Jason A. Mix

Substrate integrated waveguides optimized for ultrahigh-speed digital interconnects

This paper reports an experimental and computational study of substrate integrated waveguides (SIWs) optimized for use as ultrahigh-speed bandpass waveguiding digital interconnects. The novelty of this study resides in our successful design, fabrication, and testing of low-loss SIWs that achieve 100% relative bandwidths via optimal excitation of the dominant TE/sub 10/ mode and avoidance of the excitation of the TE/sub 20/ mode. Furthermore, our optimal structures maintain their 100% relative bandwidth while transmitting around 45/spl deg/ and 90/spl deg/ bends, and achieve measured crosstalk of better than -30 dB over the entire passband. We consider SIWs operating at center frequencies of 50 GHz, accommodating in principle data rates of greater than 50 Gb/s. These SIWs are 35% narrower in the transverse direction and provide a 20% larger relative bandwidth than our previously reported electromagnetic bandgap waveguiding digital interconnects. Since existing circuit-board technology permits dimensional reductions of the SIWs by yet another factor of 4:1 relative to the ones discussed here, bandpass operation at center frequencies approaching 200 GHz with data rates of 200 Gb/s are feasible. These data rates meet or exceed those expected eventually for proposed silicon photonic technologies.

Computational and experimental study of a microwave electromagnetic bandgap structure with waveguiding defect for potential use as a bandpass wireless interconnect

As clock rates continue to rise, problems with signal integrity, cross-coupling, and radiation may render impractical the baseband metallic interconnects presently used in computers. A potential means to address this problem is to use bandpass wireless interconnects operating at millimeter-wave center frequencies. We have conducted experimental and finite-difference time-domain (FDTD) computational studies scaled to a 10 GHz center frequency of single-row and double-row waveguiding defects within an electromagnetic bandgap structure. Our initial experimental results scaled to 10 GHz have verified the feasibility of achieving an approximately 80% bandwidth with excellent stopband, gain flatness, and matching characteristics. When scaled to millimeter-wave center frequencies above 300 GHz, this technology appears feasible of supporting data rates in the hundreds of Gb/s.

A Nonspurious 3-D Vector Discontinuous Galerkin Finite-Element Time-Domain Method

We propose a nonspurious vector discontinuous Galerkin finite-element time-domain (DG-FETD) method for 3-D electromagnetic simulation. To facilitate the implementation of numerical fluxes for domain decomposition, we construct the DG-FETD scheme based on the first-order Maxwells equations with variables E and H. The LT/QN and the CT/LN edge elements are employed to represent E and H, respectively (or vice versa), to suppress spurious modes, and the Riemann solver is utilized as the numerical flux to correct fields on the interfaces between adjacent subdomains. Numerical experiments show the nonspurious property of the proposed method.

Efficient Implicit–Explicit Time Stepping Scheme With Domain Decomposition for Multiscale Modeling of Layered Structures

An efficient time-domain technique is proposed for multiscale electromagnetic simulations of layered structures. Each layer of a layered structure is independently discretized by finite elements, and the discontinuous Galerkin method is employed to stitch all discretized subdomains together. The hybrid implicit-explicit Runge-Kutta scheme combined with subdomain-based Gauss-Seidel iteration is employed for time stepping. The block Thomas algorithm is utilized to accelerate time stepping for block tri-diagonal systems, which are frequently encountered in discretized layered structures. Numerical examples demonstrate that the proposed method is efficient in simulating multiscale layered structures.

