Les mémoires à pont conducteur (CBRAM) sont une option actuellement étudiée pour la prochaine génération de mémoires non volatiles. Le stockage des données est basé sur la commutation de la résistivité entre les états de résistance élevée (HRS) et faible (LRS). Sous polarisation électrique, on suppose qu'un trajet conducteur est créé par la diffusion des ions de l'électrode active dans l'électrolyte solide. Récemment, une attention particulière a été portée sur les dispositifs contenant un élément semi-conducteur tel que le tellure, fonctionnant avec des courants réduits et présentant moins de défaillances de rétention. Dans ces « subquantum CBRAMs », le filament est censé contenir du tellure, ce qui donne une conductance de 1 atome (G₁atom) significativement réduite par rapport aux CBRAMs standard et permettant ainsi un fonctionnement à faible puissance. Dans cette thèse, nous utilisons la spectroscopie de photoélectrons par rayons X (XPS) pour étudier les réactions électrochimiques impliquées dans le mécanisme de commutation des CBRAMs à base de Al₂O ₃ avec des alliages ZrTe et TiTe comme électrode active. Deux méthodes sont utilisées: i) spectroscopie de photoélectrons par rayons X de haute énergie non destructive (HAXPES) pour étudier les interfaces critiques entre l'électrolyte (Al₂O ₃ ) et les électrodes supérieure et inférieure et ii) les faisceaux d'ions à agrégats gazeux (GCIB), une technique de pulvérisation qui conduit à une dégradation plus faible de la structure, avec un profilage en profondeur XPS pour évaluer les distributions des éléments en profondeur. Des mesures ToF-SIMS sont également effectuées pour obtenir des informations complémentaires sur la répartition en profondeur des éléments. Le but de cette thèse est de clarifier le mécanisme de changement de résistance et de comprendre les changements chimiques aux deux interfaces impliquées dans le processus de « forming » sous polarisation positive et négative ainsi que le mécanisme de « reset ». Pour cela, nous avons effectué une comparaison entre le dispositif vierge avec un état formé, i.e. l'échantillon après la première transition entre HRS et LRS et un état reset, i.e. l'échantillon après la première transition entre LRS et HRS.L'analyse du « forming » positif pour les dispositifs ZrTe / Al₂O ₃ a montré une libération de Te liée à l’oxydation de Zr due au piégeage de l'oxygène de l'Al₂O ₃ sous l’effet du champ électrique. D'autre part, pour les dispositifs TiTe / Al₂O ₃, la présence d'une couche importante d'oxyde de titane à l'interface avec l'électrolyte a provoqué une dégradation permanente de la cellule en polarisation positive. Pour le « forming » négatif, nos résultats montrent un mécanisme hybride, à savoir une combinaison de formation de lacunes d'oxygène dans l'oxyde provoquée par la migration de O2- entraîné par le champ électrique vers l'électrode inférieure et la libération de tellure pour former des filaments conducteurs. De plus, les résultats obtenus par profilométrie XPS et ToF-SIMS ont indiqué une possible diffusion de Te dans la couche d'Al₂O ₃. Lors du « reset », il y a une recombinaison partielle des ions oxygène avec les lacunes d'oxygène près de l'interface TiTe / AlAl₂O ₃ avec une perte de Te. Un mécanisme hybride a également été observé sur les dispositifs ZrTe / Al₂O ₃ pendant le « forming » négatif. En tenant compte du rôle important de la migration d'oxygène dans la formation / dissolution des filaments, nous discutons également des résultats obtenus par XPS avec polarisation électrique in- situ (sous ultravide) pour mieux comprendre le rôle de l'oxydation de surface et des interfaces dans la commutation résistive. / Conducting bridging resistive random accessmemories (CBRAMs) are one option currently