Jean-Claude Jacquet

SThM Temperature Mapping and Nonlinear Thermal Resistance Evolution With Bias on AlGaN/GaN HEMT Devices

Channel temperature has a strong impact on the performance of a microwave power transistor. In particular, it has a strong influence on the power gain, energetic efficiency, and reliability of the device. The thermal optimization of device geometry is therefore a key issue, together with precise measurements of temperature within the channel area. In this paper, we have used scanning thermal microscopy to perform temperature mapping, at variable dc bias points, on an AlGaN/GaN high-electron mobility transistor made on epilayers grown on silicon carbide substrate. We have analyzed the variation of the thermal resistance values, which are deduced from these measurements, with bias conditions VGS and VDS. The observed nonlinear behavior is found to be in excellent agreement with physical simulations, strongly pointing out the large variability of the extension of the dissipation area with the dc bias conditions

Surface potential of n- and p-type GaN measured by Kelvin force microscopy

n- and p-type GaN epitaxial layers grown by metal-organic chemical vapor deposition with different doping levels have been characterized by Kelvin probe force microscopy (KFM). To investigate the surface states of GaN beyond instrumental and environmental fluctuations, a KFM calibration procedure using a gold-plated Ohmic contact as a reference has been introduced, and the reproducibility of the KFM measurements has been evaluated. Results show that the Fermi level is pinned for n- and p-type GaN over the available doping ranges, and found 1.34±0.15eV below the conduction band and 1.59±0.18eV above the valence band, respectively.

State of the Art 58W, 38% PAE X-Band AlGaN/GaN HEMTs Microstrip MMIC Amplifiers

This paper presents the results obtained on X-Band GaN MMICs developed in the frame of the Kerrigan project launched by the European Defense Agency. A new step was achieved, 58 W of output power with 38% PAE in X-Band were obtained using an 18 mm 2 2-stages amplifier. To our knowledge, these results present a new state-of-the-art of X-Band MMIC power amplifiers.

43W, 52% PAE X-Band AlGaN/GaN HEMTs MMIC Amplifiers

This paper presents the results obtained on X-Band GaN MMICs developed in the frame of the Korrigan project launched by the European Defense Agency. GaN has already demonstrated excellent output power levels, nevertheless demonstration of excellent PAE associated to very high power in MMIC technology is still challenging. In this work, we present State-of-the-Art results on AlGaN/GaN MMIC amplifiers. An output power of 43W with 52% of PAE was achieved at 10.5 GHz showing that high power associated with high PAE can be obtained at X-band using MMIC GaN technology.

Characterization and modeling of bias dependent breakdown and self-heating in GaInP/GaAs power HBT to improve high power amplifier design

It is usual to say that power GaInP/GaAs heterojunction bipolar transistors (HBTs) have many advantages for power amplification at microwave frequencies, because of their high gain and high power density. Furthermore, the possibility of controling the base biasing conditions (voltage, current, self-bias control) compared to a field-effect transistor offers additive degrees of freedom to make a tradeoff between linearity and power-added efficiency. Nevertheless existing devices are limited because of the relatively low breakdown voltage whereas high collector voltage swings are required to achieve high power. This drawback makes them not appropriate for use in the next generation of mobile communication base station or radar systems. Silicon technologies such as LDMOS and III-V devices (MESFET and HFET) present competitive performances in term of high power level but for medium power added efficiency. Important improvements have been made in recent years which make possible large breakdown voltages for GaInP/GaAs HBTs. Breakdown value close to 67 V has been achieved. The aim of this work is to significantly improve the modeling of the breakdown voltage on this type of transistor. Furthermore, the in depth characterization and modeling of self-heating effects have been greatly improved in order to improve thermal management solutions which enable us to enhanced design solutions of HBT high power amplifiers.

