Embedded microstrip interconnection lines for gigahertz digitalcircuits

Transmission line structures are needed for the high-performance interconnection lines of GHz integrated circuits (ICs) and multichip modules (MCMs), to minimize undesired electromagnetic wave phenomena and, therefore, to maximize the transmission bandwidth of the interconnection lines. In addition, correct and simple models of the interconnection lines are required for the efficient design and analysis of the circuits containing the interconnection lines. In this paper, we present electrical comparisons of three transmission line structures: conventional metal-insulator-semiconductor (MIS) and the embedded microstrip structures-embedded microstrip (EM) and inverted embedded microstrip (IEM). In addition, we propose closed-form expressions for the embedded microstrip structures EM and IEM and validate the expressions by comparing with empirical results based on S-parameter measurements and subsequent microwave network analysis. Test devices were fabricated using a 1-poly and 3-metal 0.6 μm Si process. The test devices contained the conventional MIS and the two embedded microstrip structures of different sizes. The embedded microstrip structures were shown to carry GHz digital signals with less loss and less dispersion than the conventional MIS line structures. S-parameter measurements of the test devices showed that the embedded microstrip structures could support the quasi-TEM mode propagation at frequencies above 2 GHz. On the other hand, the conventional MIS structure showed slow-wave mode propagation up to 20 GHz. More than 3-dB/mm difference of signal attenuation was observed between the embedded microstrip structures and the conventional MIS structure at 20 GHz. Finally, analytical RLCG transmission line models were developed and shown to agree well with the empirical models deduced from S-parameter measurements     

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     

Suppression of mode coupling in conductor-backed asymmetric coplanar strips using slow-wave electrodes

Shorted-ground conductor-backed asymmetric coplanar strips support unwanted noncoplanar modes that adversely affect the performance of such transmission lines at higher frequencies. It is shown that coupling from the desired coplanar mode into the noncoplanar modes can be suppressed using slow-wave electrodes. This suppression scheme is verified by measuring the S-parameters of both conventional and slow-wave transmission lines of this type in the 0.05-50 GHz range.     

Transmission theory of a parallel-two-wire-transmission-linecovered with three layer media

A parallel-two-wire-transmission-line covered by a three layer media has particular transmission characteristics. It is expected that this type of line might therefore be applied to new microwave circuits and antennas. Such lines have been analyzed by solving Laplace equations as a two dimensional boundary value problem. However, at higher frequencies, it is not appropriate to explain these particular properties using the quasi-TEM mode analysis. Transmission theory for these lines has to be solved using a rigorous three dimensional analysis. in this paper, we describe a new three dimensional analysis technique that is used to obtain more accurate propagation constants by considering the E_Z, H_Z components of the field. The assumed current distribution of the parallel-two-wire-line system is Fourier expanded over the angular coordinate &thetas;, and the boundary value problem is solved by the mode matching technique. It is found that mainly hybrid modes are transmitted via this type of transmission system and that the propagation constant varies discontinuously at frequencies where the dipole mode can exist on the three layer dielectric media itself. Numerical results are presented and compared with experimental data     

Hybrid-mode analysis of homogeneously and inhomogeneously dopedlow-loss slow-wave coplanar transmission lines

A hybrid-mode analysis is presented to characterize the propagation properties of uniplanar slow-wave MIS (metal-insulator-semiconductor) coplanar transmission lines. The effect of homogeneous versus gradually inhomogeneous doping profile is investigated as well as the influence of the metal conductor losses and finite metallization thickness on the slow-wave factor and the overall losses. Numerical results indicate that thick-film MIS CPWs can support a slow-wave mode with moderate loss up to 40 GHz when the line dimensions are kept in the micrometer range. Furthermore, it is found that an inhomogeneous doping profile can reduce the overall losses and that the effect of metal conductor losses in heavily doped MIS structures is only marginal. On the other hand, in weakly doped or insulating GaAs material a lossy metal conductor leads to a higher propagation constant, exhibiting a negative slope with increasing frequency     

