DESIGN AND MICROFABRICATION OF A CMOS-MEMS PIEZORESISTIVE ACCELEROMETER AND A NANO-NEWTON FORCE SENSOR

DESIGN AND MICROFABRICATION OF A CMOS-MEMS PIEZORESISTIVE ACCELEROMETER AND A NANO-NEWTON FORCE SENSOR by Mohd Haris Md Khir Adviser: Hongwei Qu, Ph.D. This thesis work consists of three aspects of research efforts: I. Design, fabrication, and characterization of a CMOS-MEMS piezoresistive accelerometer 2. Design, fabrication, and characterization of a CMOS-MEMS nano-Newton force sensor 3. Observer-based controller design of a nano-Newton force sensor actuator system A low-cost, high-sensitivity CMOS-MEMS piezoresistive accelerometer with large proof mass has been fabricated. Inherent CMOS polysilicon thin film was utilized as piezoresistive material and full Wheatstone bridge was constructed through easy wiring allowed by three metal layers in CMOS thin films. The device fabrication process consists of a standard CMOS process for sensor configuration and a deep reactive ion etching (DRIE) based post-CMOS microfabrication for MEMS structure release. Bulk single-crystal silicon (SCS) substrate was included in the proof mass to increase sensor sensitivity. Using a low operating power of 1.67 m W, the sensitivity was measured as 30.7 mV/g after amplification and 0.077 mV/g prior to amplification. With a total noise floor of 1.03 mg!-!Hz, the minimum detectable acceleration is found to be 32.0 mg for a bandwidth of I kHz which is sufficient for many applications. The second device investigated in this thesis work is a CMOS-MEMS capacitive force sensor capable ofnano-Newton out-of-plane force measurement. Sidewall and fringe capacitance formed by the multiple CMOS metal layers were utilized and fully differential sensing was enabled by common-centroid wiring of the sensing capacitors. Single-crystal silicon (SCS) is incorporated in the entire sensing element for robust structures and reliable sensor deployment in force measurement. A sensitivity of 8 m V /g prior to amplification was observed. With a total noise floor of 0.63 mg!-IHz, the minimum detection acceleration is found to be 19.8 mg, which is equivalent to a sensing force of 449 nN. This work also addresses the design and simulation of an observer-based nonlinear controller employed in a CMOS-MEMS nano-Newton force sensor actuator system. Measurement errors occur when there are in-plane movements of the probe tip; these errors can be controlled by the actuators incorporated within the sensor. Observerbased controller is necessitated in real-world control applications where not all the state variables are accessible for on-line measurements. V

Automatic Microassembly System for tissue engineering- Assisted with top-view and force control

Master'sMASTER OF ENGINEERIN

Etude et développement d'un capteur de microforce pour la caractérisation de la nanofriction multi-aspérités en micromanipulation dextre

Sensor enabling to characterize the finger/object contact involved in dexterousmicromanipulation. Theoretical studies and finite elements simulations have lead tothe conception of this piezoresistive MEMS sensor composed of a central platformwith a micro-ball and surrounded by a compliant table. According to the simulationresults, this sensor is able to independently measure the normal and friction forces(crosstalk less than 1 %) with a good sensitivity. Several runs of fabrication allowedus to obtain usable devices. The mechanical structure of such sensors has beenvalidated by the measurement of resonance frequencies that are consistent with thesimulation results. The first experimental results in terms of force measurement werethen obtained through the development of a test bench (robotic structure, actuators,cameras, etc.). We were also interested in the problem of calibration of micro andnanoforce sensors using magnetic springs connected to measurable masses. In thiscontext, we developed an estimation strategy and a passive rejection of mechanicaldisturbances using a differential principle. This approach was applied to a nanoforcesensor based on the diamagnetic levitation and yielded promising results: a resolutionlower the nanonewton level could be obtained.L’objectif de cette thèse est le développement d’un nouveau capteur de forcemulti-axes destiné à mesurer les composantes de friction impliquées dans lecontact doigt/objet lors la micromanipulation dextre. Des études théoriques etdes simulations par éléments finis ont conduit à la conception de ce capteurMEMS piézorésistif composé d’une plate-forme centrale munie d’une microbille,entourée d’une table compliante. D’après les résultats de simulations, ce capteur estcapable de mesurer indépendamment les forces normales et de frottement (couplageréciproque inférieure à 1%) avec une bonne sensibilité. Différents runs de fabricationnous ont permis d’obtenir des dispositifs exploitables. La structure mécanique de cescapteurs a été validée par la mesure des fréquences de résonance qui sont en accordavec les résultats de simulation. Des premiers résultats expérimentaux en termesde mesure de force ont ensuite été obtenus grâce au développement d’un banc detest (structure robotique, actionneurs, caméras, etc.). Nous nous sommes égalementintéressés à la problématique de l’étalonnage des capteurs de micro et nanoforceà l’aide de ressorts magnétiques reliés à des masses mesurables. Nous avons, danscette optique, mis au point une stratégie d’estimation et de compensation passivedes perturbations mécaniques en utilisant un principe différentiel. Cette approchea été appliquée à un capteur de nanoforce basé sur la lévitation diamagnétique et aabouti à des résultats prometteurs : une résolution inférieure au nanonewton a puêtre obtenue

Etude et réalisation d'un prototype avancé de plateforme de mesure de micro et nanoforce par lévitation diamagnétique