Broadband hybrid flip-chip 6-18 GHz AlGaN/GaN HEMT amplifiers

GaN Based HEMTs have shown superior power-frequency performances than lower band-gap materials. In this paper, we present the design of broadband hybrid 6-18 GHz amplifiers based on AlGaN/GaN HEMT technology with a flip chip approach. Measurements of a single ended amplifier based on a 0.6mm gate width device allow us to achieve more than 1.8W in the [6.5-16] GHz bandwidth corresponding to a power density of 3W/mm. A Maximum output power is obtained at 8 GHz at 2.7W corresponding to 4.5W/mm. Average typical PAE values higher than 17% in the bandwidth with a maximum of 39% were obtained. A balanced amplifier based on two single ended amplifiers was also realized. The output power is above 2.8W in the [7-17] GHz bandwidth corresponding to a power density of 2.4W/mm. Maximum output power is obtained at 7.5 GHz at 4.5W corresponding to 3.8W/mm.

Thermal Characterization Using Optical Methods of AlGaN/GaN HEMTs on SiC Substrate in RF Operating Conditions

Performance and reliability of wide bandgap high-power amplifiers are correlated with their thermal behavior. Thermal model development and suitable temperature measurement systems are necessary to quantify the channel temperature of devices in real operating conditions. As a direct temperature measurement within a channel is most of the time not achievable, the common approach is to measure the device temperature at different locations close to the hotspot and then to use simulations to estimate the channel temperature. This paper describes a complete thermal characterization of AlGaN/gallium nitride (GaN) on silicon carbide high electron-mobility transistors (HEMTs) when devices are operating in dc bias, pulsed, and continuous wave. Infrared thermography, charge-coupled device-based thermoreflectance microscopy, and micro-Raman spectroscopy have been performed to extract the thermal resistance of the components. Results have been compared with simulations using a 3-D finite-element model to estimate the operating channel temperature. Measurements have shown that the RF-biased thermal resistance and the dc-biased thermal resistance of GaN HEMTs are similar.

Electrical performances of AlInN/GaN HEMTs. A comparison with AlGaN/GaN HEMTs with similar technological process

A study of the electrical performances of AlInN/GaN High Electron Mobility Transistors (HEMTs) on SiC substrates is presented in this paper. Four different wafers with different technological and epitaxial processes were characterized. Thanks to intensive characterizations as pulsed-IV, [S]-parameters, and load-pull measurements from S to Ku bands, it is demonstrated here that AlInN/GaN HEMTs show excellent power performances and constitute a particularly interesting alternative to AlGaN/GaN HEMTs, especially for high-frequency applications beyond the X band. The measured transistors with 250 nm gate lengths from different wafers delivered in continuous wave (cw): 10.8 W/mm with 60% associated power added efficiency (PAE) at 3,5 GHz, 6.6 W/mm with 39% associated PAE at 10.24 GHz, and 4.2 W/mm with 43% associated PAE at 18 GHz.

InAlN/GaN heterostructures for microwave power and beyond

InAlN/GaN is indeed an alternative to the common AlGaN/GaN heterostructure in electronics and sensing. It enables operation at extremely high temperature once problems with contact metallization and passivation have been solved. It is the only heterostructure known presently, which allows overgrowth of high quality diamond films to combine two of the most stable semiconductors. Thus, applications reach from high power microwaves systems and high temperature electronics to sensing in harsh environment.

Ultra Compact X-Band GaInP/GaAs HBT MMIC amplifiers : 11W, 42% of PAE on 13mm2 and 8.7W, 38% of PAE on 9mm2

HBT power technology offers an excellent compromise for high power and high efficiency amplifiers up to the Ku band. In order to reduce cost and size of THALES T/R modules, we developed compact high power MMIC amplifiers with innovative transistor designs in X-band. In this paper, we present the performances of two GaInP/GaAs MMIC power amplifiers. The first one delivers an output power of 11.2W with 42.3% of PAE with a chip size of 13mm2. It represents a power density of 0.86W/mm2 of GaAs area. An advanced version on only 9 mm2 of GaAs gives an output power of 8.7W with 38% of PAE. This corresponds to a power density of 0.96W/mm2 of GaAs. To our knowledge, this is the state of the art performances in terms of power density per GaAs surface for MMIC power amplifiers above 8W. These power MMIC circuits constitute very attractive chips for phased array antennas, airborne radar, telecommunications or satellite links