The article describes application of Level Set method for two different microfabrication processes. First is shape
evolution of during reflow of the glass structure. Investigated problem were approximated by viscous flow of
material thus kinetics of the process were known from physical model. Second problem is isotropic wet etching
of silicon. Which is much more complicated because dynamics of the shape evolution is strongly coupled with
time and geometry shapes history. In etching simulations Level Set method is coupled with Finite Element
Method (FEM) that is used for calculation of etching acid concentration that determine geometry evolution of
the structure. The problem arising from working with FEM with time varying boundaries was solved with the use
of the dynamic mesh technique employing the Level Set formalism of higher dimensional function for geometry
description. Isotropic etching was investigated in context of mico-lenses fabrication. Model was compared with
experimental data obtained in etching of the silicon moulds used for micro-lenses fabrication.
In this study we focus on the aluminium nitride (AlN). This material shows a large number of advantages associated with
good piezoelectric properties. Therefore, AlN is an excellent candidate for MEMS actuation where low dielectric loss,
low thermal drift and high signal-to-noise ratios are required. In this paper, the case of AlN driven cantilevers composed
of three thin layers deposited on the silicon substrate will be considered. Precise knowledge of physical and material
parameters of AlN applied in these simple elements are necessary for their further applications. However, up to now,
AlN still represents a technological challenge and many of its micromechanical and piezoelectric properties are not
precisely described. That is why, our study has been concentrated on determination of such parameters like the residual
thin film stresses, thermal expansion coefficient α and piezoelectric coefficient d31. In this paper the interactions between
the theoretical solution, the numerical FEM simulations and experimental results were performed. This hybrid
methodology allows to identify the main source of behaviors discrepancy between the physical and numerical model of
tested cantilevers. Obtained knowledge leads to optimization of the technological process and required parameters of
actuator functionality achievement by better understanding of the tested microdevices properties. In experimental
procedure, it was used nanoindentation tests for obtaining an elastic properties of AlN, interferometric techniques for
performing the static and dynamic measurements of cantilevers and scanning electron microscope for measuring
topography.
We describe the fabrication of wafer-scale alkali vapor cells based on silicon micromachining and anodic bonding. The principle of the proposed micromachined alkali cell is based on an extremely compact sealed vacuum cavity of a few cubic millimeters containing caesium vapors, illuminated by a high-frequency modulated laser beam. The alkali cells are formed by sealing an etched silicon wafer between two glass wafers. The technique of cell filling involves the use of an alkali dispenser. The activation of cesium vapors is made by local heating of the dispenser below temperature range causing degradations of cesium vapor purity. Thus, the procedure avoids negative effects of cesium chemistry on the quality of cell surfaces and sealing procedure. To demonstrate the clock operation, cesium absorption as well as coherent population trapping resonance was measured in the cells.
Integrated optic interferometric systems have been developed since many years and most of them are connected with
telecommunication. In case of our group research profile we are focused on integrated optic sensors technology. One of
possible application is the atomic force microscope (AFM). In the paper is presented the new concept that combines the
AFM with the integrated optic interferometer. In the AFM system a cantilever movement control is the most important.
The main goal of the project is improving sensitivity of the AFM by means integrated optic Michelson interferometer
(IOMI). The optical waveguide structure was fabricated by surface micromachining technique, based on sandwiched
silicon oxide and silicon oxynitride layers. The standard IOMI consist of two Y-junction in which one arm is playing the
role of reference arm and other the measuring arm. Such configuration requires four fiber-to-chip connections. Thus, in
our configuration, the integrated optic loop mirror in reference arm is fabricated. In the signal arm of our chip standard
Grin lens to form an illumination cantilever optical beam is used. In the paper some theoretical descriptions and
preliminary results are presented. The possibility of applying the heterodyned detection scheme in a IOMI as a step with
sensitivity improvement is described, also.
As the project is in progress, the paper is focused in the fabrication of the optical sensor. Next step will be optimization
of the electronic part to improve the z-axis sensitivity of the AFM.
The concept of the fabrication process of glass microlenses integrated with silicon and polymer replicas is presented.
These kinds of microlenses are formed using a silicon master which is wet etched in alkaline solutions (anisotropic
etching) and/or in acid solutions (isotropic etching). The control of the times and the selection of the solutions, joined
with the designs of the mask for conventional photolithography and the quality of the silicon wafers are the key for
obtaining the desired shapes and sizes. The fabricated moulds are used to replicate microlenses in polymer by the
standard well known replication technologies and also to fabricate glass microlenses integrated on a silicon frame.