Quasi-TEM analysis of multilayered, multiconductor coplanarstructures with dielectric and magnetic anisotropy including substratelosses

A quasi-TEM (transverse electromagnetic) analysis of multiconductor planar lines embedded in a layered structure involving lossy iso/anisotropic electric and/or magnetic materials is achieved. Conditions under which a quasi-TEM assumption is valid are theoretically determined. An efficient spectral-domain analysis is used to determine the complex capacitance and inductance matrices characterizing the transmission system. computation of the inductance matrix is reduced to the computation of an equivalent capacitance matrix when media characterized for a fully general permeability tensor are present. It is also shown that most actual monolithic microwave integrated circuit (MMIC) microstrip-type structures (where semiconductor substrates are present) and possible future applications including lossy magnetic materials can be analyzed by using the simple quasi-TEM model. The validity of the results has been verified by comparison with full-wave theoretical and experimental data on microstrip lines on magnetic substrates and slow-wave structures     

Artificially integrated synthetic rectangular waveguide

A synthetic rectangular waveguide (SRW), which consists of two electrical sidewalls and two parallel periodical structures placed at the top and bottom surfaces of the waveguide, is presented. The SRW is made by multilayered integrated circuit processes, which typically have large ratios of SRW lateral dimensions to substrate thickness. Two theoretical methods, finite-element method and deembedding of composite structure consisting of SRW and mode converters, are applied to investigate the propagation characteristics of the SRW. Application of the dispersion characteristics of the two-dimensional periodical structures coupled with appropriate mode converter designs leads to results in SRW designs supporting TE/sub 10/, TM/sub 00/, and TM/sub 10/ modes. Measurements and the two theoretical approaches indicate that the slow-wave factor is 4.9 and Q-factor is 260 at 6.85 GHz for the TE/sub 10/ mode propagation with a cutoff frequency of 4.10 GHz (0.348 factor of cutoff frequency of conventional rectangular waveguide using the same material and dimensions). The theoretical data show the TM/sub 00/ mode to have a slow-wave factor of 1.8, Q-factor of 187.6 at 11.4 GHz, and cutoff frequency of 10.2 GHz. The TM/sub 10/ mode has a slow-wave factor of 1.98, Q-factor of 187.6 at 12.5 GHz, and cutoff frequency of 10.4 GHz.     

Investigation of Crosstalk and Coupling Effects of Incident Plane Waves in Orthogonal Microstrips in High-Speed Integrated Circuits Using Full-Wave and Quasi-Static Methods

The crosstalk and coupling of the external fields on orthogonal microstrip transmission lines in different layers have significant effects on signal quality in MMIC and PCBs. In this paper the crosstalk is analyzed in detail using both full-wave and quasi-static methods. The used full wave method is mixed potential integral equation method of moment (MPIEMoM). Because of the weak coupling between lines, the effect of the incident plane-wave is studied by applying transmission line theory in a scattered voltage formulation uses quasi-TEM propagation model for each interconnection and the exact distribution of the incident electric field within the layers. Afterward, by using the predetermined lumped circuit model of the cross-region, the effect of coupling between two lines is calculated and then applied to terminal voltages in 1–20 GHz frequency range which results in the final terminal voltages.     

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     

S-parameter measurements yielding the characteristic matrices ofmulticonductor transmission lines

A frequency-domain method is presented, which yields accurate characteristic matrices of uniform multiconductor transmission lines (MTLs). It uses simple two-port network analyzer S-parameter measurements of a set of open-circuit and short-circuited MTL configurations. The method eliminates the need for voltage and current probes, which introduce errors. Transversely inhomogeneous MTLs can be accurately characterized in their quasi-TEM propagation regime. The influence of the skin effect on the inductance matrix is taken into account. The technique was used to determine the inductance and capacitance matrices of a low-loss three-conductor ribbon cable above a ground plane. Comparisons with numerically and analytically obtained data are given. Measurements are found to be repeatable for lines of length ℒ<λ/4. The λ/4 requirement is not found to be a restriction in the megahertz regime and only plays a role as line-end effects become significant at gigahertz frequencies. The obtained accuracy is significantly better than previously reported results     

