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Huang S.,Hong Kong University of Science and Technology | Yang S.,Hong Kong University of Science and Technology | Roberts J.,Nitronex Corp | Chen K.J.,Hong Kong University of Science and Technology
Japanese Journal of Applied Physics | Year: 2011

The threshold voltage (Vth) instability in GaN-based metal-insulator-semiconductor high-electron mobility transistors (MIS-HEMTs) with 15-nm atomic-layer-deposited (ALD) Al2O3 as gate dielectrics is systematically investigated by dc current-voltage (I-V), high-frequency capacitance- voltage (C-V) (HFCV), and quasi-static C-V (QSCV) characterizations. Both Al2O3/GaN/AlGaN/GaN MIS diode and GaN/AlGaN/GaN Schottky diode only exhibit tiny threshold-voltage hysteresis (δVth) (> 10 mV) in double-mode (up and down sweep) HFCV characteristics as the maximum forward bias (VF,max) during the sweep is set to 0 V, while an apparent δVth (as large as 0.9 V) emerges as VF,max is increased to +5 V for the MIS diode. The stability of Vth in the corresponding MIS-HEMTs is thus studied by increasing the maximum VGS (VGS,max) in the measurement of transfer characteristics. Significant positive Vth shift occurred once the VGS,max exceeds +1 V, while such Vth-instability is still absent in Schottky-gate AlGaN/GaN HEMTs. It is suggested that the acceptor-like deep states at Al2O3/GaN interface account for the Vth-instability in Al2O3/GaN/AlGaN/GaN MIS-HEMTs. As the filling and emission processes of these interface states are slow, they are successfully captured by low-frequency QSCV techniques. © 2011 The Japan Society of Applied Physics. Source


Huang S.,Hong Kong University of Science and Technology | Yang S.,Hong Kong University of Science and Technology | Roberts J.,Nitronex Corp | Chen K.J.,Hong Kong University of Science and Technology
Physica Status Solidi (C) Current Topics in Solid State Physics | Year: 2012

The threshold-voltage (V th) instability in AlGaN/GaN MIS-HEMTs with ALD-Al 2O 3 (15 nm) as gate dielectrics is systematically investigated by dc current-voltage (I-V), high-frequency capacitance-voltage (C-V) (HFCV), and quasi-static C-V (QSCV) characterizations. For Al 2O 3/GaN/AlGaN/GaN MIS diodes, tiny V th hysteresis (ΔV th) appears in double-mode (up and down sweep) HFCV measurements if the maximum forward bias (V F,max) is only set to 0 V, while an apparent clockwise ΔV th (as large as 0.9 V) emerges as V F,max is increased to +5 V. The stability of V th in the corresponding MIS-HEMTs is thus studied by increasing the maximum V GS (V GS,max) in the measurement of double-mode transfer characteristics. Significant clockwise ΔV th also occurred once the V GS,max exceeds +1.1 V, and it increased to ∼1 V at V GS,max= +3 V. Such V th-instability is absent in AlGaN/GaN HEMTs. It is suggested that the acceptor-like deep states at Al 2O 3/GaN interface account for the V th-instability in Al 2O 3/GaN/AlGaN/GaN MIS-HEMTs, and their filling and emission processes are successfully captured by QSCV measurements. The interface state density detected is about 4.6×10 12 cm -2 using 1 Hz QSCV. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Marti D.,ETH Zurich | Tirelli S.,ETH Zurich | Alt A.R.,ETH Zurich | Roberts J.,Nitronex Corp | Bolognesi C.R.,ETH Zurich
IEEE Electron Device Letters | Year: 2012

We report a new generation of high-performance AlGaN/GaN high-electron-mobility transistors (HEMTs) grown on high-resistivity Si (111) substrates. We map out small-and large-signal device performances against technological parameters such as the gate length and the source-drain contact separation. We report the first large-signal performance for a GaN-on-Si technology offering an output power of 2 W/mm and an associated peak power-added efficiency of 13.8% (peak of 18.5%) at 40 GHz without any field plate. The technology offers measured transconductances of up to 540 mS/mm and cutoff frequencies as high as $f-{\rm T}/f-{\rm MAX} = \hbox{152/149}\ \hbox{GHz}$ at a given bias point. These are the highest cutoff frequencies to date for fully passivated AlGaN/GaN HEMTs on silicon substrates. The results confirm GaN-on-Si technology as a promising contender for low-cost millimeter-wave power electronic applications. © 2012 IEEE. Source


Lu B.,Massachusetts Institute of Technology | Piner E.L.,Nitronex Corp | Palacios T.,Massachusetts Institute of Technology
IEEE Electron Device Letters | Year: 2010

In this letter, we demonstrate 27% improvement in the buffer breakdown voltage of AlGaN/GaN high-electron mobility transistors (HEMTs) grown on Si substrate by using a new Schottky-drain contact technology. Schottky-drain AlGaN/GaN HEMTs with a total 2-μm-thick GaN buffer showed a three-terminal breakdown voltage of more than 700 V, while conventional AlGaN/GaN HEMTs of the same geometry showed a maximum breakdown voltage below 600 V. The improvement of the breakdown voltage has been associated with the planar contact morphology and lack of metal spikes in the Schottky-drain metallization. © 2010 IEEE. Source


Grant
Agency: Department of Defense | Branch: Navy | Program: SBIR | Phase: Phase I | Award Amount: 70.00K | Year: 2008

S and X-band radars are central to the Air and Missile defense capability of the US ballistic missile defense (BMD) systems. The objective of this Phase I program is to investigate various PA classes of operation and identify approaches with significantly improved efficiency. The strategy proposed in this SBIR Phase I proposal is to combine the benefits of high efficiency switching architectures with the power and bandwidth capability offered by GaN HEMTs. High efficiencies are possible through use of PA classes such as D, E or F that operate the transistor as a switch. Such approaches offer significant promise for high efficiency RF transmitters provided fundamental efforts are expended to overcome the technical challenges in the input and output matching designs posed in such approaches.

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