In recent years, due to the rapid development of electronic products, non-volatile memory has become more and more important. However, flash memory has faced some physical limits bottleneck with size scaling-down. In order to overcome this problem, alternative memory technologies have been extensively investigated, including ferroelectric random access memory (FeRAM), magneto resistive RAM (MRAM), phase-change RAM (PRAM), and resistive RAM (RRAM). All of this potential next generation non-volatile memory, the resistive random access memory has most advantages such as simple structure, lower consumption of energy, lower operating voltage, high operating speed, high storage time and non-destructive access, which make it be the most potential candidate of the next generation non-volatile memory. Many studies have proposed to explain the resistance switching phenomenon, which is due to the metallic filament or the oxygen vacancies. Therefore, in order to investigate the influence of resistance switching characteristic by metal or oxygen, we choose the non-metal contained boron oxy-nitride film as the insulator layer and successfully make the resistance has the switchable characteristic of this device. Furthermore, we improved the iv stability by using the Gadolinium-doped method in the boron oxy-nitride based film. In addition, we observed the negative current differential phenomenon during the set process, which can further controlled by lower operating voltage to achieve the interfacial resistance switching. We think that is due to the formation of nitrogen titanium oxide at the interface between insulator layer and titanium nitride electrode, which caused the Schottky barrier formation and reduced the current flow. In addition, current conduction fitting can also confirm this hypothesis. Besides, titanium nitride easily bond with oxygen ions; moreover, the oxygen ions can be easily disturbed at higher temperature ambient. We believed there may easily form the nitrogen titanium oxide layer in higher temperature environment; which also improve by a series of varied temperature experiments. However, this nitrogen titanium oxide layer formed naturally very easily, resulting in an inevitable problem of data retention time, which wish to be resolved in the future.

Since the discovery of conducting polymers three decades ago the field of organic electronics has evolved rapidly. Organic light emitting diodes have already reached the consumer market, while organic solar cells and transistors are rapidly maturing. One of the great benefits with this class of materials is that they can be processed from solution. This enables several very cheap production methods, such as printing and spin coating, and opens up the possibility to use unconventional substrates, such as flexible plastic foils and paper. Another great benefit is the possibility of tailoring the molecules through carefully controlled synthesis, resulting in a multitude of different functionalities. This thesis reports how charge transport can be altered in solid-state organic electronic devices, with specific focus on memory applications. The first six chapters give a brief review of the field of solid-state organic electronics, with focus on electronic properties, resistance switch mechanisms and systems. Paper 1 and 3 treat Rose Bengal switch devices in detail – how to improve these devices for use in cross-point arrays as well as the origin of the switch effect. Paper 2 investigates how the work function of a conducting polymer can be modified to allow for better electron injection into an organic light emitting diode. The aim of the work in papers 4 and 5 is to understand the behavior of switchable charge trap devices based on blends of photochromic molecules and organic semiconductors. With this in mind, charge transport in the presence of traps is investigated in paper 4 and photochromic molecules is investigated using quantum chemical methods in paper 5. / Elektroniska komponenter har traditionellt sett tillverkats av kisel ellerandra liknande inorganiska material. Denna teknologi har förfinats intillperfektion sedan mitten av 1900-talet och idag har kiselkretsar mycket högprestanda. Tillverkningen av dessas kretsar är dock komplicerad och är därförkostsam. Under 1970-talet upptäcktes att organiska polymerer (dvs plast) kanleda ström under vissa förutsättningar. Genom att välja lämplig polymer ochbehandla den med vissa kemikalier (så kallad dopning) kan man varieraledningsförmågan från isolerande till nästintill metallisk. Det öppnarmöjligheten för att skapa elektroniska komponenter där dessa organiskamaterial utgör den aktiva delen istället för kisel. En av de stora fördelarna medorganiska material är att de vanligtvis är lösliga i vanliga lösningsmedel. Det göratt komponenter kan tillverkas mycket enkelt och billigt genom att användakonventionell tryckteknik, där bläcket har ersatts med lösningen av detorganiska materialet. Det gör också att komponenterna kan tillverkas påokonventionella ytor såsom papper, plast eller textil. En annan spännandemöjlighet med organiska material är att dess funktioner kan skräddarsys genomvälkontrollerad kemisk syntes på molekylär nivå. Inom forskningsområdetOrganisk Elektronik studerar man de elektroniska egenskaperna i de organiskamaterialen och hur man kan använda dessa material i elektroniskakomponenter. Vi omges idag av apparater och applikationer som kräver att data sparas,som till exempel digitala kameror, datorer och mobiltelefoner. Eftersom det finnsett stort intresse från konsumenter för nya smarta produkter ökar behovet avmobila lagringsmedia med stor lagringskapacitet i rasande fart. Detta harsporrat en intensiv utveckling av större och billigare fickminnen, hårddiskar ochminneskort. Många olika typer av minneskomponenter baserade på organiskamaterial har föreslagits de senaste åren. I vissa fall har dessa påståtts kunna erbjuda både billigare och större minnen än vad dagens kiselteknologi tillåter.En typ av organiska elektroniska minnen baseras på en reversibel ochkontrollerbar förändring av ledningsförmågan i komponenten. En informationsenhet – en så kallad bit – kan då lagras genom att till exempel koda en högledningsförmåga som en ”1” och en låg ledningsförmåga som en ”0”. Den härdoktorsavhandlingen är ett försök till att öka förståelsen för sådanaminneskomponenter. Minneskomponenter bestående av det organiska materialet Rose Bengalmellan metallelektroder har undersökts. Egenskaper för system bestående avmånga sådana komponenter har beräknats. Vidare visas att minnesfenomenetinte härstammar i det organiska materialet utan i metallelektroderna.Tillsammans med studier av andra forskargrupper har det här resultatetbidragit till en debatt om huruvida minnesmekanismerna i andra typer avkomponenter verkligen beror på det organiska materialet.Olika sätt att ändra transporten av laddningar i organiska elektroniskasystem har undersökts. Det visas experimentellt hur överföringen av laddningarmellan metallelektroder och det organiska materialet kan förbättras genom attmodifiera metallelektroderna på molekylär nivå. Vidare har det studeratsteoretiskt hur laddningar kan fastna (så kallad trapping) i organiska materialoch därmed påverka ledningsförmågan i materialet.En speciell typ av organiska molekyler ändrar sin struktur, och därmedegenskaper, reversibelt när de belyses av ljus av en viss våglängd, så kalladefotokroma molekyler. Denna förändring kan användas till att ändraledningsförmågan genom en komponent och därmed skulle man kunna användamolekylerna i en minneskomponent. I den sista delen av avhandlingen användskvantkemiska metoder för att beräkna egenskaperna hos dessa molekyler för attöka förståelsen för hur de kan användas i minneskomponenter.

