Lithium Niobate Micro-transducers matrix design

In this work, a two-dimensional (2D) Lithium Niobate (LiNbO3) 36°Y-cut micro-transducers (μTs) matrix design is presented. Two main steps define the fabrication process: electrode deposition and photolithography. These steps are preceded by the optical mask conception, which defines the 2D matrix pattern. In contrary to the one element case, this μTs matrix allows to automatically scan a desired structure in real time. The μTs matrix is characterized using an impedance analyzer. Furthermore, the experimental tests carried out in order to demonstrate the matrix functionality at low frequencies [200 - 800] kHz are presented

Micro-transducer matrix design for structural health monitoring

Les réseaux de micro-transducteurs connaissent un fort développement afin de répondre aux exigences du contrôle santé intégré des structures. Ce dernier permet d'évaluer en tout moment l'état de santé de la structure tout en intégrant un système de contrôle non destructif à celle-ci. En effet, un réseau de micro-transducteurs permet d'acquérir plusieurs signaux en même temps sans effectuer un balayage spatial permettant de caractériser la structure. Parallèlement, l'utilisation des ondes guidées ultrasonores fournit un outil efficace pour la caractérisation de celle-ci. Cependant, elles présentent des caractéristiques complexes qui rend l'analyse de leurs interactions avec des défauts compliquée. Pour cela, il est souhaitable de favoriser la propagation d'un mode unique dans la structure. Dans ce contexte, le but de cette thèse est de présenter un modèle de matrice de micro-transducteurs pour la réception des ondes guidées dans une structure cylindrique, en particulier, le mode de flexion F(1,1). Dans un premier temps, la réalisation et la caractérisation des matrices de micro-transducteurs sont présentées. Les résultats ont montré la capacité de celles-ci à opérer dans la gamme fréquentielle (60 kHz - 70 kHz) malgré sa haute fréquence de résonance. Dans un deuxième temps, les mesures optiques et électriques effectuées sur la matrice ont validé l'utilisation de celle-ci pour des applications dans le CSI et le CND des structures cylindriques tout en favorisant la propagation du mode F(1,1).Micro-transducers networks are experiencing strong development in order to meet the require- ments of Structural Health Monitoring (SHM). The latter makes it possible to assess at any time the state of health of the structure while integrating a Non-Destructive Evaluation (NDE) system therein. Indeed, a network of micro-transducers makes it possible to acquire several signals at the same time without carrying out a mechanical scanning making it possible to characterise the structure. At the same time, the use of ultrasonic guided waves provides an e_ective tool for the characterisation of structures. However, they have complex characteristics which make the analysis of their interactions with defects complicated. For this, it is desirable to promote the propagation of a single-mode in the structure. In this context, this thesis aims to present a model of a micro- transducers matrix for the reception of guided waves in a cylindrical structure, in particular, the _exural mode F(1,1). First, the realisation and characterisation of the micro-transducer matrices are presented. The results showed their ability to operate in the frequency range (60 kHz - 70 kHz) despite its high resonant frequency. Second, the optical and electrical measurements carried out on the matrix validated its use for applications in the SHM and the NDE of cylindrical structures while generating the F(1,1) mode

Réalisation de matrices de micro-transducteurs acoustiques : application au controle santé intégré

Micro-transducers networks are experiencing strong development in order to meet the require- ments of Structural Health Monitoring (SHM). The latter makes it possible to assess at any time the state of health of the structure while integrating a Non-Destructive Evaluation (NDE) system therein. Indeed, a network of micro-transducers makes it possible to acquire several signals at the same time without carrying out a mechanical scanning making it possible to characterise the structure. At the same time, the use of ultrasonic guided waves provides an e_ective tool for the characterisation of structures. However, they have complex characteristics which make the analysis of their interactions with defects complicated. For this, it is desirable to promote the propagation of a single-mode in the structure. In this context, this thesis aims to present a model of a micro- transducers matrix for the reception of guided waves in a cylindrical structure, in particular, the _exural mode F(1,1). First, the realisation and characterisation of the micro-transducer matrices are presented. The results showed their ability to operate in the frequency range (60 kHz - 70 kHz) despite its high resonant frequency. Second, the optical and electrical measurements carried out on the matrix validated its use for applications in the SHM and the NDE of cylindrical structures while generating the F(1,1) mode.Les réseaux de micro-transducteurs connaissent un fort développement afin de répondre aux exigences du contrôle santé intégré des structures. Ce dernier permet d'évaluer en tout moment l'état de santé de la structure tout en intégrant un système de contrôle non destructif à celle-ci. En effet, un réseau de micro-transducteurs permet d'acquérir plusieurs signaux en même temps sans effectuer un balayage spatial permettant de caractériser la structure. Parallèlement, l'utilisation des ondes guidées ultrasonores fournit un outil efficace pour la caractérisation de celle-ci. Cependant, elles présentent des caractéristiques complexes qui rend l'analyse de leurs interactions avec des défauts compliquée. Pour cela, il est souhaitable de favoriser la propagation d'un mode unique dans la structure. Dans ce contexte, le but de cette thèse est de présenter un modèle de matrice de micro-transducteurs pour la réception des ondes guidées dans une structure cylindrique, en particulier, le mode de flexion F(1,1). Dans un premier temps, la réalisation et la caractérisation des matrices de micro-transducteurs sont présentées. Les résultats ont montré la capacité de celles-ci à opérer dans la gamme fréquentielle (60 kHz - 70 kHz) malgré sa haute fréquence de résonance. Dans un deuxième temps, les mesures optiques et électriques effectuées sur la matrice ont validé l'utilisation de celle-ci pour des applications dans le CSI et le CND des structures cylindriques tout en favorisant la propagation du mode F(1,1)

