Showing papers by "Michael Mikulla published in 2008"

35 nm metamorphic HEMT MMIC technology

Abstract: A metamorphic high electron mobility transistor (mHEMT) technology featuring 35 nm gate length has been developed. The optimized MBE grown layer sequence has a channel mobility and a channel electron density as high as 9800 cm2/Vs and 6.1times1012 cm-2, respectively. To enable a maximum extrinsic transconductance gm, max of 2500 mS/mm the source resistance has been reduced to 0.1 Omegamiddotmm. An ft of 515 GHz was achieved for a 2 times 10 mum device. Based on this advanced 35 nm mHEMT technology very compact single-stage H-band amplifiers circuits have been realized demonstrating a high small-signal gain of more than 7 dB at 270 GHz.

GaN MMIC based T/R-Module Front-End for X-Band Applications

Abstract: Amplifiers for a next generation of T/R-modules in future active array antennas are realized as monolithically integrated circuits (MMIC) on the bases of novel AlGaN/GaN HEMT structures. Both, low noise and power amplifiers are designed for X-band frequencies. The MMICs are designed, simulated and fabricated using a novel via-hole microstrip technology. Output power levels of 6.8 W (38 dBm) for the driver amplifier (DA) and 20 W (43 dBm) for the high power amplifier (HPA) are measured. The measured noise figure of the low noise amplifier (LNA) is in the range of 1.5 dB. A T/R-module front-end with mounted GaN MMICs is designed based on a multilayer LTCC technology.

High‐efficiency GaN HEMTs on 3‐inch semi‐insulating SiC substrates

Abstract: We report on device performance and reliability of our 3″ GaN high electron mobility transistor (HEMT) technology. AlGaN/GaN HEMT structures are grown on semi-insulating SiC substrates by metal-organic chemical vapor deposition (MOCVD) with sheet resistance uniformities better than 2%. Device fabrication is performed using standard processing techniques involving both e-beam and stepper lithography. AlGaN/GaN HEMTs demonstrate excellent high-voltage stability and large efficiencies. Devices with 0.5 µm gate length exhibit two-terminal gate-drain breakdown voltages in excess of 160 V and drain currents well below 1 mA/mm when biased at 80 V drain bias under pinch-off conditions. Load-pull measurements at 2 GHz return both a linear relationship between drain bias voltage and output power as well as power added efficiencies beyond 55% up to 72 V drain bias for which an output power density of 9 W/mm with 25 dB linear gain is obtained. Reliability tests indicate a promising device stability under both radio frequency (RF) and direct current (DC) stress conditions. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Reliability and degradation mechanism of AlGaN/GaN HEMTs for next generation mobile communication systems

Abstract: Excellent reliability performance of AlGaN/GaN HEMTs on SiC substrates for next generation mobile communication systems has been demonstrated using DC and RF stress tests on 8x60 μm wide and 0.5 μm long AlGaN/GaN HEMTs at a drain voltage of Vd=50V. Drain current recovery measurements after stress indicate that the degradation is partly caused by slow traps generated in the SiN passivation or in the HEMT epitaxial layers. The traps in the SiN passivation layer were characterized using high and low frequency capacitance voltage (CV) measurements of MIS test structures on thick lightly doped GaN layers.

Efficient AlGaN/GaN HEMT Power Amplifiers

Abstract: This paper describes efficient GaN/AlGaN HEMTs and MMICs for L/S-band (1-4 GHz) and X-band frequencies (8-12 GHz) on three-inch s.i. SiC substrates. Dual-stage MMICs in microstrip transmission-line technology yield a power-added efficiency of ?40% at 8.56 GHz for a power level of ?11 W. A single-stage MMIC yields a PAE of ?55% with 6 W of output power at VDS= 20 V. The related mobile communication power HEMT process yields an average power density of 10 W/mm at 2 GHz and VDS= 50 V. The average PAE is 61.3% with an average linear gain 24.4 dB and low standard deviation of all parameters. The devices yield more than 25 W/mm of output power at 2 GHz when operated in cw at VDS= 100 V with an associated PAE of ?60%. The GaN HEMT process with 0.5 ?m gate-length yields an extrapolated lifetime of 105 h when operated at VDS= 50 V at a channel temperature of 90°C. When operated at 2 GHz devices with 480 ?m gate-width yield a change of the RF power-gain of less than 0.2 dB under high gain-compression at VDS= 50 V and a channel temperature of 250°C.

Balanced Microstrip AlGaN/GaN HEMT Power Amplifier MMIC for X-Band Applications

Abstract: This paper describes a balanced AlGaN/GaN HEMT single-stage power amplifier demonstrator for X-band frequencies in microstrip line technology on thinned s.i. SiC substrates. The design features a modular circuit concept and microstrip MMIC directional couplers with low impedance levels. These 3 dB-couplers designed for a center frequency of 10 GHz show a coupling factor of 3.5 dB plusmn 0.4 dB and a low net insertion loss of 0.3 dB. The balanced amplifier reaches 11 W pulsed output power at 3 dB compression level and a maximum gain of 10 dB at 8.56 GHz with an input and output match of better than 14 dB from 8.3 to 13 GHz. This 0deg/90deg balanced microstrip AlGaN/GaN HEMT power amplifier MMIC demonstrator may be an interesting alternative to existing hybrid solutions.

High-efficiency, high-breakdown AlGaN/GaN HEMTs with lifetimes beyond 20 years

Abstract: AlGaN/GaN HEMTs on various substrates have raised a lot of interest for the application in future high-efficiency base station systems for next generation mobile communication, currently dominated by LDMOS technology. Using GaN technology in a transmitter, infrastructure equipment manufacturers will benefit from major improvements in system performance and flexibility. AlGaN/GaN HEMTs enable innovative circuit concepts and transceiver architecture (e.g. switch mode power amplifiers, SMPA) with high efficiency and high operating bias. However, besides performance it will be crucial to match or even exceed the device reliability of other technologies in order to be competitive. To meet this goal, it is vital to optimize epitaxial growth as well as process technology.