Wolfgang Heinrich

Theory and measurements of flip-chip interconnects for frequencies up to 100 GHz

A detailed investigation of flip-chip interconnects up to W-band frequencies is presented in this paper. In a coplanar 50-/spl Omega/ environment, different test structures were fabricated and measured to determine the electromagnetic characteristics of flip-chip multichip modules, such as detuning, reflection at the interconnect, and parasitic coupling. Electromagnetic simulation is used to explain the details behind the measured results. Key to high return loss at the interconnect is a small bump-pad area. Applying simple compensation structures, the frequency range of operation can be further extended. It is shown that a return loss beyond 20 dB in the frequency range up to 80 GHz is achievable along with excellent reproducibility. Measurements on detuning and isolation are also presented.

Millimeterwave characteristics of flip-chip interconnects for multi-chip modules

Electromagnetic simulations and measurement data of flip-chip transitions are presented. First-order effects are identified and design criteria for mm-wave multi-chip interconnects are derived. In coplanar environment, the flip-chip scheme provides interconnects with excellent low-reflective properties. For conductor-backed structures, the suppression of parasitic modes represents the key issue.

Model of thin-film microstrip line for circuit design

An equivalent-circuit model for the thin-film microstrip line (TFMSL) is presented in this paper. Its elements are calculated using closed-form expressions and, thus, this model can easily be implemented in common circuit design tools. For typical TFMSL dimensions, it holds from DC up to the submillimeter-wave frequency range. The model is validated by comparison to electromagnetic full-wave simulation data. Typical errors of phase constant and characteristic impedance are below 2% and 3%, respectively. Regarding attenuation, deviations below 8% are found.

Analysis of the Survivability of GaN Low-Noise Amplifiers

This paper presents a detailed analysis of the stressing mechanisms for highly rugged low-noise GaN monolithic-microwave integrated-circuit amplifiers operated at extremely high input powers. As an example, a low-noise amplifier (LNA) operating in the 3-7-GHz frequency band is used. A noise figure (NF) below 2.3 dB is measured from 3.5 to 7 GHz with NF<1.8 dB between 5-7 GHz. This device survived 33 dBm of available RF input power for 16 h without any change in low-noise performance. The stress mechanisms at high input powers are identified by systematic measurements of an LNA and a single high electron-mobility transistor in the frequency and time domains. It is shown that the gate dc current, which occurs due to self-biasing, is the most critical factor regarding survivability. A series resistance in the gate dc feed can reduce this gate current by feedback, and may be used to improve LNA ruggedness

Millimeter-wave characteristics of flip-chip interconnects for multichip modules

Electromagnetic simulation and measurement data of flip-chip transitions are presented. First-order effects are identified and design criteria for millimeter-wave multichip interconnects are derived. Results cover chip detuning and bump geometry as well as simplified modeling. In a coplanar environment, the flip-chip scheme provides interconnects with excellent low-reflective properties. For conductor-backed structures, parasitic modes occur leading to unwanted crosstalk. These effects dominate the behavior so that overall performance of the flip-chip scheme can be evaluated properly only in conjunction with the actual motherboard packaging setup.

Open and short circuits in coplanar MMIC's

Coplanar MMIC stub configurations are investigated by means of the finite-difference method in the frequency domain. The open end, the short end, and a capacitively loaded short end (MIM-short) are analyzed. Their parasitic effects are described in terms of the effective length extension l/sub ext/. The influence of the different line parameters is discussed and simple design rules are given. >

Coplanar passive elements on Si substrate for frequencies up to 110 GHz

This paper provides both modeling and design information on coplanar passive elements on a silicon substrate. The influence of substrate resistivity on coplanar waveguide (CPW) loss is discussed, and elements of a cell library for coplanar monolithic microwave integrated circuits (MMICs) on high-resistivity substrates are presented. The elements include discontinuities, junctions, and spiral inductors. The models are based on field-theoretical simulations and verified by S-parameter measurements up to 110 GHz.

Modeling dispersion and radiation characteristics of conductor-backed CPW with finite ground width

Dispersion and radiation properties of the conductor-backed coplanar waveguide (CPW) with finite ground planes are analyzed and modeled. A frequency-domain finite-difference method using the perfectly matched layer absorbing boundary condition is used as reference. Based on these results, a closed-form description is derived and implemented into an existing quasi-static CPW model. This leads to a comprehensive and efficient CPW description accounting for all relevant effects from conductor loss to high-frequency dispersion. Additionally, design rules to avoid parasitic radiation effects are given.

Optimum mesh grading for finite-difference method

The coarseness error of the finite-difference (FD) method is studied analyzing a typical planar waveguide and a rectangular coaxial geometry. Results for equidistant and graded mesh are compared in terms of accuracy and numerical efforts. Because of the field singularities involved a graded mesh proves to be superior compared to the equidistant case. A grading strategy with optimum efficiency is presented. Furthermore, the results show that the most significant improvement in accuracy can be obtained by incorporating the edge behavior into the FD scheme.

RF class-S power amplifiers: State-of-the-art results and potential

This paper reports recent results on a current-mode class-S power amplifier for the 450 MHz band, based on GaN-HEMT MMICs. We achieve a peak output power of 8.7 W for a single tone at 420 MHz, encoded in standard band-pass delta-sigma modulation with 1.68 Gbps sampling frequency. The respective efficiency is 34%. We find that these values strongly vary with coding efficiency of the modulation and reach 19 W with 59% for square-wave excitation. In order to clarify the potential of the PA in more detail, the S-class characteristics at power back-off and with varying oversampling ratio are presented as well.