Akio Wakejima

Novel AlGaN/GaN dual-field-plate FET with high gain, increased linearity and stability

We have successfully developed a novel AlGaN/GaN FET with dual field-modulating-plates (FPs). The breakdown voltage is enhanced from 125 to 250 V by adding the second FP to the conventional FP structure. Benefiting from the first FP, no current collapse is observed simultaneously. Since the second FP effectively reduces feedback capacitance, this device provides a 3-dB higher gain along with increased linearity and stability. Under a 2.15-GHz W-CDMA modulation scheme, a dual-FP-FET with a 24-mm gate periphery achieved a state-of-the-art combination of 160-W output power and a 17.5-dB linear gain

A GaAs-based field-modulating plate HFET with improved WCDMA peak-output-power characteristics

A novel GaAs power FET with a field-modulating plate (FP-FET) and operated at a drain bias voltage of 24 V was developed. Regarding the power performance of an FP-FET under wideband code division multiple access (WCDMA) operation, its peak output power significantly degraded in the saturated-output-power region when its FP length was short. However, by introducing a sufficiently large FP length, it was demonstrated that the peak-power degradation can be significantly suppressed. In particular, an FP-FET amplifier fabricated with an FP length of 1.5 /spl mu/m exhibited no WCDMA peak-power degradation and delivered an output power of 120 W with a linear gain of 14.2 dB at 2.14 GHz.

Kelvin probe force microscopy study of surface potential transients in cleaved AlGaN∕GaN high electron mobility transistors

The surface potential of cleaved cross sections of AlGaN∕GaN high electron mobility transistors was measured by Kelvin probe force microscopy. For the bias conditions of Vgs=−5V and Vds=20V, the electric field was concentrated near the GaN∕SiC interface under the gate and between the gate and drain electrodes. A negative potential that decreased over time was observed in the GaN layer beginning 10min after the bias stress was removed. The transient surface potential was found to be well described by an exponential dependence with two time constants: 11 and 55s.

Electrical properties of InAlAs/InGaAs modulation doped structure after SiN passivated annealing

The effect of thermal annealing on the InAlAs/InGaAs modulation-doped structure, passivated with a SiN film, was investigated. In contrast to the capless sample, the passivated modulation-doped sample exhibited negligible degradation in the two-dimensional electron gas concentration (NS) after annealing at 280 °C, indicating that SiN is an efficient passivation material to ensure good thermal stability for the InAlAs/InGaAs modulation-doped structure. In addition, partial recovery in NS was found by annealing the SiN-passivated sample that had experienced serious NS degradation. A series of secondary ion mass spectroscopy (SIMS) measurements and Hall effect measurements revealed that the recovery of NS is associated with the discharge of fluorine atoms from the Si-doped n-type InAlAs layer.

370-W Output Power GaN-FET Amplifier with Low Distortion for W-CDMA Base Stations

High output power and low intermodulation distortion (IMD) GaN-FET amplifiers are highly sought after for W-CDMA base stations. In order to obtain high output power, we have developed a field-modulating plate GaN-FET with a high maximum drain current and a high gate-to-drain breakdown voltage. Also, in order to suppress the memory effects that obstruct digital predistortion (DPD) linearization in W-CDMA power amplifiers, we have newly developed the bias network, in which frequency-dependent impedance at the base band of multi-carrier W-CDMA signals is reduced. As a result, the GaN-FET amplifier developed for W-CDMA base stations achieves a record 370-W W-CDMA peak output power, and a low DPD linearized IMD of less than -50 dBc at the highest W-CDMA average output power of over 60 W, resulting in a significant improvement of DPD linearization not only in IM3 but also in IMS and IM7

C-band single-chip GaN-FET power amplifiers with 60-W output power

A C-band high power amplifier was successfully developed with a single-chip GaN-based FET. At 4.0GHz, the fabricated 24-mm wide FET delivers 62 W and 156W under CW and pulsed operating conditions, respectively with a universal test fixture. The internal matching circuit was designed to be set up in a half-size package as compared to that for GaAs-based comparable- power-level amplifiers. The developed GaN-FET amplifier with 24-mm gate periphery delivers a 61W output power with 10.2dB linear gain and 42% power-added efficiency under CW operating conditions. To the best of our knowledge, this is the highest CW output power achieved from a single-chip FET power amplifier at C-band.

Field-modulating plate (FP) InGaP MESFET with high breakdown voltage and low distortion

This paper describes a successfully developed field-modulating plate (FP) InGaP MESFET with an extremely high breakdown voltage of 100 V. The FP-FET, consisting of a 2.62 mm gate width, delivered an output power of 4.3 W and an output power density of 1.6 W/mm at 1.95 GHz operated at a drain bias (Vd) of 55 V. A low 3rd-order intermodulation distortion (IM3) of -31 dBc was also achieved at 8 dB back-off from saturation power. These results show the developed FET is suited for applications in the next generation cellular base station.

Observation of cross-sectional electric field for GaN-based field effect transistor with field-modulating plate

Cross-sectional potential distribution of a GaN-based field effect transistor with a field-modulating plate has been measured by Kelvin prove force microscopy to investigate the effect of the field-modulating plate on an electric field under high-voltage biasing conditions. The observed potential distribution clearly revealed that the introduction of the field-modulating plate is effective in relaxing the peak electric field intensity at the drain side of the gate edge. Furthermore, the authors experimentally observed that the peak of electric field splits into two positions: drain-side edges of the gate and field-modulating plate electrodes.

A low-distortion 230 W GaAs power FP-HFET operated at 22 V for cellular base station

This paper describes a successfully developed L-band depletion-mode GaAs-based heterostructure FET (HFET) with a field-modulating plate (FP) for cellular base station applications. The FP-HFET power amplifier, consisting of four 86.4 mm gate-width chips, delivered a 53.6 dBm (230 W) output power at 2.1 GHz with 11 dB linear gain and 42% PAE operated at a drain bias of 22 V. A low adjacent channel leakage power ratio (ACPR) of -35 dBc with 25% PAE was obtained at an output power of 46 dBm, indicating superior linearity characteristics under elevated drain bias conditions. The device also exhibited a record saturated power density of 0.67 W/mm.

CW 20-W AlGaN/GaN FET Power Amplifier for Quasi-Millimeter Wave Applications

This paper describes an AlGaN/GaN FET power amplifier module delivering a continuous wave (CW) output power of more than 20 W at 26 GHz. To achieve high breakdown characteristics with reduced current collapse and high gain, we have developed a 0.2 µm-long recessed-gate AlGaN/GaN FET with a field-modulating plate (FP), achieving high operation voltage of 25 V even at quasi-millimeter wave frequencies. A single-ended AlGaN/GaN FP-FET amplifier module for quasi- millimeter wave frequency has been fabricated for the first time. The amplifier module developed using a 6.3-mm-wide single chip recessed-gate AlGaN/GaN FP-FET exhibited an output power of 20.7 W, a linear gain of 5.4 dB and a power-aided efficiency of 21.3% at 26 GHz. This is the highest output power in solid state power amplifiers at over 20 GHz.