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Some theories of Developmental Language Disorder (DLD) explain the linguistic deficits observed in terms of limitations in non-linguistic cognitive systems such as working memory. The goal of this research is to clarify the relationship between working memory and the processing of complex sentences by exploring the performance of 28 French-speaking children with DLD aged five to fourteen years and 48 typically developing children of the same age in memory and linguistic tasks. We identified predictive relationships between working memory and the comprehension and repetition of complex sentences in both groups. As for syntactic measures in spontaneous language, it is the complex spans that explain the major part of the variance in the control children. In children with DLD, however, simple spans are predictive of these syntactic measures. Our results thus reveal a robust relationship between working memory and syntactic complexity, with clinical implications for the treatment of children with DLD.
Banked human milk (BHM) has inherent infectious risks, even when pasteurized. Because of the ubiquity of Bacillus cereus in the environment and its ability to resist the Holder pasteurization process, there is a concern that BHM might lead to severe B. cereus infections.
We reviewed observed and published cases to determine the potential causal role of BHM as the source of these infections.
Two infants in the province of Québec (Canada) developed a B. cereus neonatal infection, and both had received BHM. We conducted bacteriological studies to compare clinical isolates and those found in these cases.
After extended culture of BHM retention lots, B. cereus was found to have been involved in batches related to the first case. However, molecular typing showed that the strain was different from the clinical isolate, therefore excluding BHM as the source of contamination. In the second case, a Brevibacillus spp was isolated, a species distinct from the clinical isolate.
Based on these cases and others reported in the literature, a causal link between B. cereus contaminated BHM and preterm neonatal infection has never been documented. Therefore, the risk that BHM can cause this infection remains theoretical. Given the widespread presence of B. cereus in the hospital environment and its capacity to resist standard cleaning procedures, it seems likely that airborne or direct or indirect contact are the main sources of most, if not all, cases of severe B. cereus neonatal infections, even in babies exposed to BHM.
This paper presents performances achieved with InAlGaN/GaN HEMTs with 0.15 µm gate length on SiC substrate. Technology Computer Aided Design simulations were used to optimize the heterostructure. Special attention was paid to the design of the buffer structure. I-V measurements with DC and pulsed bias voltages were performed. CW measurements at millimeter waves were also carried out and are detailed in the following sections. The technology, optimized for power applications up to 45 GHz, demonstrates a current gain cut-off frequency FT of 70 GHz and a maximum available gain cut-off frequency FMAG of 140 GHz. CW Load-pull power measurements at 30 GHz enable to achieve a maximum PAE of 41% associated with an output power density of 3.5 W/mm when biased at VDS = 20 V. These devices, with an improved buffer structure show, reduced recovery time in pulsed operating conditions. These improved characteristics should have a positive impact for pulsed or modulated signal applications.
This paper presents an original characterization method of trapping phenomena in gallium nitride high electron mobility transistors (GaN HEMTs). This method is based on the frequency dispersion of the output-admittance that is characterized by low-frequency S-parameter measurements. As microwave performances of GaN HEMTs are significantly affected by trapping effects, trap characterization is essential for this power technology. The proposed measurement setup and the trap characterization method allow us to determine the activation energy Ea and the capture cross-section σn of the identified traps. Three original characterizations are presented here to investigate the particular effects of bias, ageing, and light, respectively. These measurements are illustrated through different technologies such as AlGaN/GaN and InAlN/GaN HEMTs with non-intentionally doped or carbon doped GaN buffer layers. The extracted trap signatures are intended to provide an efficient feedback to the technology developments
This paper presents power results of L-band packaged hybrid amplifiers using InAlN/GaN/SiC HEMT power dies. The high-power densities achieved both in pulsed and continuous wave (cw) modes confirm the interest of such technology for high-frequency, high-power, and high-temperature operation. We present here record RF power measurements for different versions of amplifiers. Up to 260 W, i.e. 3.6 W/mm, in pulsed (10 µs/10%) conditions, and 105 W, i.e. 2.9 W/mm, in cw conditions were achieved. Such results are made possible thanks to the impressive performances of InAlN/GaN transistors, even when operating at high temperatures. Unit cell transistors deliver output powers of 4.3 W/mm at Vds = 40 V in the cw mode of operation at the frequency of 2 GHz. The transistor process is described here, as well as the amplifiers design and measurements, with a particular focus to the thermal management aspects.
A study of the electrical performances of AlInN/GaN High Electron Mobility Transistors (HEMTs) on SiC substrates is presented in this paper. Four different wafers with different technological and epitaxial processes were characterized. Thanks to intensive characterizations as pulsed-IV, [S]-parameters, and load-pull measurements from S to Ku bands, it is demonstrated here that AlInN/GaN HEMTs show excellent power performances and constitute a particularly interesting alternative to AlGaN/GaN HEMTs, especially for high-frequency applications beyond the X band. The measured transistors with 250 nm gate lengths from different wafers delivered in continuous wave (cw): 10.8 W/mm with 60% associated power added efficiency (PAE) at 3,5 GHz, 6.6 W/mm with 39% associated PAE at 10.24 GHz, and 4.2 W/mm with 43% associated PAE at 18 GHz.
The present paper presents an overview of the AlGaN/GaN-based circuits realized over the years. Two technological processes with 0.25 and 0.7 μm gate length allowed one to address applications from L- to Ku-bands. Depending on the process development and frequency of the operation, results on hybrid or MMIC technology are presented. GaN technology is evaluated through the realization of high-power amplifiers, robust low-noise amplifiers, or power switches to prepare the next generation of Tx-Rx modules.
