Propagation characteristics of MIS transmission lines withinhomogeneous doping profile

The authors present a hybrid-mode analysis of slow-wave MIS (metal-insulator-semiconductor) transmission lines with a gradually inhomogeneous doping profile. In general it was found that, in comparison with homogeneously doped semiconductor layers, a Gaussian-type doping distribution results in lower losses for the slow-wave mode in both thin- and thick-film MIS CPWs. While the effect of the doping profile is more pronounced in thin-film structures which support a slow-wave mode only up to 3 GHz, it is less significant in thick-film structures. On the other hand, numerical analysis indicates that thick-film structures can support a slow-wave mode at moderate loss up to 40 GHz. The behavior of MIS microstrip lines is similar to that of MIS CPWs, except that for thick-film transmission lines an increase in losses can be observed when the doping profile becomes inhomogeneous. The numerical investigation was carried out using the method of lines. Several transmission lines have been investigated, and results are presented for microstrip, coupled microstrips, and coplanar lines     

Quasi-TEM Analysis of "Slow-Wave" Mode Propagation on Coplanar Microstructure MIS Transmission Lines

We present a simple quasi-TEM analysis of "slow-wave" mode propagation on micron-size coplanar MIS transmission lines on heavily doped semiconductors and compare theoretical results with measurements on four such structures at frequencies from 1.0 to 12.4 GHz. Excellent agreement is found, which shows that the "slow-wave" mode propagating on these transmission lines is, in fact, a quasi-TEM mode. Relatively low-loss propagation along with significant wavelength reduction is observed. Conduction losses of the metal, which have been tacitly ignored in previously published "full-wave" treatments of "slow-wave" mode propagation, are included in the theory and are shown to dominate the attenuation at frequencies below 25 GHz and to still be significant at frequencies up to at least 100 GHz.     

Using the MIS capacitor for doping profile measurements with minimal interface state error

Doping profiles can be measured to best advantage by using MIS capacitors when one is interested in the profile either very close to the semiconductor surface or in very heavily doped semiconductors. This paper shows both experimentally and theoretically that the major error caused by interface states can be minimized by using either the pulsed capacitance voltage technique or by the second-harmonic profiling technique. This makes possible profile measurements in MIS capacitors even with very large interface state densities, and makes it advantageous to use MIS capacitors for the express purpose of profile measurements. The minimization of interface state errors is contingent upon using a high enough measurement frequency. Moreover, the closer to the interface that the profile is desired, the higher the frequency must be. At high enough frequencies, the intrinsic resolution of the method allows accurate measurement of the doping profile only to within a few extrinsic Debye lengths of the Si-SiO2interface. Curves are presented indicating the closeness to the interface attainable within a 2 percent profile error as a function of measurement frequency, doping level, and temperature. Comparison of experimental measurements with theory on uniformly doped samples at 5 and 30 MHz substantiates our analysis of interface state effects. Finally, a nonuniform profile is measured to illustrate the method.     

Slow-Wave Coplanar Waveguide on Periodically Doped Semiconductor Substrate

A metal-insulator-semiconductor (MIS) coplanar waveguide with periodically doped substrate is described. An efficient numerical method is introduced in order to obtain the propagation constants and the characteristic impedances of the constituent sections of each period. Using the results, the characteristic of the periodic MIS coplanar waveguide is analyzed by Floquet's theorem. The theoretical study shows reduction of attenuation and enhancement of the slow-wave factor at certain frequencies, compared to the uniform MIS coplanar waveguide. This structure is experimentally simulated and shows good agreement theory.     

The use of active traveling-wave structures in GaAs MMIC's

A coplanar waveguide has been fabricated on a modulation doped GaAs substrate in order to evaluate the potential of traveling-wave structures in microwave applications. The use of a Schottky contact center conductor enables the line to function as a slow wave structure in which the rf propagation characteristics can be modified with a dc bias. Measurements are reported at 10 GHz on simple structures, some of which incorporated an additional dielectric layer. Results show that slow-wave factors of between 8 and 24 are readily obtained with a loss per slow-wave factor of about 0.7 dB/mm. The practical issues relating to the application of such structures in phase shifters, chip size reduction, compact active filters and resonators are examined     

Determination of the semiconductor doping profile right up to its surface using the MIS capacitor

A new method has been developed by which the doping profile of the semiconductor can be obtained right up to its surface. Contrary to the well known dC/dV-method, which is valid only in the depletion range, we have considered the majority carriers in deriving relations for doping density as well as distance from the semiconductor surface, in terms of the space charge capacitance and its derivative with respect to the surface potential. This method can be realized experimentally on any MIS structure. Measurements on MOS capacitors with steam grown oxides showed a drooping profile towards the SiSiO₂ interface for boron doped and a rising one for phosphorus doped silicon. Post-oxidation annealing in dry nitrogen at 1200°C produced a uniform profile for phosphorus doped silicon.     

