abstract: Programmable Metallization Cell (PMC) is a resistance-switching device based on migration of nanoscale quantities of cations in a solid electrolyte and formation of a conducting electrodeposit by the reductions of these cations. This dissertation presents electrical characterization results on Cu-SiO2 based PMC devices, which due to the na- ture of materials can be easily integrated into the current Complimentary metal oxide semiconductor (CMOS) process line. Device structures representing individual mem- ory cells based on W bottom electrode and n-type Si bottom electrode were fabricated for characterization. For the W bottom electrode based devices, switching was ob- served for voltages in the range of 500mV and current value as low as 100 nA showing the electrochemical nature and low power potential. The ON state showed a direct de- pendence on the programming current, showing the possibility of multi-bit storage in a single cell. Room temperature retention was demonstrated in excess of 105 seconds and endurance to approximately 107 cycles. Switching was observed for microsecond duration 3 V amplitude pulses. Material characterization results from Raman, X-ray diffraction, Rutherford backscattering and Secondary-ion mass spectroscopy analysis shows the influence of processing conditions on the Cu concentration within the film and also the presence of Cu as free atoms. The results seemed to indicate stress-induced void formation in the SiO2 matrix as the driving mechanism for Cu diffusion into the SiO2 film. Cu/SiO2/nSi based PMC devices were characterized and were shown to have inherent isolation characteristics, proving the feasibility of such a structure for a passive array. The inherent isolation property simplifies fabrication by avoiding the need for a separate diode element in an array. The isolation characteristics were studied mainly in terms of the leakage current. The nature of the diode interface was further studied by extracting a barrier potential which shows it can be approximated to a Cu-nSi metal semiconductor Schottky diode. / Dissertation/Thesis / Ph.D. Electrical Engineering 2011

Ce travail s'intéresse au suivi spatio-temporel par imagerie ultrasonore de la cavitation acoustique. Celle-ci est un phénomène physique complexe utilisé au cours de certaines techniques de thérapie par ultrasons, correspondant à la formation de bulles de gaz qui oscillent et éclatent. Initialement, la méthode TD-PAM (Time Domain Passive Acoustic Mapping, en anglais), a été développée pour cartographier l’activité de cavitation à partir des signaux acoustiques émis par les bulles, enregistrés passivement par une sonde linéaire d'imagerie ultrasonore. Toutefois, le TD-PAM souffre d’une trop faible résolution et de nombreux artefacts de reconstruction. De plus, il est lourd en temps de calcul car il est formalisé dans le domaine temporel (TD). Pour pallier ces deux limitations, il est proposé d'étudier, de comparer et de développer des méthodes avancées d'imagerie ultrasonore passive. Ce manuscrit s'articule autour de trois contributions principales : Une méthode adaptative originale a été formalisée dans le domaine temporel, reposant sur la compression d'amplitude des signaux ultrasonores par racine pième : le TD-pPAM. Cette approche améliore la résolution et le contraste des cartes de cavitation pour un temps de calcul équivalent au TD-PAM. La notion de matrice de densité inter-spectrale a été introduite pour l'imagerie de la cavitation. Dès lors, quatre méthodes dans le domaine de Fourier (FD) ont été étudiées et comparées : le FD-PAM (non-adaptatif), la méthode Robuste de Capon FD-RCB (adaptatif, par optimisation), le Functional Beamforming FD-FB (adaptatif, par compression non-linéaire) et la méthode MUltiple Signal Classification FD-MUSIC (adaptatif, par projection en sous-espaces). Les performances de ces méthodes FD ont été étudiées expérimentalement in vitro cuve d’eau avec une comparaison par imagerie optique. Les méthodes adaptatives FD proposées ont démontré leur potentiel à améliorer le suivi spatio-temporel des bulles. Le FD-RCB offre une localisation supérieure au FD-PAM mais souffre d'une importante complexité algorithmique. Les performances du FD-FB sont intermédiaires à celles du FD-PAM et du FD-RCB, pour une complexité de calcul équivalente au FD-PAM. Le FD-MUSIC a le potentiel de mettre en évidence de faibles sources acoustiques, mais ne conserve pas leurs quantifications relatives / This work focuses on the spatio-temporal monitoring of acoustic cavitation by ultrasonic imaging. This is a complex physical phenomenon used in some ultrasound therapy techniques, corresponding to the formation of gas bubbles that oscillate and implode. Initially, the TD-PAM (Time Domain Passive Acoustic Mapping) method was developed to map cavitation activity from acoustic signals emitted by bubbles, passively recorded by a linear ultrasonic imaging probe. However, the TD-PAM suffers from too low resolution and many reconstruction artifacts. In addition, it is time-consuming because it is formalized in the time domain (TD). To overcome these two limitations, it is proposed to study, compare and develop advanced methods of passive ultrasound imaging. This manuscript is structured around three main contributions: An original adaptive method has been formalised in the time domain, based on the amplitude compression of ultrasonic signals by root pth: TD-pPAM. This approach improves the resolution and contrast of cavitation maps for a computing time equivalent to the TD-PAM. The notion of cross-spectral density matrix has been introduced for cavitation imaging. Four Fourier domain (FD) methods were therefore studied and compared: FD-PAM (non-adaptive), Capon Robuste FD-RCB (adaptive, by optimization), Functional Beamforming FD-FB (adaptive, by non-linear compression) and MUltiple Signal Classification FD-MUSIC (adaptive, by subspaces projection). The performance of these FD methods was studied experimentally in vitro in water tank with a comparison by optical imaging. The proposed adaptive FD methods have demonstrated their potential to improve the spatial and temporal tracking of bubbles. The FD-RCB offers a superior localization to the FD-PAM but suffers from a high algorithmic complexity. The performance of the FD-FB is intermediate to that of the FD-PAM and the FD-RCB, for a calculation complexity equivalent to the FD-PAM. The FD-MUSIC has the potential to highlight weak acoustic sources, but does not keep their relative quantifications