Bertrand Grimbert

Amplified piezoelectric transduction of nanoscale motion in gallium nitride electromechanical resonators

A fully integrated electromechanical resonator is described that is based on high mobility piezoelectric semiconductors for actuation and detection of nanoscale motion. We employ the two-dimensional electron gas present at an AlGaN/GaN interface and the piezoelectric properties of this heterostructure to demonstrate a resonant high-electron-mobility transistor enabling the detection of strain variation. In this device, we take advantage of the polarization field divergence originated by mechanical flexural modes for generating piezoelectric doping. This enables a modulation of carrier density which results in a large current flow and thus constitutes a motion detector with intrinsic amplification.

Searching for THz Gunn oscillations in GaN planar nanodiodes

A detailed study of GaN-based planar asymmetric nanodiodes, promising devices for the fabrication of room temperature THz Gunn oscillators, is reported. By using Monte Carlo simulations, an analysis of the static I-V curves and the time-domain evolution of the current obtained when varying some simulation parameters in the diodes has been made. Oscillation frequencies of hundreds of GHz are predicted by the simulations in diodes with micrometric channel lengths. Following simulation guidelines, a first batch of diodes was fabricated. It was found that surface charge depletion effects are stronger than expected and inhibit the onset of the oscillations. Indeed, a simple standard constant surface charge model is not able to reproduce experimental measurements and a self-consistent model must be included in the simulations. Using a self-consistent model, it was found that to achieve oscillations, wider channels and improved geometries are necessary.

First Demonstration of High-Power GaN-on-Silicon Transistors at 40 GHz

In this letter, high-output-power-density GaN-based high-electron-mobility transistors grown on a 100-mm silicon substrate is demonstrated for the first time at 40 GHz. The use of an optimized double heterostructure based on ultrathin barrier AlN/GaN allows both high current density and low leakage current, resulting in high-frequency performance (fmax close to 200 GHz). Furthermore, the control of the trapping effects on these highly scaled devices enabled to set a first benchmark at 40 GHz with 2.5 W/mm at VDS = 15 V, mainly limited by RF losses and thermal issues. These results show that an AlN/GaN/AlGaN heterostructure grown on silicon substrate is a viable technology for cost-effective high-power millimeter-wave amplifiers fully compatible with standard Si-based devices.

Experimental demonstration of direct terahertz detection at room-temperature in AlGaN/GaN asymmetric nanochannels

The potentialities of AlGaN/GaN nanodevices as THz detectors are analyzed. Nanochannels with broken symmetry (so called self switching diodes) have been fabricated for the first time in this material system using both recess-etching and ion implantation technologies. The responsivities of both types of devices have been measured and explained using Monte Carlo simulations and non linear analysis. Sensitivities up to 100 V/W are obtained at 0.3 THz with a 280 pW/Hz1/2 noise equivalent power.

Effects of AlGaN Back Barrier on AlN/GaN-on-Silicon High-Electron-Mobility Transistors

In this work, the effects of an AlGaN back barrier in the dc and RF performances of AlN/GaN high-electron-mobility transistors (HEMTs) grown on 100 mm Si substrates have been investigated. It is shown that the outstanding dc performance in highly scaled AlN/GaN-on-Si HEMTs can be fully preserved when introducing an AlGaN back barrier while significantly reducing the sub-threshold drain leakage current and enhancing the RF performance by the reduction of short-channel effects. Therefore, the AlN/GaN/AlGaN double heterostructure enables high-aspect-ratio devices generating extremely high current density, low leakage current, and high voltage operation.

Low-Noise Microwave Performance of AlN/GaN HEMTs Grown on Silicon Substrate

Microwave noise performance of state-of-the-art AIN/GaN high-electron-mobility transistors (HEMTs) grown on 100-mm Si substrate has been investigated. DC and RF measurements show the outstanding potential of this structure for high power millimeter-wave (mmW) applications. A maximum output current density of about 2 A/mm, together with a low gate leakage current, and a record GaN-on-Si extrinsic transconductance above 600 mS/mm are demonstrated. The current gain cutoff frequency fT and the maximum oscillation frequency fmax were 85 and 103 GHz, respectively, with a 0.16-μm gate length. At VDS = 4 V, the device exhibits a minimum noise figure (NFmin) of 1 dB (1.8 dB) with an associated gain (GA) of 12 dB (10 dB) at 10 GHz (18 GHz) favorably comparable to the best reported GaN-on-Si HEMTs. These results show that AIN/GaN HEMTs grown on silicon substrate are promising for the integration of cost effective, low noise, and high power mmW amplifiers.

Above 600 mS/mm Transconductance with 2.3 A/mm Drain Current Density AlN/GaN High-Electron-Mobility Transistors Grown on Silicon

AlN/GaN high-electron-mobility transistors (HEMTs) capped with an in-situ grown SiN have been successfully developed on 100 mm Si substrates. A unique combination of maximum output current density exceeding 2 A/mm and a record extrinsic transconductance above 600 mS/mm has been reached, which is well beyond the highest reported values of any GaN-on-Si HEMTs. The current gain extrinsic cutoff frequency fT and the maximum oscillation frequency fmax were 85 and 103 GHz with 0.16-?m gate length, respectively, resulting in a high fT?Lg product that promises low-cost, high performance millimeter wave electronics.

Record Combination of Power-Gain Cut-Off Frequency and Three-Terminal Breakdown Voltage for GaN-on-Silicon Devices

We report on an emerging GaN double heterostructure grown on silicon, which enables the simultaneous achievement of high breakdown voltage and high frequency performance. The use of an AlN barrier layer capped by an in situ SiN layer, and the introduction of an AlGaN back barrier layer in addition to standard field plates enabled the achievement of a remarkable three-terminal breakdown voltage VBK of over 100 V together with a power gain fmax above 200 GHz for the first time on GaN devices grown on silicon substrates. This results in a record combination of fmaxVBK of above 20 THz V, promising breakthrough performance for widespread millimeter-wave applications.

Sub-1-dB Minimum-Noise-Figure Performance of GaN-on-Si Transistors Up to 40 GHz

We report on the millimeter-wave noise performance of AlN/GaN/AlGaN double heterostructure (DHFET) grown on a 100-mm Si substrate with low-noise properties up to 40 GHz. The ultrathin-barrier GaN DHFETs simultaneously exhibit high current density, high transconductance, and high frequency performance (above 100 GHz) while showing low dc-to-RF dispersion and low gate and drain leakage currents. Consequently, sub-1-dB minimum noise figure at 36 GHz with an associated gain of 7.5 dB has been achieved. To our knowledge, this is the best noise performance reported in the Ka-band for any GaN device.

High electron mobility in high-polarization sub-10 nm barrier thickness InAlGaN/GaN heterostructure

We report on the improvement of the electron transport properties of the two-dimensional electron gas (2DEG) confined at a nearly lattice-matched quaternary barrier InAlGaN/AlN/GaN heterostructure using a sub-10 nm ultrathin barrier. Electron mobilities of 1800 (RT) and 6800 cm2 V−1 s−1 (77 K) are achieved while delivering a high electron density of 1.9 × 1013 cm−2, resulting in extremely low sheet resistances of 191 Ω/ at RT and below 50 Ω/ at 77 K. These 2DEG properties exceed the best ones ever reported for III–N structures. The excellent current and power gain cut-off frequencies of 60 and 190 GHz at VDS = 15 V obtained using 0.25 µm technology reflect the outstanding 2DEG properties.