Design And Fabrication of Condenser Microphone Using Wafer Transfer And Micro-electroplating Technique

A novel fabrication process, which uses wafer transfer and micro-electroplating technique, has been proposed and tested. In this paper, the effects of the diaphragm thickness and stress, the air-gap thickness, and the area ratio of acoustic holes to backplate on the sensitivity of the condenser microphone have been demonstrated since the performance of the microphone depends on these parameters. The microphone diaphragm has been designed with a diameter and thickness of 1.9 mm and 0.6 $\mu$m, respectively, an air-gap thickness of 10 $\mu$m, and a 24% area ratio of acoustic holes to backplate. To obtain a lower initial stress, the material used for the diaphragm is polyimide. The measured sensitivities of the microphone at the bias voltages of 24 V and 12 V are -45.3 and -50.2 dB/Pa (at 1 kHz), respectively. The fabricated microphone shows a flat frequency response extending to 20 kHz.Comment: Submitted on behalf of EDA Publishing Association (http://irevues.inist.fr/handle/2042/16838

Design and fabrication of a miniature silicon microphone.

Silicon micromachining techniques were developed and used to batch fabricate a new type of heavily doped p-type (or p") silicon etch stop structure on glass that could be suitable for implementation of a condenser microphone. This involved study, development and use of techniques such as mask design, lithography, oxidation, diffusion, thin film deposition, electrostatic bonding, many different etching techniques, freeze drying, packaging/interfacing and testing. The condenser microphone structure consisted of a thin conductive diaphragm suspended above a back plate electrode in order to form a capacitive device. A narrow gap between the two plates constituted the capacitor plate separation and the air occupying the gap was the dielectric material. Two versions of this condenser microphone structure were fabricated with over all dimensions of 2mm2 x 8-12 Jlm, air gap sizes of 0.5-1.5 Jlm and lum thick diaphragms. The first design utilised a square diaphragm with an area of lrnm" while the second incorporated a circular diaphragm with a diameter of lrnm. Fabrication of the back chambers was implemented with an innovative double thermal oxidation technique. Signals of up to ImVIPa were obtained in the audio range for one of the circular p+ silicon microphone structures, but the frequency response measured was not consistent with the desired frequency response for a condenser microphone. Thin film thicknesses, silicon etch rates and electrode metallisation conductivity were characterised using specially designed test structures and innovative electrical and opticalmeasurement techniques so that fabrication accuracy and reproducibility could be monitored. As a result of the investigations carried out to develop novel p" silicon microphone structures, this thesis also identifies important areas which warrant further research, and provides a foundation, in terms of theory and fabrication, for future development of more advanced and appropriate p + microstructures for application as condenser microphones

Micro-mechanical sensor for the spectral decomposition of acoustic signals

An array of electret-biased frequency-selective resonant microelectromechanical system (MEMS) acoustic sensors was proposed to perform analysis of stress pulses created during an impact between two materials. This analysis allowed classification of the stiffness of the materials involved in the impact without applying post-impact signal processing. Arrays of resonant MEMS sensors provided filtering of the incident stress pulse and subsequent binning of time-domain waveforms into frequency-based spectra. Results indicated that different impact conditions and materials yielded different spectral characteristics. These characteristics, as well as the resulting sensor array responses, are discussed and applied to impact classification. Each individual sensor element in the array was biased by an in situ charged electret film. A microplasma discharge apparatus embedded within the microsensor allowed charging of the electret film after all device fabrication was complete. This enabled electret film integration using high-temperature surface micromachining processes that would typically lead to discharge of traditionally formed electret materials. This also eliminated the traditional wafer-bonding and post-fabrication assembly processes required in conventional electret integration approaches. The microplasma discharge process and resulting electret performance are discussed within the context of the MEMS acoustic sensor array.Ph.D.Committee Chair: Allen, Mark; Committee Member: Brand, Oliver; Committee Member: Michaels, Jennifer; Committee Member: Michaels, Thomas; Committee Member: Ready, Jud W