High-Q Slow-Wave Coplanar Transmission Lines on 0.35 $mu$m CMOS Process

In this letter, experimental results and trends for shielded coplanar waveguide transmission lines (S-CPW) implemented in a 0.35 $mu$m CMOS technology are provided. Because of the introduction of floating strips below the CPW transmission line, high effective dielectric permittivity and quality factor are obtained. Three different geometries of S-CPW transmission lines are characterized. For the best geometry, the measured effective dielectric permittivity reaches 48, leading to a very high slow-wave factor and high miniaturization. In addition, measurements demonstrate a quality factor ranging from 20 to 40 between 10 and 40 GHz, demonstrating state-of-the-art results for transmission lines realized in a low-cost CMOS standard technology.      

The Generation and Propagation of Acoustic Surface Waves at Microwave Frequencies

The generation and propagation of acoustic surface waves is reviewed with particular emphasis on the microwave-frequency range. Theoretical work on optimizing the generation efficiency and the bandwidth of interdigital transducers is compared with recent experimental results. The minimum Iinewidth of 0.9 /spl mu/m which can be produced by optical photolithographic techniques places an upper limit of about 1 GHz on the maximum frequency that can be generated at the fundamental mode. Overtone operation has been used to generate 3 GHz surface waves on LiNbO/sub 3/ but this method has the disadvantage of reduced efficiency plus the complication of volume-wave generation. A better solution for generation above 1 GHz is the fabrication of interdigital transducers by means of electron beam exposure of the photoresist. The surface-wave propagation loss gives a significant contribution to the total insertion loss of delay lines operating at microwave frequencies. Losses of 1.1 dB//spl mu/s and 3.8 dB//spl mu/s at 0.9 GHz and 2 GHz, respectively, have been measured for propagation along the Z-direction of Y-cut LiNbO/sub 3/ by means of a laser deflection method. Larger losses have been observed for quartz. The additional complexities for surface-wave propagation due to the anisotropic single-crystal substrates which are necessary at microwave frequencies are also described.     

Exploiting CMOS reverse interconnect scaling in multigigahertzamplifier and oscillator design

The increasing number of interconnect layers that are needed in a CMOS process to meet the routing and power requirements of large digital circuits also yield significant advantages for analog applications. The reverse thickness scaling of the top metal layer can be exploited in the design of low-loss transmission lines. Coplanar transmission lines in the top metal layers take advantage of a low metal resistance and a large separation from the heavily doped silicon substrate. They are therefore fully compatible with current and future CMOS process technologies. To investigate the feasibility of extending CMOS designs beyond 10 GHz, a wide range of coplanar transmission lines are characterized. The effect of the substrate resistivity on coplanar wave propagation is explained. After achieving a record loss of 0.3 dB/mm at 50 GHz, coplanar lines are used in the design of distributed amplifiers and oscillators. They are the first to achieve higher than 10 GHz operating frequencies in a conventional CMOS technology     

Coplanar transmission lines on thin substrates for high-speedlow-loss propagation

We investigate the attenuation and phase velocity characteristics of coplanar strip (CPS) transmission lines designed for high-speed, low-loss propagation at sub-THz frequencies. Photoconductor switches driven by femtosecond optical pulses were used to generate propagating picosecond electrical transients. External electrooptic sampling was used to measure the time-domain impulse-response characteristics with subpicosecond time resolution. The finite-difference transmission-line-matrix (FD-TLM) numerical method was used to model picosecond pulse propagation on identical transmission lines. The experiment and the numeric simulations have clarified nonquasistatic high-frequency effects and were shown to agree over a 500 GHz frequency range. Additionally, analytic quasi-static velocity and characteristic impedance formulas have been verified and their frequency range of validity established for the investigated CPS geometries. Radiation into the substrate is the dominant loss mechanism at frequencies above ~100 GHz for the CPS lines on thick substrates. CPS transmission line fabrication on thin substrates has been proposed as a method for reducing high-frequency loss and increasing the microwave propagation velocity. CPS transmission lines fabricated on 8-μm-thick Si membranes have been studied and demonstrated to possess the desired high-speed, low-loss properties     