Characterization of MIS structure coplanar transmission lines forinvestigation of signal propagation in integrated circuits

A full-wave analysis of metal-insulator-semiconductor (MIS) structure micron coplanar transmission lines on doped semiconductor substrates is carried out using a finite-difference time-domain approach. Metal conductor loss is taken into account in the analysis. Line parameters and electromagnetic field distributions are calculated over a wide frequency range involving slow-wave and dielectric quasi-transverse-electromagnetic mode limits. Measurements of these line parameters, varying substrate resistivity from 1 to 1000 Ω-cm, in the frequency range up to 40 GHz are also presented, and these agree with the analysis quite well. On the basis of these results, an equivalent circuit line model is induced and some considerations on the relationship between line structure and properties made     

A Variational Theory for Wave Propagation in Inhomogeneous Dielectric Slab Loaded Waveguides

A novel numerical technique based on the variational formulation defined only in the slab is developed to study the loaded rectangular waveguide with an inhomogeneous dielectric slab. The variational equation for the boundary value problem is formulated and solved numerically, using the finite element method with piecewise quadratic trial functions. A comparison of this new technique with the conventional variational ones is presented. Various propagation characteristics, such as the phase constant, useful bandwidth, power handling capacity, and attenuation constants due to conductor and dielectric losses, are investigated for the waveguide centrally loaded with a slab of parabolic dielectric profile. The effects of changes in dielectric profiles are discussed by examining the results for the slabs with constant and parabolic profiles.     

New prospective coplanar metal-insulator-semiconductor (MIS)monolithic structure

Research work on various MIS transmission lines is well documented. Useful slow-wave propagation with low loss is always exhibited in recently proposed lower frequency ranges (several GHz). The author is concerned with the essential properties of the micrometre-size coplanar MIS lines. A new loss-reducing monolithic MIS is proposed with reference to physical considerations to ensure a low-cost mechanism     

Guided Waves in Inhomogeneous Focusing Media Part III: Wall Effects, Losses, and the Transition from Fast to Slow Waves

This paper is concerned with the determination of field patterns, propagation constants, and losses for axially propagating modes guided by an enclosed circular cylindrical, radially inhomogeneous dielectric of the type discussed in Parts I and II. The homogeneous outer medium (/spl gamma/ /spl ges/ /a) is assumed to have a large relative permittivity /spl epsiv//sub 2/, and the analysis includes the perfect conductor case /spl epsiv//sub 2/ /spl rarr/ /spl infin/. The transition to trapped waves as the binding effect increases is demonstrated. Propagation constants in the case with loss are determined using a perturbation technique.     

Electric-magnetic-electric slow-wave microstrip line and bandpass filter of compressed size

This paper presents a novel integrated microstrip low-loss slow-wave line. The new microstrip replaces the conventional metal strip by composite metals paralleling the electric surface and magnetic surface (MS). The MS made of an array of coupled inductors shows a high-impedance state in the stopband, below which the propagation properties can be well controlled by varying the dimensions of the electric surface and MS. The dispersion curves obtained by matrix-pencil analyses closely correspond to those obtained by scattering-parameter extraction. Theoretical results, as confirmed experimentally, indicate that an increase of over 60% in the slow-wave factor can be achieved without sacrificing propagation losses, using the proposed structure. This electric-magnetic-electric (EME) microstrip is insensitive to the alignment position of the periodical structure, and can be constructed using conventional printed-circuit-board fabrication processes and integrated with other microwave components in a multilayered circuit. A compact EME bandpass filter (BPF) with suppressed harmonic responses is presented. The length of the filter is reduced by 26%, and the measured insertion loss and fractional bandwidth is comparable to that of a conventional microstrip BPF on the same substrate.     

Slow-Wave Propagation Along Variable Schottky-Contact Microstrip Line

Schottky-contact microstrip lines (SCML) are a special type of transmission line on the semiconducting substrate: the metallic-strip conductor is specially selected to form a rectifying metal-semiconductor transition while the ground plane exhibits an ohmic metallization. Thus the cross section of SCML is similar to that of a Schottky-barrier diode. The resulting voltage-dependent capacitance per unit length causes the nonlinear behavior of such lines. In this paper a detailed analysis of the, slow-wave propagation on SCML is presented, including the effect of metallic losses. Formulas for the propagation constant and characteristic impedance are derived and an equivalent circuit is presented. Conditions for slow-mode behavior are given, particularly taking into account the influence of imperfect conductors and defining the range of many interesting applications. Experimental results performed on Si-SCML are compared with theory.     

Time-domain response of MIS coplanar waveguides for MMICs

An MIS coplanar waveguide propagating a slow-wave mode has been characterised in the time domain. The theoretical analysis proposed to obtain the time-domain response of the line gives results in good agreement with measurements. The circuit analysis used is suitable for the determination of spurious propagation effects, inherent to the use of miniature waveguides encountered in MMICs, such as Schottky contact coplanar lines and coupled microstrip lines laid on MIS substrates.     

