Simple method for monitoring the switching activity in memristive cross-point arrays with line resistance effects

A simple method for monitoring the switching activity (forming, set, reset events and stuck-at-0/1 faults) in memristive cross-point arrays with line resistance effects is proposed. The method consists in correlating incremental current changes in a four-terminal configuration with the location of the switching cell within the array. The potential drops in the interconnection wires as well as the nonlinearity of the switching elements are considered within this approach. The problem is solved by iterating the Kirchhoff's current law for the coupled word and bit lines with appropriate boundary conditions. The main experimental advantage of the proposed method is that only four SMUs (source-measurement unit) are needed to identify the switching cell. In this way, our method could contribute to foster the system-level reliability analysis of cross-point arrays since additional circuitry for the individual addressing of the switching device is not required

A new method for estimating the conductive filament temperature in OxRAM devices based on escape rate theory

Because of the atomic nature of the system under study, an estimation of the temperature of the conductive filament (CF) in OxRAM devices as a function of the applied bias can only be obtained by means of indirect methods, usually electrothermal simulations. In this paper, a heuristic approach that combines time-dependent dielectric breakdown (TDDB) statistics for the electroformed device with field and temperature-assisted ionic transport within the framework of escape rate theory is presented. Extended expressions for the time-to-failure acceleration law (E-model) and for the Kramers' rate compatible both with the standard models at moderate/high biases and with the principle of detailed balance at equilibrium are proposed. An approximate expression for the CF temperature is reported. For the investigated stress voltage range (0.30 V-0.65 V), the estimated CF temperature at the SET condition is found to be in the range 350 K-600 K

Oxide Breakdown Spot Spatial Patterns as Fingerprints for Optical Physical Unclonable Functions

Dielectric Breakdown (BD) of the gate oxide in a Metal-Insulator-Semiconductor (MIS) or Metal-Insulator-Metal (MIM) structure has been traditionally considered a major drawback since such event can seriously affect the electrical performance of the circuit containing the device. However, since BD is an inherently random process, when externally detectable by optical means, the phenomenon can be used to generate cryptographic keys for Physically Unclonable Functions (PUFs). This is the case discussed here. Images containing BD spot spatial distributions in MIM devices were binarized and their uniformity, uniqueness and reproducibility evaluated as fingerprints for security applications such as anti-counterfeiting purposes, secure identification and authentication of components. The obtained results are highly promising since it is demonstrated that the generated fingerprints meet all the mandatory requirements for PUFs, indicating that the proposed approach is potentially useful for this kind of applications

Failure analysis of large area pt/hfo 2 /pt capacitors using multilayer perceptrons

In this work, we investigated the spatial distribution of failure sites in large area Pt/HfO 2 /Pt capacitors using simple neural networks as classifiers. When an oxide breakdown (BD) occurs due to severe electrical stress, a mark shows up in the top metal electrode at the location where the failure event took place. The mark is the result of a microexplosion occurring inside the dielectric film. Large area devices need to be studied because the number of generated spots must be the required for statistical analysis. The obtained results using multilayer perceptrons with different number of neurons and hidden layers indicate that the largest breakdown spots tend to concentrate towards the center of the device. This observation is consistent with previous exploratory analysis carried out using spatial statistics techniques. This exercise shows the suitability of multilayer perceptrons for investigating the distribution of failure sites or defects on a given surface

Detection of inhibitory effects in the generation of breakdown spots in HfO2-based MIM devices

In this work, the connection between the generation of catastrophic breakdown (BD) spots in metal-insulator-metal capacitors with a high-permittivity dielectric film (HfO2) and their spatial distribution was investigated. To gain insight into this issue, large area devices (104 μm2) were constant voltage stressed at high electric fields (3.5 MV/cm) with the aim of generating a large number of spots in a single device. The set of BD spots was analysed as a point pattern with attributes (their sizes) using the methods of spatial statistics. Our study reveals that beyond the visible damage on the top metal electrode, the spots exhibit soft inhibitory regions around them where the creation of new spots is less likely. The origin of these inhibitory regions is ascribed to structural modifications of the dielectric layer in the vicinity of the spots caused by the huge thermal effects occurring at the very moment of the BD event