La technologie CMOS-MEMS pour des applications acoustiques

ISBN : 978-2-11-129183-6Recently, several teams have demonstrated a MEMS fabrication process based on a CMOS technology combined with a surface micromachining not requiring an etching mask. Unlike an earlier CMOS-based approach, where the release of MEMS structures is made by the silicon etching, the proposed technology etches oxide sacrificial layers to release the MEMS structures made of metallic layers of the CMOS process. In this project, we propose to fabricate MEMS-based acoustic devices with the AMS 0.35 μm standard CMOS process. The work is divided in two parts. In the first part, we have developed a complete etching process (etching type, etching time). After considering different aspects of the CMOS-MEMS technology available in the literature, the CMOS-MEMS process has been defined. This process consists of silicon dioxide sacrificial layers etching to release MEMS structures made by metallic layers of the AMS 0.35 μm CMOS process. Microstructures, like cantilever beams or fixed-fixed beams, have been used to develop and validate this process. The second part of the work was focused on the validation of the CMOS-MEMS process based on the AMS 0.35 μm CMOS technology for the fabrication of a capacitive MEMS microphone. A lumped parameters equivalent circuit, based on the electro-acoustic and electro-mechanical analogies, has been realized and used for the simulation of the capacitive MEMS microphone. The model takes into account various aspects of the industrial AMS 0.35 μm CMOS process (materials, dimensions, design rules,...). Each parameter of the equivalent circuit is determined with a help of analytical relations and simulation software based on the finite element method (ANSYS, CoventorWare). After the modeling, the layout of several MEMS microphones structures has been finalized in Cadence Virtuoso software and sent to AMS foundry. After the completion of the CMOS process, the etching process, studied previously, was applied in order to release the MEMS microphones and other test structures. Finally, electrical and mechanical measurements have been performed, firstly, on the MEMS microphones to determine its characteristics (resonant frequency, sensitivity,...) and secondly, on the test microstructures, to estimate the mechanical properties (Young's modulus and residual stress) of the metallic layers used to form the microphones structures. Thus, the equivalent circuit was improved according to obtained results and validated.Récemment, des travaux montrant la faisabilité des MEMS à base de la technologie CMOS complétée par un micro-usinage en surface sans masque ont été publiés. A la différence de l'approche plus ancienne où la libération des composants MEMS a été faite par une gravure du silicium, la technologie proposée consiste en la gravure des couches d'oxyde afin de libérer les couches métalliques issues de la technologie CMOS. Ce sujet de thèse propose donc de fabriquer des microsystèmes à vocation acoustique à partir d'une technologie CMOS standard : AMS 0.35 μm. Il sera, pour cela, composé de deux parties. Dans la première partie, il s'agit de développer un procédé technologique (déterminer le type de gravure, les temps de gravure, ainsi que les dimensions extrêmes réalisables pour les structures simples en technologie CMOS). En effet, après avoir étudié les différentes possibilités de la technologie CMOS-MEMS proposées dans la littérature, un procédé CMOSMEMS a été mis au point. Ce procédé consiste à graver une couche sacrificielle d'oxyde afin de libérer des microstructures constituées des couches métalliques issues de la technologie CMOS 0.35 μm d'AMS. Le procédé est premièrement testé sur des échantillons contenant des microstructures telles que des ponts et des poutres. La seconde partie du travail est consacrée à la validation du procédé CMOS-MEMS par un développement de structures MEMS acoustiques représentées par un microphone MEMS capacitif. Dans un premier temps, un microphone MEMS capacitif a été réalisé à partir de la technologie CMOS 0.35 μm d'AMS. Après avoir pris connaissance des différents aspects de la technologie CMOS 0.35 μm d'AMS (matériaux, dimensions, règles de dessin,...), une modélisation de microphone MEMS capacitifs est proposée grâce à la réalisation d'un schéma électrique équivalent basé sur les analogies entre les domaines électrique, mécanique et acoustique. Chaque paramètre de ce circuit est déterminé par l'intermédiaire de relations connues et par des logiciels de simulation utilisant la méthode des éléments finis (ANSYS, CoventorWare). Une fois les performances des microphones estimés à partir de ce circuit équivalent, un layout, représentant les différents microphones conçus, a été créé sous Cadence afin d'être envoyé au fondeur AMS. Dès la réception des échantillons, le procédé CMOSMEMS mise en oeuvre précédemment a été appliqué afin de libérer les structures des différents dispositifs. Ensuite, une série de caractérisations a pu être réalisée sur les premiers échantillons. Ces caractérisations visent à déterminer les performances des différents dispositifs fabriqués, mais aussi à estimer les propriétés mécaniques des différentes couches utilisées pour former la structure des microphones. De cette façon, le circuit équivalent pourra être validé ou être amélioré selon les résultats obtenus

Stacked Disks Resonators and Micromachined Microphones: Design and Modeling

In this thesis, the design and modeling of two micromachined systems are presented. The two devices are a novel stacked disks resonator designed for radio frequency systems and a set of microphones with released membrane designs for photoacoustic gas sensing for CO2 monitoring in demand controlled ventilation systems. For the novel stacked disk resonator design, an analytical model for the frequency separation is derived and verified using finite element analysis. The model provides useful insight into the coupling mechanisms of two or more vertically stacked disks connected via a central stem. One unsuccessful and one incomplete fabrication trial is presented and analyzed. In addition, an analytical model for support losses adapted from a simple model for soil-structure interaction is investigated and found useful for estimating the support losses. The novelty of stacked disk resonator is vertical integration of devices previously only demonstrated integrated in-plane. Vertical integration allows smaller footprint. Although fabrication has yet proved unsuccessful, useful models have been developed and insight into the coupling mechanisms gained. Two different designs of the miniaturized microphones have been designed, fabricated and characterized. Both designs feature released membranes, but of different thickness. They are designed for high sensitivity at low frequencies. Compared to a similar microphone published in the literature, the microphones presented here feature a doubling and thirty fold improvement in sensitivity for the frequency range of interest for the two designs

Index to 1984 NASA Tech Briefs, volume 9, numbers 1-4

Short announcements of new technology derived from the R&D activities of NASA are presented. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This index for 1984 Tech B Briefs contains abstracts and four indexes: subject, personal author, originating center, and Tech Brief Number. The following areas are covered: electronic components and circuits, electronic systems, physical sciences, materials, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences

