Wet thermal oxidations of polycrystalline Si₀.₅₄Ge₀.₄₆ films at 600°C for 30 and 50 min were carried out. A stable mixed oxide was obtained for films that were oxidized for 50 min. For film oxidized for 30 min, however, a mixed oxide with Ge nanocrystallites embedded in the oxide matrix was obtained. A trilayer gate stack structure that consisted of tunnel oxide/oxidized polycrystalline Si₀.₅₄Ge₀.₄₆/rf sputtered SiO₂ layers was fabricated. We found that with a 30 min oxidized middle layer, annealing the structure in N₂ ambient results in the formation of germanium nanocrystals and the annealed structure exhibits memory effect. For a trilayer structure with middle layer oxidized for 50 min, annealing in N₂ showed no nanocrystal formation and also no memory effect. Annealing the structures with 30 or 50 min oxidized middle layer in forming gas ambient resulted in nanocrystals embedded in the oxide matrix but no memory effect. This suggests that the charge storage mechanism for the trilayer structure is closely related to the interfacial traps of the nanocrystals. / Singapore-MIT Alliance (SMA)

Aim of this work was, to investigate the preparation of Si NC memories by sputter deposition. The milestones are as follows: - Review of relevant literature. - Development of processes for an ultrathin tunnel-oxide and high quality sputtered SiO2 for use as control-oxide. - Evaluation of methods for the preparation of an oxygen-deficient silicon oxide inter-layer (the precursor of the Si NC layer). - Characterization of deposited films. - Establishment of techniques capable of probing the phase separation of SiOx and the formation of Si NC. - Establishment of annealing conditions compatible with the requirements of current CMOS technology based on experimental results and simulations of Si NC formation. - Preparation Si NC memory capacitors using the developed processes. - Characterization of these devices by suitable techniques. Demonstration of their memory functionality.

Aim of this work was, to investigate the preparation of Si NC memories by sputter deposition. The milestones are as follows: - Review of relevant literature. - Development of processes for an ultrathin tunnel-oxide and high quality sputtered SiO2 for use as control-oxide. - Evaluation of methods for the preparation of an oxygen-deficient silicon oxide inter-layer (the precursor of the Si NC layer). - Characterization of deposited films. - Establishment of techniques capable of probing the phase separation of SiOx and the formation of Si NC. - Establishment of annealing conditions compatible with the requirements of current CMOS technology based on experimental results and simulations of Si NC formation. - Preparation Si NC memory capacitors using the developed processes. - Characterization of these devices by suitable techniques. Demonstration of their memory functionality.

A metal-insulator-semiconductor (MIS) device with a trilayer insulator structure consisting of sputtered SiO₂ (~50nm)/evaporated pure germanium (Ge) layer (2.4nm)/rapid thermal oxide (~5nm) was fabricated on a p-type Si substrate. The MIS device was rapid thermal annealed at 1000°C. Capacitance-voltage (C-V) measurements showed that, after rapid thermal annealing at 1000°C for 300s in Ar, the trilayer device exhibited charge storage property. The charge storage effect was not observed in a device with a bilayer structure without the Ge middle layer. With increasing rapid thermal annealing time from 0 to 400s, the width of the C-V hysteresis of the trilayer device increased significantly from 1.5V to ~11V, indicating that the charge storage capability was enhanced with increasing annealing time. High-resolution transmission electron microscopy results confirmed that with increasing annealing time, the 2.4nm amorphous middle Ge layer crystallized gradually. More Ge nanocrystals were formed and the crystallinity of the Ge layer improved as the annealing time was increased. When the measurement temperature was increased from –50°C to 150°C, the width of the hysteresis of the MIS device reduced from ~10V to ~6V. This means that the charge storage capability of the trilayer structure decreases with increasing measurement temperature. This is due to the fact that the leakage current in the trilayer structure increases with increasing measurement temperature. / Singapore-MIT Alliance (SMA)

Electrets are materials capable of storing oriented dipoles or an electric surplus charge for long periods of time. The term "electret" was coined by Oliver Heaviside in analogy to the well-known word "magnet". Initially regarded as a mere scientific curiosity, electrets became increasingly imporant for applications during the second half of the 20th century. The most famous example is the electret condenser microphone, developed in 1962 by Sessler and West. Today, these devices are produced in annual quantities of more than 1 billion, and have become indispensable in modern communications technology. Even though space-charge electrets are widely used in transducer applications, relatively little was known about the microscopic mechanisms of charge storage. It was generally accepted