The fabrication of high-resistivity ZnO-based thin films lattice-matched to AlGaN/GaN structures has been developed. It relies on low-temperature reactive sputter deposition of ZnO:Sb from ZnSb target. Taking into account the hygroscopic nature of ZnO surface, an additional coating by Si3N4 films is applied to ensure the humidity protecition. The developped passivation suppresses leakage currents in Schottky diods, and substantially improves output characteristics of AlGaN/GaN HEMT.
A series of isothermal annealing experiments have been performed in the range 790–920°C under N2 flow in order to study the deuterium out-diffusion kinetics of Mg-doped GaN grown on sapphire under deuterated ammonia. The deuterium concentration was measured by SIMS analysis before and after each annealing step. The kinetics closely follow a first-order law. The activation energy related to the deuterium out-diffusion process is 3.1 eV. In addition, deuterium effusion measurements were performed measuring the molecular HD flux while the specimens were annealed in ultra high vacuum with a linear heating rate. In contrast to SIMS, this method detects the species that migrated out of the sample. Effusion peaks of the HD flux at 360 and 490°C are attributed to the fragmentation of adsorbed CHxDy complexes. The molecular HD flux starts increasing at 800°C which is the onset of the GaN decomposition and has its maximum at 920°C. This HD flux is accompanied by the desorption of H and D containing radicals and molecules desorbing above 900°C.
High power RF device performance
decreases as operation temperature increases (e.g. decreasing electron
mobility affects cut-off frequencies and degrades device reliability).
Therefore determination of device temperature is a key issue for device
topology optimisation. In this work the temperature variation of AlGaN/GaN
high-electron-mobility transistors grown either on silicon or sapphire
substrate under bias operation was measured by micro Raman scattering
spectroscopy. Temperature measurements up to power dissipation of 16 W for
4 mm development devices were carried out and a peak temperature of 650 K was
determined. The difference of thermal resistance for similar devices grown
on the two different substrates was assessed. The thermal resistances of
different device topologies were compared to optimise the component design.
We have studied the influence of a deuterium diffusion on the electrical characteristics of the 2D gas present in AlGaN/GaN heterostructures. The deuterium diffusion is performed by exposing the structures to a rf remote deuterium plasma. We find that both the sheet carrier concentration and the electron mobility decrease and that these effects are partly reversible under thermal annealing. These results suggest that deuterium behave as acceptors in the 2D gas region. The negatively charged deuterium act as additional scattering centers for electrons.
The high power RF device performance decreases as the operation
temperature increases (e.g. fall of electron mobility impacting
the cut-off frequencies and degradation of device reliability).
Therefore the determination of device temperature is a key issue
for device topology optimisation. In this work the temperature
variation of AlGaN/GaN high-electron-mobility transistors grown
either on silicon or sapphire substrates under bias operation was
measured by micro Raman scattering spectroscopy. The differences
in thermal resistance for similar devices grown on the two
different substrates were assessed. The thermal resistances of
different device topologies were compared in order to optimise
the component design. The temperature measurement across the gate
and along the component fingers were made to quantify the thermal
gradient of the device. Temperature measurement up to a power
dissipation of 16 W for a 4 mm development device was carried out
and the peak temperature of 650 K was determined.
Using a waveguide spectrometer chip as an example, we describe how high index contrast waveguides systems such as silicon-on-insulator can be combined with microphotonic design rules to extend the performance of waveguide devices. The challenges arising in the implementation of silicon microphotonic technology are discussed, and recent work addressing the issues of waveguide coupling, polarization sensitivity, waveguide loss and massively parallel data acquisition is reviewed.
The high power RF device performance decreases as operation
temperature increases (e.g. fall of electron mobility impacting the cut-off frequencies
and degradation of device reliability). Therefore the determination of device
temperature is a key issue for device topology optimisation. This work presents the
comparison between pulsed I-V at different temperature and DC measurements of
AlGaN/GaN HEMTs grown on two different substrates: sapphire and silicon. This
technique allows the determination of mean channel temperature and the device
thermal resistance. The thermal resistance is a classical way to define the average
channel temperature as a function of the dissipated power. In this work the thermal
resistance ratio of the HEMT grown on sapphire compared to the one grown on silicon
is found to be 1.7 instead of 3 as expected from straightforward thermal conductivity
ratio. This lower difference is clearly attributed to the contribution of the GaN buffer
This paper reports on the LP-MOCVD growth optimisation of GaAlN/GaN heterostructures grown on Silicon Carbide substrates for HEMT applications, and on the first device performances obtained with these structures. The critical impact of some growth parameters on the physical properties of the GaAlN/GaN epilayers has been identified and studied using High Resolution X-Ray diffraction (HR-XRD), AFM, C-V and sonogauge measurements. The SiC substrate surface preparation (both ex-situ and in-situ) and the nucleation layer growth conditions (growth temperature, thickness, composition and strain) have been found to be key steps of the GaAlN/GaN/SiC growth process. SiC substrates from different suppliers have been evaluated and their influence on the physical properties of the GaAlN/GaN HEMT structures investigated. Static characteristics of the devices such as maximum drain current Idss or pinch-off voltage have been correlated with the nucleation layer composition of the HEMT structure and the defect density of the SiC substrate. First devices measured at 10 GHz using a load pull system exhibited CW output power in excess of 2.8 W/mm for a gate length of 0.5 μm. Under static measurements, we found an Idss around 1 A/mm and a pinch-off voltage of –5 V.