Masaaki Kuzuhara

10-W/mm AlGaN-GaN HFET with a field modulating plate

AlGaN-GaN heterojunction field-effect transistors (HFETs) with a field modulating plate (FP) were fabricated on an SiC substrate. The gate-drain breakdown voltage (BV/sub gd/) was significantly improved by employing an FP electrode, and the highest BV/sub gd/ of 160 V was obtained with an FP length (L/sub FP/) of 1 /spl mu/m. The maximum drain current achieved was 750 mA/mm, together with negligibly small current collapse. A 1-mm-wide FP-FET (L/sub FP/=1 /spl mu/m) biased at a drain voltage of 65 V demonstrated a continuous wave saturated output power of 10.3 W with a linear gain of 18.0 dB and a power-added efficiency of 47.3% at 2 GHz. To our knowledge, the power density of 10.3 W/mm is the highest ever achieved for any FET of the same gate size.

Application of GaN-based heterojunction FETs for advanced wireless communication

We review the features of GaN-based FETs and describe their expected development direction, GaN has a high breakdown field, but this does not necessarily mean it is suitable for high-voltage and high-power applications. The main advantage is that it enables scaling down beyond the silicon MOSFET miniaturization limitation from the Maxwell-Boltzmann distribution. Thus, fine gate patterns together with a high carrier velocity make GaN-based FETs be suited for millimeter and near millimeter wavelength high-power applications. In addition, by using large-area sapphire substrates, high-performance and low-cost MMICs can be produced on GaN. We expect that such devices will be the key to future advanced wireless communication systems.

Novel high power AlGaAs/GaAs HFET with a field-modulating plate operated at 35 V drain voltage

This paper reports novel high power AlGaAs/GaAs heterostructure FET with a field-modulating plate (FP-HFET), which accomplished dramatic increase of the gate-drain breakdown voltage with greatly suppressed drain-current pulse-dispersion characteristics. The fabricated FETs exhibited excellent power performance up to 35 V at L-band, delivering the maximum power density of 1.7 W/mm.

Infrared rapid thermal annealing of Si‐implanted GaAs

Conditions for post‐implantation capless annealing of GaAs, called infrared rapid thermal annealing (IRTA) using halogen lamps, were investigated. Si‐implanted GaAs (5×1012 cm−2, 150 keV) was annealed at temperatures ranging from 700 to 1100 °C for various annealing times. Annealed GaAs at 950 °C for 2–4 s shows about 75% electrical activation and 3700 cm2/Vs electron mobility without noticeable dopant diffusion and surface decomposition. Planar metal‐semiconductor field‐effect transistors (MESFET’s) fabricated on the active layer formed by this annealing method show that the technique is promising as a post‐implantation annealing method for the fabrication of GaAs MESFET’s and GaAs integrated circuits (IC’s).

Compact DC-60-GHz HJFET MMIC switches using ohmic electrode-sharing technology

Compact DC-60-GHz heterojunction field-effect transistor (HJFET) monolithic-microwave integrated-circuit (MMIC) switches have been demonstrated for millimeter-wave communications and radar systems. To reduce the MMIC chip size, a novel ohmic electrode-sharing technology (OEST) has been developed for MMIC switches with series-shunt FET configuration. Four FETs of the series-shunt single-pole double-throw (SPDT) MMIC switch were integrated into an area of approximately 0.018 mm/sup 2/. The developed MMIC switches have a high power-handling capability with low insertion loss (IL) and high isolation (Iso) at millimeter-wave frequencies. From DC to 60 GHz, the single-pole single-throw (SPST) MMIC switch achieved the IL and Iso of better than 1.64 and 20.6 dB, respectively. At 40 GHz, the IL increases by 1 dB at the input power of 21 dBm. A novel large-signal FET model for the switch circuit is presented. The simulated power-transfer performance shows the excellent agreement with the measured one. The developed MMIC switches will contribute to the low-cost and high-performance millimeter-wave communications and radar systems.