that the surplus charges are stored in some form of physical or chemical traps. However, trap depths of less than 2 eV, obtained via thermally stimulated discharge experiments, conflicted with the observed lifetimes (extrapolations of experimental data yielded more than 100000 years). Using a combination of photostimulated discharge spectroscopy and simultaneous depth-profiling of the space-charge density, the present work shows for the first time that at least part of the space charge in, e.g., polytetrafluoroethylene, polypropylene and polyethylene terephthalate is stored in traps with depths of up to 6 eV, indicating major local structural changes. Based on this information, more efficient charge-storing materials could be developed in the future. The new experimental results could only be obtained after several techniques for characterizing the electrical, electromechanical and electrical properties of electrets had been enhanced with in situ capability. For instance, real-time information on space-charge depth-profiles were obtained by subjecting a polymer film to short laser-induced heat pulses. The high data acquisition speed of this technique also allowed the three-dimensional mapping of polarization and space-charge distributions. A highly active field of research is the development of piezoelectric sensor films from electret polymer foams. These materials store charges on the inner surfaces of the voids after having been subjected to a corona discharge, and exhibit piezoelectric properties far superior to those of traditional ferroelectric polymers. By means of dielectric resonance spectroscopy, polypropylene foams (presently the most widely used ferroelectret) were studied with respect to their thermal and UV stability. Their limited thermal stability renders them unsuitable for applications above 50 °C. Using a solvent-based foaming technique, we found an alternative material based on amorphous Teflon® AF, which exhibits a stable piezoelectric coefficient of 600 pC/N at temperatures up to 120 °C. / Elektrete sind Materialien, welche orientierte elektrische Dipole oder eine elektrische Überschussladung über längere Zeit speichern können. Der Begriff wurde 1885 von Oliver Heaviside in Anlehnung an das Wort "Magnet" eingeführt. Zunächst nur als wissenschaftliche Kuriosität betrachtet, wurden sie seit Mitte des 20. Jahrhunderts in zunehmendem Maße für technische Anwendungen interessant. Als bekanntestes Beispiel sei hier das 1962 von Sessler und West entwickelte Elektret-Kondensator-Mikrofon erwähnt, welches in jährlichen Stückzahlen von mehr als 1 Milliarde hergestellt wird und aus der modernen Kommunikationstechnik nicht mehr wegzudenken ist. Trotz der weit verbreiteten Anwendungen in der Sensorik war bisher nur wenig über die mikroskopischen Mechanismen der Ladungsspeicherung bekannt. Allgemein wird davon ausgegangen, dass die Überschussladungen in physikalischen oder chemischen Haftstellen gespeichert sind. Bisherige Experimente zur thermisch stimulierten Entladung ergaben Bindungsenergien unterhalb von 2 eV, was im Widerspruch zu den beobachteten Lebensdauern (extrapoliert wurden Werte von mehr als 100000 Jahren) steht. Mittels photostimulierter Entladung sowie simultaner Messung des Ladungsprofils konnte nun für eine Reihe wichtiger Elektret-Polymere (darunter das unter dem Handelsnamen Teflon® bekannte Polytetrafluorethylen, Polypropylen und Polyethylenterephthalat) erstmals gezeigt werden, dass zumindest ein Teil der Ladungen in tiefen Haftstellen von bis zu 6 eV gespeichert wird, was auf eine tiefgreifende lokale Strukturänderung hinweist. Ausgehend von dieser Information könnten in Zukunft Materialien mit verbesserter Ladungsspeicherung gezielt entwickelt werden. Die neuen Messungen waren erst möglich, nachdem mehrere Verfahren zur Bestimmung elektrischer, elektromechanischer und mechanischer Eigenschaften von Elektreten für einen In Situ-Einsatz weiterentwickelt wurden. So konnten z. B. durch Anregung von kurzen Wärmepulsen in der Polymerfolie Informationen über das Tiefenprofil der Raumladung in Echtzeit gewonnen werden. Die schnelle Abtastung ermöglichte darüber hinaus die dreidimensionale Kartierung von Polarisationsprofilen und Raumladungen. Ein zur Zeit sehr aktives Forschungsgebiet ist die Entwicklung piezoelektrischer Sensorfolien aus geschäumten Elektret-Polymeren. Nach elektrischer Aufladung in einer Korona-Entladung werden Ladungen an der Innenseite der Gasbläschen gespeichert, wodurch das Material piezoelektrische Eigenschaften erhält, welche deutlich besser sind als die der herkömmlichen ferroelektrischen Polymere. Für die bisher gebräuchlichen Polypropylenschäume wurde neben der Temperaturstabilität mittels dielektrischer Resonanzspektroskopie auch das Verhalten unter UV-Bestrahlung untersucht. Aufgrund ihrer beschränkten thermischen Stabilität sind diese Schäume nicht für Anwendungen oberhalb von 50 °C geeignet. Mittels eines Lösungsmittel-basierten Schäumungsverfahrens wurde ein alternativer Werkstoff auf der Basis von amorphem Teflon® AF entwickelt, welcher einen stabilen piezoelektrischen Koeffizienten von 600 pC/N bei Temperaturen von bis zu 120 °C aufweist.