Degradación y conducción multifilamentaria en estructuras MIS/MIM basadas en HfO2

En aquesta tesi doctoral es realitza una extensa investigació sobre el fenomen de la ruptura dielèctrica en dispositius metall-aïllant-semiconductor (MIS) i metall-aïllant-metall (MIM) basats en HfO2. Més específicament, s’han estudiat dispositius MIS/MIM amb HfO2 com a dielèctric i dispositius MIS dielèctric dels quals es un penta-nanolaminat composat per capes interposades de HfO2 i de Al2O3. Al llarg dels quatre extensos capítols que formen aquesta tesi, més un últim capítol conclusiu, s’ha realitzat un exhaustiu estudi de la ruptura dielèctrica des de punts de vista completament diferents. Iniciant per un capítol introductori al fenomen de la ruptura dielèctrica, en el que s’exposa els aspectes generals a tenir en compte, cadascun dels tres capítols experimentals posteriors giren al voltant d’un efecte particular d’aquest fenomen. A la vegada, només s’avalua un tipo de dispositiu en cada capítol. Inicialment, utilitzant les estructures MIS basades en HfO2, es realitza un anàlisis en profunditat dels canvis estructurals induïts en la intercara metall-aïllant dels dispositius degut a la ruptura dielèctrica. Per a fer-ho, en aquest capítol es recorren a poderoses tècniques de caracterització física como el microscopi electrònic de rastreig, el microscopi de forces atòmiques o la espectrometria de dispersió de energia de raigs X. A la vegada, es realitza un estudi sobre els efectes de la commutació resistiva en els canvis induïts en els dispositius. En el següent capítol, utilitzant les estructures MIS basades en HfO2/Al2O3, es realitza un anàlisis de la estadística de la ruptura dielèctrica dependent del temps, així com dels esdeveniments de ruptura successius. Utilitzant un gran arsenal de models i tècniques estadístiques, s’aconsegueix reproduir les tendències experimentals el quals no son reproduïbles amb el model de Weibull, indicació d’una ruptura dielèctrica no homogènia. A la vegada, es proporciona una hipòtesis que permet explicar el comportament observat. Seguidament, en l’últim capítol experimental, es realitza un anàlisis exhaustiu i extens de la estadística espacial dels esdeveniments de ruptura mitjançant els dispositius MIM basats en HfO2. Utilitzant aquestes tècniques, s’aconsegueix avaluar la correlació entre els esdeveniments de ruptura, així com la que existeix entre la localització i la mida dels esdeveniments. Finalment, en el capítol conclusiu es presenten tant les conclusions més rellevants de la investigació realitzada com una valoració dels possibles nous estudis que s’originen d’aquest treball.En esta tesis doctoral se realiza una extensa investigación sobre el fenómeno de la ruptura dieléctrica en dispositivos metal-aislante-semiconductor (MIS) y metal-aislante-metal (MIM) basados en HfO2. Más específicamente, se han estudiado dispositivos MIS/MIM con HfO2 como dieléctrico y dispositivos MIS cuyo dieléctrico es un penta-nanolaminado compuesto por capas interpuestas de HfO2 y de Al2O3. A lo largo de los cuatro extensos capítulos que conforman esta tesis, más un último capítulo conclusivo, se ha realizado un exhaustivo estudio de la ruptura dieléctrica desde puntos de vista completamente diferentes. Empezando por un capítulo introductorio al fenómeno de la ruptura dieléctrica, en el que se exponen los aspectos generales a tener en consideración, cada uno de los tres capítulos experimentales posteriores giran en torno a un efecto particular de este fenómeno. A su vez, solo se evalúa un tipo de dispositivo en cada capítulo. Inicialmente, utilizando las estructuras MIS basadas en HfO2, se realiza un análisis en profundidad de los cambios estructurales