Effect of Anodic Oxidation on the Characteristics of Lattice-Matched AlInN/GaN Heterostructures

The effect of anodic oxidation on the electronic characteristics of lattice-matched AlInN/GaN heterostructures was investigated using field-effect transistor (FET) structures with the gate areas in direct contact with the electrolytes. The gate surface of the FETs was subjected to anodic oxidation in 0.1 M KOH. The oxidized heterostructures were analyzed by electrochemical impedance spectroscopy and by modeling the characteristics of the electrolyte-gate FETs and the energy-band diagram of the heterostructures. This analysis suggested that the anodic treatment induced a bulk oxidation of the AlInN barrier. The Fermi level at the oxidized AlInN surface was shifted deep into the bandgap. The oxidation led to a reduction of the carrier mobility and to partial depletion of the channel.     

Ultrathin barrier GaN-on-Silicon devices for millimeter wave applications

In this paper, the possibility to use GaN-on-Silicon devices for millimeter wave applications by means of ultrathin barrier layers is reviewed. In particular, an emerging double heterostructure high electron mobility transistor (DHFET) based on AlN/GaN/AlGaN grown on silicon substrate is described, which enables a unique simultaneous achievement of high breakdown voltage and high frequency performance. This configuration system allowed for 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 for the first time on this new class of RF devices, showing promising device stability.     

Power measurement setup for large signal microwave characterization at 94 GHz

We report the development of a power measurement setup in order to characterize devices at 94GHz. A very careful calibration of the setup has been performed in order to take into account in a most accurate way the losses through the different parts of the bench and in particular through the tuner. These aware power measurements have allowed to demonstrate state of the art power results on two different devices. We reached at 94GHz an output power of 876mW/mm associated to a 7.5-dB power gain and a power added efficiency (PAE) of 33% on a pseudomorphic high electron mobility transistor (PHEMT) on GaAs substrate. We achieved a 260-mW/mm maximum output power density with 5.9-dB power gain and 11% PAE on an InAsP channel HEMT on InP substrate.     

Barrier-Layer Scaling of InAlN/GaN HEMTs

We discuss the characteristics of high-electron mobility transistors with barrier thicknesses between 33 and 3 nm, which are grown on sapphire substrates by metal-organic chemical vapor deposition. The maximum drain current (at V_G = 2.0 V) decreased with decreasing barrier thickness due to the gate forward drive limitation and residual surface-depletion effect. Full pinchoff and low leakage are observed. Even with 3-nm ultrathin barrier, the heterostructure and contacts are thermally highly stable (up to 1000degC).     

Combining diamond electrodes with GaN heterostructures for harsh environment ISFETs

Electrochemistry and biochemistry have always been ideal applications for diamond due to its chemical inertness and stability, sensitivity and biocompatibility. Several diamond ChemFET concepts have been proposed to date, however further improvements are still needed to obtain functional devices that can be operated efficiently beyond the reach of the well established silicon ISFET technology [P. Bergveld, Sensor and Actuators B, Chem. 88 (2003), pp. 1].In this paper we describe a novel ISFET structure in which a boron doped diamond electrochemical gate electrode is combined and monolithically integrated with an InAlN/GaN HEMT structure. The new device merges the high chemical stability of diamond with the high transconductance and low pinch-off voltage of InAlN/GaN heterostructure FETs, resulting in a highly stable ISFET with high sensitivity. First devices have been fabricated and electrochemically characterized, expressing high current levels, a pH sensitivity of about 50 mV/pH, complete current modulation when operated within the electrochemical window of the electrode in the range of pH 1 to pH 13 and high stability upon pH cycling and the application of high anodic overpotentials.     

Low On-Resistance High-Breakdown Normally Off AlN/GaN/AlGaN DHFET on Si Substrate

Ultrathin-barrier normally off AlN/GaN/AlGaN double-heterostructure field-effect transistors using an in situ SiN cap layer have been fabricated on 100-mm Si substrates for the first time. The high 2DEG density in combination with an extremely thin barrier layer leads to enhancement-mode devices with state-of-the-art combination of specific on-resistance that is as low as 1.25 $hbox{m}Omegacdothbox{cm}^{2}$ and breakdown voltage of 580 V at ${V}_{rm GS} = hbox{0} hbox{V}$ . Despite the 2-$muhbox{m}$ gate length used, the transconductance peaks above 300 mS/mm. Furthermore, pulsed measurements show that the devices are dispersion free up to high drain voltage ${V}_{rm DS} = hbox{50} hbox{V}$. More than 200 devices have been characterized in order to confirm the reproducibility of the results.      

Characteristics of Al/sub 2/O/sub 3//AllnN /GaN MOSHEMT

InAlN/GaN is a new heterostructure system for HEMTs with thin barrier layers and high channel current densities well above 1 A/mm. To improve the leakage characteristics of such thin-barrier devices, AlInN/GaN MOSHEMT devices with a 11 nm InAlN barrier and an additional 5 nm Al₂O₃ barrier (deposited by ALD) were fabricated and evaluated. Gate leakage in reverse direction could be reduced by one order of magnitude and the forward gate voltage swing increased to 4 V without gate breakdown. Compared to HEMT devices of similar geometry, no degradation of the current gain cutoff frequency was observed. The results showed that InAlN/GaN FETs with high channel current densities can be realised with low gate leakage characteristics and high structural aspect ratio by insertion of a thin Al₂O ₃ gate dielectric layer     

Viscoelastic,thermal and environmental characteristics of poly(lactic acid), linear low-density polyethylene and low-density polyethylene ternary blends and composites

Poly(lactic acid) (PLA)/(linear low-density polyethylene (LLDPE)–low-density polyethylene (LDPE)) PLA/(LLDPE-LDPE) ternary blends were prepared and characterized as function of the PLA content. (50/50) PLA/(LLDPE–LDPE) blend was also compatibilized using maleic anhydride grafted low-density polyethylene (PE-g-MA) incorporated with a concentration of 5 wt.%. PLA/(LLDPE–LDPE) blend composites have been prepared by dispersing 5 wt.% of an organophilic montmorillonite (Org-MMT), added according to two different mixing methods. These materials were subjected to several investigations such as X-rays diffraction (XRD), dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry, and environmental tests. In the PLA glassy region, DMTA results showed that the storage modulus of PLA/(LLDPE–LDPE) blends decreases upon decreasing the PLA content. When PE-g-MA and Org-MMT were added, PLA exhibited a noticeable increase in the storage modulus across the glass transition region due the interface reinforcement and the enhancement of the blends stiffness. The decrease in the magnitude of the PLA tan δ peak was attributed to the decrease in the molecular mobility that could result from the increase in the interfacial resistance. XRD analysis showed that the method of dispersion of the nanoclay controls the final structural properties of the composites. (50/50) PLA/(LLDPE-LDPE) blend and composites revealed a satisfactory aptitude to biodegradation.