investigated for the next generation of non volatile memories. Data storage is based on switching the resistivity between high (HRS) and low (LRS) resistance states. Under electrical bias,a conductive path is assumed to be created by ions diffusion from the active electrode into the solid electrolyte. Recently, special attention has been drawn to devices containing an elemental semiconductor such as tellurium, operating with reduced currents and less retention failures. In these subquantum CBRAM cells, the filament is thought to contain tellurium , yielding a 1-atomconductance (G₁atom) significantly reduced compared to standard CBRAMs and thus allowing low power operation. In this thesis, we use X-rayphotoelectron spectroscopy (XPS) to learn about electrochemical reactions involved in the switching mechanism of Al₂O₃ based CBRAMswith ZrTe and TiTe alloys as active electrode. Two methods are used: i) non-destructive Hard X-ray photoelectron spectroscopy (HAXPES) to investigate the critical interfaces between the electrolyte (Al₂O₃) and the top and bottom electrodes and ii) Gas Cluster Ion Beams (GCIB), a sputtering technique that leads to lower structure degradation, combined with XPS depth profiling to evaluate chemical depth distributions. To FSIMS measurements are also performed to get complementary in-depth chemical information.The aim of this thesis is to clarify the driving mechanism and understand the chemical changes at both interfaces involved in the forming process under positive and negative polarization as well as the mechanism of the reset operation. For that,we performed a comparison between as-grown state, i.e. the pristine device with a formed state,i.e. the sample after the first transition between HRS and LRS, and reset state, i.e. the sample after the first transition between LRS and HRS.Conducting bridging resistive random access memories (CBRAMs) are one option currently investigated for the next generation of non-volatile memories. Data storage is based on switching the resistivity between high (HRS) and low (LRS) resistance states. Under electrical bias,a conductive path is assumed to be created byions diffusion from the active electrode into the solid electrolyte. Recently, special attention has been drawn to devices containing an elemental semiconductor such as tellurium, operating with reduced currents and less retention failures. In these subquantum CBRAM cells, the filament is thought to contain tellurium , yielding a 1-atom conductance (G₁atom) significantly reduced compared to standard CBRAMs and thus allowing low power operation. In this thesis, we use X-ray photoelectron spectroscopy (XPS) to learn about electrochemical reactions involved in the switching mechanism of Al₂O₃ based CBRAMs with ZrTe and TiTe alloys as active electrode. Twomethods are used: i) non-destructive Hard X-rayphotoelectron spectroscopy (HAXPES) toinvestigate the critical interfaces between the electrolyte (Al₂O₃) and the top and bottom electrodes and ii) Gas Cluster Ion Beams (GCIB), a sputtering technique that leads to lower structure degradation, combined with XPS depth profiling to evaluate chemical depth distributions. To FSIMS measurements are also performed to get complementary in-depth chemical information.The aim of this thesis is to clarify the driving mechanism and understand the chemical changes at both interfaces involved in the forming process under positive and negative polarization as well as the mechanism of the reset operation. For that,we performed a comparison between as-grown state, i.e. the pristine device with a formed state,i.e. the sample after the first transition between HRS and LRS, and reset state, i.e. the sample after the first transition between LRS and HRS.