inducidos en la intercara metal-aislante de los dispositivos debido a la ruptura dieléctrica. Para ello, en este capítulo se recurren a poderosas técnicas de caracterización física como el microscopio electrónico de barrido, el microscopio de fuerzas atómicas o la espectrometría de dispersión de energía de rayos X. A su vez, se realiza un estudio sobre los efectos de la conmutación resistiva en los cambios inducidos en los dispositivos. En el siguiente capítulo, utilizando las estructuras MIS basadas en HfO2/Al2O3, se realiza un análisis de la estadística de la ruptura dieléctrica dependiente del tiempo, así como de los eventos de ruptura sucesivos. Utilizando un gran arsenal de modelos y técnicas estadísticas, se consigue reproducir las tendencias experimentales las cuales no son reproducibles con el modelo de Weibull, indicación de una ruptura dieléctrica no homogénea. A su vez, se proporciona una hipótesis que permite explicar el comportamiento observado. Seguidamente, en el último capítulo experimental, se realiza un análisis exhaustivo y extenso de la estadística espacial de los eventos de ruptura a través de los dispositivos MIM basados en HfO2. Utilizando estas técnicas, se consigue evaluar la correlación entre los eventos de ruptura, así como la que hay entre la localización y el tamaño de los eventos. Finalmente, en el capítulo conclusivo se presentan tanto las conclusiones más relevantes de la investigación realizada como una valoración de los posibles nuevos estudios que se originan de este trabajo.In this doctoral thesis the dielectric breakdown (BD) phenomenon in metal-insulator-semiconductor (MIS) and metal-insulator-metal (MIM) structures based on HfO2 is investigated. More specifically, the analyzed devices are MIS/MIM devices with HfO2 as dielectric and MIS devices with a penta-nanolaminate as dielectric based on Al2O3/HfO2. Throughout the four long chapters that make up this thesis, plus a final conclusive chapter, an exhaustive study of the BD phenomenon has been carried out from completely different points of view. Starting with an introductory chapter to the BD, where the general aspects of this phenomenon are explained, each of the three subsequent experimental chapters revolve around an aspect of this phenomenon. In fact, in each chapter a different type of device is evaluated. Initially, the structural changes induced in the metal-insulator interface of the HfO2-based MIS devices due to the BD are analyzed. This is performed by using powerful physical characterization techniques such as the scanning electron microscope, the atomic force microscope and the energy dispersive X-ray spectroscopy. Moreover, the effects that resistive switching mechanism has on the physical changes induced in the devices after the BD are also evaluated. In the next chapter, the time dependent dielectric breakdown is analyzed in the MIS structures based on Al2O3/HfO2. Using different models and statistical techniques, the successive dielectric breakdown statistics of these devices is evaluated. In this case, the devices shown a non-homogenous time distribution i.e. it cannot be reproduced by the Weibull model. Then, in the last experimental chapter, the spatial statistics of the BD events is evaluated in MIM devices based on HfO2. Using the spatial statistic techniques and methods, it is possible to evaluate the correlation between the BD events, as well as the correlation between their location and their size. Finally, the concluding chapter presents the most relevant conclusions of this research as well as the possible new studies that originate from this work.Universitat Autònoma de Barcelona. Programa de Doctorat en Enginyeria Electrònica i de Telecomunicaci

