The dc small-signal, and microwave power output characteristics of AlGaN/GaN HEMTs are presented. A maximum drain current greater than 1 A/mm and a gate-drain breakdown voltage over 80 V have been attained. For a 0.4 /spl mu/m gate length, an f/sub T/ of 30 GHz and an f/sub max/ of 70 GHz have been demonstrated. Trapping effects, attributed to surface and buffer layers, and their relationship to microwave power performance are discussed. It is demonstrated that gate lag is related to surface trapping and drain current collapse is associated with the properties of the GaN buffer layer. Through a reduction of these trapping effects, a CW power density of 3.3 W/mm and a pulsed power density of 6.7 W/mm have been achieved at 3.8 GHz.

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Trapping effects and microwave power performance in AlGaN/GaN HEMTs

It is well known that trapping effects can limit the output power performance of microwave field-effect transistors (FETs). This is particularly true for the wide bandgap devices. In this paper we review the various trapping phenomena observed in SiC- and GaN-based FETs that contribute to compromised power performance. For both of these material systems, trapping effects associated with both the surface and with the layers underlying the active channel have been identified. The measurement techniques utilized to identify these traps and some of the steps taken to minimize their effects, such as modified buffer layer designs and surface passivation, are described. Since similar defect-related phenomena were addressed during the development of the GaAs technology, relevant GaAs work is briefly summarized.

Trapping effects in GaN and SiC microwave FETs

High-voltage Al/sub 0.22/Ga/sub 0.78/N-GaN high-electron mobility transistors have been fabricated using multiple field plates over dielectric passivation layers. The device breakdown voltage was found to increase with the addition of the field plates. With two field plates, the device showed a breakdown voltage as high as 900 V. This technique is easy to apply, based on the standard planar transistor fabrication, and especially attractive for the power switching applications.

/pdf/high-breakdown-voltage-algan-gan-hemts-achieved-by-multiple-2ef11ts9i7.pdf

High breakdown voltage AlGaN-GaN HEMTs achieved by multiple field plates

In a base-bias-control-type high-frequency power amplifier with a plural stage configuration, a rising voltage of a base bias current supplied to an initial stage transistor is made lower than a rising voltage of a base bias current supplied to a second stage transistor by a bias circuit, and a difference between the both voltages is set to be smaller than a base-emitter voltage of an amplifying stage transistor. Also, a rising voltage of a base bias current supplied to a third stage transistor is made equal to the rising voltage of the base bias current supplied to an initial stage transistor. Accordingly, a technology capable of improving the power control linearity can be provided in a high-frequency power amplifier used in a polar-loop transmitter or the like.

High frequency power amplifier

© Cambridge University Press 2007 and Cambridge University Press, 2009.This 2007 book is a comprehensive exposition of FET modeling, and is a must-have resource for seasoned professionals and new graduates in the RF and microwave power amplifier design and modeling community. In it, you will find descriptions of characterization and measurement techniques, analysis methods, and the simulator implementation, model verification and validation procedures that are needed to produce a transistor model that can be used with confidence by the circuit designer. Written by semiconductor industry professionals with many years' device modeling experience in LDMOS and III-V technologies, this was the first book to address the modeling requirements specific to high-power RF transistors. A technology-independent approach is described, addressing thermal effects, scaling issues, nonlinear modeling, and in-package matching networks. These are illustrated using the current market-leading high-power RF technology, LDMOS, as well as with III-V power devices.

Modeling and Characterization of RF and Microwave Power FETs

The authors determined that RF drain current degradation is responsible for the poor power performance of wide-recessed pseudomorphic high-electron-mobility transistors (PHEMTs). A model based on surface states was proposed to explain this phenomenon, which then led to the use of charge-screen layers and a double-recessed gate process to suppress surface effects. Combined, these two modifications increased the device's gate-drain reverse breakdown voltage without causing a degradation in the transistor's RF drain current. This allowed the simultaneous achievement of high power-added efficiency and high power density which established a new performance record for power PHEMTs at X- and Ku-bands. Delay time analysis of single- and double-recessed PHEMTs revealed that the benefit of a larger breakdown voltage in the latter device design came at the cost of a larger drain delay time. Drain delay accounted for 45% of the total delay when the 0.35- mu m double-recessed PHEMT was biased at V/sub ds/=6 V. >

An AlGaAs/InGaAs pseudomorphic high electron mobility transistor with improved breakdown voltage for X- and Ku-band power applications

Many papers and textbooks and the leading CAD (computer-aided design) packages state that a two-port is stable if and only if K>1 and mod Delta /sup s/ mod >

Instabilities diagnosis and the role of K in microwave circuits

The authors build and utilized a pulsed I-V system which is capable of reaching any current-voltage point of three-terminal devices from any arbitrarily chosen DC bias point. The system, which can be used on wafer, serves as an invaluable tool for device modeling and process diagnostics. Direct dependence of the pulsed I-V curves on the DC bias was found in GaAs MESFETs and HEMTs (high-electron mobility transistors). >

Characterization of GaAs devices by a versatile pulsed I-V measurement system

A circuit topology for realizing a BPSK (180 degree) modulator without the use of reactive phase determining networks is presented for the first time. This physically small circuit employs a trio of enhancement mode MESFETs which are uniquely configured to extend the upper frequency response of the design to in excess of 1.7 GHz. This approach is particularly noteworthy as it is implemented using less than 3 V dc and precludes the need for negative gate voltages making it attractive for use in wireless applications. >

A novel MMIC biphase modulator with variable gain using enhancement-mode FETS suitable for 3 V wireless applications

The design and performance of power amplifiers for Ka-band applications is presented. A three-stage amplifier demonstrated 22 dB small signal gain from 26.5 GHz to 31.5 GHz and saturated output power of 4W with 28% power added efficiency from 28 GHz to 31 GHz. Record power density of 670 mW per mm of device output periphery was achieved. The amplifiers were fabricated on a selective double-recess 0.2 /spl mu/m GaAs power pHEMT process.

A. Platzker

Papers

An AlGaAs/InGaAs pseudomorphic high electron mobility transistor with improved breakdown voltage for X- and Ku-band power applications

Instabilities diagnosis and the role of K in microwave circuits

Characterization of GaAs devices by a versatile pulsed I-V measurement system

A novel MMIC biphase modulator with variable gain using enhancement-mode FETS suitable for 3 V wireless applications

2 and 4 watt Ka-band GaAs PHEMT power amplifier MMICs