This article will present the technologies and markets trends, as well as the latest R&D developments, in MEMS and MOEMS for optical telecom. Today, the MEMS technology has found the optical telecommunication market as a new "killer applications" (following the IT, automotive and medical markets). This overview will describe the current state-of-the-art in MEMS manufacturing for optical functions in optical networks. Switching is a crucial function in the future all-optical networks and MEMS and MOEMS are ideal candidates for this. After an over-estimation of the needs in optical switching in 2000, components manufacturers are today targeting market where low and medium size switches are needed. In this article, a specific focus on switching will be made with comparison between the MEMS technology and others switching technologies (thermo-optical, LC, holography...). The current industrial offer for MEMS (3D, 2D and 1D) will be described. The presentation will also give market figures and forecast for MEMS and MOEMS in optical telecom.

A novel low cost technology for fabrication of micro-opto-electro-mechanical devices based on plasma enhanced chemical vapor deposition (PECVD) of dielectric materials is presented. Applying surface micromachining, we produce suspended dielectric membranes and cantilevers by involving a common photo resist as sacrificial layer. The intrinsic stress in the layers is adjusted using an interlacing of high (13.56MHz) and low (130kHz) plasma excitation frequencies in the PECVD. A diffraction image method and microstructures are used for the homogeneous stress evaluation. The stress of silicon nitride can be varied in a wide range between +850MPa compressive and −300MPa tensile and no dependence of the frequency on silicon dioxide intrinsic stress is noticed. Depending on lateral design and gradient stress variation, Fabry-Perot filter membranes with radius of curvature (ROC) between −1.7mm and 51mm as well as cavity lengths between 2.3μm and 13.5μm are implemented. Thus, convex, concave and plane membranes are produced. Furthermore, a thermally tuned air-gap Fabry-Perot filter with 8nm FWHM and a tunability of 15nm/mA is fabricated. Strategies of combining these filters with organic laser materials are developed. For this purpose, molecular glasses capable of amplified spontaneous emission (ASE) are chosen, e.g. the molecular glass 4-Spiro which shows an amplified spontaneous emission line at a low threshold of 3.2μJ/cm² pump laser power density.

Continuously tunable Fabry-Perot filters manufactured using multiple air-gap MOEMS technology are studied and presented. The InP/air-gap filters optimized for optical telecommunication systems using the third optical telecommunication window (1550nm) exhibit a wide tuning range of 142nm and an extremely wide stop-band of 550nm (1250nm-1800nm). The tuning is continuously adjustable requiring ultra-low actuation voltages between 0V (1599nm) and 3.2V (1457nm). The filters are based on a relatively simple vertical structure which is fabricated by few surface micro machining steps. No mirror alignment or subsequent micro mounting are necessary facilitating a compact batch process production.

Wavelength Division Multiplexing has become a leading technology for long haul transmission systems which operate at 1550 nm wavelength. One of the key components of such systems are tunable filters. Beside low insertion loss, polarisation insensitivity and large tuning range there is a strong demand for cost effectiveness and reliability. Two-chip micromachined filters are very promising candidates to fulfil these demands. In this paper we present and discuss a tunable optical filter structure which uses a simple bulk-micromachining process based on low-cost dielectric Bragg mirrors. The tuning is achieved by current induced thermal heating of the membrane suspensions. Common micromachined tunable optical filters either employ semiconductor Bragg mirrors with current induced heating or dielectric membrane mirrors with electrostatic actuation. The new concept combines the advantages of both types, the low-cost dielectric material and the simple actuation principle by current flow to create a best-of-breed two-chip solution. The alignment process of the two-chip cavity has been simplified to the point where a simple place-and-fix strategy can be applied. By matching the exciting Gaussian input beam to the stable half-symmetric cavity a fiber coupled and packaged tunable optical filter has been realized based on this concept. These micromachined tunable membranes are in general applicable to a wide variety of tunable components for wavelength division multiplexing systems, such as tunable optical filters, receivers and vertical cavity surface emitting lasers (VCSEL).

Design, manufacture and reliability of 2D MEMS optical switches 2D Optical switches are an ideal solution for several optical switching applications in telecommunications including optical cross-connects, reconfigurable optical add-drop multiplexers and fiber-optic protection switching and monitoring. In this paper we address aspects of the design and manufacturing of 2D MEMS based optical switches. Important design areas such as MEMS, optics, packaging and optical performance are discussed. Reliability is an extremely important aspect for all devices used in telecom systems. We will address potential reliability issues as well as their resolution and verification.