Invited paper Characteristics of travelling waves along the non-linear transmission lines for monolithic integrated circuits: a review

A general analysis of non-linear wave propagation along transmission lines with voltage-dependent capacitance is presented. In particular, slow-wave structures like MIS and Schottky-barrier strip lines are examined. A spatial periodicity is included explicitly. The theoretical treatment is based on suitable equivalent circuits leading to characteristic wave equations. With regard to practical devices, the solutions show a variety of different phenomena as determined by the parameters of the non-linearity, dispersion and dissipation and the boundary conditions. Experimental results performed on a slow-wave model line are included.     

MIS slow-wave structures over a wide range of parameters

Lossy multilayer, multiconductor MIS microstrip structures are analyzed with the spectral-domain approach over a wide range of frequency and substrate loss. The modal attenuation and propagation constants are presented for two- and four-conductor structures as a function of the substrate loss tangent. Single-conductor structures are characterized with contour plots showing the complex effective dielectric constant as a function of both frequency and conductivity. MIS slow-wave structures are analyzed for both Si-SiO₂ and GaAs configurations     

毫米波螺旋线行波管慢波系统高频损耗

基于夹持杆分层螺旋带模型和三维电磁场分析研究了毫米波螺旋线行波管慢波系统的导体和介质损耗。螺旋带模型中介质损耗考虑为纵向传播常数的虚部,给出螺旋带中电磁场的解析解,导体损耗由螺旋线和管壳表面的面电流不连续性获得。三维电磁场分析通过本征模法,求解单周期结构的品质因数和周期储能获得有限导电率导体和夹持杆陶瓷损耗角带来的慢波系统高频损耗。结果表明,毫米波段螺旋线的导体损耗和夹持杆的介质损耗远大于管壳导体损耗,介质损耗与陶瓷损耗角呈线性关系,对高频损耗的影响不可忽略。     

Metal–Dielectric Slot-Waveguide Structures for the Propagation of Surface Plasmon Polaritons at 1.55 μm

We present a deep-subwavelength-size metal slot-waveguide structure which can efficiently propagate surface plasmon polaritons (SPPs) at 1.55 mum within a high-index material. Through a systematic design analysis, we investigate the intrinsic tradeoffs and suggest solutions to substantially increase the propagation length of SPPs combining high-index dielectrics and metal structures. By studying several metal/dielectric geometries, we have found that the slot-waveguide size can be significantly decreased by the use of high-index materials without compromising the overall propagation losses. Our analysis also indicates that the device size-scaling is ultimately limited by a cutoff thickness for the metal film in which the slot is defined. For film thicknesses below cutoff, radiation modes exist which leak out of the guiding region. For certain operating frequencies, the radiant energy leaks out into both free space modes as well as surface plasmons guided along the top/bottom metal surfaces of the device. We have shown that, by using a silicon filling, the cutoff thickness of a 100-nm-wide slot waveguide can be as small as 90 nm, compared with 750 nm for the unfilled reference structures. In addition, we have demonstrated that by the use of SiO₂ gap regions surrounding the Si dielectric core in a 200times400-nm silver slot region (partially filled metal slot), we can considerably reduce the overall propagation losses to less than 0.14 dB/mum, corresponding to a propagation length of approximately 50 mum     

Wave Propagation in Coaxial-Cylindrical Slow-Wave Systems (Correspondence)

Recent interest in E-type traveling-wave tubes, in which a ribbon-shaped electron beam is caused to follow a circular path by balancing the centrifugal force of the particle against a steady radial electric tield force, has led to an investigation of wave propagation in azimuthally reentrant and nonreentrant coaxial-cylindrical slow-wave structures. The study is facilitated by the simplifying approximation that the actual azimuthally-periodic slow-wave circuit, situated along the inner conductor, can be replaced by a smooth dielectric cylinder. While such a dielectric cylinder would probably not be employed in the construction of an actual tube, because of its small value of surface impedance, it serves as a convenient model in determining the general forms of functional dependence for the field equations.     

Effect of process variables on the microwave conductivity of thick-film conductors

This letter presents the preliminary results of an investigation into the effect of process variables on the microwave conductivity of thick-film conductors. The quality factor Q0 of 50 ? closed resonators has been measured as a function of the firing temperature of the conductor and the mesh printing size. The results show that fine-mesh screens can be used without increasing the conductor losses, and that a high peak-firing temperature reduces the losses. The radio-frequency conductivity of the films as a fraction of bulk metal ranges from 0.45 at 1 GHz to 0.65 at 12 GHz.     

Limitations of the MIS capacitance method resulting from semiconductor properties

The influence of doping profiles, traps and grain boundaries in the semiconductor on the C-V characteristics of ideal MIS diodes is calculated. In addition, it is shown that losses and frequency dispersion as well as hysteresis effects can result from traps in the semiconductor. If these semiconductor properties are ignored misinterpretations in terms of interface state density will arise which can be about 10¹² cm⁻². In the case of decreasing doping profiles and traps in a n-type semiconductor one will get an apparent positive surface charge while an apparent negative surface charge will result from increasing profiles and grain boundaries. A method for the experimental determination of the C-V characteristics of ideal MIS diodes is developed. This method is applicable to stable diodes with only shallow traps in the semiconductor.