Energy Conversion Using New Thermoelectric Generator

During recent years, microelectronics helped to develop complex and varied technologies. It appears that many of these technologies can be applied successfully to realize Seebeck micro generators: photolithography and deposition methods allow to elaborate thin thermoelectric structures at the micro-scale level. Our goal is to scavenge energy by developing a miniature power source for operating electronic components. First Bi and Sb micro-devices on silicon glass substrate have been manufactured with an area of 1cm2 including more than one hundred junctions. Each step of process fabrication has been optimized: photolithography, deposition process, anneals conditions and metallic connections. Different device structures have been realized with different micro-line dimensions. Each devices performance will be reviewed and discussed in function of their design structure.Comment: Submitted on behalf of TIMA Editions (http://irevues.inist.fr/tima-editions

AlGaN/GaN MIS-HEMT gate structure improvement using Al2O3 deposited by PEALD

International audienceThe enhancement of electric properties of MIS structures on an AlGaN/GaN heterostructure using Al2O3 a gate dielectric are investigated using C(V) and Id(Vg) measurements. The Al2O3 layer was deposited using two types of atomic layer deposition (ALD) techniques: thermal ALD and plasma enhanced ALD. Using PEALD over thermal ALD led to an increase of the threshold voltage Vth of 4V, and the suppression of non-uniform C(V) behavior by reducing traps at the Al2O3/AlGaN interface. Gate leakage current was also reduced by 6 decades and an Ion/Ioff ratio of 109 was achieved, with a subthreshold slope of 81mV/decades. Further improvements were achieved by gate recess etching before the high-k deposition through BCl3 reactive ion etching (RIE). We were able to further increase Vth by 4V while reducing gate leakage current, achieving a 1010 Ion/Ioff ratio, without degrading the subthreshold slope and the abruptness of the transition

Coherent tunneling in an AlGaN/AlN/GaN heterojunction captured through an analogy with a MOS contact

International audienceDue to their wide band gaps, III-N materials can exhibit behaviors ranging from the semiconductor class to the dielectric class. Through an analogy between a Metal/AlGaN/AlN/GaN diode and a MOS contact, we make use of this dual nature and show a direct path to capture the energy band diagram of the nitride system. We then apply transparency calculations to describe the forward conduction regime of a III-N heterojunction diode and demonstrate it realizes a tunnel diode, in contrast to its regular Schottky Barrier Diode designation. Thermionic emission is ruled out and instead, a coherent electron tunneling scenario allows to account for transport at room temperature and higher

Treatment of sac expansion after endovascular aneurysm repair with obliterating endoaneurysmorrhaphy and stent graft preservation

International audienceBackground Persistent type II endoleaks (T2Ls) with sac enlargement after endovascular abdominal aortic aneurysm repair are still of concern in view of the potential for rupture. Current treatments (embolization and stent graft [SG] explantation) are associated with lack of efficacy or high perioperative morbidity and mortality. This study evaluated an alternative technique that combines sacotomy, ligation of patent back-bleeding vessels, and SG preservation for T2L or unspecified endoleak repair. Methods This multicenter study in France included 28 patients (27 men; median age, 78 years). Twenty-one patients (75%) had a bifurcated SG (including 3 fenestrated SGs) and seven (25%) had an aortouniiliac SG (2 for ruptured aneurysm). Unsuccessful embolization had been performed in 10 patients (36%). Four patients (14%) presented sac enlargement with no endoleak visible on computed tomography. The origin of the endoleak remained unspecified in three patients 3 (11%). The median diameter of the aneurysmal sac was 78 mm (vs 55 mm at the time of endovascular abdominal aortic aneurysm repair) after a median follow-up of 24 months. Results A transperitoneal approach was used in 21 patients (75%) and a retroperitoneal approach was used in seven (25%). A guidewire was placed in the supraceliac aorta in 14 patients, and an occlusion balloon was temporarily inflated in six. Aortic cross-clamping was performed in five patients. T2Ls were identified in 26 patients, and associated with a distal type I endoleak in 1 patient, a type III endoleak in 3, and a type IV endoleak in 1. Two patients presented with endotension. All the endoleaks were treated successfully, with a mean operating time of 120 minutes and a mean blood loss of 450 mL. One SG was explanted 12 days after the procedure because of early infection. One patient died during SG explantation for an aortoduodenal fistula 26 months after the endoaneurysmorrhaphy. During a median follow-up of 24 months, the control computed tomography scan showed shrinkage of the aneurysmal sac with stable diameters in all patients. No missed T2Ls, no recurrence of T2L, and no SG migration or disjunction was observed. Conclusions Obliterating endoaneurysmorrhaphy with SG preservation can be considered as an alternative to SG removal in cases of persistent T2L responsible for aneurysmal sac enlargement after embolization failure. By avoiding extensive dissection for surgical aortic cross-clamping, minimizing hemodynamic changes, and reducing blood loss and operating time, this procedure can be performed even in patients initially considered unfit for surger

Study of an Al₂O₃/GaN Interface for Normally Off MOS-Channel High-Electron-Mobility Transistors Using XPS Characterization: The Impact of Wet Surface Treatment on Threshold Voltage <i>V</i>_TH

International audienceUnderstanding the impact of GaN surface treatment conditions on dielectric/GaN interface chemical properties is critically important for device performance. This point is under intensive research for the dielectric/GaN structure because GaN does not have a good native oxide quality such as SiO2 used in silicon technologies. The effects of different wet treatments prior to atomic layer deposition (ALD) of thin Al2O3 on Ga-polar GaN were studied by X-ray photoelectron spectroscopy (XPS). The same wet treatments have been applied to the recessed region of AlGaN/GaN heterostructures, followed by ALD of 30 nm Al2O3 in order to form MOS-channel high-electron-mobility transistors (MOSc-HEMTs) on 200 mm GaN-on-Si wafers with CMOS compatible processing. The resulting transistors exhibited a normally off behavior (threshold voltage VTH = 0.4–0.6 V) and their VTH was correlated to the oxidation at the Al2O3/GaN interface, suggesting the presence of donor defects