In view of the importance of charge storage in polymer electrets for electromechanical transducer applications, the aim of this work is to contribute to the understanding of the charge-retention mechanisms. Furthermore, we will try to explain how the long-term storage of charge carriers in polymeric electrets works and to identify the probable trap sites. Charge trapping and de-trapping processes were investigated in order to obtain evidence of the trap sites in polymeric electrets. The charge de-trapping behavior of two particular polymer electrets was studied by means of thermal and optical techniques. In order to obtain evidence of trapping or de-trapping, charge and dipole profiles in the thickness direction were also monitored. <br><br> In this work, the study was performed on polyethylene terephthalate (PETP) and on cyclic-olefin copolymers (COCs). PETP is a photo-electret and contains a net dipole moment that is located in the carbonyl group (C = O). The electret behavior of PETP arises from both the dipole orientation and the charge storage. In contrast to PETP, COCs are not photo-electrets and do not exhibit a net dipole moment. The electret behavior of COCs arises from the storage of charges only. <br><br> COC samples were doped with dyes in order to probe their internal electric field. COCs show shallow charge traps at 0.6 and 0.11 eV, characteristic for thermally activated processes. In addition, deep charge traps are present at 4 eV, characteristic for optically stimulated processes. <br><br> PETP films exhibit a photo-current transient with a maximum that depends on the temperature with an activation energy of 0.106 eV. The pair thermalization length (rc) calculated from this activation energy for the photo-carrier generation in PETP was estimated to be approx. 4.5 nm. The generated photo-charge carriers can recombine, interact with the trapped charge, escape through the electrodes or occupy an empty trap. <br><br> PETP possesses a small quasi-static pyroelectric coefficient (QPC): ~0.6 nC/(m²K) for unpoled samples, ~60 nC/(m²K) for poled samples and ~60 nC/(m²K) for unpoled samples under an electric bias (E ~10 V/µm). When stored charges generate an internal electric field of approx. 10 V/µm, they are able to induce a QPC comparable to that of the oriented dipoles. Moreover, we observe charge-dipole interaction. Since the raw data of the QPC-experiments on PETP samples is noisy, a numerical Fourier-filtering procedure was applied. Simulations show that the data analysis is reliable when the noise level is up to 3 times larger than the calculated pyroelectric current for the QPC. <br><br> PETP films revealed shallow traps at approx. 0.36 eV during thermally-stimulated current measurements. These energy traps are associated with molecular dipole relaxations (C = O). On the other hand, photo-activated measurements yield deep charge traps at 4.1 and 5.2 eV. The observed wavelengths belong to the transitions in PETP that are analogous to the π - π* benzene transitions. The observed charge de-trapping selectivity in the photocharge decay indicates that the charge detrapping is from a direct photon-charge interaction. Additionally, the charge de-trapping can be facilitated by photo-exciton generation and the interaction of the photo-excitons with trapped charge carriers. These results indicate that the benzene rings (C6H4) and the dipolar groups (C = O) can stabilize and share an extra charge carrier in a chemical resonance. In this way, this charge could be de-trapped in connection with the photo-transitions of the benzene ring and with the dipole relaxations. <br><br> The thermally-activated charge release shows a difference in the trap depth to its optical counterpart. This difference indicates that the trap levels depend on the de-trapping process and on the chemical nature of the trap site. That is, the processes of charge detrapping from shallow traps are related to secondary forces. The processes of charge de-trapping from deep traps are related to primary forces. Furthermore, the presence of deep trap levels causes the stability of the charge for long periods