In this study, The bottom electrode¡]TiN¡^, middle insulator ¡]Sn¡GSiO2¡^, and top electrode ¡]Pt¡^ were deposited respectively by sputtering technique for fabricating the resistive random access memory with metal-insulator-metal structure. Experimental results were indicated that Sn-dopped SiO2 RRAM could be operated over 105 times and retention time was kept stable at thermal stress up to 85 ¢J over 104 s. In the previous researches, we had known that the supercritical carbon dioxide¡]SCCO2¡^ fluids could efficiently to passivate the traps in the devices. The leakage current of dielectric film would be reduced significantly after SCCO2 fluids treatment. To improve the dielectric properties of Sn-dopped SiO2 films, the SCCO2 fluids technology was introduced in this study. After SCCO2 fluids treatment, the leakage current of devices was reduced significantly, because the HRS conduction mechanism was transformed from Poole-Frenkel conduction to Schottky emission and the LRS conduction mechanism was transformed from Ohmic conduction to Hopping conduction. Addtionally, RTA treatment was introduced to improve the Sn-dopped SiO2 films. It could also reduce leakage current of devices after RTA treatment. At last, we used constant current forming to find the process of electrons hopping conduction.

In this thesis, the resistance switching characteristic of Zn:SiO2 -based memory was studied. The resistive memory was fabricated by sputtering to deposit the Metal/Insulator/Metal (MIM) structure. The top and bottom layers were made by Pt and TiN respectively, and the insulator was Zn:SiO2 grown by co-sputtering with SiO2 and Zinc. We found that doping Zinc into SiO2 insulator induced the resistive switching characteristic. By the treatment of supercritical carbon dioxide (SCCO2) in Zn:SiO2 -based device,the operation current would decrease. In the result of x-ray electron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) , it showed that the defects in Zn:SiO2 thin-film were reduced. And the electric conduction mechanism of low resistance state made a change from ohmic conduction to hopping conduction. To emerge spontaneous phenomenon of hopping conduction, the memory devices were fabricated with a multi-layer structure. In Auger electron spectroscopy (AES), we found the signal of zinc, split into three different kinds of peaks, which met the multi-layer structure. From I-V sweep measurement, the multi-layer structure device could be appeared the spontaneous hopping conduction mechanism. In order to find out the initial state of electric conduction mechanism .We measured the device of Pt/Zn:SiO2/TiN with constant current forming. We found the initial state of electric conduction path out successfully, and it¡¦s operation current below 10 uA.

The operating characteristics of non-volatile memory for modern requirement are high-density , low power consumption, fast read and write speed, and good reliability. The floating gate memory generated leakage path in the tunnel oxide during the trend of scaling down, which will result in the loss of all stored charge to the silicon substrate. As the data retention time and endurance are taken into consideration, the thickness of tunnel oxide exist a physical limit, owing to the demand of high-density capacities. RRAM is offered as an option in the next generation non-volatile memories, due to the following advantages: (1) simple structure and easy to process, and low cost ; (2) less restrictive in the scaling-down process; (3) with the multi-bit data storage features; (4) high speed operation; (5) Repeat write and read is more than one million. In the thesis, we use a simple and low-temperature process to form the silicon germanium oxide (Si-Ge-O) RRAM and silicon germanium oxide RRAM with nitrogen doping between the electrode and silicon-germanium oxide interface. By sputtering at argon and oxygen (Ar/O2), and sputtering at argon and ammonia (Ar/NH3) with silicon-germanium target to form silicon germanium oxide RRAM and silicon germanium oxide (Si-Ge-O)/silicon germanium oxnitride (Si-Ge-O-N) RRAM. By informing a SiGeON layer between the interface of electrode and silicon-germanium oxide improve the stability of write voltage and endurance reliability. In addition, both silicon and germanium are useful as materials in the optoelectronics industry and extensively studied in material science. Based on the two materials, the smiting characterizations of RRAM will be improved in the read-write stability and operation reliability.