On the Understanding of Cathode Related Trapping Effects in GaN-on-Si Schottky Diodes

International audienceCathode related current collapse effect in GaN on Si Schottky barrier diodes is investigated in this paper. Capacitance and current relaxation measurements on diodes and gated-Van Der Pauw are associated with temperature dependent dynamic ${R_{\mathrm{ ON}}}$ transients analysis to identify the parasitic trapping locations in the devices. We show here that the main part of the current collapse at the cathode comes from a combination of electron trapping in the passivation layer and in a carbon related trap in the GaN buffer layers ( ${E_{A}} = \mathrm {E_{T}} - {E_{V}} \simeq 0.9 \,\mathrm {eV}$ ) that can be studied independently by using the appropriate stress configurations. These two parasitic effects can lead to long recovery time (>1 ks) after reverse bias stress

On the Understanding of Cathode Related Trapping Effects in GaN-on-Si Schottky Diodes

International audienceCathode related current collapse effect in GaN on Si Schottky barrier diodes is investigated in this paper. Capacitance and current relaxation measurements on diodes and gated-Van Der Pauw are associated with temperature dependent dynamic ${R_{\mathrm{ ON}}}$ transients analysis to identify the parasitic trapping locations in the devices. We show here that the main part of the current collapse at the cathode comes from a combination of electron trapping in the passivation layer and in a carbon related trap in the GaN buffer layers ( ${E_{A}} = \mathrm {E_{T}} - {E_{V}} \simeq 0.9 \,\mathrm {eV}$ ) that can be studied independently by using the appropriate stress configurations. These two parasitic effects can lead to long recovery time (>1 ks) after reverse bias stress

On the influence of gate length on pBTI in GaN-on-Si E-mode MOSc-HEMT

session 7A: WB GaNInternational audienceIn this paper we explore the influence of the fully recessed gate length on Vth instabilities with ultra-fast pBTI measurements (< 10µs) on GaN-on-Si E-mode MOSc-HEMTs

Impact of Substrate Biasing During AlN Growth by PEALD on Al 2 O 3 /AlN/GaN MOS Capacitors

Abstract In this article, the role of the substrate biasing during the passivation of GaN with AlN deposited by plasma enhanced atomic layer deposition (PEALD) is investigated. In addition to a commonly used remote inductively‐coupled plasma source, the PEALD reactor is equipped with another power supply allowing the substrate to be biased and to adjust the ion energy impinging on the substrate surface. The presence is reported of a narrow bias window where the GaN passivation is significantly improved compared to a standard AlN film deposited without bias. It is found that the AlN film quality is enhanced and the crystallographic structure changes from a well‐ordered epitaxial relationship with the GaN substrate to textured films when applying a bias. Finally, the capacitance–voltage characteristics ( C–V ) of Al 2 O 3 /n‐GaN and Al 2 O 3 /AlN/n‐GaN metal‐oxide‐semiconductor (MOS) capacitors are also studied. It is shown that the addition of an AlN interlayer deposited with the appropriate bias is essential to positively shift the flatband voltage of the C–V characteristics while preserving high AlN/n‐GaN interface quality. Therefore, the GaN passivation with AlN deposited using substrate biasing provides a promising pathway towards the manufacturing of normally‐off MOS‐channel high electron mobility transistors

Low baseline and subsequent higher aortic abdominal aneurysm FDG uptake are associated with poor sac shrinkage post endovascular repair

International audiencePurposeThe growth phases of medically treated abdominal aortic aneurysms (AAA) are frequently associated with an 18F–fluorodesoxyglucose positron emission tomography (FDG-PET) pattern involving low baseline and subsequent higher FDG uptake. However, the FDG-PET patterns associated with the endovascular aneurysm repair (EVAR) of larger AAA are presently unknown. This study aimed to investigate the relationship between serial AAA FDG uptake measurements, obtained before EVAR and 1 and 6 months post-intervention and subsequent sac shrinkage at 6 months, a well-recognized indicator of successful repair.MethodsThirty-three AAA patients referred for EVAR (maximal diameter: 55.4 ± 6.0 mm, total volume: 205.7 ± 63.0 mL) underwent FDG-PET/computed tomography (CT) before EVAR and at 1 and 6 months thereafter, with the monitoring of AAA volume and of a maximal standardized FDG uptake [SUVmax] averaged between the axial slices encompassing the AAA.ResultsSac shrinkage was highly variable and could be stratified into three terciles: a first tercile in which shrinkage was absent or very limited (0–29 mL) and a third tercile with pronounced shrinkage (56–165 mL). SUVmax values were relatively low at baseline in the 1st tercile (SUVmax: 1.69 ± 0.33), but markedly increased at 6 months (2.42 ± 0.69, p = 0.02 vs. baseline). These SUV max values were by contrast much higher at baseline in the 3rd tercile (SUVmax: 2.53 ± 0.83 p = 0.009 vs. 1st tercile) and stable at 6 months (2.49 ± 0.80), while intermediate results were documented in the 2nd tercile. Lastly, the amount of sac shrinkage, expressed in absolute values or in percentages of baseline AAA volumes, was positively correlated with baseline SUVmax (p = 0.001 for both).ConclusionA low pre-EVAR FDG uptake and increased AAA FDG uptake at 6 months are associated with reduced sac shrinkage. This sequential FDG-PET pattern is similar to that already shown to accompany growth phases of medically treated AAA