of time. / Angesichts der Bedeutung der Ladungsspeicherung in Polymerelektreten für viele Anwendungen, wie z.B. in elektromechanischen Wandler, ist es das Ziel dieser Arbeit, zum Verständnis der zugrundeliegenden Mechanismen der kurz- und langfristigen Ladungsstabilisierung beizutragen sowie mögliche Haftstellen zu identifizieren. Ladungs- und Entladungsprozesse in Elektreten geben Hinweise auf Ladungshaftstellen. Diese Prozesse wurden mit thermischen und optischen Methoden bei gleichzeitiger Messung von Ladungs- und Polarisationprofilen untersucht. Die experimentellen Untersuchungen der vorliegenden Arbeit wurden an Polyethylenterephthalat (PETP) und an Cyclischen-Olefin Copolymeren (COC) durchgeführt. <br><br> PETP ist ein Photoelektret und weist in der Carbonylgruppe (C = O) ein Dipolmoment auf. Die Elektreteigenschaften ergeben sich sowohl aus der Orientierungspolarisation als auch aus der Ladungsspeicherung. Im Gegensatz zu PETP ist COC kein Photoelektret und zeigt auch keine Orientierungspolarisation. Deshalb folgen die Elektreteigenschaften des COC ausschließlich aus der Ladungsspeicherung. Die COC-Proben wurden mit Farbstoffen dotiert, um das innere elektrische Feld zu untersuchen. Diese Systeme zeigen flache Ladungshaftstellen bei 0,6 und 0,11 eV, die durch thermisch stimulierte Prozesse entladen werden sowie tiefe Haftstellen bei 4 eV, die optisch stimuliert werden können. <br><br> PETP-Filme zeigen einen transienten Photostrom mit einem Maximalwert ( jp), der von der Temperatur mit einer Aktivierungsenergie von 0,106 eV abhängt. Der thermische Paarabstand (rc) kann für die Photoladungsgeneration in PETP auf ca. 4,5 nm abgeschätzt werden. Die Photoladungsträger können rekombinieren, mit den gespeicherten Ladungen interagieren, über die Elektroden entkommen oder eine leere Haftstelle einnehmen. <br><br> PETP zeigt einen kleinen quasi-statischen pyroelektrischen Koeffizienten (QPC) von ca. 0,6 nC/(m²K) für nicht polarisierte Proben, ca. 60 nC/(m²K) für polarisierte Proben und ca. 60 nC/(m²K) für nicht polarisierte Proben mit Vorspannung (E ~10 V/µm). Wenn die gespeicherten Ladungen ein internes elektrisches Feld von ca. 10 V/µm generieren können, sind sie in der Lage, einen QPC herbeizuführen, der vergleichbar mit dem von orientierten Dipolen ist. Es ist außerdem möglich, eine Ladungs-Dipol-Wechselwirkung zu beobachten. Da die QPM-Daten von PETP auf Grund des geringen Signals verrauscht sind, wurde ein numerisches Fourier-Filterverfahren angewandt. Simulationen zeigen, dass eine zuverlässige Datenanalyse noch bei einem Signal möglich ist, dessen Rauschen bis zu 3-mal größer ist als der berechnete pyroelektrische Strom. <br><br> Messungen der thermisch stimulierten Entladung von PETP-Filmen ergaben flache Haftstellen bei ca. 0,36 eV, welche mit der Dipolrelaxation der Carbonylgruppe (C = O) assoziiert sind. Messungen der photostimulierten Entladung ergaben tiefe Haftstellen bei 4,1 und 5,2 eV. Die beobachteten Wellenlängen entsprechen Übergängen in PETP analog den π - π* Übergängen in Benzol. Die beobachtete Selektivität bei der photostimulierten Entladung lässt auf eine direkte Wechselwirkung von Photonen und Ladungen schließen. Einen zusätzlichen Einfluß auf die Entladung hat die Erzeugung von Photo-Exzitonen und deren Wechselwirkung mit den gespeicherten Ladungsträgern. Diese Ergebnisse deuten darauf hin, dass die Phenylringe (C6H4) und die Dipolgruppen (C = O) eine zusätzliche Ladung in einer chemischen Resonanz stabilisieren und miteinander teilen können. Daher kann die gebundene Ladung auch durch einen Photoübergang im Benzolring oder durch eine Dipolrelaxation freigesetzt werden. <br><br> Die mittels thermisch stimulierter Entladung bestimmte Tiefe der Haftstellen unterscheidet sich deutlich von den mittels photostimulierter Entladung gemessenen Werten. Flachere Haftstellen werden bei der thermisch stimulierten Entladung gefunden und können sekundären Kräften zugeordnet werden. Die tieferen Haftstellen sind chemischer Natur und können primären Kräften zugeordnet werden. Letztere sind für die Langzeitstabilität der Ladung in Polymerelektreten verantwortlich.