In this paper vibration characterization of MEMS cantilevers are presented using lens-less in-line digital holographic
microscope (LDHM). In-line digital holography provides larger information capability with higher phase sensitivity,
and full CCD sensor area is utilized for real image reconstruction. In lensless in-line digital holographic microscope, a
highly diverging beam replaces the conventional microscope objectives to provide the required magnification. The
diverging wave geometry also reduces the effect of twin-image wave caused by the in-line holographic geometry. For
vibration analysis, the time averaged holograms were recorded corresponding to different vibration states of the
cantilevers. Direct numerical evaluation of the amplitude and phase information from single time averaged hologram
provides the full-field real time quantitative analysis. The experimental study of vibration measurements of Aluminum
nitride (AlN) driven cantilevers is performed. The full field study shows the simultaneous vibration behavior of many
cantilevers corresponding to same input conditions. Our study shows the shift in the resonant condition of cantilevers
both for first and second resonant frequencies. This kind of analysis is most suitable to optimize and monitoring the
fabrication process of cantilevers.
The subject of this paper is the use of aluminum nitride (AlN) as an actuation layer in MEMS/MOEMS systems. This
material shows a good piezoelectric properties related to deposition conditions. AlN is a promising candidate for the
acoustic wave devices, MEMS applications and sensors what have been already proposed. Up to now, AlN is still a
technological challenge and many of its micromechanical and piezoelectric properties are not precisely described. That is
why our study has been focused on the determination of the material parameters like Young's modulus, residual thin film
stress, piezoelectric coefficient d31 and mechanical behaviour of especially designed cantilevers. To ensure the optimum
design, functionality and reliability of those actuators the theoretical solution and the numerical simulations of
mechanical performance by the Finite Element Method (FEM) were performed. The created model of device takes into
account multiple film stacking. For the characterization it was chosen a full-field optical technique applied in a
multifunctional interferometric platform. Proposed set-up performs the measurement in static and dynamic regimes with
nanometer sensitivity and high spatial resolution. The hybrid method of analysis combining the experimental and
numerical results has been used to better understand the properties of these microdevices, facilitate their designing and to
optimize their technological process. The optimum goal is a developing of the high quality and reliable AlN-driven
cantilevers for use in MEMS/MOEMS.
We discuss on-going reliability studies of micro-optical components and assemblies as conducted in the EU FP6 Network of Excellence on Micro-Optics "NEMO". We focus on three case studies including first biaxial fatigue testing of micro-optical components, second reliability testing and quality control of MEMS and third micro-interferometric tomography for measuring optical fibre refractive index changes. For each of these case studies we discuss the dedicated measurement and characterization methods as well as first results and the perspectives for future research.
The goal of this study was the investigation of reliability of AlN driven cantilevers, operating as MEMS actuators. Some of the fabrication steps being critical in regards to reliability issues, these steps have been firstly optimized. Then the monitoring of fatigue effects produced by thermal loading (130° C) of cantilevers, introducing the evolution of micromechanical parameters has been obtained by Twyman-Green interferometry. The measurements of evolution of resonance frequencies and displacement amplitudes permit the estimation of the long-term stability of such AlN based actuators.
In the paper the new concept of fully integrated scanning confocal optical microscope on-chip is proposed. The operation of this microscope combines the 3-D transmissive scanning of VCSEL laser beam by use of two MOEMS scanners, and active signal detection, based on the optical feedback in the VCSEL laser cavity. The silicon-based electrostatically driven scanners provide controlled movement of two convex microlenses, working as an objective lens of microscope. Glass microlenses are monolithically integrated on movable silicon tables of scanners. The first results of technological investigation on the microscope components are presented.
There is a great need for techniques that will permit the evaluation of the micromechanical state of micro-electro-mechanical system (MEMS) devices, at all steps of manufacturing, with respect to material properties, as well as of lifetime and for monitoring mechanical performances of MEMS actuators. We propose a new approach, based on integrated optical read-out using a Mach-Zehnder interferometer (MZI), monolithically integrated on the top of an electrostatically rotatable micromirror loaded with the sensing arm of MZI. The working principle of MZI read-out is based on the local change of the effective refractive index of guided waves of MZI, induced by strains of the deformable structure. A single-mode buried channel waveguide based on the silica/silicon oxinitride/silica structure is used, presenting optical attenuation of 0.6 dB/cm. The coupling of the standard optical fiber to the waveguide is based on the V-groove technique, supplemented by micromechanical sawing of the silicon substrate. For TE polarization, the set of obtained parameters is a coupling efficiency of about 55% with a horizontal misalignment of ±0.5 µm, a vertical misalignment of ±0.7 µm, and angular precision of ±0.2 deg on <110> directions of the silicon substrate.
