Frank Schnieder

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.

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.

De-embedding of MMIC transmission-line measurements

The determination of transmission-line characteristic impedance and propagation constants from two-port S-parameter measurements is disturbed by half-wavelength resonances. We demonstrate this effect for on-wafer measurements of coplanar lines. Two networks representing end effects embed the line and strongly enhance the resonant effect. The de-embedding consists in determining these networks and subtracting them from the measured chain matrix. It is shown that simple shunt admittances are sufficient for modeling of the end effects. Three methods of de-embedding are presented.<<ETX>>

Laser-assisted processing of VIAs for AlGaN/GaN HEMTs on SiC substrates

Vertical interconnect accesses (VIAs) were fabricated between the source electrode on the front and the ground on the backside of high-power microwave AlGaN/GaN high-electron mobility transistors (HEMTs) on /spl sim/400-/spl mu/m-thick silicon carbide substrates. Through-wafer microholes with an aspect ratio of up to /spl sim/ 8 were drilled using pulsed UV-laser machining and subsequently metallized using electroplating. The successful implementation of the laser-assisted VIA technology into device processing was proven by dc and RF characterization. When biased at 26 V, a saturated output power of 41.6 W with an associated power-added efficiency of 55% at 2 GHz was achieved for a 20-mm AlGaN/GaN HEMT with through-wafer VIAs.

Improving the Linearity of GaN HEMTs by Optimizing Epitaxial Structure

This paper presents an effective method of improving the linearity of GaN/AlGaN high-electron mobility transistors (HEMTs) by optimizing barrier (AlGaN Layer) thickness or implementing doped GaN cap or a combination of both. HEMT devices with different epitaxial structures were simulated, fabricated, and measured to demonstrate this. Third-order intermodulation distortion and adjacent channel power ratio measurements were performed in order to compare linearity experimentally. A significant improvement of linearity is observed for an optimized architecture.

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

Dispersion and radiation properties of the conductor-backed CPW are studied. A frequency-domain finite-difference method using the PML absorbing boundary condition is used. The different types of higher-order modes are identified and design rules to avoid parasitic effects are given. Radiation is found to be considerably smaller than for infinite ground width.

Broadband characterization of a microwave probe for picosecond electrical pulse measurements

The time-domain characterization of high-frequency devices with coaxial connectors requires the transfer of picosecond electrical pulses between coplanar and coaxial lines. Microwave probes are often used for this purpose. In this paper, the propagation of ultrashort electrical pulses over a microwave probe attached to a coplanar waveguide is experimentally studied by time-domain electro-optic sampling. From the experimental data, the attenuation and dispersion constants of the probe are determined up to 400 GHz. Moreover, the complex reflection and transmission coefficients of the junction between the microwave probe and the coplanar waveguide are extracted. Simple approximations are given for these quantities. These data can be used to predict the amplitude and shape of ultrashort electrical pulses after propagation over the microwave probe for arbitrary input pulses in the considered frequency range.

Thin-film microstrip lines and coplanar waveguides on semiconductor substrates for sub-mm wave frequencies

It is shown that both thin-film microstrip lines (TFMSLs) and miniaturized coplanar waveguides (CPWs) offer low-dispersive propagation properties up to 1 THz. At the same time, they are fully compatible with monolithic integration. Radiation and dispersion effects are discussed and basic rules are presented how CPWs should be designed in order to reach the desired sub-mm-wave performance. Index Terms – thin-film microstrip line, coplanar waveguide, MMIC, modeling

Small- and large-signal modeling of InP HBTs in transferred-substrate technology

In this paper, the small- and large-signal modeling of InP heterojunction bipolar transistors (HBTs) in transferred substrate (TS) technology is investigated. The small-signal equivalent circuit parameters for TS-HBTs in two-terminal and three-terminal configurations are determined by employing a direct parameter extraction methodology dedicated to III–V based HBTs. It is shown that the modeling of measured S-parameters can be improved in the millimeter-wave frequency range by augmenting the small-signal model with a description of AC current crowding. The extracted elements of the small-signal model structure are employed as a starting point for the extraction of a large-signal model. The developed large-signal model for the TS-HBTs accurately predicts the DC over temperature and small-signal performance over bias as well as the large-signal performance at millimeter-wave frequencies.

Modal Behavior, Spatial Coherence, and Beam Quality of a High-Power Gain-Guided Laser Array

In this paper, we investigate the modal behavior and the spatial coherence properties of a gain-guided laser array emitting an optical output power of more than 50 W in quasi-continuous-wave operation at a wavelength of 1070 nm and above. The lateral near- and far-field intensity profiles and the Wigner distribution function were measured from low to high output power. The array modes were calculated by solving the waveguide equation taking into account the power-dependent temperature distribution and were also experimentally determined by a modal decomposition of the cross spectral density. The analysis revealed that, at a low power, a single array mode lases, whereas at high power, multiple single stripe modes dominate the lasing due to the thermally induced index rise under the stripes.