L'objectif de ce travail de thèse est de participer à l'élaboration de nanocristaux (NCs) de germanium et de mettre en évidence certaines propriétés de structures Si(n)/SiO2 contenant ces NCs non recouverts sur leur surface par l'utilisation de la technique nano-EBIC (courant induit par bombardement électronique et collecté par un nano-contact). La particularité de cette technique basée le même principe que l'EBIC classique est l'utilisation d'une pointe AFM conductrice à la place de l'électrode standard. Nous avons particulièrement ciblé le comportement d'un NC (ou d'un nombre très réduit de NCs) à piéger et émettre des porteurs de charge suite à un bombardement électronique non continu. La structure contenant les NCs peut être polarisée sous une tension nulle (alignement des niveaux de Fermi) ou sous une tension faible. Suite à cette procédure, des durées de charge ont été mesurées et les valeurs se trouvent dépendre de la taille moyenne des NCs. En effet, le processus de charge est plus long dans un NC de petite taille du fait de sa faible efficacité de stockage. D'un autre côté, le courant collecté présente une valeur de saturation plus élevée dans le cas des petits NCs. Ces deux effets (durée élevée et courant de saturation élevé dans les petits NCs) ont été expliqués par l'abaissement de la barrière d'énergie au niveau du contact pointe/NC qui résulte de l'élargissement du gap du NC et de l'augmentation du champ électrique dans la couche d'oxyde et dans la zone de désertion du substrat de silicium sous une tension de polarisation donnée. Enfin, la procédure, par son originalité, a aussi permis d'accéder à la résistivité électrique de la couche d'oxyde mince (5 nm). / The objective of this work is to contribute to the production of germanium nanocrystals (NCs) and to highlight some electronic properties of Si(n)/SiO2 structures containing those uncovered NCs on top thanks to the nano-EBIC technique (electron beam induced current collected by a nano-contact). The distinctive feature of this technique based on classic EBIC is the use of an AFM conducting probe instead of the standard electrode. Our study focuses on the capability of a single NC (or a few number of NCs) to trap and to release charge carriers as a result of a non-continuous electronic irradiation. The structure containing NCs can be connected to the ground (ensuring the Fermi levels alignment) or polarized under a low voltage. With this procedure, carriers charging times had been measured and their values depend on the mean diameter of the NCs. Indeed, the charging process takes more time in small NCs due to their weak storage efficiency. Nonetheless, the collected current reaches a higher saturation value in small NCs. Both of these effects (large charging time and high saturation current for small NCs) are explained by the lowering of the energy barrier at the AFM-tip/NCs contact, which results from the widening band-gap of NCs and the increase of the electric field across the oxide and in the Si depletion zone at a given bias voltage for small NCs. At last, this novel procedure allows measuring the electric resistivity of the 5 nanometers thin oxide.