Micro-Electro-Mechanical Systems are nowadays frequently used in many fields of industry. The number of their applications increase and their functions became more complex and demanding. Therefore precise knowledge about their static (shape, deformations, stresses) and dynamic (resonance frequencies, amplitude and phase of vibration) properties is necessary. Two beam laser interferometry is one of the most popular testing methods of micromechanical elements as a non-contact, high-accurate method allowing full-field measurement. First part of the paper present microbeam actuators designed for MEMS/MOEMS applications. The proposed structures are the straight silicon microbeams formed by KOH etching of Si wafer. Aluminium nitride (AlN) thin films are promising materials for many acoustic and optic applications in MEMS field. In the proposed architecture the actuation layer is sandwiched between two metal electrodes on the top of beam. In the second part we describe the methodology of the actuator characterization. These methods applied are: stroboscopic interferometry and active interferometry (LCOS SLM is used as a reference surface in Twyman-Green interferometer). Moreover some results of FEM analysis of the sample are shown and compared with experimental results. Dynamic measurements validate the design and simulations, and provide information for optimization of the actuator manufacturing process.
A new concept of the fabrication process for glass microlenses (external diameter ED<1 mm, focal length a few millimeters), based on the silicon master mask-less anisotropic wet etching in KOH, vacuum anodic bonding and re-flow of borosilicate glass, followed by the precise wafer-scale polishing and DRIE has been presented. A single spherical microlens as well as an array of spherical microlenses with focal length between 44.8 and 8.6 mm and external diameter 0.35 to 0.985 mm have been repeatable manufactured.
There is a great need for techniques that will permit the evaluation of MEMS devices, in all stages of manufacturing, with respect to material and micromechanical properties. In this contribution we propose a new approach, based on the integrated optical read-out using a Mach-Zehnder interferometer, monolithically integrated into the PZT actuated membrane and electrostatically actuated torsional micromirror. The application of membrane-type structure is in the area of pressure sensors. The monolithically integrated MZI on movable torsional mirror seems to be an easy solution for monitoring mechanical performances during lifetime of micromirror.
While testing electrical properties in microsystems is a well-developed art, the testing of mechanical properties of MEMS devices is not. There is a great need for techniques that will permit the evaluation of MEMS devices, in all stages of manufacturing, with respect to material and micromechanical properties. In this contribution we propose a new approach, based on the integrated optical read-out using a Mach-Zehnder interferometer (MZI). MZI is monolithically integrated on top of a electrostatically rotatable micromirror loaded with the sensing arm of MZI. A single mode buried channel waveguide based on silica/silicon oxinitride/silica structure is used. It performs a low optical attenuation and a coupling efficiency of 55% from waveguide to a standard fiber, connecting MZI to outside world (light source and detector). The working principle of MZI read out is based on the change of effective refractive index of guided waves of MZI induced by displacement of the deformable structure, obtained via the elastooptic effect. The technology process steps with special emphasis to the fiber-to-waveguide coupling based on V-grooves is detailed here. Our goal is aiming to obtain an angular alignment of ± 0.2 deg. of V-groove walls with <110> directions and the vertical misalignment not, exceeding ± 0.6 μm.
In this article we present a new micromachined platform for coupling the optical fibers to waveguides of Mach-Zehnder interferometers, supporting fibers in the same wafer as a waveguide wafer. Using standard CMOS technologies, like a UV photolithography, KOH wet etching of Si(100) wafer, sputtering of metal layers, RIE etching the fabrication of a very precise platform is demonstrated.
In the last decade, the advances in the MEMS technology lead to the integration of optical structures with MEMS. This association between MEMS technologies and integrated optical structures may provide complex functionality such as sensing, modulation or switching. Optical MEMS integrated on silicon are very attractive in terms of potential for cheap mass production and compatibility with CMOS technologies. In this paper we present the technology of SiON waveguide fabrication including aspects of PECVD and micromachining. PECVD process optimisation in order to increase the waveguide performances is presented. Finally the integrated opto-mechanical sensing structures are discussed.
A gas analyzer based on chromatography method using silicon- glass components has been built. Its main components were made by using MAMS-like technology, and its conception is concurrent to the idea of an integrated silicon chromatography proposed by SC Terry.
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