Jean-Claude De Jaeger

Robust Surface-Potential-Based Compact Model for GaN HEMT IC Design

We present an accurate and robust surface-potential-based compact model for simulation of circuits designed with GaN-based high-electron mobility transistors (GaN HEMTs). An accurate analytical surface-potential calculation, which we developed, is used to develop the drain and gate current model. The model is in excellent agreement with experimental data for both drain and gate current in all regions of device operation. We show the correct physical behavior and mathematical robustness of the model by performing various benchmark tests, such as DC and AC symmetry tests, reciprocity test, and harmonic balance simulations test. To the best of our knowledge, this is the first time a GaN HEMT compact model passing a range of benchmark tests has been presented.

AlGaN/GaN HEMTs on (001) Silicon Substrate With Power Density Performance of 2.9 W/mm at 10 GHz

AlGaN/GaN High Electron Mobility Transistors (HEMT) on a (001)-oriented silicon (Si) substrate are fabricated. The device with a gate length of 300 nm and a total gate periphery of 300 μm exhibits a maximum dc drain current density of 600 mA/mm at VGS = 0 V with an extrinsic transconductance (gm) of about 200 mS/mm. An extrinsic current gain cutoff frequency (ft) of 37 GHz and a maximum oscillation frequency (fmax) of 55 GHz are deduced from S-parameter measurements. At 10 GHz, an output power density of 2.9 W/mm associated to a power-added efficiency (PAE) of 20% and a linear gain of 7 dB are obtained at VDS = 30 V and VGS = -2 V. To our knowledge, these power results represent the highest output power density ever reported at this frequency on GaN HEMT grown on (001) Si substrate.

Dual-purpose BGaN layers on performance of nitride-based high electron mobility transistors

A GaN/ultrathin BGaN/GaN heterojunction is used in AlGaN/GaN high electron mobility transistors (HEMTs) to provide an electrostatic barrier to electrons and to improve the confinement of the 2-dimensional electron gas. BGaN back-barrier layers limit leakage in the GaN buffer thanks to two effects: a polarization-induced band discontinuity and a resistive barrier originating from excellent insulation properties of BGaN. Compared to conventional AlGaN/GaN HEMTs, structures grown with BGaN back-barrier showed a significant improvement of static performances, transport properties, and trapping effects involving a limited current collapse in dynamic regime. A DC maximum current increase of 58.7% was observed.

Power Performance at 40 GHz of AlGaN/GaN High-Electron Mobility Transistors Grown by Molecular Beam Epitaxy on Si(111) Substrate

This letter reports on the demonstration of microwave power performance at 40 GHz on AlGaN/GaN high-electron mobility transistor grown on silicon (111) substrate by molecular beam epitaxy. A maximum dc current density of 1.1 A· mm-1 and a peak extrinsic transconductance of 374 mS · mm-1 are obtained for 75-nm gate length device. At VDS = 25 V, continuous-wave output power density of 2.7 W · mm-1 is achieved at 40 GHz associated with 12.5% power-added efficiency and a linear power gain (G p) of 6.5 dB. The device exhibits an intrinsic current gain cutoff frequency FT of 116 GHz and a maximum oscillation frequency FMAX of 150 GHz. This performance demonstrates the capability of low cost microwave power devices up to Ka-band.

Using low frequency noise characterization of AlGaN/GaN HEMT as a tool for technology assessment and failure prediction

AlGaN/GaN HEMTs are promising devices not only for high frequency power amplification but also for non-linear applications such as VCO. Therefore an assessment of their low frequency noise (LFN) is needed since it can be up-converted around the RF carrier. We have therefore compared different devices either made on sapphire or silicon in order to know which ones feature the lowest LFN. This study involves static and low frequency noise measurements (two different LFN set-up will be used and compared). GaN HEMT devices featuring several gate dimensions have been measured for different biasing conditions both in ohmic and saturation regime. We have compared sapphire based devices with silicon based ones with respect to their LFN levels. In a second part of this work, we report on some reliability results of HEMT on sapphire substrates: identification of defects has been achieved with the help of static measurements, and we make use of low frequency noise as well as physical simulation in order to understand the operating mode of the device. For the first time, we correlate the γ of the 1/fγ LFN spectrum with transport mechanisms of the carriers: we found that γ strongly depends on the carriers conduction path. This hypothesis has been checked for HEMT on silicon substrate.

