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L'enjeu du travail est d'apporter une preuve de concept d'une architecture simplifiée de spectromètre en utilisant comme détecteur un réseau ultra-dense de NEMS associés à des éléments de circuit CMOS afin d'amplifier le signal in situ et de les adresser individuellement. Depuis plusieurs années, l'équipe du professeur Roukes à CALTECH a présenté une démonstration de spectrométrie de masse avec un NEMS. En parallèle, le CEA/LETI-MINATEC a développé une approche de fabrication dite VLSI de NEMS et de simulation électromécanique de ces éléments. Le premier but de la thèse est l'étude des phénomènes de bruit limitant la résolution en masse afin d'atteindre 10 Da au lieu des 1000 Da actuels sur des rangs de masses large allant de 10Da à 1MDa. Dans un second temps, La concept de spectrométrie de masse à base de NEMS est validé en comparant des spectres obtenus sur des nano-agrégats de quelques nanomètres de diamètres avec ceux fournis par un spectromètre de masse temps-de-vol conventionnel. Puis, un système d'adressage fréquentiel de réseau de NEMS est mis en place pour permettre la mesure quasi simultanée de 20 résonateurs. Enfin, le réseau de NEMS est inséré dans le banc de nano-aggrégats pour mesurer 20 spectres de masses en parallèle et valider une première preuve de concept. / The aim of the project is to bring a proof of concept of a simplified mass spectrometer architecture using an ultra dense network of NEMS in association with elements of CMOS circuit as sensors in order to amplify the signal in situ and adress them individually. Since several years, Roukes' team at Caltech has demonstrated a mass spectrometry with a NEMS. In parallel, the CEA/LETI-MINATEC has developped a fabrication approach called VLSI of NEMS and an electromecanical simulation method of these elements The first objective of this thesis is to study the noise phenomenon currently limiting our mass resolution in order to reach 10 Da instead of current 1000 Da on ranges going from 10 Da to 1MDa. In a second step, the concept of NEMS-based mass spectrometry is validated by comparison a nanometric cluster spectra with those from a conventional time-of-flight mass spectrometer. Then, a frequency addressing technique is applied on an NEMS array to allow for quasi simultaneous tracking of 20 different resonators. Finally, the NEMS array is inserted in the nanocluster bench to measure 20 spectra in parallel and validate a first proof of concept.

Microelectromechanical structures (MEMS) are used commercially in sensor applications and in recent years much research effort has been done to implement them in wireless communication. Electron beam lithography and other advancements in fabrication technology allowed to shrink the size of MEMS to nanomechanical systems (NEMS). Since NEMS are just a couple of 100 nm in size, highly integrated sensor applications are possible. Since NEMS consume only little energy, this will allow continuous monitoring of all the important functions in hospitals, in manufacturing plants, on aircrafts, or even within the human body. This thesis discusses the modeling of NEM resonators. Loss mechanisms of macroscale resonators, and how they apply to NEM resonators, will be reviewed. Electron beam lithography and the fabrication process of Silicon NEM resonator will be described. The emphasis of this work was to build a test setup for temperature dependant measurements. Therefore different feasible techniques to detect nanoscale vibration will be compared and the setup used in this work will be discussed. The successful detection of nanoscale vibration and preliminary results of the temperature dependence of the quality factor of a paddle resonator will be reported. A new approach to fabricate NEM resonator using electrofluidic assembly will be introduced. / Master of Science

