Obtaining the specific contact resistance from transmission line model measurements

In characterizing ohmic contacts using the transmission line model, it is necessary to make a measurement referred to as the contact end resistance, as a result of modification to the sheet resistance under the contact. In this article we show that this contact end resistance and the consequent specific contact resistance can be deduced from simple resistance measurements carried out between contacts on a standard, transmission line model test pattern.     

Quasi-two-dimensional transmission line model (QTD-TLM) for planarohmic contact studies

An analytical quasi-two-dimensional transmission tine model (QTD-TLM) has been formulated to more accurately extract the specific contact resistance (ρ_c) of ohmic contacts than the conventional one-dimensional TLM (1D-TLM). Similar to 1D-TLM, the extraction of ρ_c using QTD-TLM is straightforward. By means of the conformal mapping technique, the two-dimensional (2-D) (or lateral) current flow and current crowding, owing to the presence of a gap between the TLM mesa and contacts, are jointly incorporated into our model using a single shunt resistor. QTD-TLM is generalized as it is applicable to a variety of contact dimensions and gap widths, and to both alloyed and nonalloyed contacts. The validity of QTD-TLM has been verified experimentally using two alloyed and two nonalloyed ohmic contacts, and by comparison with results from a 2-D numerical model     

An analytical model for alloyed ohmic contacts using a trilayer transmission line model

This paper describes a Transmission Line Model approach to the modeling and analysis of alloyed planar ohmic contacts. It briefly reviews the standard Transmission Line Model (TLM) commonly used to characterize a planar ohmic contact. It is shown that in the case of a typical Au-Ge-Ni alloyed ohmic contact, a more realistic model based on the TLM should take into account the presence of the alloyed layer at the metal-semiconductor interface. In this paper, such a model is described. It is based on three layers and the two interfaces between them, thus forming a Tri-Layer Transmission Line Model (TLTLM). Analytical expressions are derived for the contact resistance Re and the contact end resistance Rc of this structure, together with a current division factor, S. Values for the contact parameters of this TLTLM model are inferred from experimentally reported values of Re and Re for two types of contact. Using the analytical outcomes of the TLTLM, it is shown that the experimental results obtained using a standard TLM can have considerable discrepancies.<>     

Accurate analysis of carbon nanotube interconnects using transmission line model

A new technique for analysing the time-domain response of carbon nanotube (CNT) interconnects, based on transmission line modelling, that takes the effects of both contact and fundamental (quantum) resistances into account is introduced. A new sixth-order linear parametric expression for the transfer function of these lines has been presented for the first time. For verification purposes, the step response of a driver-CNT bundle-load configuration for a 32 nm technology node, using the new technique and HSPICE simulation have been compared, with which the obtained results show an excellent match. Also the effect of contact resistance on the step response, especially the propagation delay, has been studied. The obtained results show that for the length of a CNT bundle equal to 50 mum with the diameter of each individual CNT 1 nm, the propagation delay changes from 0.138 to 5.58 ns for the contact resistance values from 1 to 50 k Omega, i.e. a variation range of 39.43 times the minimum value. The related delay variations for the length values 200 mum, 500 mum and 1000 mum, are 31.37, 22.61 and 15.42 times the minimum value, respectively.     

Analysis of transmission line circuits using multidimensional model reduction techniques

This paper presents a new technique to reduce the order of transmission line circuits simultaneously with respect to multiple parameters. The reduction is based on multidimensional congruence transformation. The proposed algorithm provides efficient means to estimate the response of large distributed circuits simultaneously as a function of frequency and other design parameters.     

Rigorous analysis of a circular patch antenna excited by amicrostrip transmission line

Boundary conditions are enforced on a portion of the microstrip feed line as well as the patch antenna. The integral equation for the unknown currents on the antenna and feed is solved by applying the Galerkin method of moments in the Fourier transform domain. The validity of the solution is tested by comparison of computed results with experimental data. The theoretical treatment proves to be applicable to the most common feeding arrangements, namely, the direct edge-feed and proximity coupling excitation. In the latter case, two-layer substrates having distinct dielectric constants are studied. The purpose of the study is to deduce, for a given overall substrate thickness, the smallest line-ground plane separation for which a match of the radiator to the feed line is still possible. The advantages of such a configuration are discussed     

Fast transmission line coupling calculation using a convolutiontechnique

A fast method for the calculation of the mutual coupling between transmission lines is presented. The method is based on using the convolution of the incident field and the current induced by a Dirac impulse type field. Only first-order coupling between the lines is taken into account. This means that only the current induced by the source line is taken into account and all currents resulting from induction by this induced current are discarded. The technique is orders of magnitude faster than traditional moment method techniques because no large matrix equations need to be solved     

Calculation of transverse waves in a shielded transmission line containing circular cylindrical conductors

A method is proposed for calculating a shielded homogeneous multiconductor transmission line containing conductors of circular cross section. Formulas are obtained for the matrix of the conductor capacitance per unit length and the electric parameters of transverse electromagnetic waves.     