Optimization of

In this paper, we propose to optimize Al0.29Ga0.71N/GaN heterostructures on silicon substrate to obtain high electron mobility transistors featuring high-power/frequency performances. The polarization electric fields are engineered by varying the layer thicknesses of the cap and the barrier, and by changing the type of buffer (GaN or AlGaN). The aim of this paper is to find the best tradeoff between the active layer thickness reduction and the achievement of a reasonable drain current to satisfy the requirements for high performances. The optimum heterostructure device presents an output power density of 1.5 W/mm at 40 GHz, among the best reported on silicon substrate.

{\rm Al}_{0.29}{\rm Ga}_{0.71}{\rm N}/{\rm GaN}

Depletion-mode high-electron mobility transistors (HEMTs) based on a quaternary barrier In0.11Al0.72Ga0.17N/GaN heterostructure on sapphire substrate are fabricated and characterized. This structure shows a very high Hall electron mobility of 2200 cm2/V·s, which is the highest value ever reported on In-containing GaN-based HEMTs. For T-shaped gate transistor with a gate length of 75 nm, current gain (ft) and power gain (fmax) cutoff frequencies of 113 and 200 GHz are extracted from S-parameter measurements, respectively. Nonlinear characterization of a T-shaped gate device with a gate length of 225 nm gives an output power density of 2 W/mm at 40 GHz. These results clearly demonstrate the capabilities of such quaternary barrier-based devices.

High Electron Mobility Heterostructures for High-Power/Frequency Performances

This letter reports on a new method for the characterization of transistors transient self-heating based on gate end-to-end resistance measurement. An alternative power signal is injected to the device output (between drain and source) at constant gate-to-source voltage. The dependence of gate resistance with temperature is used to extract the thermal impedance of the device in frequency domain via electrical measurement. This new method is validated on common-gate AlGaN/GaN high-electron-mobility transistors on Si substrate under different experimental conditions, which demonstrates its potential to provide complete dynamic self-heating models for power transistors.

Power Performance at 40 GHz on Quaternary Barrier InAlGaN/GaN HEMT

Un modele pseudo bidimensionnel est propose afin d’etablir les possibilites dumisfetInP en regimes d’enrichissement et d’appauvrissement et une validation des resultats est obtenue a partir de resultats experimentaux On determine les caracteristiques courant de drain enfonction des tensions drain-source et grille-source ce qui permet d’estimer la valeur maximale du courant de drain et de la tension de claquage qui constituent des parametres importants pour des applications de puissance. De plus, on en deduit les principaux parametres de la structure ainsi que les performances hyperfrequences potentielles. Les resultats montrent que lemisfet InP constitue une possibilite tres interessante pour l’ amplification hyperfrequence de puissance.A pseudo two-dimensional model is proposed in order to describe the possibilities of the InPmisfet in enhancement and depletion modes, and a validation of the results is determined from experimental measurements. The drain current versus drain-source and gate-source voltages characteristics are established. They make possible to value the maximum drain current and the breakdown voltage which constitute important parameters for power applications. Moreover, the main device parameters and the determination of the potential microwave performances are deduced. The results show that the InPmisfet is a very interesting alternative for microwave power amplification.RésuméUn modèle pseudo bidimensionnel est proposé afin d’établir les possibilités dumisfetInP en régimes d’enrichissement et d’appauvrissement et une validation des résultats est obtenue à partir de résultats expérimentaux On détermine les caractéristiques courant de drain enfonction des tensions drain-source et grille-source ce qui permet d’estimer la valeur maximale du courant de drain et de la tension de claquage qui constituent des paramètres importants pour des applications de puissance. De plus, on en déduit les principaux paramètres de la structure ainsi que les performances hyperfréquences potentielles. Les résultats montrent que lemisfet InP constitue une possibilité très intéressante pour l’ amplification hyperfréquence de puissance.