Dans un contexte de besoin grandissant en précision dans la mesure des faibles courants pour les instituts nationaux de métrologie, l’industrie, les fabricants d’instruments et la physique fondamentale, l’étude des dispositifs à un électron (SET) capables de générer un courant continu directement proportionnel à une fréquence et la charge élémentaire, couplés à un amplificateur de courant très performant, le comparateur cryogénique de courant (CCC), devient pertinente pour réaliser un étalon quantique de courant. Dans ce contexte, les travaux ont été poursuivis au LNE sur l’étude de nouveaux dispositifs SET et le développement de nouveaux CCC. Durant cette thèse, un montage expérimental a été mis en place afin d’évaluer les performances d’un nouveau CCC, constitué d’une conception originale et de 30 000 tours. Les résultats expérimentaux obtenus sont satisfaisant par rapport aux objectifs fixés, que ce soit en termes de résolution en courant, d’erreurs, de stabilité des mesures et de reproductibilité. Le CCC développé durant la thèse peut donc être utilisé pour quantifier de manière métrologique les dispositifs à un électron. De plus, une modélisation réalisée à partir d’un schéma électrique équivalent a été mis en place afin de simuler le comportement réel du CCC en prenant en compte les aspects magnétiques et électriques mis en jeu. Cette simulation a permis la quantification de l’erreur due aux fuites de courants au travers des capacités parasites entourant les enroulements. Les résultats de la simulation indiquent que cette erreur atteint 10 10 à la fréquence de travail, ce qui est inférieure de deux ordres de grandeurs à l’erreur maximale tolérable : 10-8. Les résultats expérimentaux et de modélisation fournissent de nouveaux éléments d’amélioration de la conception de CCCs de grand gain. Enfin, la modélisation développée, une fois insérée dans une routine d’optimisation, pourra aussi être un outil de conception des CCCs très utile. / In a context of growing need of precision in measuring low currents for national metrology institutes, industry, instrument manufacturers and fundamental physics, study of single-electron tunneling (SET) devices capable of generating a direct current directly proportional to the frequency and the elementary charge, coupled with a high performance current amplifier, the cryogenic current comparator (CCC), becomes relevant to realize a quantum current standard. In this framework, at LNE, study of new SET devices and the development of CCCs continues. In this thesis, an experimental setup was implemented to evaluate the performance of a new CCC, consisting of a new design and 30 000 turns. The experimental results fulfill our goals, whether in terms of current resolution, errors, measurement stability and reproducibility. The CCC developed during the thesis can thus be used to metrologically quantify SET devices. In addition, a model based on an equivalent circuit diagram has been developed to simulate the actual behavior of the CCC, taking into account the magnetic and electrical aspects involved. This simulation allows the quantification of the error due to currents leakage through parasitic capacitances surrounding the windings. Results of the simulation indicate that this error reaches 10 10, which is less, by two orders of magnitude, than the maximum tolerable error: 10 8. Results obtained experimentally and by simulation provide new improvement elements in the design of high ratio CCCs. The developed model, once inserted into an optimization routine, can also be a very useful design tool of CCCs.

