We report on an accelerometer micro-sensor based on epitaxial gallium nitride and silicon. The device is a vibrating beam accelerometer fabricated with a micro-electro-mechanical-system technology starting from an AlGaN/GaN heterostructure grown on silicon. The vibrating GaN beam has integrated high electron mobility transducers, whereas a high aspect ratio proof mass is engineered in the silicon substrate. The sensor response was investigated for several modes and features a scale factor up to 160 Hz/g, with unconventional dependence vs the mode number. To account for this, we propose an analytical model of the accelerometer scale factor that takes into account the built-in stress during epitaxy. This proof-of-concept device opens perspectives for inertial sensors taking advantage of GaN properties.

GaN based self-switching diodes (SSDs) have been fabricated for the first time on SiC substrate. They have been characterized as RF power detectors in a wide frequency range up to 220 GHz, showing a cutoff frequency of about 200 GHz. At low-frequency, RF measurements exhibit a square law detection with a responsivity that well agrees with the calculations performed by means of a quasi-static model based on the shape of the I-V curve. Exploiting such a model, a simple DC characterization allows defining design rules for optimizing the practical operation of the diode arrays as RF power detectors. As strategy to improve the performance of SSDs operating as zero-bias detectors at room temperature, in terms of responsivity and noise equivalent power, we suggest: (i) the reduction of the channel width and (ii) the increase of the number of diodes in parallel in order to reduce the total device impedance to a value that coincides with 3 times that of the transmission line (or antenna) to which they are connected.

We report on AlN/GaN double heterostructures for high frequency applications. 600h preliminary reliability assessment has been performed on these emerging RF devices, showing promising millimeter-wave 100nm gate length GaN-on-Si device stability for the first time. A 150nm AlN/GaN double heterostructure has been developed and evaluated on SiC substrate. State-of-the-art CW power-added-efficiencies (PAE) up to 40GHz have been achieved on ultrathin barrier (6nm) GaN devices while operating at a drain bias exceeding 30V.

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-10nm ultrathin barrier. Electron mobilities of 1800 (RT) and 6800 cm(2)V(-1)s(-1) (77 K) are achieved while delivering a high electron density of 1.9 x 10(13)cm(-2), resulting in extremely low sheet resistances of 191 Omega/square. at RT and below 50 Omega/square at 77 K. These 2DEG properties exceed the best ones ever reported for III-N structures. The excellent current and power gain cutoff frequencies of 60 and 190GHz at V-DS = 15V obtained using 0.25 mu m technology reflect the outstanding 2DEG properties. (C) 2015 The Japan Society of Applied Physics

A three-terminal breakdown voltage over 3 kV is reported on AlGaN/GaN high-electron-mobility transistors (HEMTs) grown on silicon (Si) (111) substrate with a buffer thickness of 5.5 mu m. The breakdown voltage of the 1.5 x 50 mu m(2) devices has been improved by more than 200% by applying a local substrate removal all around the drain of the transistors in order to suppress the parasitic substrate conduction phenomenon. This establishes a new record breakdown voltage for GaN-on-silicon lateral power devices while maintaining a low specific on-resistance of about 10 m Omega center dot cm(2).

A 3-terminal breakdown voltage of 2.3 kV has been achieved on an AlN/GaN heterostructure grown on silicon (111) substrate using an optimized local substrate removal. The epitaxy was grown by metal organic chemical vapor deposition with a total buffer thickness of 5.5 μm. In order to suppress the parasitic substrate conduction phenomena under high electric field, the Si substrate has been locally etched in the high electric field region. After local substrate removal, the device breakdown voltage increased from 1.6 kV to 2.3 kV for 30 μm gate-drain distance in spite of the use of a 6.0 nm ultrathin barrier layer. The high 2DEG carrier density (2×10 cm) provided by the high polarization AlN barrier results in an extremely low specific on-resistance of 4.6 mっ.cm.

We report on Gallium Nitride Self switching Diode used as detector in a terahertz imaging system. We propose to use the ionic implantation to define the nano-channels in the device, leading to an improved sensitivity in the mm-wave/THz regime. Preliminary results are given at 200 GHz.

This paper reports on the use of plasma assisted molecular beam epitaxy of AlGaN/GaN high electron mobility transistors (HEMTs) grown on silicon substrate. Surface passivation effects on AlGaN/GaN HEMTs were studied using SiO2/SiN dielectric layers grown by plasma enhanced chemical vapor deposition. The direct current measurement, pulsed characteristics and microwave small-signal characteristics were studied before and after passivation. An improvement of drain-source current density and the extrinsic transconductance was observed on the passivated HEMTs when compared with the unpassivated HEMTs. An enhancement of cut-off frequency (ft) and maximum power gain (fmax) was also observed for the devices with full SiO2/SiN passivation. A good correlation is found between pulsed and power measurements.

We report on the development of an emerging AlN/GaN/AlGaN double heterostructure for millimeter-wave applications. These types of novel heterostructures are indeed extremely promising for high frequency applications, however, limited today in terms of drain bias operation typically around 20 V and power-added-efficiency (PAE). In this work, high RF output power density at drain bias above 30 V is demonstrated for the first time on a 6 nm ultrathin barrier AlN/GaN double heterostructure. Furthermore, state-of-the-art PAE has been achieved up to 40 GHz owing to the control of device leakage current, material and processing quality and current collapse under high electric field in spite of the very close proximity of the surface charges and the 2DEG.

We report on AlN/GaN double heterostructures for high frequency applications. 600 hours preliminary reliability assessment has been performed on these emerging RF devices, showing promising millimeter-wave 100 nm gate length GaN-on-Si device stability for the first time. A 150 nm AlN/GaN double heterostructure has been developed and evaluated on SiC substrate. State-of-the-art CW power-added-efficiencies (PAE) at 10 and 18 GHz have been achieved on ultrathin barrier (6 nm) GaN devices while operating at a drain bias exceeding 30 V.

In this paper, an emerging double heterostructure high electron mobility transistor (DHFET) based on AlN/GaN/AlGaN grown on silicon substrate is presented. This configuration system allowed state-of-the-art GaN-on-silicon DC, RF output power and noise performances at 40 GHz, paving the way for high performance mmW cost-effective amplifiers. Preliminary reliability assessment has been performed on this new class of RF devices, showing promising mmW GaN-on-Si device stability for the first time.

We present electrical rectification up to 300 GHz with novel asymmetric nanochannels realized for the first time on AlGaN/GaN material system. At zero bias, sensivities of 100 V/W/Hz1/2 are obtained at room temperature.

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 K-a-band for any GaN device.

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.

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.