Ultrahigh efficiency obtained with GaAs-on-insulator MESFETtechnology

Significant results of measurement and calculation of power-added efficiency (PAE) and drain efficiency are presented for MESFET's that use GaAs-on-insulator. Ultrahigh PAE of 89% was obtained at 8 GHz with a gain of 9.6 dB using a 3-V supply. When the voltage was increased to 4 V, the peak PAE was 93% at 210 mW/mm with 9.2-dB gain. The ideal current-voltage characteristics with practically zero leakage current and large transconductance near pinchoff yielded PAE values approaching the theoretical limits of overdriven operation. The application of conventional assumptions concerning drain efficiency is discussed relative to devices that approach these theoretical limits. Also discussed are the pitfalls of various figures of merit of efficiency when applied to these devices. Hence, there are two types of technical barriers associated with very-high-efficiency devices: the physical realization and their characterization     

Short channel AlGaN/GaN MODFET's with 50-GHz fT and1.7-W/mm output-power at 10 GHz

A thin barrier-donor layer of 200 Å was used to increase the active input capacitance and improve the extrinsic current-gain cutoff frequency (f_t) of short-gate-length AlGaN/GaN MODFETs. 0.2-μm gate-length devices fabricated on such an epi-structure with sheet carrier density of ~8×10¹² cm^-2 and mobility of 1200 cm²/Vs showed a record f_t of 50 GHz for GaN based FETs. High channel saturation current and transconductance of 800 mA/mm and 240 mS/mm respectively were also achieved along with breakdown voltages of 80 V per μm gate-drain spacing. These excellent characteristics translated into a CW output power density of 1.7 W/mm at 10 GHz, exceeding previous record for a solid-state HEMT     

Very high-power-density CW operation of GaAs/AlGaAs microwaveheterojunction bipolar transistors

Thermal instability of multi-emitter high-power microwave heterojunction bipolar transistors (HBTs) was eliminated using a novel heat spreading technique that regulates internal device currents to avoid the formation of hot spots. Devices with 2- and 3-μm minimum emitter sizes and no intentional ballast resistors showed unconditionally stable CW operation up to the device electronic limitations. A record 10-mW/μm² power density was obtained at 10 GHz with 7-dB gain and 60% power-added efficiency. The highest efficiency was 67.2% at 9.3-mW/μm² power density. It was shown that stable high-power-density operation can be maintained at multiwatt output power levels     

High Al-content AlGaN/GaN MODFETs for ultrahigh performance

The use of an AlGaN layer with high Al mole-fraction is proposed to increase the equivalent figures of merit of the AlGaN/GaN MODFET structure. It is shown that the room temperature mobility has little degradation with increasing Al mole-fraction up to 50%. 0.7-μm gate-length Al_0.5Ga_0.5N/GaN MODFETs by optical lithography exhibit a current density of 1 A/mm and three-terminal breakdown voltages up to 200 V. These devices on sapphire substrates without thermal management also show CW power densities of 2.84 and 2.57 W/mm at 8 and 10 GHz, respectively, representing a marked performance improvement for GaN-based FETs     

Microwave operation of high power InGaP/GaAs heterojunction bipolar transistors

The first high power demonstration of an InGaP/GaAs heterojunction bipolar transistor is presented. Multifinger selfaligned HBTs were tested at 3 GHz. A maximum output power of 2.82 W CW was obtained for a 600 mu m/sup 2/ emitter area device (4.7 mW/ mu m/sup 2/ power density) with an attendant gain of 6.92 dB; simultaneously, the device exhibited 55.2% power added efficiency, 69.1% collector efficiency and 8.0*10/sup 4/ A/cm/sup 2/ emitter current density.<>     

High-power microwave GaN/AlGaN HEMTs on semi-insulating siliconcarbide substrates

Record performance of high-power GaN/Al_0.14-Ga_0.86 N high-electron mobility transistors (HEMTs) fabricated on semi-insulating (SI) 4H-SiC substrates is reported. Devices of 0.125-0.25 mm gate periphery show high CW power densities between 5.3 and 6.9 W/mm, with a typical power-added efficiency (PAE) of 35.4% and an associated gain of 9.2 dB at 10 GHz. High-electron mobility transistors with 1.5-mm gate widths (12×125 μm), measured on-wafer, exhibit a total output power of 3.9 W CW (2.6 W/mm) at 10 GHz with a PAE of 29% and an associated gain of 10 dB at the -2 dB compression point. A 3-mm HEMT, packaged with a hybrid matching circuit, demonstrated 9.1 W CW at 7.4 GHz with a PAE of 29.6% and a gain of 7.1 dB. These data represent the highest power density, total power, and associated gain demonstrated for a III-nitride HEMT under RF drive     

Highest efficiency, linear X-band performance using InP DHBTs - 48%PAE at 30 dB C/IM3

InP single heterojunction bipolar transistors have previously demonstrated 5-10 dB lower third-order intermodulation products (IM3) compared to GaAs heterojunction bipolar transistors (HBTs) under low voltage (2 V) operation. This paper reports excellent single-tone and two-tone X-band operation, including high two-tone power-added efficiency (PAE), on linear InP double heterojunction bipolar transistors (DHBTs) operated at V_ce=4 V. The InP DHBT demonstrated a 30 dB carrier to third-order intermodulation product (C/IM3) output power ratio simultaneously with 48% two-tone PAE. This is the highest known efficiency of an X-band device under linear (30 dB C/IM3) operation. This is especially significant for microwave power amplifiers for satellite communication transmitters, where lower intermodulation distortion is normally accomplished by backing off in RF drive and output power, thus sacrificing PAE performance     

Microwave performance of AlGaN/GaN inverted MODFET's

A continuous wave output power of 1.5 W/mm with a power added efficiency of 17.5% has been achieved at 4 GHz in inverted AlGaN/GaN MODFET's (IMODFET's) with 2 μm gate lengths and 78 μm gate widths. The current gain and available power gain cutoff frequencies were 6 and 11 GHz, respectively. We suggest that the input characteristics of GaN-based FET's play an important role in the output power that can be obtained. In the present devices, high transconductance, 100 mS/mm, retained over a 5 V input swing is thought to alleviate the limitations imposed by the input characteristics. Moreover, the buried AlGaN buffer layer is suggested as having assisted in the reduction of the output conductance which aids the power gain     

Ultrahigh-efficiency power amplifier for space radar applications

This paper describes a broad-band switch mode power amplifier based on the indium phosphide (InP) double heterojunction bipolar transistor (DHBT) technology. The amplifier combines the alternative Class-E mode of operation with a harmonic termination technique that minimizes the insertion loss of matching circuitry to obtain ultrahigh-efficiency operation at X-band. For broad-band Class-E performance, the amplifiers output network employs a transmission line topology to achieve broad-band harmonic terminations while providing the optimal fundamental impedance to shape the output current and voltage waveforms of the device for maximum efficiency performance. As a result, 65% power-added efficiency (PAE) was achieved at 10 GHz. Over the frequency band of 9-11 GHz, the power amplifier achieved 49%-65% PAE, 18-22 dBm of output power, and 8-11 dB gain at 4 V supply. The reported power amplifier achieved what is believed to be the best PAE performance at 10 GHz and the widest bandwidth for a switch-mode design at X-band.