MILO实验模型的频移问题研究

针对目前磁绝缘线振荡器(MILO)实验研究中测量频率与数值模拟所得结果相差较远的问题，利用适用于冷腔的三维电磁场程序对MILO的冷腔结构进行了细致的数值模拟和理论分析。研究发现：该MILO的主慢波结构工作在近π模状态时，其电磁模武除设计的基模TM01外，还存在高阶非轴对称的TM21模式，实验中很可能是由于某种非对称激励导致该系统工作在高阶非轴对称模式，从而使得测量频率与理论设计不符。     

Systematic determination of the propagation characteristics ofcoplanar lines on semiconductor substrate

A method allowing the systematic determination of the propagation characteristics of micron-size waveguides and overcoming the influence of feeding access discontinuities is presented. The complex propagation constant and characteristic impedance of a slow-wave Schottky contact coplanar line are determined in the 1 to 26 GHz frequency range under different DC bias conditions. This method is successfully used to characterize the Schottky contact coplanar line of micron size under drastic conditions, that is, high value of slow-wave factor, significant attenuation, dispersive transmission line, and strong mismatches between feeding line and device under test. Comparisons with transmission line model theoretical results show very good agreement, despite the large slow-wave factor, attenuation, and dispersion of the waveguide. The electric schemes of the feeding access discontinuities are also presented     

Low-loss slow-wave propagation along a microstructure transmission line on a silicon surface

We report observations of relatively low-loss propagation in the frequency range of 1.0 to 12.4 GHz using a micrometer-size coplanar MIS transmission line fabricated on a heavily doped N + silicon surface. This low-loss mode of propagation is found to be accompanied by significant wavelength reduction which suggests that such lines may be useful as transmission media for distributed components in silicon monolithic microwave integrated circuits (MMICs).     

Characterization of Co-Planar Silicon Transmission Lines With and Without Slow-Wave Effect

Co-planar lines on silicon substrates with and without slow-wave effect are characterized using time-domain reflectometry (TDR) and vector network analyzer (VNA) measurements, and simulated using a proposed nonphysical resistance-inductance-conductance-capacitance (RLGC) model. The silicon co-planar lines are characterized based on comparison to package transmission lines. Co-planar silicon lines without slow-wave mode are modeled in the same way as package transmission lines, but co-planar lines with slow-wave mode are modeled in a different way from package transmission lines. Hence, a nonphysical RLGC model including slow-wave mode is proposed along with the extraction method from VNA measurements. Simulation results correlate well with time- and frequency-domain measurements for the co-planar silicon lines.     

Transient analysis of coupled, tapered transmission lines witharbitrary nonlinear terminations

A fast and efficient method of simulating the time-domain transient response of coupled, tapered transmission lines is presented. A time-domain scattering parameter formulation is used to derive the simple closed-form expression for the voltage variables for uniform lossless lines; this expression is applied to tapered lines by dividing the lines into many uniform section. Computational efficiency and stability are achieved using recursive time-domain algorithms. When a quasi-TEM propagation mode is assumed, the method is applicable to nonlinear terminations and inhomogeneous dielectric media. Memory requirements are minimized and are independent of the number of time steps. Simulation results showed good agreement with experimental results     

UC-PBG结构创建准TEM波导的仿真分析

光子带隙(Photonic BandGap, PBG),是指人造的周期性电介质结构,它使得在一定频率范围内的电磁波是禁止传播的,而单平面紧凑型光子带隙结构(UC-PBG)是一种以微带基片为载体的周期性平面光子带隙结构。该文用UC-PBG结构置换标准矩形波导窄边,可在UC-PBG结构的谐振频率点附近将TE10模转变成准TEM模。通过对整个系统进行仿真计算,证实了此方法切实有效,在Ku波段转换带宽达到450 MHz。