Design and fabrication of electromagnetic micro-relays using the UV-LIGA technique

This dissertation reports a research effort to microfabricate an electromagnetic relay for power applications using a multilayer UV-LIGA process. A mechanically wrapped coil was used and very simple design for the magnetic circuit was adopted to increase the design flexibility and performances. The broad material selection and the capability of making high aspect ratio microstructures of the UV-LIGA make the technology best suited for fabricating microelectromechanical power relays. Fabrication of the device required significant advances in the optical lithography of SU-8 negative photoresist. Research proved that aspect-ratios up to 40:1 in isolated open field structures of thickness between 1 and 1.5 mm can be obtained a standard broadband UV source. The principal factor in this achievement is the reduction of internal stress during the post-exposure bake process that eliminates large plastic deformations present during standard bake procedures. Another challenging issue associated with producing high aspect ratio microstructures is the development narrow groves and deep holes in SU-8 lithography. To overcome this obstacle, megasonic agitation was applied to the developer bath, which resulted in faster development rates, more uniform development, and the ability to produce structures with higher aspect ratios. To date, this process has been used to achieve 100:1 aspect ratio open field features and 45:1 intact cylinder arrays. A multi-layer SU-8 optical lithography and metal electrodeposition process was developed to fabricate the relay. The design required implementation of high aspect ratio lithographic processing techniques to produce a tall nickel magnetic core and insulated magnetic cup in which a pre-wrapped solenoid would be placed for electromagnetic driving. After insertion of the solenoid a Ni-Fe actuator was bonded to the relay base to complete the device. To better understand the fatigue life of electroplated microstructures, a theoretical model was developed determine the possible fracture mechanics properties and fatigue life of LIGA fabricated nickel and nickel-iron alloys for use in microsystems applications. The prototype micro-relays were tested for the dynamic characteristics and power capacity. The experimental results have confirmed that reasonably large current capacity and fast response speed can be achieved using electromagnetic actuation and the multi-layer UV-LIGA fabrication process developed

Design et développement d'un capteur acoustique imprimé.

The objective of this work was to design and fabricate a low cost resonant capacitive acoustic sensor using printing techniques. It falls within the frame of a collaborative research project named “Spinnaker”, set up by TAGSYS RFID, a French company, which has planned to integrate this sensor to improve the geolocalization of their RFID tags. This work started with the design and optimization of the sensor using finite element modeling (COMSOL) and design of experiments (DOE). This first step has enabled the identification of the optimum set of parameters and demonstrated that the output responses were in accordance with the specifications. Then, we have developed the different technological building blocks required for the fabrication of the prototypes using jointly the 2D inkjet printing technique and 3D printing method. The functionality of the sensors has been characterized using both capacitive and acoustic measurements using laser Doppler vibrometer. Experimental results showed that sensitivity and selectivity were within the specifications and in good agreement with the modeling results. Finally, we investigated the piezoelectric approach which could be an interesting option to the capacitive one. Since no inkjet printable piezoelectric ink is commercially available, stable inkjet printable polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) ink has been developed. PVDF-TrFE layers were then successfully printed and characterized. The results were quite promising, however further improvements of the ink and printing process are required before stepping towards piezoelectric based device fabrication.L’objectif de ce travail était de concevoir et réaliser par impression un capteur acoustique capacitif résonant bas coût. Il s’inscrit dans le cadre d’un projet collaboratif de recherche intitulé « Spinnaker », défini par la société Tagsys RFID qui souhaite intégrer ce capteur afin d’améliorer la géolocalisation des étiquettes RFID. Ce travail a débuté par la conception et l’optimisation du design en utilisant la simulation par éléments finis (COMSOL) ainsi que des plans d’expériences (DOE : Design of Experiment). Cette première étape a permis de déterminer les paramètres optimaux et démontrer que les performances obtenues étaient conformes aux spécifications. Nous avons ensuite développé les différentes briques technologiques nécessaires à la réalisation des prototypes en utilisant conjointement l’impression 2D par inkjet et l’impression 3D. Nous avons vérifié la fonctionnalité de ces capteurs à l’aide de mesures électriques capacitives et acoustiques par vibrométrie laser. Nous avons démontré la sélectivité en fréquence des capteurs réalisés et comparé les résultats expérimentaux à ceux obtenus par simulation. Enfin, nous avons enfin exploré la « voie piezoélectrique » qui nous semble être une alternative intéressante au principe capacitif. En l’absence d’encre piézoélectrique commerciale imprimable par jet de matière, nous avons formulé une encre imprimable à base du co-polymère PVDF-TrFE et démontré le caractère piézoélectrique des couches imprimées. Les résultats sont prometteurs mais des améliorations doivent encore être apportées à cette encre et au procédé d’impression avant de pouvoir fabriquer des premiers prototypes

METAL MOLD FABRICATION BY PROTON BEAM WRITING AND ITS APPLICATIONS

Ph.DDOCTOR OF PHILOSOPH