structure patterning. Both SiO₂ and SiN dielectric processes are made in plasma-enhanced chemical vapor deposition processes, from SiH₄ precursor with addition of, respectively, N₂O or NH₃. Cu contamination is shown to occur during the dielectric deposition onto Cu, and is enhanced by the fluorine presence in the deposition chamber. Deposition processes were evaluated in order to lower Cu contamination in the dielectric bulk. On an other hand, a noticeable degradation in Cu layer resistance was evidenced after dielectric deposition due to copper contamination during the dielectric deposition process. This issue can be addressed by the optimization of the dielectric deposition process.     

糖果型电阻膜宽带超材料吸波器的设计

提出了一种糖果型电阻膜宽带超材料吸波器。该吸波器的单元结构采用电阻膜-介质-电阻膜结构,其中顶层电阻膜为糖果型, 介质层由多种材料叠加而成, 介质层材料从顶至底依次为PET、FR-4、PMMA 和PET。CST 软件仿真结果表明本吸波器吸收率的峰值可达100%,吸收率超过99% 的频带宽度约为2.5 GHz, 超过90% 的频段能够完全覆盖X 波段, 部分覆盖Ku 波段,相对带宽为70%。随着电磁波入射角度的变化, 吸收峰所对应的中心频率稳定, 能够实现对相应频段的完美吸波,并且具有宽带吸波特性。     

Electrical characteristics of textured polysilicon oxide preparedby a low-temperature wafer loading and N2 preannealingprocess

A low-temperature wafer loading and N₂ preannealing process was used to grow a thin textured polysilicon oxide. The polyoxide grown on the heavily doped polysilicon film exhibits less oxide tunneling leakage current and higher dielectric strength when the top electrode is positively biased     

Dielectric ring resonators loaded in waveguide and on substrate

A rigorous mode matching technique is used to analyze the dielectric ring resonators loaded in a waveguide and on top of a substrate. Variation of several lowest order modes' resonant frequencies as a function of structure parameters is presented and is shown to be helpful for optimization of spurious mode separation. Two-dimensional electric and magnetic field line patterns and three-dimensional field intensity distributions of the ring resonators are plotted and provide information for mode excitation, coupling, and spurious mode suppression. Coupling between two dielectric ring resonators loaded in a metallic cavity are analyzed. The dielectric ring resonators are used to design a C-band elliptic function dual mode bandpass filter employing HE₁₁ modes. Experimental results are presented and show excellent agreement with the analytical solutions     

Low-Power and Nanosecond Switching in Robust Hafnium Oxide Resistive Memory With a Thin Ti Cap

The memory performance of hafnium oxide (HfO_x)-based resistive memory containing a thin reactive Ti buffer layer can be greatly improved. Due to the excellent ability of Ti to absorb oxygen atoms from the HfO_x film after post-metal annealing, a large amount of oxygen vacancies are left in the HfO_x layer of the TiN/Ti/HfO_x/TiN stacked layer. These oxygen vacancies are crucial to make a memory device with a stable bipolar resistive switching behavior. Aside from the benefits of low operation power and large on/off ratio (>100), this memory also exhibits reliable switching endurance (>10⁶ cycles), robust resistance states (200°C), high device yield (~100%), and fast switching speed (<10 ns).     

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     

Input impedance of annular-ring microstrip antennas with adielectric cover

A theoretical and numerical analysis of the annular-ring microstrip antenna with a dielectric cover is performed. The problem is formulated in the Hankel transform domain, taking a coaxial feed into consideration. The integral equations for the surface current density on the patch are derived. Galerkin's method is used to solve for the surface current density, and a stationary formula for the input impedance is obtained. Numerical results showing the effects of a dielectric cover on the TM₁₂ mode of the annular ring are given. It is found that the dielectric cover reduces the resonant frequency, decreases the resonant resistance, and increases the impedance bandwidth