In recent years, the conventional Flash memory with floating structure is expected to reach physical limits as devices scaling down in near future. In order to overcome this problem, alternative memory technologies have been widely investigated. And the resistance random access memory (RRAM) has attracted extensive attention for the application in next generation nonvolatile memory, due to the excellent memory property including lower consumption of energy, lower operating voltage, higher density, fast operating speed, simple structure, higher endurance, retention and process compatibility with CMOS. In this study, the tungsten-based oxide is chosen as RRAM switching layer because the tungsten is compatible with the present complementary metal oxide semiconductor (CMOS) process. The Pt/WOX/TiN structure device cells had the resistance switching property successfully. However, the experiment result revealed the inferior resistance switching property. The resistance switching characteristic of the WOX thin film is extremely unstable, it is impossible to become the products. Compared with WOX, the resistance switching property of WSiOX RRAM device is improved substantially such as stability of resistance states and reliability of device. In second parts, we purposed two methods to enhance the device switching characteristic, including controlling the filament formation/ interruption in the W doped SiOX layer and restricting oxygen movement in the WSiON layer. Finally, the transport mechanisms of carrier is analyzed and researched from the current-voltage (I-V) switching characteristic of the device. A designed circuit was used in this study to accurately observe the resistance switching process with a pulse generator and oscilloscope, which reveals that the switching process is related to both time and voltage. The oxygen movement will drift in the low temperature due to the electrical field and restricted the crystal lattice vibration. But, it will diffuse through thermal dynamics in the high temperature.