L’extrême sensibilité des résonateurs mécaniques (NEMS) aux variations physiques à l’échelle atomique a permis le développement d’un nouveau concept de spectrométrie de masse à base de NEMS capable de mesurer la taille d’une particule unique. L’utilisation de large réseau de capteurs doit permettre à terme de palier la faible surface de capture des résonateurs tout en ouvrant de nouvelles perspectives pour les applications qui nécessitent des informa- tions sur la répartions spatiale des particules au sein du faisceau de mesure. Pour réaliser un spectromètre de masse à base de NEMS viable pour des applications de mesures réelles, il est impératif de développer une technologie de co-intégration NEMS CMOS permettant de fortement densifier le niveau d’interconnexion entre le capteur et l’électronique de lecture. Dans ce travail, nous présentons les premiers résultats mettant en oeuvre une telle techno- logie au travers de mesures de laboratoire et de la conception de circuit intégré co-intégré avec les résonateurs mécaniques. L’électronique de lecture capable de suivre la fréquence de nombreux NEMS simultanément est encore un facteur limitant la forte intégration nécessaire à la lecture de grand réseau de NEMS (>1000), les travaux de cette thèse mettent l’accent sur les problématiques liées à la lecture d’un grand nombre de résonateurs en termes de surface de silicium, de consommation et de performances. Nous présentons dans ce manuscrit une nouvelle architecture d’oscillateur hétérodyne bimode qui doit permettre de répondre à la fois au besoin de compacité tout en assurant le suivi simultané des différents modes de résonances des capteurs. Les travaux présentent également l’effort de modélisation et de co-simulation électro mécanique mis en oeuvre pour la conception des trois circuits. Enfin, nous présentons les résultats de mesure physique obtenue avec l’un des circuits revenus de fabrication et testé au sein du banc de spectrométrie de masse mise en place par les équipes du CEA/LETI. / The extreme sensitivity of nano electro mechanical system (NEMS) to atomic scale physical variations has led to the breakthrough development of NEMS- based mass spectrometry sys- tems capable of measuring a single molecule. Parallel sensing using thousands of devices will help to circumvent the small effective sensing area while opening new perspectives for applica- tions which require spatial mapping. While the development of NEMS CMOS co-integration technology is of paramount importance to achieve high density sensor arrays (>1000 devices), the readout circuitry capable of tracking NEMS resonator frequency shifts is still the limiting factor for the very large scale integration of individually addressed sensors. Moreover, in order to resolve the mass and position of an adsorbed analyte, single particle mass sensing appli- cations require to track simultaneously and in real time at least two modes of the resonators. This requirement adds complexity to the design of the overall system. To respond to the size, power consumption and resolution constraints linked to NEMS array measurement, this work focuses on the development of a new readout architecture based upon a dual mode heterodyne oscillator. This work also emphasis the effort made on the modelization and co-simulation of the NEMS devices with their readout electronics. Then, the manuscript describe the first results of the CEA/LETI CMOS co-integraton process developed to tackle the sensor density challenge of mass spectrometry application. Finally, present the two integrated circuit that were designed during this thesis. The first one was a proof of concept for the aforementioned oscillator architecture while the second one combine the architecture with the co-integration processus developed.

Au cours de ces dernières années, les progrès technologiques dans le domaine dumicro-usinage sur silicium ont permis le développement de Micro/Nano SystèmesÉlectro Mécaniques (M/NEMS) pour réaliser des capteurs ou des actionneurs.Dans le domaine des NEMS, dont les dimensions sont par définition submicroniques,les propriétés obtenues permettent de viser des applications en analyse biochimiqueou biomédicale. Il a été démontré que ces nano capteurs de masse (ou de force)atteignent des résolutions de l’ordre du zeptogramme (10−21 g) ou du picoNewtonce qui permet d’envisager des diagnostics précoces de certains cancers.Tous ces systèmes utilisent `a l’heure actuelle des moyens d’actionnement et dedétection électriques: de nombreuses équipes ont néanmoins démontré que la photoniqueactionne et détecte des mouvements de très faibles amplitudes, de l’ordredu femtomètre. Cette technologie hybride, circuit photonique associé au M/NEMS,offre potentiellement un gain de performance important par rapport aux moyens detransduction électromécanique.L’objectif de la thèse est le développement de la transduction optomécanique afinde détecter le déplacement de résonateurs NEMS. Un simple modèle analytique estproposé avec le support d’un simulation numérique. Les performances de transductionoptique sont comparées aux caractéristiques de la transduction électrique. Lacomparaison se base sur des critères objectifs (sensibilité, bruit, encombrement) puisde proposer des structures optomécaniques originales. Un banc de caractérisationoptique et mécanique est développé pour la caractérisation des échantillons dans unenvironnement contrôlé. Des mesures sur des composants fabriqués permettent demieux appréhender les contraintes de dimensionnement et, de façon plus général, latransduction optomécanique appliqué aux dispositifs NEMS. / During several last years, technological advances in the field of silicon micromachininghave initiated the industrial growth of Micro/Nano Electro Mechanical Systems(M/NEMS) for fabricating sensors or actuators.In the field of NEMS with sub-micron sizes, the properties allow for targeting applicationsin biomedical or biochemical analyses. It has been demonstrated that thesenano mass (or force) sensors achieve resolutions of the order of zeptogram (10−21 g)or picoNewton, hence allowing early diagnosis of certain cancers.Transduction schemes of these systems are currently based on electrical principles:many teams have nevertheless shown that photonics operates and detects tiny displacementin the order of femtometer. This hybrid technology, photonic circuitassociated with M/NEMS, potentially offers a significant improvement compared toelectrical transduction.The purpose of the thesis consists of developing the optomechanical transductionfor NEMS resonators displacement. A simple analytical model is presented togetherwith a numerical simulation. The performance of optical detection is compared toelectrical detection features. The comparison is based on objective criteria (sensitivity,noise, crowding) for designing original optomechanical structures. A dedicatedbench has been developed for the optical and mechanical characterizations of thesamples placed in a controlled environment. Measurements on fabricated devicesallow a better understanding of the design constrains and, more in general, of theoptomechanical detection applied to NEMS.i