A broad-band transmission line model for a rectangular microstripantenna

A method is developed using the transmission line model to predict the input characteristics of rectangular microstrip antennas over a wide band of frequencies. A series combination of transmission lines is used to represent each transverse magnetic (TM) model. Following a brief summary of the basic transmission line model, the idea of an equivalent length, width, and feed offset are introduced to model each mode. The results predicted by the model compared well with experimental results that assumed varying feed positions. The concept of equivalent length, width, and feed offset was validated by experimental results but shows that the equivalent offset term needs some improvement. The number of modes incorporated in the model depends on the frequency range over which the antenna must be modeled. Using three transmission lines gives good results up to the frequency at which the TM₀₂ mode is excited     

Impedance transformation using a hyperbolic cosine-squared tapered transmission line

A closed-form equation for the impedance transformation of an arbitrarily complex load, using a hyperbolic cosine-squared tapered transmission line, is presented. Design charts are also given. A numerical example is considered and results indicate a tremendous reduction in size, in comparison to other forms of lines, when hyperbolic cosine-squared lines are employed to match a large complex impedance to a real 50 Ω impedance.     

Linear tunable phase shifter using a left-handed transmission line

We demonstrate a compact, linear, and low loss variation hybrid phase shifter using a left-handed (LH) transmission line. For frequencies from 4.3 to 5.6 GHz, this phase shifter gives a nearly linear phase variation with voltage, with a maximum deviation of /spl plusmn/7.5/spl deg/. Within this frequency range, the maximum insertion loss is 3.6 dB, and the minimum insertion loss is 1.8 dB over a continuously adjustable phase range of more than 125/spl deg/, while minimum return loss is only 10.2 dB. Furthermore, this phase shifter requires only one control line, and it consumes almost no power.     

Measurement of contact resistance distribution using a 4k-contactsarray

A new test structure suitable for measuring a contact resistance distribution has been developed. It includes the following two components: a 256 row, 16 column (= 4096) four-terminal cross-contact array; and peripheral circuits, which consist of an eight-stage CMOS binary counter and 256-bit CMOS decoders. It was found that contact resistance can be fitted by a Gaussian distribution for more than three standard deviations of the mean value. The relationship between the contact size and the standard deviation of the contact resistance has been discussed for two types of contacts: Al/TiN/TiSi₂-n⁺Si, and WSi₂/poly-n⁺Si. This test structure can simultaneously measure the series resistance of a two-terminal contact chain and the individual contact resistance. By comparing the results of the two measurement modes, it was found that there are three kinds of contact resistance distribution in the chips which have high series resistance of the two-terminal contact chain     

Specific contact resistance and noise in contacts on thin layers

A method is presented for the calculation of the specific contact resistance and noise of contacts on thin layers. The contribution to the contact resistance and noise of the interface between the contact and the layer is determined from experimental results. Using the developed method on thin Cu_xS layers with a sheet resistance of 42.5 Ω values for the specific contact resistance of 4 × 10^?2 Omega; cm² and 2.5 Ω cm² were observed for two different contact technologies.     

Analysis of transmission line structures using a new image-modeGreen's function

A hybrid image-mode-moment method for the quasi-transverse-electromagnetic (quasi-TEM) analysis of transmission lines of arbitrary cross section and number, suspended between infinite parallel ground planes is discussed. This method systematically combines, in a single formulation, the conventional moment method with a new image-mode Green's function. The moment method is used to model the interaction between transmission lines, and the new image-mode method is used to furnish the Green's function of the parallel plates. Several configurations are studied and compared, where possible, with work given in the references     

The determination of diode resistance from the transmission using awaveguide/coaxial line tee junction