abstract: Programmable Metallization Cell (PMC) technology has been shown to possess the necessary qualities for it to be considered as a leading contender for the next generation memory. These qualities include high speed and endurance, extreme scalability, ease of fabrication, ultra low power operation, and perhaps most importantly ease of integration with the CMOS back end of line (BEOL) process flow. One area where detailed study is lacking is the reliability of PMC devices. In previous reliability work, the low and high resistance states were monitored for periods of hours to days without any applied voltage and the results were extrapolated to several years (>10) but little has been done to analyze the low resistance state under stress. With or without stress, the low resistance state appears to be highly stable but a gradual increase in resistance with time, less than one order of magnitude after ten years when extrapolated, has been observed. It is important to understand the physics behind this resistance rise mechanism to comprehend the reliability issues associated with the low resistance state. This is also related to the erase process in PMC cells where the transition from the ON to OFF state occurs under a negative voltage. Hence it is important to investigate this erase process in PMC cells under different conditions and to model it. Analyzing the programming and the erase operations separately is important for any memory technology but its ability to cycle efficiently (reliably) at low voltages and for more than 1E4 cycles (without affecting the cells performance) is more critical. Future memory technologies must operate with the low power supply voltages (<1V) required for small geometry nodes. Low voltage programming of PMC memory devices has previously been demonstrated using slow voltage sweeps and small numbers of fast pulses. In this work PMC memory cells were cycled at low voltages using symmetric pulses with different load resistances and the distribution of the ON and OFF resistances was analyzed. The effect of the program current used during the program-erase cycling on the resulting resistance distributions is also investigated. Finally the variation found in the behavior of similar resistance ON states in PMC cells was analyzed more in detail and measures to reduce this variation were looked into. It was found that slow low current programming helped reducing the variation in erase times of similar resistance ON states in PMC cells. This scheme was also used as a pre-conditioning technique and the improvements in subsequent cycling behavior were compared. / Dissertation/Thesis / Ph.D. Electrical Engineering 2011

abstract: Advances in software and applications continue to demand advances in memory. The ideal memory would be non-volatile and have maximal capacity, speed, retention time, endurance, and radiation hardness while also having minimal physical size, energy usage, and cost. The programmable metallization cell (PMC) is an emerging memory technology that is likely to surpass flash memory in all the listed ideal memory characteristics. A comprehensive physics-based model is needed to fully understand PMC operation and aid in design optimization. With the intent of advancing the PMC modeling effort, this thesis presents two simulation models for the PMC. The first model is a finite element model based on Silvaco Atlas finite element analysis software. Limitations of the software are identified that make this model inconsistent with the operating mechanism of the PMC. The second model is a physics-based numerical model developed for the PMC. This model is successful in matching data measured from a chalcogenide glass PMC designed and manufactured at ASU. Matched operating characteristics observable in the current and resistance vs. voltage data include the OFF/ON resistances and write/erase and electrodeposition voltage thresholds. Multilevel programming is also explained and demonstrated with the numerical model. The numerical model has already proven useful by revealing some information presented about the operation and characteristics of the PMC. / Dissertation/Thesis / PMC numerical model written in M for Octave/MATLAB / M.S. Electrical Engineering 2013

Metal oxides exhibit a wide range of chemical and electronic properties, making them an extremely interesting subject for numerous applications in modern electronics. The primary goal of this research is to develop metal-oxide-based electronic devices, including thin-film transistors (TFTs), resistance random-access memory (RRAM) and planar nano-devices. This research requires different processing techniques, novel device design concepts and optimisation of materials and devices. The first experiments were carried out to optimise the properties of zinc oxide (ZnO) semiconductors, in particular the carrier concentration, which determines the threshold voltage of the TFTs. Thermal annealing is one common method to affect carrier concentration and most work in the literature reports performing this process in a single-gas environment. In this work, however, annealing was carried out in a combination of air and nitrogen, and it was found that the threshold voltage could be tuned over a wide range of pre-determined values.Further experiments were undertaken to enhance the carrier mobility of ZnO TFTs, which is the most important material quality parameter. By optimising deposition conditions and incorporating a high-k gate dielectric layer, the devices showed saturation mobility values over 50 cm2/Vs at a low operating voltage of 4 V. This is, to our knowledge, one of the highest field-effect mobility values achieved in ZnO-based TFTs by room temperature sputtering. As an important type of metal-oxide-based novel memory devices, which have been studied intensively in the last few years, RRAM devices were also explored. New materials, such as tin oxide (SnOx), were tested, exhibiting bipolar-switching operations and a relatively large resistance ratio. As a novel process variation, anodisation was performed, which yielded less impressive results than SnOx, but with a potential for ultra-low-cost manufacturing. Finally, novel planar nano-devices were explored, which have much simpler structures than conventional multi-layered transistors and diodes. Three types of ZnO-based nano-devices (a side-gated transistor, a self-switching diode and a planar inverter) were fabricated using both e-beam lithography and chemical wet etching. After optimisation of the challenging wet etching procedure at nanometre scale, ZnO nano-devices with good reproducibility and reliability have been demonstrated.