Degradación y conducción multifilamentaria en estructuras MIS/MIM basadas en HfO2

En aquesta tesi doctoral es realitza una extensa investigació sobre el fenomen de la ruptura dielèctrica en dispositius metall-aïllant-semiconductor (MIS) i metall-aïllant-metall (MIM) basats en HfO2. Més específicament, s'han estudiat dispositius MIS/MIM amb HfO2 com a dielèctric i dispositius MIS dielèctric dels quals es un penta-nanolaminat composat per capes interposades de HfO2 i de Al2O3. Al llarg dels quatre extensos capítols que formen aquesta tesi, més un últim capítol conclusiu, s'ha realitzat un exhaustiu estudi de la ruptura dielèctrica des de punts de vista completament diferents. Iniciant per un capítol introductori al fenomen de la ruptura dielèctrica, en el que s'exposa els aspectes generals a tenir en compte, cadascun dels tres capítols experimentals posteriors giren al voltant d'un efecte particular d'aquest fenomen. A la vegada, només s'avalua un tipo de dispositiu en cada capítol. Inicialment, utilitzant les estructures MIS basades en HfO2, es realitza un anàlisis en profunditat dels canvis estructurals induïts en la intercara metall-aïllant dels dispositius degut a la ruptura dielèctrica. Per a fer-ho, en aquest capítol es recorren a poderoses tècniques de caracterització física como el microscopi electrònic de rastreig, el microscopi de forces atòmiques o la espectrometria de dispersió de energia de raigs X. A la vegada, es realitza un estudi sobre els efectes de la commutació resistiva en els canvis induïts en els dispositius. En el següent capítol, utilitzant les estructures MIS basades en HfO2/Al2O3, es realitza un anàlisis de la estadística de la ruptura dielèctrica dependent del temps, així com dels esdeveniments de ruptura successius. Utilitzant un gran arsenal de models i tècniques estadístiques, s'aconsegueix reproduir les tendències experimentals el quals no son reproduïbles amb el model de Weibull, indicació d'una ruptura dielèctrica no homogènia. A la vegada, es proporciona una hipòtesis que permet explicar el comportament observat. Seguidament, en l'últim capítol experimental, es realitza un anàlisis exhaustiu i extens de la estadística espacial dels esdeveniments de ruptura mitjançant els dispositius MIM basats en HfO2. Utilitzant aquestes tècniques, s'aconsegueix avaluar la correlació entre els esdeveniments de ruptura, així com la que existeix entre la localització i la mida dels esdeveniments. Finalment, en el capítol conclusiu es presenten tant les conclusions més rellevants de la investigació realitzada com una valoració dels possibles nous estudis que s'originen d'aquest treball.En esta tesis doctoral se realiza una extensa investigación sobre el fenómeno de la ruptura dieléctrica en dispositivos metal-aislante-semiconductor (MIS) y metal-aislante-metal (MIM) basados en HfO2. Más específicamente, se han estudiado dispositivos MIS/MIM con HfO2 como dieléctrico y dispositivos MIS cuyo dieléctrico es un penta-nanolaminado compuesto por capas interpuestas de HfO2 y de Al2O3. A lo largo de los cuatro extensos capítulos que conforman esta tesis, más un último capítulo conclusivo, se ha realizado un exhaustivo estudio de la ruptura dieléctrica desde puntos de vista completamente diferentes. Empezando por un capítulo introductorio al fenómeno de la ruptura dieléctrica, en el que se exponen los aspectos generales a tener en consideración, cada uno de los tres capítulos experimentales posteriores giran en torno a un efecto particular de este fenómeno. A su vez, solo se evalúa un tipo de dispositivo en cada capítulo. Inicialmente, utilizando las estructuras MIS basadas en HfO2, se realiza un análisis en profundidad de los cambios estructurales inducidos en la intercara metal-aislante de los dispositivos debido a la ruptura dieléctrica. Para ello, en este capítulo se recurren a poderosas técnicas de caracterización física como el microscopio electrónico de barrido, el microscopio de fuerzas atómicas o la espectrometría de dispersión de energía de rayos X. A su vez, se realiza un estudio sobre los efectos de la conmutación resistiva en los cambios inducidos en los dispositivos. En el siguiente capítulo, utilizando las estructuras MIS basadas en HfO2/Al2O3, se realiza un análisis de la estadística de la ruptura dieléctrica dependiente del tiempo, así como de los eventos de ruptura sucesivos. Utilizando un gran arsenal de modelos y técnicas estadísticas, se consigue reproducir las tendencias experimentales las cuales no son reproducibles con el modelo de Weibull, indicación de una ruptura dieléctrica no homogénea. A su vez, se proporciona una hipótesis que permite explicar el comportamiento observado. Seguidamente, en el último capítulo experimental, se realiza un análisis exhaustivo y extenso de la estadística espacial de los eventos de ruptura a través de los dispositivos MIM basados en HfO2. Utilizando estas técnicas, se consigue evaluar la correlación entre los eventos de ruptura, así como la que hay entre la localización y el tamaño de los eventos. Finalmente, en el capítulo conclusivo se presentan tanto las conclusiones más relevantes de la investigación realizada como una valoración de los posibles nuevos estudios que se originan de este trabajo.In this doctoral thesis the dielectric breakdown (BD) phenomenon in metal-insulator-semiconductor (MIS) and metal-insulator-metal (MIM) structures based on HfO2 is investigated. More specifically, the analyzed devices are MIS/MIM devices with HfO2 as dielectric and MIS devices with a penta-nanolaminate as dielectric based on Al2O3/HfO2. Throughout the four long chapters that make up this thesis, plus a final conclusive chapter, an exhaustive study of the BD phenomenon has been carried out from completely different points of view. Starting with an introductory chapter to the BD, where the general aspects of this phenomenon are explained, each of the three subsequent experimental chapters revolve around an aspect of this phenomenon. In fact, in each chapter a different type of device is evaluated. Initially, the structural changes induced in the metal-insulator interface of the HfO2-based MIS devices due to the BD are analyzed. This is performed by using powerful physical characterization techniques such as the scanning electron microscope, the atomic force microscope and the energy dispersive X-ray spectroscopy. Moreover, the effects that resistive switching mechanism has on the physical changes induced in the devices after the BD are also evaluated. In the next chapter, the time dependent dielectric breakdown is analyzed in the MIS structures based on Al2O3/HfO2. Using different models and statistical techniques, the successive dielectric breakdown statistics of these devices is evaluated. In this case, the devices shown a non-homogenous time distribution i.e. it cannot be reproduced by the Weibull model. Then, in the last experimental chapter, the spatial statistics of the BD events is evaluated in MIM devices based on HfO2. Using the spatial statistic techniques and methods, it is possible to evaluate the correlation between the BD events, as well as the correlation between their location and their size. Finally, the concluding chapter presents the most relevant conclusions of this research as well as the possible new studies that originate from this work