La miniaturisation des composants électroniques conduit aujourd’hui au développement de capteurs ultra-sensibles. En particulier, les capteurs NEMS (systèmes électromécaniques nanométriques) ont maintenant une sensibilité suffisante pour détecter des molécules uniques. Ceci permet d’intégrer ces capteurs dans des dispositifs de spectrométrie de masse dont la particularité sera d’opérer en mode comptage de molécules uniques. Notre travail consiste à reconstruire le spectre de masse de la solution analysée à partir des signaux fréquentiels délivrés par les NEMS. Nous nous plaçons dans le cadre des approches problèmes inverses et des méthodes d’inférence bayésienne. Nous modélisons le système de mesure qui lie les inconnues aux signaux observés par un modèle graphique hiérarchique et nous introduisons un modèle de signal de type processus ponctuel marqué. Nous le comparons à un modèle de type processus à temps discret. Nous mettons en place un algorithme de déconvolution impulsionnelle intégrant une exploration de modèles qui réalise la détection des molécules analysées, l’estimation de leur masse et le comptage, afin de reconstruire le spectre de masse de la solution analysée. Nous présentons des résultats sur données simulées et sur des données expérimentales acquises au CEA/INAC sur des agrégats de Tantale en utilisant des capteurs NEMS développés au CEA-Leti/DCOS. Relativement aux méthodes de l’état de l’art, la méthode que nous proposons améliore le taux de comptage tout en gardant un taux de fausses détections suffisamment bas. Notre méthode délivre également les incertitudes sur les paramètres reconstruits. Enfin, nous développons le cas particulier de la reconstruction de spectres de masse discrets. / The miniaturization of electronic components drives the development of very sensitive sensors. In particular, NEMS (Nano ElectroMechanical Systems) are now sensitive enough to detect single molecules. This enables to use these sensors in order to design mass spectrometry devices, in an individual molecules counting mode. Our objective is to reconstruct the mass spectrum of the analyzed solution, based on the NEMS output signals. We use inverse problems approach and Bayesian framework. We model the acquisition system linking the unknown parameters to the observable signals with a hierarchical graphical model. We propose a marked-point process model of signal that we compare with discrete-time process one. We develop an impulse deconvolution algorithm which relies on a model exploration scheme. This enables us to detect the molecules, to quantify their mass and to count them in order to estimate the mass spectrum of the analyzed solution. We show results on simulated data and on experimental ones acquired in CEA/INAC using Tantalum nano-aggregates and devices developed in CEA-Leti/DCOS. Compared to state-of-the-art, our method offers high counting rate and keeps a low false detection rate. It also permits the computation of uncertainties on estimated values. Finally, we propose a derivation of the method to deal with the reconstruction of discrete mass spectra.

In this thesis, the design, fabrication and characterisation of graphene electromechanical resonators have been presented. Graphene features ultrahigh Young’s modulus and large surface to volume ratio that make it ideal for radio frequency (RF) components, sensors and other micro/nano-electromechanical systems (MEMS/NEMS). A novel batch fabrication process for graphene electromechanical resonators has been developed by using poly-Si film as sacrificial layer. Previously reported fabrication processes of graphene resonators use SiO2 as sacrificial layer only because graphene is visible on 300nm SiO2/Si substrate. However, the wet etching of SiO2 involves HF, which is not compatible with metal connections or SiO2 serving as dielectric or passivation layer in graphene NEMS devices. Moreover, the liquid surface tension during drying after wet etching could damage graphene bridges even critical point drying is used. Therefore, in this work, poly-Si is adopted as the sacrificial material. To facilitate the fabrication of graphene resonators, a poly-Si/SiO2/Si substrate has been designed and optimised to make graphene visible under optical microscope for the first time to the author’s knowledge. Chemical vapour deposition (CVD)-grown monolayer graphene sheet has been transferred onto the optimised poly-Si/SiO2/Si substrate and patterned into strips. Metal electrodes have been deposited by lift-off process to make electrical connections, which is prerequisite for integrating graphene resonator into practical devices. The graphene bridges have been released by etching the poly-Si layer with XeF2 in vapour phase, which completely avoids the capillary force induced damage to the graphene bridges. De-fluorination process has been performed by hydrazine reduction to recover graphene’s conductivity. This fabrication process is scalable for massive production of graphene electromechanical resonators, thus furthering their practical application. One-source current mixing characterisation setup has been constructed to test the graphene resonators. Besides the fundamental peak, the activation and enhancement of the second mode of doubly clamped resonator by electrostatic actuation have been observed for the first time. The second mode amplitude reaches 95% of the fundamental mode, whereas only odd higher modes of small intensity have been reported before in other MEMS/NEMS resonators actuated by electrostatic force or magnetomotive force. The findings in this thesis could lead to substantial increase of the sensitivity of sensors based on the graphene resonators. Modal analysis based on Euler-Bernoulli equation has been performed to understand the mechanism behind the activation and enhancement of the second mode. Finite element analysis agrees very well with experimental results and complies with the theoretical model. Finally, a set of novel alignment marks has been designed, which can be incorporated to process mechanically exfoliated 2D material flakes of micron size and irregular shape with conventional photolithography tools, as have been demonstrated by the successful fabrication of a graphene transistor. This optical alignment technique provides an alternative for prototype device development besides electron beam lithography to prevent electron-induced damage to fragile 2D materials.

