Nicolas Defrance

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.

InAlN/GaN HEMTs on Sapphire Substrate With 2.9-W/mm Output Power Density at 18 GHz

In this letter, small- and large-signal measurements of an In_0.15Al_0.82N/AlN/GaN high-electron-mobility transistor (HEMT) grown on a sapphire substrate with a 225-nm T-shaped gate are described. A maximum dc current density of 1.2 A/mm and a peak extrinsic transconductance of 460 mS/mm are obtained. The device exhibits a current gain cutoff frequency (<i>F</i>_T) and a power gain cutoff frequency (<i>F</i>_MAX) of 52 and 120 GHz, respectively. At <i>V</i>_DS = 15 V, a continuous-wave output power density of 2.9 W/mm was achieved at 18 GHz with an associated power-added efficiency of 28% and a power gain of 15 dB. It is the best value ever reported from InAlN/GaN HEMTs grown on a sapphire substrate.

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.

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 paper reports the capability of AlGaN/GaN HEMTs on Si (111) substrates for microwave power applications above 30GHz. A current gain cut-off frequency ft=90GHz and a maximum power gain cut-off frequency fmax=135GHz are obtained for a 80nm gate-length transistor. These results, associated with low lag effects, demonstrate the capability of these transistors for high performance, cost effective, MMIC fabrication on a Si substrate for high frequency microwave power applications.

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

This paper shows the capability of AlGaN/GaN high electron mobility transistors (HEMTs) on (001) oriented silicon substrate with 300 nm gate length using unstuck Gamma gate for low cost device microwave power applications. The total gate periphery of 300 mum, exhibits a maximum DC drain current density of 600 mA/mm at VDS=7V with an extrinsic transconductance (gm max) around 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 Sij-parameters 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.

AlGaN/GaN HEMT on Si (111) substrate for millimeter microwave power applications

The role that the mother substrate plays to influence the performance of InGaN/GaN-based light-emitting diodes (LEDs) onto the adhesive flexible tapes is addressed in this letter. For this purpose, the electroluminescent (EL) spectra and current density-voltage (J-V) characteristics of flexi-LEDs are studied under different convex bending configurations (from a curvature radius of infinity to 1.4 cm), showing only one peak around 442 nm in all the cases. Both the EL spectra and J-V characteristics are affected by the applied tensile stress when the flexi-LED is bent. In fact, an increase of the applied tensile strain from 0.02% to 0.09% results in a red-shift of the EL peak energy by 3 meV at 0.7 mA, and a drop of the current at high forward bias. In addition, such flexi-LEDs exhibit a reversible response when a significant mechanical deformation is applied.

Performance of Unstuck - Gate AlGaN/GaN HEMTs on (001) Silicon Substrate at 10 GHz

The aim of this paper is to optimize the epitaxial layer structure of an AlGaN/GaN high electron mobility transistor (HEMT) for high power density at high frequency. The idea is to play on the polarization engineering with the different layers of the epitaxial stack. The influence of the cap and barrier layer thicknesses, the aluminum content in the barrier and the insertion of an AlGaN buffer layer are studied through the electron gas density, electron mobility and sheet resistance. This permits to find out the best trade-off in order to satisfy the requirements for high performances.

Impact of the Bending on the Electroluminescence of Flexible InGaN/GaN Light-Emitting Diodes

A delay time analysis is carried out for SiN-passivated AlGaN/GaN High Electron Mobility Transistors (HEMTs) on silicon substrate featuring gate length of 90 nm. The influence of high parasitics in the access pads is considered using de-embedding procedure from the measured S parameters. From the obtained transit delay contributions, the effective electron velocity is estimated to 0.85×107 cm.s-1. In addition, the effect of the image charge on the drain delay is experimentally demonstrated through the extraction of the mirroring coefficient a close to the predicted simulation value.