La mesure de micro- et nano-force fait partie des mesures nécessaires à la caractérisation des interactionsou des propriétés mécaniques intervenant à l échelle micrométrique. Dans cette optique,nous avons poursuivi un travail de conception initié au Laboratoire d Automatique de Besançon en2002 pour développer un prototype avancé de capteur de micro- et nano-force par lévitation diamagnétique.Le transducteur force-déplacement de ce capteur est un microcapillaire rigide en verred une dizaine de centimètres. Ce microcapillaire est en lévitation passive stable dans l espace grâceà l action conjuguée de forces magnétiques et diamagnétiques créant ainsi un ressort magnétiquevirtuel. La mesure d une force externe appliquée à l extrémité du capillaire est rendue possible grâceà la connaissance de la mesure du déplacement du capillaire et de la raideur du ressort magnétique.La plage de mesure de ce capteur varie entre +-40 N avec une résolution de l ordre du nanonewton.Les avancées présentées dans ce manuscrit ont porté sur la détermination des efforts diamagnétiquesengendrés par l utilisation des plaques de graphite. Ce travail a permis une optimisation dudesign global du dispositif et son transfert à l entreprise STIL SA. De plus un processus d estimationpar déconvolution a été développé pour tenir compte du comportement dynamique du micro capillaireet des bruits de mesure du déplacement. Les domaines d applications potentiels de ce dispositifconcernent notamment la caractérisation des interactions mécaniques quasi-statiques pouvant intervenirentre deux micro-objets et la détermination de propriétés mécaniques propres à un micro-objet.The measurement of micro- and nano-force is necessary to characterize the mechanical propertiesand interactions occurring at micrometer scale. In this context, we work on an advanced design ofmicro- and nano-force sensor based on diamagnetic levitation initiated at Laboratoire d Automatiquede Besançon in 2002. The force-displacement transducer of this sensor is a ten centimeter long glassmicro capillary. This micro capillary levitates passively and stably thanks to the combined action ofmagnetic and diamagnetic forces which create a virtual magnetic spring. Measuring an external forceapplied to the end of the capillary is made possible through knowledge of the capillary displacementand the stiffness of magnetic spring. The measuring range of the sensor varies between +-40 N witha resolution about a nanonewton. Advances presented in this thesis focused on the determinationof the diamagnetic forces generated by the use of graphite plates. This work has allowed us tooptimize the overall design of the device and transfer it to our industrial partner STIL SA. Moreovera deconvolution estimation process was developed to take into account the dynamic behavior of themicro capillary and measurement noises. Potential fields of application of this device concern themechanical characterization of quasistatic interactions which may occur between two micro-objectsand the determination of intrinsic mechanical properties of a micro-objectBESANCON-Bib. Electronique (250560099) / SudocSudocFranceF

Préhenseurs, conditions et stratégies pour une micromanipulation de précision

Currently microsystems consist of more and more functionalities in even smaller volumes. Components size has then to be reduced as well, coming through micro- and then nanoscale. The industrial equipments dedicated to their fabrication and assembly have comparatively a huge size, but one observes now a new and welcome trend for reducing their overall dimensions. However the latest robotic technologies allow achieving nanometric resolution and precision of positioning. Microcomponents assembly is still yet badly controlled and many surprising effects can occur without understanding of the real phenomenon. In fact, below one millimeter size objects are becoming insensitive to gravity comparing to surface forces. The manipulation of such components needs new and innovative ways to control these forces and so on to allow the release. In this study pick and place operations have been analyzed with an adimensional parameter Γ. It represents the ratio of the forces that act at the "object – gripper" and "object – target surface" interface. The adhesion effect is then taken into account in a comparative manner. The advantage of such procedure is due to the large amount of uncontrolled or unknown parameters that are needed to evaluate the adhesive forces. The behaviors of the micro object during pick and place operations are then studied on the base of Γ. Characteristics allowing a reliable transfer can be extracted with focus on the ones that generate fewer disturbances on the position. Generalization of the models allows finally to study different manipulation principles. The conception of microgrippers needs to consider the adhesion effects. Thus a methodology is proposed. Its main point concerns the importance of a strong interaction between the designers of the different elements that are the component, the receiver and the gripper. In such a way optimal choices for the surfaces and principles of manipulation can be done. After having defined the main trends theoretically, the difficult evaluation of the adhesion effect in real conditions causes the need to check rapidly by experiments the feasibility of the pick&place operations. A micromanipulation setup has been developed in order to make comparative tests between the different gripper principles. Gripper characterization means in particular the measurement of the positioning errors induced during the placing step. Several gripper families were conceived during this study: microtweezers, inertial gripper based on adhesion, capillary grippers that use the condensation/evaporation of the relative humidity, electrostatic grippers as well as vacuum gripper. Experiments were conducted with polystyrene spheres of ∅ 50µm. A high sensitivity to the alignment between finger tip or gripper tip and micro object was observed. It concerns in fact mainly the need to limit the force applied on the component during manipulation. The gripper withdrawal direction has also showed to be of the most importance to control the operations and their reliability. Finally robotic assembly of MEMS components was realized to get a 3D structure. The methodology was experimented on this application. The importance of a close interaction of the different designers has been demonstrated. We proposed here an approach as well as the models allowing studying the main trends with taking into account the adhesion forces. The whole arrangement of the contact areas as well as each force present during the operations is included into the models. The interfaces characteristics can so be analyzed. This allows defining the optimal strategy. This study is a tool for the designer of microassembly equipment. With the proposed methodology we hope or rather give the opportunity to stimulate integration or combination of innovative micromanipulation principles