This thesis contains four parts. In the first part, we investigate the post treatment of low-temperature-deposited high dielectric constant (high-k) thin films to enhance their properties. The high-pressure oxygen (O2 and O2+UV light) is employed to improve the properties of low-temperature-deposited metal oxide dielectric films and interfacial layer. In this study, 13nm HfO2 thin films are deposited by sputtering method at room temperature. Then, the oxygen treatments with a high-pressure of 1500 psi at 150 ¢J are performed to replace the conventional high temperature annealing. According to the XPS analyses, integration area of the absorption peaks of O-Hf and O-Hf-Si bonding energies apparently raise and the quantity of oxygen in deposited thin films also increases from XPS measurement. In addition, the leakage current density of standard HfO2 film after O2 and O2+UV light treatments can be improved from 3.12¡Ñ10-6 A/cm2 to 6.27¡Ñ10-7 and 1.3¡Ñ10-8 A/cm2 at |Vg| = 3 V. The leakage current density is significantly suppressed and the current transport mechanism is transformed from trap-assisted tunneling to Schottky-Richardson emission due to the passivation of traps inside HfO2 film and interfacial layer. The proposed treatment is applicable for the future flexible electronics. In the second part of this thesis, we study the memory characteristics of CoSi2 nanocrystals with SiO2 or Al2O3/HfO2 multiple layer tunnel oxide. Due to the property of high-k, it can provide thicker physics thickness than thermal oxide (SiO2) under identical equivalent oxide thickness (EOT) and enhances the reliability without reducing the programming speed. By engineering the different dielectric constant materials and the energy band structure, the performance of nonvolatile memory can be improved. The device that employs HfO2/Al2O3/HfO2 as tunnel oxide exhibits better memory window and carrier injection efficiency than the device employing thermal oxide. Furthermore, the device employs Al2O3/HfO2/Al2O3 as tunnel oxide present the better retention characteristics than the device employs HfO2/Al2O3/HfO2 as tunnel oxide. The corresponding mechanisms were also discussed. For the advanced nonvolatile application, high-k material - hafnium oxide was applied on the resistance switching nonvolatile memory device as resistive switching layer with TiN/Ti/HfO2/TiN structure in the third part of this thesis. By using a thin Ti layer as the reactive buffer layer into the anode side, the proposed device exhibits superior bistable characteristics. Since the Ti can easily absorb oxygen atoms from buried HfO2, the TiN/Ti bi-layer can greatly improve the resistive switching characteristics. The mechanism of the proposed device is dominated by the redox reaction between the Hf and HfOX. In addition, the proposed device has multi-bit storage ability to enhance the storage density. From the temperature-dependent measurements, the low ambient temperatures would cause the formation and rupture of the conduction path with discordant quality and quantity during every switching cycle, which give rise to a wide distribution of the HRS and LRS resistance and instability of resistive switching properties. In the fourth part of this thesis, we investigate the characteristics of an advanced Cu-induced resistance switching non-volatile memory with Pt/Cu/SiON/TiN/SiO2/Si structure. By inserting a Cu ultra thin film between the SiON layer and Pt top electrode, the device exhibits bipolar resistive switching characteristics after a forming process at 13.6 V. However, the forming and resistive switching process can not be observed in the device if the Cu thin film is omitted. Additionally, we employ a two-step forming process to reduce the forming voltage to 7.5 V. During the forming process, the bias-induced Cu could form a filament-like stretched electrode, but the ¡§set¡¨ and ¡§forming¡¨ voltage of the proposed device take place on different polarity. Therefore, we suppose a bipolar switching mechanism, and our device is dominated by the formation and rupture of the oxygen vacancies in a conduction path between the Cu filament and TiN button electrode. The device also demonstrates stable resistance states during 105 cycling bias pulse operations and acceptable retention characteristics after an endurance test at 85¢J. The I-V switching curves are analyzed to realize the carrier transport mechanisms in different bias regions and resistance states. Additionally, the effective thickness of the resistance switching layers (deff) for the samples with different SiON thickness is also extracted from the related mechanism and demonstrated that the deff is independent with the initial SiON thickness. The corresponding mechanisms and the deff verify the bipolar switching is dominated by the formation and rupture of the oxygen vacancies in conduction path between Cu filament and TiN bottom electrode.

This study is focuses on the resistance switching physical mechanism in hafnium oxide (HfO2) of resistive random access memory (RRAM). HfO2 was taken as the resistance switching layer because HfO2 is extremely compatible with the prevalent complementary metal oxide semiconductor (CMOS) process. The detail physical mechanism is studied by the stable RRAM device (Ti/HfO2/TiN), which is offered from Industrial Technology Research Institute (ITRI). In this study, the resistance switching property of two different forming conductions are compared, including DC sweeping forming and AC pulse forming. In general, forming is a pivotal process in resistance random access memory (RRAM) to activate the resistance switching behavior. However, over forming would lead to device damage. The overshoot current has been considered as a degradation reason during the forming process. The circuit design is used to obtain the overshoot effect of DC sweeping forming by oscilloscope and semiconductor parameter analyzer system. The quantity of charge through the switching layer has been proven as the key element in the formation of the conduction path. Ultra-fast pulse forming can form a discontinuous conduction path to reduce the operation power.

