M. J. Poulton

High power, high efficiency, AlGaN/GaN HEMT technology for wireless base station applications

We report AlGaN/GaN high-electron-mobility-transistors (HEMT) on SiC substrates with field modulation plates (FP) of various dimensions and different gate widths. As a measure of the status of GaN technology achieved in this work, small periphery 150 μm HEMT demonstrated a continuous wave (CW) output power density of 22.7 W/mm at 2.14 GHz with power added efficiency (PAE) of 54% when biased at a drain-source voltage (V D S ) of 80 V. As a demonstration of the sealability of this technology, a 20-mm-wide device exhibited 100 W CW output power and a simultaneous peak PAE of 55.3% at 2.14 GHz when biased at class AB and V D S =48V. WCDMA measurements on the 20mm part demonstrated ACP of -35 dBc at 42.5 dBm output power and 30% PAE under the same bias condition. Analysis of FP related performance tradeoffs are also presented in this work.

Performance and RF Reliability of GaN-on-SiC HEMT's using Dual-Gate Architectures

AlGaN/GaN HEMTs on SiC have been fabricated with dual and single gate device geometries. Subthreshold characteristics and drain bias dependence of large signal parameters were compared to identify differences in electric field. Degradation under RF stress reveals the relative impact of temperature and electric field. The results illustrate the beneficial effects of the dual gate geometry for performance and reliability

Wideband 400 W pulsed power GaN HEMT amplifiers

We have developed 400 W pulsed output power GaN HEMT amplifiers with 2.9 – 3.5 GHz bandwidth. Operating the amplifier from a 65 V drain supply under pulsed operation with 10% duty cycle and 100μs pulse width obtains an output power in the range of 401 – 446 W over the band with a drain efficiency of 48 – 55%. The amplifier uses AlGaN/GaN HEMTs with a total device periphery of 44.4 mm and advanced source connected field plates for high breakdown voltage. These wideband high power amplifiers are suitable for use in pulsed radar applications.

RF Breakdown and Large-Signal Modeling of AlGaN/GaN HFET's

HFETs fabricated from nitride-based wide bandgap semiconductors can produce RF output power greater than an order of magnitude compared to devices fabricated from traditional semiconductors such as GaAs and InP. Nitride-based HFETs can support drain bias voltages in the range of 40-50 V, and have been biased as high as 120 V using device designs that make use of field-plate technology. However, the RF power produced by these devices is still limited by breakdown phenomena. Breakdown can occur at the gate electrode on the drain side due to a tunnel leakage mechanism, and by RF breakdown in the conducting channel. In this work it is demonstrated that RF breakdown in the conducting channel is the primary mechanism limiting the RF power performance of these devices. Gate leakage current under RF drive produces reliability degradation. A new large signal model that includes RF breakdown is proposed, and it is demonstrated that the new model produces excellent agreement with experimental data

A 250W S-Band GaN HEMT Amplifier

We report an efficient 250 W GaN HEMT power amplifier with 2.1 -2.5 GHz bandwidth. The amplifier employs AlGaN/GaN HEMTs with advanced source connected field plates, which are suitable for 48 V operation. The package combines two 22.2 mm periphery devices to obtain 54.0 dBm output power at 2.14 GHz and 54.6 dBm at 2.5 GHz, under pulsed condition with 10% duty cycle and 20mus pulse width. To our knowledge this is one of the widest bandwidth reported at this power level and frequency. These amplifiers are targeted for wideband digital cellular infrastructure; satellite communication, avionics and ISM band applications.

A Classic Nonlinear FET Model for GaN HEMT Devices

This paper shows the effective modeling of GaN HEMT devices using Agilent EEHEMT, a commercially available model in Agilent ADS, Microwave Office, etc. Using a series of pulsed IV, DC, S-parameter and Load-pull measurements, a nonlinear large-signal model is extracted to fit the circuit behavior of the device in a real application. Detailed steps are shown in extracting extrinsic and intrinsic parameters in addition to peculiarities of GaN HEMTs in challenging the conventional FET modeling practices. Simulation capabilities of the model are demonstrated through prediction of experimental output power, PAE and input reflection characteristics of a practical amplifier.

Voltage Dependent Characteristics of 48V AlGaN/GaN High Electron Mobility Transistor Technology on Silicon Carbide

Gallium nitride based HEMTs are a promising technology for high voltage, high power, high frequency applications. In addition to the potential for high operating voltage, this technology may also be suited for applications that utilize modulation of the drain voltage to improve overall amplifier efficiency. RFMD has developed a GaN HEMT technology platform on semi-insulating SiC substrates. This technology includes a 0.5 mum gate process and advanced field plate designs to maximize device performance. We report on devices from this technology, operated over a range of drain bias conditions. Performance and reliability results illustrate the compatibility of this device technology for high voltage and variable voltage applications.

GaN Wide Band Power Integrated Circuits

Gallium nitride (GaN) amplifiers have demonstrated very high power density as well as wide bandwidth in previous research. This paper examines their use in supplying flat gain, power, and linearity across a large bandwidth. It demonstrates two types of power amplifiers: a Ft Doubler (FT2) amplifier and a Cascode amplifier, both of which require a simple PCB tune. Both amplifiers show 0.2 to 4GHz bandwidth with 30 dBm PldB output power. The 3GPP WCDMA output power is 20 dBm at -45 dBc ACLR. Also, a WiMAX design is presented for the 3.2-3.8 GHz band to show the feasibility of a GaN HEMT amplifier in a relatively broad band, high linearity commercial application, with 27 dBm output at 2% EVM

A 65-W high-efficiency UHF GaN power amplifier

This paper presents a high-efficiency UHF power amplifier (PA) using a GaN HEMT on a SiC substrate transistor as the active device. The PA delivers 65W with 82% power added efficiency (PAE), and 45W with 84% PAE at 370MHz, with supply voltages of 35V and 28 V, respectively. Load pull techniques under Class-E conditions are used for device characterization and matching network design. The PA is implemented in a hybrid circuit with mixed lumped-element and transmission-line matching networks. A weighted Euclidean distance is defined to enable tradeoff studies between output power (POUT) and efficiency, in order to find the final optimal amplifier design.

Status of GaN HEMT performance and reliability

This report will focus on the status of GaN HEMT based amplifier technology development at RFMD. This technology is based around GaN on semi-insulating SiC substrates for optimal thermal performance. RFMDs 0.5μm gate technology features high performance advanced field plate structures, including a unit power cell producing high gain (21dB), high power density (3-5W/mm at 28V) and high efficiency (65-70 percent) at cellular frequencies. We will report on transistor and module performance relevant to applications ranging from high power, high bandwidth amplifiers, to switches and ICs for radar, electronic warfare, cellular infrastructure and homeland security. Additionally, we will report on reliability results that demonstrate capability for dependable, high voltage operation.