A method of finding the resistance and conductance of a diode terminating the coaxial arm of a tee junction from the minimum transmission obtained by adjusting the position of the diode, from the effect of an incremental change in this position, or from the frequency bandwidth of the transmission characteristic, is described. The method avoids the direct measurement of high reflection encountered at the extremes of bias with diode terminations. The parameters of the junction needed in the derivation are found experimentally. Allowing for loss in the coaxial line, the resistance of diodes determined at 9.4 GHz was in good agreement with the results of coaxial line measurements at 500 MHz and 3 GHz. The effect of the reactances of the diode capsule, not allowed for in the determination, is considered briefly     

Analysis of a shielded transmission line containing circular cylindrical conductors and coplanar lines on a grounded shield

For the first time, a method is proposed for numerical calculation of a monolithic multiconductor shielded transmission line integrated with planar coupling circuits. Formulas for the matrix of the per-unit-length capacitance of coupled conductors are derived. The electric parameters of fundamental modes are calculated in the quasi-static approximation. The computation results can be used for designing monoblock microwave filters.     

An enhanced transmission line model for conducting wires

The "standard" transmission line model describes accurately the propagation of electric signals along conducting wires, if the distance between them is much smaller than both their length and the smallest characteristic wavelength of the signals. This paper presents an "enhanced" transmission line model that is able to describe the propagation along perfectly conducting wires in a homogeneous dielectric, and also when the distance between the wires is comparable with the smallest characteristic wavelength of the signals. The enhanced model is obtained, with suitable approximations, starting from a full-wave analysis of the problem and using an integral formulation based on the electromagnetic potentials satisfying the Lorentz gauge. It differs from the standard transmission line model, only in its constitutive relations, that is, in the relation between the per unit length (p.u.l.) magnetic flux and the current intensity, and in the relation between the electric voltage and the p.u.l. electric charge. In the standard model, these relations are of the algebraic type, and in the enhanced one they are of the convolution type, expressing nothing more than a very simple physical fact: the values of the p.u.l. flux and voltage at the generic abscissa along the wires depend on the entire distribution of the current and the p.u.l. charge, respectively. The kernels of the convolution integrals have the logarithmic singularity typical of the surface distributions and takes into account proximity effects. The solution of the enhanced model highlights the high-frequency effects due to dispersion and radiation that the standard model is unable to provide. Good agreement with the solutions obtained by a full-wave electromagnetic numerical code is achieved.     

Analog transmission line model for simulation of systemiccirculation

A simple four-tube arteries-microvessels-veins system which simulates a more realistic loading for human circulation was built using transmission line network. Hemodynamic data from literature are used in the fluid-circuit analogy, and the flow leakage and viscoelastic properties of the blood vessels have been considered. The effect of veins on the input impedance spectrum was found to be negligibly small above 0.5 Hz. The predicted input impedance spectra agree reasonably well with the published measurements both in shape and magnitude. Parametric analysis shows that the changes of vascular properties in the lower body affect the first minimum, and the changes in the upper body influence the second minimum. The blood flow in and out of kidney and liver dominates the aortic impedance from 0 to 5 Hz. Decreasing capacitance (i.e., increasing arterial stiffness due to aging), reducing the lumen area, or decreasing the length of blood vessels result in an increase in the impedance modulus, and the first minimum shift to a higher frequency which agree well with experiments. In the current model, the pressure, flow waveform, and local impedance can be predicted at any location along the circulatory tree. The characteristic of arterial pulse propagation resembles published measurements     

Exponentially tapered transmission line model of the arterialsystem

The arterial systemic tree is intricate and complex due to its numerous branches, nonuniform cross section and elasticity, and the rich harmonic composition of its pressure- and flow-pulses. To deal with this complexity, the modeling of the arterial system based on the technique of nonuniform transmission lines was undertaken. The main advantages of the technique are that it maintains a satisfactory response over a wide range of frequencies and that it analyzes the impedance and local reflection factor of various segments. The model, which utilizes far fewer parameters than previous models, supplies important information about reflections at bifurcations and impedance matching at the termination line     

Proposal for a 94-GHz phase-reversal optical modulator using a loaded transmission line

One of the most important problems associated with the design of external travelling wave optical modulators operating at very high frequency is the reduction of microwave loss associated with the electrode structure. With this in view, a new design for a Ti:LiNbO/sub 3/ narrow-band optical modulator is proposed for operation at 94 GHz. It uses a low-loss loaded transmission line with dielectric overlay and uses phase-reversals to achieve phase matching. Numerical simulations predict a required 21-dBm drive power for full on-off switching at 94 GHz.