Mattias Südow

Large-signal modelling and comparison of AlGaN/GaN HEMTs and SiC MESFETs

The Large Signal (LS) model for GaN and SiC FET devices was developed and evaluated with DC, S, and LS measurements. Special attention was paid to improve the management of harmonics and to provide a more physical treatment of the dispersion. The model was implemented in a commercial CAD tool and exhibits good overall accuracy.

An AlGaN/GaN HEMT-Based Microstrip MMIC Process for Advanced Transceiver Design

A MMIC process in AlGaN/GaN technology for advanced transceiver design has been developed. The process is based on microstrip technology with a complete model library of passive elements and AlGaN/GaN HEMTs. The transistor technology in this process is suitable for both power and low noise design, demonstrated with a power density of 5 W/mm, and an NFmin of 1.4 dB at X-band. Process stability of subcircuits, complementary to power amplifiers and LNAs, in a transceiver system have been investigated. The results indicate that an all AlGaN/GaN MMIC transceiver is realizable using this technology.

Thermal Study of the High-Frequency Noise in GaN HEMTs

The high-frequency noise performance of the GaN HEMT is studied for temperatures between 297-398 K. The access resistances RS and RD have a limiting effect on the noise performance, and in this paper, their temperature dependence is studied in detail for a 2 times 100 mum GaN HEMT. RS and RD show an increase of 0.71 and 0.86 %/K, respectively. The self-heating effect due to dissipated power is also studied to allow accurate intrinsic small-signal and noise parameter extraction. The thermal resistance is measured by infrared microscopy. Based on these results, a temperature dependent noise model including self-heating and temperature-dependent access resistances is derived and verified with measurements.

An SiC MESFET-Based MMIC Process

A monolithic microwave integrated circuit (MMIC) process based on an in-house SiC MESFET technology has been developed. The process uses microstrip technology, and a complete set of passive components, including MIM capacitors, spiral inductors, thin-film resistors, and via-holes, has been developed. The potential of the process is demonstrated by an 8-W power amplifier at 3 GHz, a high-linearity S-band mixer showing a third-order intercept point of 38 dBm, and a high-power limiter

SiC Varactors for Dynamic Load Modulation of High Power Amplifiers

SiC Schottky diode varactors with a high breakdown voltage, a high tuning ratio, and a low series resistance have been designed and fabricated. These characteristics are particularly necessary for the dynamic load modulation of high power amplifiers (PAs), which is an attractive alternative to other efficiency enhancement techniques. For a SiC Schottky diode varactor with a 50- radius fabricated by using a graded doping profile, a breakdown voltage of 40 V, a tuning range of 5.6, and a series resistance of 0.9 were achieved. The results show the great potential of this type of varactors for the use in the dynamic load modulation of high power amplifiers.

A Single-Ended Resistive

A broadband highly linear X-band mixer in AlGaN/GaN monolithic microwave integrated circuit technology has been designed, processed, and characterized. The design is based on a 4 times 100 mum AlGaN/GaN HEMT in a single-ended circuit topology. The mixer has an IF bandwidth of 2 GHz with a conversion loss (CL) of < 8 dB across the X-band with a minimum CL of 6.9 dB at 11 GHz. The large-signal performance is exemplified by IIP 3 levels of 22 and 30 dBm at local oscillator drive levels of 15 and 23 dBm, respectively. A minimum noise figure of 9 dB is achieved at 11.6 GHz.

X

Titanium nitride (TiN) thin film resistors (TFRs) have been fabricated by reactive sputter deposition. The TFRs were characterized in terms of composition, thickness, and resistance. Furthermore, a first assessment of the resistor reliability was made by measurements of the resistivity (rho) versus temperature, electrical stress, long-term stability, and thermal infrared measurements. TiN layers with thicknesses up to 3560 angstrom, corresponding to a sheet resistance (R-s) of 10 Omega/square, were successfully deposited without any signs of stress in the films. The critical dissipated power (P-c) showed a correlation with the resistor footprint-area indicating that Joule-heating was the main cause of failure. This was partly substantiated by the thermal infrared measurements.

-Band AlGaN/GaN HEMT MMIC Mixer

A high-level double balanced SiC Schottky diode mixer in SiC monolithic microwave integrated circuit (MMIC) technology has been designed, processed and characterized. The mixer is a single ended in- and output circuit with coupled transformers as baluns to enable a compact design, resulting in a total area of 2.2/spl times/2.2mm/sup 2/. The mixer has a maximum IIP/sub 3/ of 38dBm and IIP/sub 2/ of 58dBm at 3.3GHz, and a typical P/sub 1 dB/ of 23dBm in the S-band. The minimum conversion loss was 12dBm at 2.4GHz. The high power operation of the mixer shows that SiC MMIC can perform well in high microwave radiation environments.

TiN thin film resistors for monolithic microwave integrated circuits

The influence of field plates and surface traps on silicon carbide MESFETs for microwave operation was investigated. By increasing the length of gate-connected field plates from 50 to 800 nm, it was possible to increase the gate-drain breakdown voltage of the devices from 125 to 170 V. At the same time, the current slump effect of traps in the passivation oxide was reduced. By using a combination of field plates and a passivation oxide with low interface trap density, it was possible to reach an output power density of 8 W/mm at 3 GHz.

A highly linear double balanced Schottky diode S-band mixer

The noise parameters of AlGaN/GaN-HEMTs are measured between 298 K and 423 K. The temperature dependent access resistances are de-embedded and the intrinsic noise parameters are studied as a function of temperature. It is shown that the parasitic access resistances are limiting the high-frequency noise performance of the AlGaN/GaN-HEMT.The intrinsic noise sources are extracted and a noise model is derived and verified for a MMIC amplifier.