Biaxial piezoelectric MEMS mirrors with low absorption coating for 1550 nm long-range LIDAR

This paper presents the fabrication and characterization of a biaxial MEMS (MicroElectroMechanical System) scanner based on PZT (Lead Zirconate Titanate) which incorporates a low-absorption dielectric multilayer coating, i.e., a Bragg reflector. These 2 mm square MEMS mirrors, developed on 8-inch silicon wafers using VLSI (Very Large Scale Integration) technology are intended for long-range (>100 m) LIDAR (LIght Detection And Ranging) applications using a 2 W (average power) pulsed laser at 1550 nm. For this laser power, the use of a standard metal reflector leads to damaging overheating. To solve this problem, we have developed and optimised a physical sputtering (PVD) Bragg reflector deposition process compatible with our sol-gel piezoelectric motor. Experimental absorption measurements, performed at 1550 nm and show up to 24 times lower incident power absorption than the best metallic reflective coating (Au). Furthermore, we validated that the characteristics of the PZT, as well as the performance of the Bragg mirrors in terms of optical scanning angles, were identical to those of the Au reflector. These results open up the possibility of increasing the laser power beyond 2W for LIDAR applications or other applications requiring high optical power. Finally, a packaged 2D scanner was integrated into a LIDAR system and three-dimensional point cloud images were obtained, demonstrating the scanning stability and operability of these 2D MEMS mirrors.This research was funded by ECSEL Joint Undertaking (JU) grant number No. 826600 (project VIZTA).Peer ReviewedPostprint (published version

A major development project of the Northern area of the Amun-Re precinct at Karnak during the reign of Shabaqo

International audienceThis article presents preliminary observations concerning a building programme of the King Shabaqo in the northern area of the Amun's precinct at Karnak. Through the excavations led by the CFEETK at the temple of Ptah and the Treasury of Shabaqo it is possible to define, east of the Way of Ptah, a project of an architectural development of nearly one hectare

Modification of porous SiOCH by first contact with water vapor after plasma process

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Study of SiO2 on Ni and Ti Silicide After Different Oxidation Techniques Investigated by XRR, SEM and Ellipsometry

International audienceAlthough silicide oxidation was studied 20years ago, the interest in obtaining a robust process for new applications remains significant today. Indeed, the new architectural development process requires dense and narrow spaces. In this study, attempts were made to bury a silicide layer under a protective silica layer in order to keep the physical and electrical properties of the silicide constant after oxidation. Thus, we first tried to reproduce and study these conditions and, once acquired, aimed to decrease the oxidation temperature in order to meet industrial requirements. Titanium (Ti) and nickel (Ni) were chosen for their metallurgical interest and their integration capability in devices. Four different groups of silicide (TiSi, TiSi2, Ni2Si, NiSi) were targeted by adjusting the temperature. Then, all of the silicides, including one pure Si wafer, were oxidized using dry, wet and plasma techniques. In situ scanning electron microscopy, spectroscopic ellipsometry and X-ray reflectivity measurements were carried out simultaneously before and after oxidation of the silicide to characterize the SiO2 and silicide morphology, thickness and density. We found that after 800 degrees C dry oxidation, Ti silicide was totally oxidized, which was an unexpected result. But, Ni silicide showed an agglomeration phenomenon after 500 degrees C and 800 degrees C dry oxidation. Although, after wet oxidation, it was confirmed that the highest SiO2 thickness formed, the NiSi surface roughness was higher. In the case of plasma oxidation, we obtained a thin layer (approximate to 1nm) of SiO2 on NiSi with an extremely smooth surface

Shockley-Read-Hall and Auger non-radiative recombination in GaN based LEDs A size effect study

International audienceGaN-based micro light-emitting diode (mu LED) arrays are very promising devices for display applications. In these arrays, each mu LED works as a single pixel of a whole image. The electro-optical performance of these mu LEDs is an important subject to study. Here, we investigate the influence of LED size on the radiative and non-radiative recombination. The standard ABC model has been widely used to describe the efficiency of GaN based LEDs. Using this model, we extract A, B, and C coefficients for various LED sizes, showing how the competition between radiative and non-radiative recombination processes varies with the LED geometry. Time-resolved photoluminescence allows us to determine coefficient B, related to radiative recombination. Through current-voltage-luminance characterizations, we determine parameters A and C related to Shockley-Read-Hall and Auger recombination. We find that coefficient A is strongly dependent on LED size, indicating a drastic effect of sidewall defects on the performance of LEDs. On the other hand, coefficient C is independent of LED size. This latter result demonstrates that efficiency droop does not depend on LED size

Effect of the molecular weight on the depth profiling of PMMA thin films using low‐energy Cs + sputtering

International audienceIn this work, we investigate the influence of the molecular weight of poly (methyl methacrylate) (PMMA) thin films coated on silicon wafer on the ToF SIMS (Time of Flight Secondary Ion Mass Spectrometry) sputtering mechanisms and kinetics during depth profiling using low energy monoatomic caesium ions. The sputtering yield volumes are determined as function of molecular weight, film thickness and beam energy. The results show that the sputtering yield volume decreases with increasing molecular weight Mw down to a threshold value below which it becomes nearly constant, as previously observed with argon cluster ions. The relevance of physical parameters such as the glass transition temperature Tgdetermined here from ellipsometry measurements-and the entanglement of the polymer chains to account for this behaviour is discussed. The variation of the sputtering yield was also found to vary logarithmically with the primary beam energy. In addition, preliminary experiments carried out using a low molecular weight PMMA (4 kg/mol) evidenced a nano-confinement effect similar to that observed with argon cluster sputtering but of lower magnitude

Interaction of humidity with plasma-damaged porous low-k

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