Metal-Organic Frameworks (MOFs) are porous materials consisting of organic ligands connected by inorganic nodes. Their structural uniformity, high surface area, and synthetic tunability, position these frameworks as suitable active materials to achieve efficient and clean electrochemical energy storage. In spite of recent demonstrations of MOFs undergoing diverse electrochemical processes, a fundamental understanding of the mechanism of electron, proton, and ion transport in these porous structures is needed for their application in electronic devices. The current work focuses on contributing to such understanding by investigating proton-coupled electron transfer, capacitance performance, and the relative contribution of electron and ionic transport in the voltammetry of zirconium-based MOFs. First, we investigated the effects that the quinone ligand orientation inside two new UiO-type metal-organic frameworks (2,6-Zr-AQ-MOF and 1,4-Zr-AQ-MOF) have on the ability of the MOFs to achieve proton and electron conduction. The number of electrons and protons transferred by the frameworks was tailored in a Nernstian manner by the pH of the media, revealing different electrochemical processes separated by distinct pKa values. In particular, the position of the quinone moiety with respect to the zirconium node, the effect of hydrogen bonding, and the amount of defects in the MOFs, lead to different PCET processes. The ability of the MOFs to transport discrete numbers of protons and electrons, suggested their application as charge carriers in electronic devices. With that purpose in mind, we assembled 2,6-Zr-AQ-MOF and 1,4-Zr-AQ-MOF into two different types of working electrodes: a slurry-modified glassy carbon electrode, and as solvothermally-grown MOF thin films. The specific capacitance and the percentage of quinone accessed in the two frameworks were calculated for the two types of electrodes using cyclic voltammetry in aqueous buffered media as a function of pH. Both frameworks showed an enhanced capacitance and quinone accessibility in the thin films as compared to the powder-based electrodes, while revealing that the structural differences between 2,6-Zr-AQ-MOF and 1,4-Zr-AQ-MOF in terms of defectivity and the number of electrons and protons transferred were directly influencing the percentage of active quinones and the ability of the materials to store charge. Additionally, we investigated in detail the redox-hopping electron transport mechanism previously proposed for MOFs, by utilizing the chronoamperometric response (I vs. t) of three metallocene-doped metal-organic frameworks (MOFs) thin films (M-NU-1000, M= Fe, Ru, Os) in two different electrolytes (TBAPF6 and TBATFAB). We were able to elucidate, for the first time, the diffusion coefficients of electrons and ions (De and Di, respectively) through the structure in response to an oxidizing applied bias. The application of a theoretical model for solid state-voltammetry to the experimental data revealed that the diffusion of ions is the rate-determining step at the three different time stages of the electrochemical transformation. Remarkably, the trends observed in the diffusion coefficients (De and Di) of these systems obtained in PF61- and TFAB1- based electrolytes at the different stages of the electrochemical reaction, demonstrated that the redox hopping rates inside frameworks can be controlled through the modifications of the self-exchange rates of redox centers, the use of large MOF channels, and the utilization of smaller counter anions. These structure-function relationships provide a foundation for the future design, control, and optimization of electronic and ionic transport properties in MOF thin films. / PHD

A técnica de injeção de cargas por feixe eletrônico em materiais poliméricos pode ser utilizada como uma importante ferramenta no estudo das propriedades elétricas destes materiais. Fenômenos tais como a emissão eletrônica secundária, o transporte e armazenamento de portadores de carga no volume do material, fenômenos de injeção e condutividade induzida por radiação podem ser observados em películas finas de dielétricos lançando mão desta poderosa técnica. Neste trabalho, utilizamos um canhão de elétrons de energia variável (O a 10 keV) na irradiação de amostras de polianilinas, por nós sintetizadas, para o estudo da emissão secundária e de transporte no volume. Alguns experimentos foram também realizados com o poli(fluoreto de vinilideno), que é um polímero bem mais resistivo que as polianilinas. As medidas de emissão eletrônica foram feitas em circuito aberto, enquanto as medidas de transporte foram obtidas em circuito fechado. Neste segundo tipo de configuração, procuramos fazer uma análise do comportamento da corrente através da amostra pela observação de transientes rápidos (da ordem de 10 ms) de corrente gerados pela injeção de pacotes de carga de penetração bem definida a partir da superfície bombardeada. Propriedades elétricas intrínsecas como a condutividade do material e a permissividade elétrica, e extrínsecas como a condutividade na região irradiada foram utilizadas como parâmetros no ajuste dos resultados experimentais. / Charge injection in polymeric materials by electron beam is a powerful technique in the study of electrical properties of such materials. Secondary emission, transport and storage phenomena, as well as radiation-induced conductivity are among the subjects related to dielectrics that can be investigated. At present work we used an electron beam system (O to 10 keV) to irradiate polyaniline films, synthesized in our laboratory, and to perform studies of secondary emission and transport phenomena. Some experiments were also carried out with poly(viny1idene fluoride), a more resistivity polymer. Secondary emission measurements were carried out in an open-circuit configuration while the transport ones used a short circuit mode. Fast transient phenomena (about 10 ms) were also studied in details. Intrinsic electric properties, such as conductivity and dielectric constant, and extrinsic ones, like the induced conductivity in the irradiated region of the sample, were obtained in the fitting between the model and the experimental results.