Simple method for monitoring the switching activity in memristive cross-point arrays with line resistance effects

A simple method for monitoring the switching activity (forming, set, reset events and stuck-at-0/1 faults) in memristive cross-point arrays with line resistance effects is proposed. The method consists in correlating incremental current changes in a four-terminal configuration with the location of the switching cell within the array. The potential drops in the interconnection wires as well as the nonlinearity of the switching elements are considered within this approach. The problem is solved by iterating the Kirchhoff's current law for the coupled word and bit lines with appropriate boundary conditions. The main experimental advantage of the proposed method is that only four SMUs (source-measurement unit) are needed to identify the switching cell. In this way, our method could contribute to foster the system-level reliability analysis of cross-point arrays since additional circuitry for the individual addressing of the switching device is not required

A new method for estimating the conductive filament temperature in OxRAM devices based on escape rate theory

Because of the atomic nature of the system under study, an estimation of the temperature of the conductive filament (CF) in OxRAM devices as a function of the applied bias can only be obtained by means of indirect methods, usually electrothermal simulations. In this paper, a heuristic approach that combines time-dependent dielectric breakdown (TDDB) statistics for the electroformed device with field and temperature-assisted ionic transport within the framework of escape rate theory is presented. Extended expressions for the time-to-failure acceleration law (E-model) and for the Kramers' rate compatible both with the standard models at moderate/high biases and with the principle of detailed balance at equilibrium are proposed. An approximate expression for the CF temperature is reported. For the investigated stress voltage range (0.30 V-0.65 V), the estimated CF temperature at the SET condition is found to be in the range 350 K-600 K

Exploratory study and application of the angular wavelet analysis for assessing the spatial distribution of breakdown spots in Pt/HfO2/Pt structures

The angular wavelet analysis is applied for assessing the spatial distribution of breakdown spots in Pt/HfO2/Pt capacitors with areas ranging from 104 to 105 μm2. The breakdown spot lateral sizes are in the range from 1 to 3 μm, and they appear distributed on the top metal electrode as a point pattern. The spots are generated by ramped and constant voltage stresses and are the consequence of microexplosions caused by the formation of shorts spanning the dielectric film. This kind of pattern was analyzed in the past using the conventional spatial analysis tools such as intensity plots, distance histograms, pair correlation function, and nearest neighbours. Here, we show that the wavelet analysis offers an alternative and complementary method for testing whether or not the failure site distribution departs from a complete spatial randomness process in the angular domain. The effect of using different wavelet functions, such as the Haar, Sine, French top hat, Mexican hat, and Morlet, as well as the roles played by the process intensity, the location of the voltage probe, and the aspect ratio of the device, are all discussed