Actuellement, l'étude et le développement d'oxydes à commutation de résistance pour des dispositifs mémoires (Resistive RAM, ou ReRAM) constituent un domaine d'activité intense sur le plan international. Les ReRAMs sont des structures MIM (Métal-Isolant-Métal) dont la résistance peut être modulée par l’application d’une tension. A ce jour, les mécanismes qui régissent la transition de résistance dans les dispositfs ReRAM sont toujours l’objet de débats. Le travail développé dans cette thèse représente une contribution au développement des mémoires ReRAM à base de HfO2. Nous nous intéressons plus particulièrement aux ReRAMs « à pont conducteur » (Conducting Bridge RAM, ou CBRAM) pour lesquelles la transition de résistance est provoquée par la diffusion du métal d’anode. Nous cherchons à améliorer la compréhension des phénomènes qui contrôlent le passage d’un état isolant à un état conducteur. Dans ce cadre, notre travail se focalise sur l’influence des métaux d'électrodes. Le rôle de l’anode et de la cathode sont précisés. Un modèle qualitatif est présenté permettant d’expliquer la commutation de résistance. Nous discutons également des mécanismes de conduction dans l’état de faible résistance. Enfin, l’impact de la structure de l’oxyde est étudié. / The Resistive Random Access Memory (ReRAM) technology is attracting growing interest as a potential candidate for the next generation of nonvolatile memories. ReRAMs are MIM (Metal-Insulator-Metal) devices whose resistance can be tuned by voltage bias. Today the physical mechanisms at the origin of resistance switching are not yet fully understood and are still under debate. In the present work, we are interested in HfO2-based ReRAMs, with a focus on Conducting Bridge RAM (CBRAM) devices in which resistance transition is ascribed to anode metal diffusion. Our goal is to better identify phenomena which govern the high to low resistance transition. In this context, we study the impact of different metal electrodes. The role played by the anode and the cathode is elucidated. A qualitative model describing resistance transition is proposed. Conduction mechanisms in the low resistive state are also discussed. Finally, the impact of oxide structure is studied.

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

La mémoire Flash est célèbre dans le domaine des mémoires non volatiles ; elle est actuellement extrêmement utilisée pour le stockage des données numériques dans presque tous type d'appareil électronique nomade (ordinateur portable, téléphone mobile, tablette, …). Pour dépasser ses limites actuelles (densité d'informations, rapidité d'accès, endurance), un grand nombre de recherches se développent, explorant notamment le concept de mémoires résistives (Re-RAM), qui repose sur la commutation entre deux états de résistance (ou plus) via l'application d'une tension. Les mémoires Re-RAM dont la variation de résistance dépend de réactions électrochimiques sont potentiellement de bonnes candidates ; les mécanismes d'oxydo-réduction impliqués sont cependant souvent de type filamentaire, mettant notamment en jeu des migrations de cations d’éléments métalliques (provenant des électrodes), ou de lacunes d’oxygène. Ce caractère filamentaire rend difficilement atteignable la miniaturisation extrême, à l’échelle nanométrique.Dans ce but, une classe de matériaux complètement différente -utilisée dans le domaine du stockage d'énergie- est explorée. L’objectif de cette thèse est ainsi d’approfondir l’étude des phénomènes de commutation de résistance observés sur des films de LixCoO2. Nous caractérisons d'abord les propriétés structurales et électriques, à l'échelle nanométrique, de tels films déposés sur divers types de substrats. Nous cherchons ensuite à déterminer les mécanismes électrochimiques à l’origine des modifications : celles-ci vont en effet en sens inverse pour un même signe de tension, selon que l’on se trouve dans la configuration d’un contact nanométrique pointe AFM/film, ou dans la configuration d’un contact micrométrique électrode/film/électrode. Dans la première configuration nous déterminons les réactions électrochimiques impliquées. Dans la deuxième, nous proposons un mécanisme radicalement différent, corroboré par plusieurs résultats convergents. Enfin, nous exposons de premiers résultats prometteurs, relatifs à l’applicabilité potentielle de ces films aux mémoires Re-RAM, et au-delà, aux circuits neuromorphiques (états multiples de résistance – phénomènes d'additivité). / Flash memory has been famous in the field of non-volatile memory; currently it is extremely used for digital data storage in almost type of mobile electronic device (laptop, mobile phone, tablet ...). To overcome its current limitations (information density, access speed, endurance), a large number of research develop, especially exploring the concept of resistive memory (Re- RAM), which is based on switching between two resistance states (or more) via the application of a voltage.The Re-RAM whose resistance change depends on electrochemical reactions are potentially good candidates; the involved redox mechanisms are often, with particular cations migration of metal elements (between the electrodes), or oxygen deficiencies. This filamentary nature makes difficult to achieve extreme miniaturization at the nanoscale.For this purpose, a completely different class of materials - used in the field of energy storage - is explored. The objective of this thesis is thus to deepen the study of resistance switching phenomena observed in films LixCoO2. We first characterize the structural and electrical properties at the nanoscale, such films deposited on various types of substrates. We then seek to determine the electrochemical mechanisms underlying modification: they are in effect in reverse for the same sign of potential, as it is in the configuration of a contact nanoscale AFM tip / film, or in the configuration of a micrometer contact electrode / film / electrode. In the first configuration we determine the electrochemical reactions involved. In the second, we propose a radically different mechanism, supported by several converging results. Finally, we present promising first results regarding the potential applicability of these films to Re - RAM, and beyond, the neuromorphic circuits (multiple resistance states - additivity phenomena).

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