High-Speed Flex-Circuit Chip-to-Chip Interconnects

High-speed chip-to-chip interconnect utilizing flex-circuit technology is investigated for extending the lifetime of copper-based system-level channels. Proper construction of the flex ribbon is shown to improve the raw bandwidth over standard FR-4 boards by about three times. Active testing results from a 130-nm CMOS test vehicle show the potential of up to two times higher data rates. The next-generation test vehicle with 90-nm CMOS circuits gives improved voltage and timing margins at 20 Gb/s. In an interconnect limited case a channel with 36 in (91.4 cm) of flex runs at 18.2 Gb/s data rate at a bit-error ratio (BER) of better than 10-12. The channel includes two 90-nm CMOS test chips, two organic flip-chip package substrates, and two flex connectors; crosstalk is not included in this experiment. High-speed connector solutions, including results from a ldquosplit socketrdquo assembly test vehicle, are discussed in detail. The characterization of two top-side flex connector prototypes demonstrates their basic durability and good high-frequency performance. Samples survive 100 mating cycles at an average contact resistance of less than 30 mOmega, adequate for high-speed signaling. Measured differential insertion loss is less than 1.5 dB up to 10 GHz and less than 3.5 dB up to 20 GHz. Near-end and far-end crosstalk measurements indicate that the connectors exceed crosstalk specifications.

Extracting physical IC models using near-field scanning

Accurate modeling of chip and chip-package is critical for EMI (Electromagnetic Interference) and RFI (RF Interference) analysis and prediction. In this paper, a model based on an array of dipoles from near-field measurement is proposed. A simple active circuit is simulated in a 3-D full-wave simulation tool, and the dipole model is calculated from the near-field data in the simulation using inverse method with regularization technique. This model has clear physical meaning, and it is validated using field at other place.

Heat-Sink Modeling and Design With Dipole Moments Representing IC Excitation

Electromagnetic field coupling and radiation from a heat sink is a challenging issue in the electromagnetic compatibility design of high-speed circuits. In order to accurately predict the fields excited by a heat sink, an approach is proposed in this paper to include the equivalent excitation of the heat sink, which is described by some dipole moments constructed from the near-field scanning of the integrated circuit beneath the heat sink. With both the dipole moments and the passive heat-sink structure incorporated in a full-wave model, near-field coupling and far-field radiation can be estimated, and the heat-sink structure can be optimized for mitigating unintentional interferences. Two examples are used to validate and demonstrate the proposed approach.

A Hybrid SIM-SEM Method for 3-D Electromagnetic Scattering Problems

A new method combining the spectral integral method and spectral element method (SIM-SEM) is proposed to simulate 3-D electromagnetic scattering from inhomogeneous objects. In this hybrid technique (a special case of the finite element boundary integral (FEM-BI) combination), the SEM with the mixed-order curl conforming vector Gauss-Lobatto-Legendre (GLL) basis functions are used to represent the interior electric field with high accuracy, while the SIM on a cuboid surface is used as an exact radiation boundary condition. The Toeplitz property of the SIM matrix is utilized to reduce the memory and CPU time costs in an iterative solver by using the fast Fourier transform algorithm. Unlike the traditional FEM-BI combination where the BI portion usually dominates the computational complexity, the computational costs are much lower in the SIM-SEM method. Numerical results verify the accuracy and capability of this method, confirming that the SIM-SEM method is a good alternative for solving scattering problems from inhomogeneous objects.

High-Speed Flex Chip-to-Chip Interconnect

Signaling rates up to 20 Gb/s on a flex-circuit chip-to-chip interconnect are reported in active testing based on 90-nm CMOS circuits. The characterization of two flex connector prototypes demonstrates their basic durability and good high-frequency performance

Advances in hyperspeed digital interconnects using electromagnetic bandgap technology: measured low-loss 43-GHz passband centered at 50 GHz

We have performed a computational and experimental study of a promising new wireless interconnect for high-speed digital circuits employing linear defects in electromagnetic bandgap structures at 50 GHz center frequency. Our recent results confirm the scalability of this technology. We found that employing low-loss dielectrics can maintain the approximately 80% bandwidth with excellent stopband, gain flatness, and matching characteristics previously observed at 10 GHz. When further scaled to millimeter-wave center frequencies above 300 GHz (to leverage emerging silicon transistor technology), EBG wireless interconnects should be able to support data rates in the hundreds of Gbit/s, assuming the availability of suitable low-loss dielectrics.