Study of Leakage Current Transport Mechanisms in Pseudo-Vertical GaN-on-Silicon Schottky Diode Grown by Localized Epitaxy

In this work, a GaN-on-Si quasi-vertical Schottky diode was demonstrated on a locally grown n-GaN drift layer using Selective Area Growth (SAG). The diode achieved a current density of 2.5 kA/cm2, a specific on-resistance RON,sp of 1.9 mΩ cm2 despite the current crowding effect in quasi-vertical structures, and an on/off current ratio (Ion/Ioff) of 1010. Temperature-dependent current–voltage characteristics were measured in the range of 313–433 K to investigate the mechanisms of leakage conduction in the device. At near-zero bias, thermionic emission (TE) was found to dominate. By increasing up to 10 V, electrons gained enough energy to excite into trap states, leading to the dominance of Frenkel–Poole emission (FPE). For a higher voltage range (−10 V to −40 V), the increased electric field facilitated the hopping of electrons along the continuum threading dislocations in the “bulk” GaN layers, and thus, variable range hopping became the main mechanism for the whole temperature range. This work provides an in-depth insight into the leakage conduction transport on pseudo-vertical GaN-on-Si Schottky barrier diodes (SBDs) grown by localized epitaxy

Lithium Niobate Micro-transducers matrix design

In this work, a two-dimensional (2D) Lithium Niobate (LiNbO3) 36°Y-cut micro-transducers (μTs) matrix design is presented. Two main steps define the fabrication process: electrode deposition and photolithography. These steps are preceded by the optical mask conception, which defines the 2D matrix pattern. In contrary to the one element case, this μTs matrix allows to automatically scan a desired structure in real time. The μTs matrix is characterized using an impedance analyzer. Furthermore, the experimental tests carried out in order to demonstrate the matrix functionality at low frequencies [200 - 800] kHz are presented

Mobility Extraction Using Improved Resistance Partitioning Methodology for Normally-OFF Fully Vertical GaN Trench MOSFETs

International audienceIn this work, fully vertical GaN trench MOSFETs were fabricated and characterized to evaluate their electrical performances. Transistors show a normally-OFF behavior with a high ION/IOFF (~109) ratio and a significantly small gate leakage current (10−11 A/mm). Thanks to an improved resistance partitioning method, the resistances of the trench bottom and trench channel were extracted accurately by taking into account different charging conditions. This methodology enabled an estimation of the effective channel and bottom mobility of 11.1 cm2/V·s and 15.1 cm2/V·s, respectively

Low leakage and high breakdown voltage GaN-on-GaN Schottky diode by TMAH surface treatment.

International audienceIn this study, the impact of surface treatment by TMAH and HF on the electrical characteristics of GaNon-GaN Schottky diode is explored by I-V and C-V characterisation. TMAH surface treatment leads to an improvement in the forward and reverse characteristics ofthe device and improvement in breakdown voltage (BV) by almost 200V compared to just HF treated sample. Additional XPS characterisations reveals reduction in both O and C concentration due to TMAH treatment

Low leakage and high breakdown voltage GaN-on-GaN Schottky diode by TMAH surface treatment.

International audienceIn this study, the impact of surface treatment by TMAH and HF on the electrical characteristics of GaNon-GaN Schottky diode is explored by I-V and C-V characterisation. TMAH surface treatment leads to an improvement in the forward and reverse characteristics ofthe device and improvement in breakdown voltage (BV) by almost 200V compared to just HF treated sample. Additional XPS characterisations reveals reduction in both O and C concentration due to TMAH treatment

Micro-Raman characterization of vertical GaN Schottky and PN diodes

In this work, measurements from Cathodo-Luminescence (CL), micro-Raman spectroscopy and Breakdown Voltage (BV) have been coupled to assess the effects of physical parameters such as threading dislocations and effective doping level homogeneity on the electrical performances of vertical GaN Schottky and PN diodes. Two different substrates from Saint Gobain Lumilog and Sumitomo Electric with different threading dislocation densities have been compared