W. Bachtold

Technology independent degradation of minimum noise figure due to pad parasitics

In order to investigate the influence of pad parasitics on device noise performance, noise parameters on Si CMOS, GaAs MESFET and GaAs p-HEMT transistors were determined. Measurements of devices with various gate widths demonstrate that the parasitic losses of the pads substantially influence the noise performance independent of FET technology. To accurately separate the noise contribution of the pad and the device, a noise parameter de-embedding procedure has been developed. It is shown that for an improvement of minimum noise figure NF/sub min/ of devices on non ideal substrates, pad losses must be minimized. Especially for small input transistors of amplifiers, pad parasitics must be considered during device modeling and design. A mathematical procedure using noise correlation matrices allows the embedding and de-embedding of noise parameters.

Analytical bias dependent noise model for InP HEMT's

A practical device model for both high frequency small signal and noise behavior of InP-HEMTs depending on both gate and drain voltage has been developed. The model is based on the two-piece linear approximation using charge control and saturation velocity models. Combining large signal model and analytical expressions for the noise source parameter P, R, and C, an analytical bias-dependent noise model can be obtained. For implementation into high frequency simulation software, the exact calculated bias dependence was mathematically fitted by elementary functions. It could be shown that lowest noise is observed when the drain current for maximum gain is reduced to a third while the drain voltage is reduced to the start of the saturation region V/sub ds/=0.6 V. Modeling scaling effects of the noise behavior shows that lowest noise is observed for a gate width of 1/spl times/40 /spl mu/m. Multi-finger layouts are preferable for gate widths above 70 /spl mu/m. Furthermore it is shown, that the optimum width of each finger decreases with the number of fingers. >

Mode spectroscopy and level coupling in ballistic electron waveguides

A tunable quantum point contact with modes occupied in both transverse directions is studied by magnetotransport experiments. We find conductance quantization that can be suppressed by degeneracies of one-dimensional modes. The mode spectrum is determined as a function of the magnetic field of different orientations with respect to the quantum wire. A magnetic field applied parallel to the direction of the current flow couples the modes. This can be described by an extension of the Darwin-Fock model. Anticrossings are observed as a function of the parallel magnetic field, but not for zero field or perpendicular field directions, indicating coupling of the subbands due to nonparabolicity in the electrical confinement.

High-frequency electrical pulse generation using optical rectification in bulk GaAs

We present the realization of a traveling-wave electrical pulse generator using pure nonresonant instantaneous optical rectification in bulk GaAs. The optical excitation was achieved by far-infrared pulses of 1–6 ps duration in the wavelength range from 8 to 15 μm, generated by a free-electron laser. The coupling of the optical rectification polarization into the fundamental mode of the microstrip transmission line is verified by angle-resolved measurements. Since optical femtosecond pulses are now becoming readily available, this alternative technique, which gains in efficiency at shorter pulses, may find growing importance for ultrafast pulse generation.

Low-noise properties of dry gate recess etched InP HEMTs

Lattice-matched InAlAs-InGaAs HEMTs with dry etched and wet etched gate recesses have been fabricated and both high-frequency and noise measurements have been carried out. The highly selective dry etching process ensures uniform device parameters. The small signal and noise performance shows only minor differences between the two transistor types. There is no evidence of detrimental effects caused by dry etching that reduce the electrical and noise performance of the device at high frequencies. These results show that dry etched InP HEMTs have suitable characteristics for the fabrication of MM-wave integrated circuits.

On the design of MMIC multi-harmonic load terminations for class-F amplifiers

In this paper, four multi-harmonic transmission-line load networks suitable for class-F amplifiers are analysed and compared in terms of harmonic suppression and their effects on output power and efficiency. Based on this study a design of a monolithic microwave integrated circuit (MMIC) class-F amplifier has been carried out at K-band. The fabricated amplifier achieves state-of-the-art efficiency. Moreover, without the need of supplementary filtering sections, harmonic suppression is better than -25 dBc for operation well into compression. To the best knowledge of the authors, this is the first experimental verification of harmonic suppression of transmission-line load networks suitable for class-F tuning

A 48 GHz monolithically integrated frequency tripler with InP HEMTs

We present a single-device 16 - 48 GHz frequency tripler realized with a 0.2 /spl mu/m InP HEMT process using coplanar waveguide technology. The fabricated circuit presents a maximum third harmonic conversion gain of -10.5 dBm, a maximum output power of -9 dBm, a first harmonic suppression of more than 25 dB, and a peak third harmonic conversion efficiency of 5.5%. This characteristics make it a suitable candidate for the generation of a stable high-frequency local oscillator.

High speed, monolithically integrated pin-HEMT photoreceiver fabricated on InP with a tunable bandwidth up to 22 GHz using a novel circuit design

High speed monolithically integrated photoreceivers were fabricated showing flat photo response and a state of the art bandwidth of 18 GHz, which should be sufficient for data transmission systems well beyond 20 Gbit/s. The circuitry consists of a high input impedance front-end design followed by an equalizing second stage to compensate the input capacitance. A state of the art input noise current of 12 pA//spl radic/Hz within the bandwidth was obtained. The bandwidth of the photoreceiver can be tuned with the bias voltages. For a 3 dB peak at 15 GHz a total bandwidth of 22 GHz was obtained.

Quasi-analytic formalism for mode characteristics in highly overmoded rectangular dielectric waveguide bends

A fast and simple quasi-analytic method to simulate mode characteristics in highly overmoded rectangular dielectric waveguide bends is presented. Fast mode-based bend models are necessary, since overmoded rectangular waveguides have become very popular in optical interconnects on printed circuit boards. The proposed method combines a simple mode solver with the formalism that was proposed by Melloni et al. [J. Lightwave Technol. 16, 571 (2001)], yielding to a very convenient and accurate quasi-analytic formalism for the bend transfer function based on matrix notation. For that purpose, a simple method to approximate leaky modes is introduced. The model offers the ability to predict individual modal phases and amplitudes within a given bend as well as the calculation of coupling losses and was validated using three-dimensional beam-propagation-method simulation software.

A novel asymmetric gate recess process for InP HEMTs

An asymmetric gate recess process has been developed for the fabrication of InP-based HEMTs with improved breakdown voltage. This process is based on a double e-beam exposure of a 4-layers stack of PMGI and PMMA resists. Vertical patterns can be fabricated that can otherwise not be achieved with standard e-beam lithography processes. A 30% improvement of the on-state breakdown voltage of 0.2 /spl mu/m InP HEMTs was obtained without marked degradation of f/sub max/.