In dieser Arbeit werden Speichertransistoren mit Oxid-Nitrid-Oxid-Speicherschicht und lokaler Ladungsspeicherung untersucht, die zur nichtflüchtigen Speicherung von Informationen genutzt werden. Charakteristisch für diese Transistoren ist, dass an beiden Enden des Transistorkanals innerhalb der Isolationsschicht Informationen in Form von Ladungspaketen unabhängig und getrennt voneinander gespeichert werden. Für das Auslesen, Programmieren und Löschen der Speichertransistoren werden die physikalischen Hintergründe diskutiert und grundlegende Algorithmen zur Implementierung dieser Operationen auf einer typischen Speicherfeldarchitektur aufgezeigt. Für Standard-MOS-Transistoren wird ein Kurzkanal-Schwellspannungsmodell abgeleitet und analytisch gelöst. Anhand dieser Modellgleichung werden die bekannten Kurzkanaleffekte betrachtet. Weiterhin wird ein Modell zur Berechnung des Drainstroms von Kurzkanaltransistoren im Subthreshold-Arbeitsbereich abgeleitet und gezeigt, dass sich die Drain-Source-Leckströme bei Kurzkanaltransistoren vergrößern. Die Erweiterung des Schwellspannungsmodells für Standard-MOS-Transistoren auf den Fall der lokalen Ladungsspeicherung innerhalb der Isolationsschicht erlaubt die Ableitung eines Schwellspannungsmodells für Oxid-Nitrid-Oxid-Transistoren mit lokaler Ladungsspeicherung. Dieses Modell gestattet die qualitative und quantitative Diskussion der Erhöhung der Schwellspannung durch die lokale Injektion von Ladungsträgern beim Programmiervorgang. Weiterhin ist es mit diesem Modell möglich, die Trennung der an beiden Kanalenden des Transistors gespeicherten Informationen beim Auslesevorgang qualitativ zu erklären und diese Bittrennung in Abhängigkeit von der Drainspannung zu berechnen. Für Langkanalspeichertransistoren wird eine analytische Näherungslösung des Schwellspannungsmodells angegeben, während das Kurzkanalverhalten durch die numerische Lösung der Modellgleichung bestimmt werden kann. Für Langkanalspeichertransistoren wird ein Subthreshold-Modell zur Berechnung des Drainstroms abgeleitet. Dieses Modell zeigt, dass sich die Leckströme von programmierten Speichertransistoren im Vergleich zu Standard-MOS-Transistoren gleicher Schwellspannung vergrößern. Die Ursache dieses Effekts, die Verringerung der Subthreshold-Steigung von Transistoren im programmierten Zustand, wird analysiert. Für einige praktische Beispiele wird die Anwendung der hergeleiteten Modellgleichungen beim Entwurf von Flash-Speichern demonstriert. / In this work, memory transistors with an oxide-nitride-oxide trapping-layer and local charge storage, which are used for non-volatile information storage, are examined. Characteristic for these transistors is an independent and separated storage of information by charge packages, located at both sides of the transistor channel, in the insulation layer. The physical backgrounds for reading, programming and erasing the memory transistors are discussed, and basic algorithms are shown for implementing these operations on a typical memory array architecture. For standard MOS-transistors a short channel threshold model is derived and solved analytically. By using these model equations, the known short channel effects are considered. Further, a model for calculating the drain current of short channel transistors in the subthreshold operation region is derived. This model is used to show the increase of drain-source leakage currents in short channel transistors. By extending the standard MOS-transistor threshold voltage model for local charge storage in the insulation layers, the derivation of a threshold voltage model for oxide-nitride-oxide transistors with local charge storage is enabled. This model permits the quantitative and qualitative discussion of the increase in threshold voltage caused by local injection of charges during programming. Furthermore, with this model, the separation of the information, which are stored at both sides of the transistor channel, in the read-out operation is explained qualitatively, and the bit separation is calculated dependent on the drain voltage. For long channel memory transistors an analytical approximation of the threshold voltage model is given, whereas the short channel behaviour can be determined by solving the model equation numerically. For long channel memory transistors, a subthreshold model for calculating the drain current is derived. This model shows the increase in leakage current of programmed memory transistors in comparision to standard MOS-transistors. The root cause of this effect, the reduced subthreshold swing of transistors in the programmed state, is analysed. The application of the derived model equations for the development of flash memories is demonstrated with some practical examples.