The pressure between two parallel planar surfaces at equal electric potentials is derived using the modified Poisson-Boltzmann (MPB) equation to account for finite ion size. The effects of finite ion size are presented for a z:z symmetric electrolyte and compared with the pressure derived by the classical Poisson-Boltzmann (PB) equation. The pressures predicted by the two models differ more as the bulk ion concentration, surface potential, and ion size increase. The ratio of the pressures predicted by the two models is presented by varying the ion concentration, surface potential, ion size and distance of separation. The ratio of pressures is relatively independent of the distance of separation between the two surfaces. An elastic beam suspended horizontally over a substrate in liquid electrolyte is subjected to electric, osmotic, and van der Waals forces. The continuous beam structure, not a discrete spring, which is governed by four nondimensional parameters, is solved using the finite element method. The effects of ion concentration and electric potentials to the pull-in instability are especially focused by parametric studies with a carbon nanotube cantilever beam. The pull-in voltage of a double-wall carbon nanotube suspended over a graphite substrate in liquid can be less than or greater than the pull-in voltage in air, depending on the bulk ion concentration. The critical separation between the double-walled carbon nanotube (DWCNT) and the substrate increases with the bulk ion concentration. However, for a given bulk ion concentration, the critical separation is independent of the electric potentials. Furthermore, the critical separation is approximately equal in liquid and air. Stiction, the most common failure mode of the cantilever-based devices, is studied in a liquid environment, including elastic energy, electrochemical work done, van der Waals work done and surface adhesion energy. We extend the classical energy method of the beam peeling for micro-electro-mechanical systems (MEMS) in the air to an energy method for nano-electro-mechanical systems (NEMS) in liquid electrolyte. We demonstrate a useful numerical processing method to find the parameters to free the stiction of the beams and to obtain the detachment length of the beams.

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Since the introduction of Complementary-Metal-Oxide-Semiconductor (CMOS) technology, the chip industry has enjoyed many benefits of transistor feature size scaling, including higher speed and device density and improved energy efficiency. However, in the recent years, the IC designers have encountered a few roadblocks, namely reaching the physical limits of scaling and also increased device leakage which has resulted in a slow-down of supply voltage and power density scaling. Therefore, there has been an extensive hunt for alternative circuit architectures and switching devices that can alleviate or eliminate the current crisis in the semiconductor industry. The Nano-Electro-Mechanical (NEM) relay is a promising alternative switch that offers zero leakage and abrupt turn-on behaviour. Even though these devices are intrinsically slower than CMOS transistors, new circuit design techniques tailored for the electromechanical properties of such devices can be leveraged to design medium performance, ultra-low power integrated circuits. In this thesis, we deal with a new generation of such devices that is built in the back end of line (BEOL) CMOS process and is an ideal option for full integration with current CMOS transistor technology. Simulation and verification at the circuit and system level is a critical step in the design flow of microelectronic circuits, and this is especially important for new technologies that lack the standard design infrastructure and well-known verification platforms. Although most of the physical and electrical properties of NEM structures can be simulated using standard electronic automation software, there is no report of a reliable behavioural model for NEMS switches that enable large circuit simulations. In this work, we present an optimised model of a BEOL nano relay that encompasses all the electromechanical characteristics of the device and is robust and lightweight enough for VLSI applications that require simulation of thousands of devices. To verify the performance of the proposed model, complex logic circuits built exclusively with relays, and also, hybrid CMOS-NEM circuits are simulated and verified. Finally, these novel topologies are reviewed and discussed as low-power alternatives to current CMOS topologies.