No description available.

No description available.

Le cerveau humain est composé d’un grand nombre de réseaux neuraux interconnectés, dont les neurones et les synapses en sont les briques constitutives. Caractérisé par une faible consommation de puissance, de quelques Watts seulement, le cerveau humain est capable d’accomplir des tâches qui sont inaccessibles aux systèmes de calcul actuels, basés sur une architecture de type Von Neumann. La conception de systèmes neuromorphiques vise à réaliser une nouvelle génération de systèmes de calcul qui ne soit pas de type Von Neumann. L’utilisation de mémoire non-volatile innovantes en tant que synapses artificielles, pour application aux systèmes neuromorphiques, est donc étudiée dans cette thèse. Deux types de technologies de mémoires sont examinés : les mémoires à changement de phase (Phase-Change Memory, PCM) et les mémoires résistives à base d’oxyde (Oxide-based resistive Random Access Memory, OxRAM). L’utilisation des dispositifs PCM en tant que synapses de type binaire et probabiliste est étudiée pour l’extraction de motifs visuels complexes, en évaluant l’impact des conditions de programmation sur la consommation de puissance au niveau du système. Une nouvelle stratégie de programmation, qui permet de réduire l’impact du problème de la dérive de la résistance des dispositifs PCM est ensuite proposée. Il est démontré qu’en utilisant des dispositifs de tailles réduites, il est possible de diminuer la consommation énergétique du système. La variabilité des dispositifs OxRAM est ensuite évaluée expérimentalement par caractérisation électrique, en utilisant des méthodes statistiques, à la fois sur des dispositifs isolés et dans une matrice complète de mémoire. Un modèle qui permets de reproduire la variabilité depuis le niveau faiblement résistif jusqu’au niveau hautement résistif est ainsi développé. Une architecture de réseau de neurones de type convolutionnel est ensuite proposée sur la base de ces travaux éxperimentaux. La tolérance du circuit neuromorphique à la variabilité des OxRAM est enfin démontrée grâce à des tâches de reconnaissance de motifs visuels complexes, comme par exemple des caractères manuscrits ou des panneaux de signalisations routières. / The human brain is made of a large number of interconnected neural networks which are composed of neurons and synapses. With a low power consumption of only few Watts, the human brain is able to perform computational tasks that are out of reach for today’s computers, which are based on the Von Neumann architecture. Neuromorphic hardware design, taking inspiration from the human brain, aims to implement the next generation, non-Von Neumann computing systems. In this thesis, emerging non-volatile memory devices, specifically Phase-Change Memory (PCM) and Oxide-based resistive memory (OxRAM) devices, are studied as artificial synapses in neuromorphic systems. The use of PCM devices as binary probabilistic synapses is studied for complex visual pattern extraction applications, evaluating the impact of the PCM programming conditions on the system-level power consumption.A programming strategy is proposed to mitigate the impact of PCM resistance drift. It is shown that, using scaled devices, it is possible to reduce the synaptic power consumption. The OxRAM resistance variability is evaluated experimentally through electrical characterization, gathering statistics on both single memory cells and at array level. A model that allows to reproduce OxRAM variability from low to high resistance state is developed. An OxRAM-based convolutional neural network architecture is then proposed on the basis of this experimental work. By implementing the computation of convolution directly in memory, the Von Neumann bottleneck is avoided. Robustness to OxRAM variability is demonstrated with complex visual pattern recognition tasks such as handwritten characters and traffic signs recognition.