3 V operation L-band power double-doped heterojunction FETs

The microwave power performance of double-doped AlGaAs/InGaAs/GaAs pseudomorphic heterojunction field-effect transistors (HJFETs) operated at a DC drain bias of 3 V is presented. The fabricated 1.1- mu m-gate-length HJFET with an undoped AlGaAs Schottky layer exhibited a maximum drain current of 220 mA/mm, a peak transconductance of 200 mS/mm, and a gate-to-drain breakdown voltage of 21 V. Power performance evaluated at a 3-V drain bias for a 12-mm-gate-periphery device demonstrated a maximum output power of 1.4 W with a 61% power-added efficiency at 950 MHz. The results indicate that the double-doped pseudomorphic HJFETs have a high potential for battery-operated portable power applications.<<ETX>>

High-power recessed-gate AlGaN-GaN HFET with a field-modulating plate

Recessed-gate AlGaN-GaN heterojunction field-effect transistors (FETs) with a field-modulating plate (FP) have been successfully fabricated for high-voltage and high-power microwave applications. The developed recessed-gate FP-FET with a gate length of 1 /spl mu/m exhibited an increased transconductance of 200 mS/mm. A series of current collapse measurements revealed that the recessed-gate FP-FET is highly desirable for collapse-free high-voltage power operation. Equivalent circuit analysis demonstrated that the gain loss due to the additional gate feedback capacitance associated with the FP electrode is considerably compensated by increasing the drain bias voltage to more than 30 V. A 48-mm-wide recessed-gate FP-FET biased at a drain voltage of 48 V exhibited a record saturated output power of 197 W with a linear gain of 10.1 dB and a power-added efficiency of 67% at 2 GHz.

Characterization of Ga out‐diffusion from GaAs into SiOxNy films during thermal annealing

The out‐diffusion of Ga atoms during thermal annealing from a GaAs substrate into an SiOxNy encapsulating film has been studied using secondary ion mass spectrometry. The concentration of Ga atoms detected within the SiOxNy encapsulant annealed at 850 °C is found to increase with increasing the oxygen content of the encapsulant. The results are well correlated with the concentration change of the electron trap EL5 (Ec−ET =0.42 eV) evaluated from deep‐level transient spectroscopy. We conclude that the controlled Ga out‐diffusion by SiOxNy capped annealing causes enhanced electrical activation of Si implants and the generation of the EL5 trap during thermal annealing is ascribed to the Ga out‐diffusion.

Infrared rapid thermal annealing for GaAs device fabrication

A new post‐implantation annealing technique, called infrared rapid thermal annealing (IRTA), is discussed for fabricating GaAs devices using ion implantation technology. The IRTA apparatus and capless annealing conditions are described. Also, electrical property and its uniformity of n or n+ type GaAs layers made by Si implantation to semi‐insulating GaAs followed by IRTA are presented, and compared with those made by Si3N4 capped furnace annealing. A steeper carrier concentration profile with a higher peak carrier concentration in the n type active layer made by IRTA results in a higher transconductance without any anomalous characteristics on the GaAs metal–semiconductor field‐effect transistor.

30-GHz-band over 5-W power performance of short-channel AlGaN/GaN heterojunction FETs

This paper describes the small-signal characterization through delay-time analysis and high-power operation of the Ka-band of AlGaN/GaN heterojunction field-effect transistors (FETs). An FET with a gatewidth of 100 /spl mu/m and a gate length of 0.09 /spl mu/m has exhibited a current gain cutoff frequency (f/sub T/) of 81 GHz, a maximum frequency of oscillation (fmax) of 187 GHz, and a maximum stable gain of 10.5 dB at 30 GHz (8.3 dB at 60 GHz). Delay-time analysis has demonstrated channel electron velocities of 1.50/spl times/10/sup 7/ to 1.75/spl times/10/sup 7/ cm/s in a gate-length range of 0.09-0.25 /spl mu/m. State-of-the-art performance-saturated power of 5.8 W with a linear gain of 9.2 dB and a power-added efficiency of 43.2%-has been achieved at 30 GHz using a single chip having a gatewidth of 1.0 mm and a gate length of 0.25 /spl mu/m.