Exploiter des effets dépendants du temps pour induire et contrôler des courants à travers des conducteurs mésoscopiques et nanoscopiques est un enjeu majeur dans le domaine du transport quantique. Dans cette thèse, nous considérons deux systèmes de taille nanométrique pour lesquels un courant est induit grâce au couplage entre champs extérieurs dépendants du temps et le transport d'électrons. Nous étudions d'abord un problème de pompage quantique au sein d'un système à trois sites en configuration d'anneau, en considérant la possibilité d'induire un courant continu par modulation temporelle des paramètres de contrôle. Nous nous intéressons en particulier à la transition entre régime adiabatique et antiadiabatique en présence d'un mécanisme de dissipation modélisé par un couplage entre le système et un bain extérieur.Nous montrons que le modèle dissipatif admet une solution analytique complète valable pour la composante DC du courant à fréquence arbitraire. Ceci nous permet de bien comprendre comment le courant induit dépend de la fréquence de pompage. Nous nous concentrons ensuite sur un autre système de contrôle du courant exploitant le phénomène des oscillations tunnel à un électron (SETOs). Contrairement au cas précédent, ici la circulation d'un courant continu à travers un circuit comportant une jonction tunnel produit, pour le régime approprié, un courant quasi-périodique d'électrons. On étudie le spectre de bruit à température nulle d'une jonction tunnel dans différents environnements résistifs dans le but de déterminer les limites du régime des SETOs et de quantifier leur degré de périodicité. Nous généralisons par la suite les résultats à température finie et discutons des effets des fluctuations quantiques. / Exploiting time-dependent effects to induce and control currents through mesoscopic and nano\-scopic conductors is a major challenge in the field of quantum transport. In this dissertation we consider two nanoscale systems in which a current can be induced through intriguing mechanisms of coupling between excitations by external fields and electron transport.We first study a quantum pumping problem, analyzing the possibility to induce a DC response to an AC parametric driving through a three-site system in a ring configuration. We are interested in particular in the crossover between adiabatic and antiadiabatic driving regimes and in the presence of dissipation, which is accounted for by coupling with an external bath. We show that for a clever choice of this coupling the dissipative model admits a full analytical solution for the steady state current valid at arbitrary frequency, which allows us to fully understand the pumping-frequency dependence of the induced current. We then focus on a different current-controlling scheme exploiting the phenomenon of single-electron tunneling oscillations (SETOs). In this case, opposite to what happens for pumping, an AC effect, an almost periodic current of single electrons, arises through a tunnel junction circuit as a consequence of a DC bias. We study the zero-temperature noise spectrum of a tunnel junction in different resistive environments with the aim to determine the boundaries of the SETOs regime and quantify their quality in terms of periodicity. We then discuss the finite-temperature generalization and the possibility to account for the effects of quantum fluctuations.

Although scalingof CMOS technology has been predicted to continue for another decade, novel technological solutions are required to overcome the fundamental limitations of the decananometer MOS transistors. Single Electron Transistor (SET) has attracted attention mainly because of its unique Coulomb blockade oscillations characteristics, ultra low power dissipation and nanoscale feature size. Despite the high potential, due to some intrinsic limitations (e.g., very low current drive) it will be very difficult for SET to compete head-to-head with CMOS’s large-scale infrastructure, proven design methodologies, and economic predictability. Nevertheless, the characteristics of SET and MOS transistors are quite complementary. SET advocates low-power consumption and new functionality (related to the Coulomb blockade oscillations), while CMOS has advantages like high-speed driving and voltage gain that can compensate the intrinsic drawbacks of SET. Therefore, although a complete replacement of CMOS by single-electronics is unlikely in the near future, it is also true that combining SET and CMOS one can bring out new functionalities, which are unmirrored in pure CMOS technology. As the hybridization of CMOSand SET is gaining popularity, silicon SETs are appearing to be more promising than metallic SETs for their possible integration with CMOS. SETs are normally studied on the basis of the classical Orthodox Theory, where quantization of energy states in the island is completely ignored. Though this assumption greatly simplifies the physics involved, it is valid only when the SET is made of metallic island. As one cannot neglect the quantization of energy states in a semi conductive island, it is extremely important to study the effects of energy quantization on hybrid CMOSSET integrated circuits. The main objectives of this thesis are: (1) understand energy quantization effects on SET by numerical simulations; (2) develop simple analytical models that can capture the energy quantization effects; (3)analyze the effects of energy quantization on SET logic inverter, and finally; (4)developa CAD framework for CMOS-SETco-simulation and to study the effects of energy quantization on hybrid circuits using that framework. In this work the widely