Diego Marti

Fully Passivated AlInN/GaN HEMTs With

We report the fabrication and characterization of 30-nm-gate fully passivated AlInN/GaN high-electron mobility transistors (HEMTs) with cutoff frequencies <i>f</i>_T and <i>f</i>_MAX simultaneously exceeding 200 GHz at a given bias point. The current gain cutoff frequency does not vary significantly for 2.5 <; <i>V</i>_DS <; 10 V, while <i>f</i>_MAX reaches a maximum value of <i>f</i>_MAX = 230 GHz at <i>V</i>_DS = 6 V. This is the first realization of fully passivated AlInN/GaN HEMTs with <i>f</i>_T/<i>f</i>_MAX ≥ 205 GHz, a performance enabled by the careful shaping of the gate electrode profile and the use of a thin 60-nm SiN encapsulation film.

f_{\rm T}/f_{\rm MAX}

We report high-speed fully passivated deep submicrometer (Al,Ga)N/GaN high-electron mobility transistors (HEMTs) grown on (111) high-resistivity silicon with current gain cutoff frequencies of as high as fT = 107 GHz and maximum oscillation frequencies reaching fMAX = 150 GHz. Together, these are the highest fT and fMAX values achieved for GaN-based HEMTs implemented on silicon substrates to date. The performance reported here is competitive with recently published results for similar geometry high-performance passivated HEMTs on semi-insulating silicon-carbide substrates.

of 205/220 GHz

We report the first 94-GHz (W-band) large-signal performance of AlInN/GaN high-electron-mobility transistors (HEMTs) grown on high-resistivity silicon (111) substrates. A maximum output power density of 1.35 W/mm and peak power-added-efficiency of 12% are measured at 94 GHz. The devices exhibit a dc maximum current drain density of 1.6 A/mm and a peak transconductance of 650 mS/mm. In small-signal operation, cutoff frequencies fT/fMAX = 141/232 GHz are achieved. The large-signal performance of our AlInN/GaN HEMTs on silicon at 94 GHz stills lags the best reported results one on SiC substrates but nevertheless confirms the tremendous interest of GaN-on-Si HEMT technology for low-cost millimeterwave electronic applications.

107-GHz (Al,Ga)N/GaN HEMTs on Silicon With Improved Maximum Oscillation Frequencies

We report the large-signal performance of high electron mobility transistors (HEMTs) fabricated on GaN- and AlN-capped AlInN/GaN epilayers grown on semi-insulating SiC substrates. Large-signal measurements at 10 and 40 GHz are presented with both gate and drain dynamic loadlines to clarify the factors limiting the high-power performance. Devices fabricated with AlN-capped epilayers show a marginal advantage in terms of higher current and reduced dispersion, but GaN-capped epilayers perform better in terms of reduced short-channel effects and better channel control. In large-signal operation at 40 GHz, both device types delivered power densities in excess of 4.5 W/mm. A maximum power density of 5.8 W/mm is achieved on GaN-capped devices which is, to the best of our knowledge, the highest power density reported at 40 GHz in AlInN/GaN-based HEMTs.

94-GHz Large-Signal Operation of AlInN/GaN High-Electron-Mobility Transistors on Silicon With Regrown Ohmic Contacts

A new W-band active load-pull system is presented. It is the first load-pull system to implement a 94 GHz load by means of an active loop exploiting frequency conversion techniques. The active loop configuration demonstrates a number of advantages that overcome the typical limitations of W-band passive tuners or conventional active open-loop techniques in a cost-effective way: load reflection coefficients ΓL as high as 0.95 in magnitude can be achieved at 94 GHz, thus providing a nearly full coverage of the Smith chart. Possible applications of the setup include technology assessment, large-signal device model verification at sub-terahertz frequencies, and W-band monolithic microwave integrated circuit design and characterization. The availability of direct and accurate load-pull measurements at W-band should prove an asset in the development of sub-terahertz integrated circuits. First measurements performed on high-performance InP double heterojunction bipolar transistors and GaN high electron-mobility transistors are presented.

AlInN-Based HEMTs for Large-Signal Operation at 40 GHz

A comparison of the microwave small-signal performance of 0.1 µm AlGaN/GaN high electron mobility transistors (HEMTs) grown on (111) high-resistivity (HR) Si and on insulating sapphire substrates is performed. With resistivities <20 kΩcm, HR-Si is not semi-insulating, and potential substrate loading effects and/or parasitic conduction through the buffer layers might affect device performance. The extracted small-signal equivalent circuit models reveal no differences attributable to the different substrates. Coplanar waveguides built on the GaN buffer on the HR-Si substrate show a loss of 0.82 dB/mm at 110 GHz, also confirming the potential of GaN-on-HR-Si technology for millimeter-wave applications.

A

We report on the low-temperature growth of heavily Si-doped (>1020 cm−3) n+-type GaN by N-rich ammonia molecular beam epitaxy (MBE) with very low bulk resistivity (<4 × 10−4 Ω·cm). This is applied to the realization of regrown ohmic contacts on InAlN/GaN high electron mobility transistors. A low n+-GaN/2 dimensional electron gas contact resistivity of 0.11 Ω·mm is measured, provided an optimized surface preparation procedure, which is shown to be critical. This proves the great potentials of ammonia MBE for the realization of high performance electronic devices.

W

We report the characterization of GaN high electron mobility transistors (HEMTs) using a new AlN-capped AlInN/GaN epilayer structure developed to achieve high current densities and reduced gate leakage currents. Devices with gate lengths of 75 and 200 nm and various and source-drain separations were fabricated simultaneously, allowing the selection of the most favorable configuration for power performance. We show that, as anticipated, aggressive scaling of source-drain spacing and gatelength does not benefit power performance because of early breakdown and more pronounced short-channel effects. For a non-field-plated 0.2 mu m gate length in a 4 mu m source-drain gap, the new epitaxial structure achieved a power density of 4.5W/mm at 40 GHz. To the best of our knowledge, this is the highest power reported at 40 GHz for AlInN/GaN-based transistors, and the first report of the large-signal performance of an AlN-capped AlInN/GaN-based HEMT. (c) 2013 The Japan Society of Applied Physics