accepted SIMON Monte Carlo (MC) simulator for single electron devices and circuits is used to study the effects of energy quantization. So far SIMON has been used to study SETs having metallic island. In this work, for the first time, we have shown how one can use SIMON to analyze SET island properties having discrete energy states.It is shown that energy quantization mainly changes the Coulomb Blockade region and drain current of SET devices and thus affects the noise margin, power dissipation, and the propagation delay of SET logic inverter. Anew model for the noise margin of SET inverter is proposed, which includes the energy quantization term. Using the noise margin as a metric, the robustness of SET inverter is studied against the effects of energy quantization. An analytical expression is developed, which explicitly defines the maximum energy quantization (termedas “Quantization Threshold”)that an SET inverter logic circuit can withstand before its noise margin upper bound crosses the acceptable tolerance limit. It is found that SET inverter designed with CT : CG =0.366 (where CT and CG are tunnel junction and gate capacitances respectively) offers maximum robustness against energy quantization. Then the effects of energy quantization are studied for Current biased SET (CBS), which is an integral part of almost all hybrid CMOS-SET circuits. It is demonstrated that energy quantization has no impact on the gain of the CBS characteristics though it changes the output voltage levels and oscillation periodicity. The effects of energy quantization are further studied for two circuits: Negative Differential Resistance (NDR) and Neurone Cell, which use CBS. A new model for the conductance of NDR characteristics is also formulated that includes the energy quantization term. A novel CAD framework is then developed for CMOS-SET co-simulation, whichuses MCsimulator for SET devices alongwithconventional SPICE. Using this framework, the effects of energy quantization are studied for some hybrid circuits, namely, SETMOS, multiband voltage filter, and multiple valued logic circuits. It is found that energy quantization degrades the performance of hybrid circuit, which could be compensated by properly tuning the bias current of SET devices. Though this study is primarily done by exhaustive MC simulation, effort has also been put to develop first order compact model for SET that includes energy quantization effects. Finally it has been demonstrated that the SET behavior under energy quantization can be predicted byslightlymodifyingthe existing SETcompact models that are valid for metallic devices having continuous energy states.

The subject of this thesis is to study the interaction between carbon nanotubes (CNTs) and antiferromagnetic tetrametallic molecules attached to them. By employing quantum transport measurements, the sensitivity to sense the interactions is greatly increased, because the quantum dot is very susceptible to changes in its environment. The properties of carbon nanotubes can be altered by chemical functionalization with the aforementioned molecules, where the attachment is performed covalently via a ligand exchange with the CNT. The thesis is partitioned into two main parts: the first part presents experiments performed on tetramanganese functionalized CNTs, whereas for the second similar studies are conducted, except manganese is replaced by cobalt. Both complexes exhibit an antiferromagnetic ground state, yet the metal spin of manganese (S=5/2) is reduced to S=3/2 for cobalt. Additionally, an altered device preparation has been employed during the second part, leading to a strong suppression of the background signal. Quantum transport measurements at T=4K on manganese-functionalized CNTs show a very regular pattern of Coulomb diamonds, indicating only a mild disturbance of the quantum dot's electron system by the covalent bond. Moreover, the charging energy reveals a wave function extending over the entire device dimensions. However, at T=30mK in the tunneling current a strong noise emerges, when repeatedly measuring over an hour while keeping external biases constant. Additionally, these time traces are superimposed by a long-term background, which is removed by a correction algorithm plus a subsequent digitization. The remaining signal reveals a random telegraph signal (RTS) which is extensively studied and from its statistics the equivalent temperature of T=654mK for the excitation of the system is extracted. The quantum transport experiments conducted on cobalt-functionalized CNTs show a much better data quality of the coulomb diamonds, which is ascribed to the alteration in the device's preparation. From the line shape of the Coulomb oscillations as well as from the Coulomb staircases an electron temperature of about T=500mK is extracted. Moreover, a magnetic field dependence of the stability diagrams is apparent, attributable to Zeeman splitting. The respective Landé factor of g=1.73 is, compared to similar CNT quantum dot systems, unusually low. It is as attributed to an increased spin-orbit interaction between the conduction electrons and the cobalt's nuclei. The respective time traces exhibit or lack an RTS signal, depending on their external biases. Regarding the Coulomb diamonds, an essential prerequisite for the occurrence of an RTS is the proximity to a resonance, which is equatable to a high sensitivity of the quantum dot detector. Considering the available energy, the underlying process that is the cause for the emergence of the RTS is ascertained to be an internal excitation of the antiferromagnetic states of the metallic core.