Micro Opto Electro Mechanical Systems (MOEMS) gain more and more importance in technical applications. The combination of optical actuators and micromachined silicon technology arise possibilities to realize equipment in high volumes for reasonable prices, that have formerly been expensive laboratory equipment. This paper reports on the realization of a spectrometer in MOEMS technology. It is based on a scanning mirror chip with a grating structure on top. Thus a spectrometer was realized, on which the wavelength range can be selected. The resolution is not limited by line width of a multisensor detector, as it is the case for state of the art low cost spectrometers. A single detector is used, cheaper than arrays and available for all wavelength ranges. The setup can be small and light, the grating withstands shocks and vibration much better than a classical spectrometer. The grating moves with a frequency of 500 Hz respectively 1000 Hz, a whole spectrum is acquired within milliseconds. The resolution is given by the grating line density and the spectrometer dimensions, as it is valid for every single detector spectrometer. Depending on the number of systems built, a price of the system can be expected significantly below those of low cost systems with fixed grating.

The state-of-the-art characteristics of micromachined polycrystalline SiGe microbolometer arrays are reported. An average NETD of 85 mK at a time constant of 14 ms is already achievable on typical self-supported 50 μm pixels in a linear 64-element array. In order to reach these values, the design optimization was performed based on the performance characteristics of linear 32-, 64- and 128-element arrays of 50-, 60- and 75-μm-pixel bolometers on several detector lots. The infrared and thermal modeling accounting for the read-out properties and self-heating effect in bolometers resulted in improved designs and competitive NETD values of 80 mK on 50 μm pixels in a 160x128 format at standard frame rates and f-number of 1. In parallel, the TCR-to-1/f noise ratio and the mechanical design of the pixels were improved making poly-SiGe a good candidate for a low-cost uncooled thermal array. The technological CMOS-based process possesses an attractive balance between characteristics and price, and allows the micromachining of thin structures, less than 0.2 μm. The resistance and TCR non-uniformity with σ/μ better than 0.2% combined with 99.93% yield are demonstrated. The first lots of fully processed linear arrays have already come from the IMEC process line and the results of characterization are presented. Next year, the first linear and small 2D arrays will be introduced on the market.

Novel micro all optical devices (MOD) and micro electro-optical devices (MEOD) are proposed for 2-D optical cross-connect. The MOD and MEOD consist of an array of control units and polarization beam splitters (PBS). The control units for the MOD and MEOD are optical control units (OCU) and electro-optical control units (EOCU), respectively. The proposed systems will either pass the light straight through or deflect it by 90 degrees, depending on the input of the control units.

We propose the use of digital holography (DH) as a metrological tool for inspection and characterization of MEMS structures. We show that DH can be efficiently employed to assess the fabrication process of micro structures as well as to test their behavior in operative conditions. DH allows reconstructing both the amplitude and phase of microscopic objects and, compared to traditional microscopy, it provides quantitative phase determination. We demonstrate that DH allows determination of full field deformation maps that can be compared with analytical and/or numerical models of the deformed microstructure. Application of DH on structures with several different geometries and shapes, like cantilever beams, bridges and membranes is reported and result will be discussed. Dimensions of the inspected microstructures ranging from 1 to 50μm. Examples of application are presented were DH allows determination with high accuracy out of plane deformations due to the residual stress introduced by the fabrication process. An optical set-up for recording digital holograms based on a Mach-Zehnder interferometer was adopted and a laser source which wavelength is λ=532nm was employed. The light reflected by the object under investigation was made to interfere with a plane wave front. Holograms were recorded by a CCD array with 1024 x 1280 square pixels with 6.7 μm size. A mirror mounted on a piezo-actuator was inserted along the reference arm of the interferometric in order to introduce controlled phase steps and to employ phase shifting technique. This technique allows suppressing both the zeroth-order and the conjugate wave-front in the numerical holographic reconstruction process. A method for compensating numerically curvature of the wave front and introduced by the microscopic objective lens is proposed and discussed.

In this paper, we present a method for the internal stress characterization of silicon membranes with silicon oxynitride thin films (SiO_xN_y) deposited by PECVD (plasma enhanced chemical vacuum deposition). Connecting the interferometric measurements (Twyman-Green interferometer) of out-of-plan displacements of SiO_xN_y-loaded membranes with evaluation of micromechanical parameters (Young's modulus, Poisson ratio) obtained by nanoindentation we evaluated the residual stress of SiO_xN_y thin films via point-wise deflection technique. The magnitude of stress is monitored as a function of the refractive index of SiO_xN_y establishing the relationship between the optical and micromechanical properties of deposited films.

Reduction in the size of produced parts, increases the difficulty for precise manufacturing observation-processes and it makes manufacturing control cycles even more complex. Among all the production steps for micro-systems, assembly seems to be specially affected with this manufacturing handicap. Usual sensors used for the macro-world have to be modified or redesigned in order to address its use for the micro-world. This document presents the integration of a white light interferometer into a flexible fibre-scope used already for process monitoring purposes and which is mounted into a gripping-tool. The goal is to achieve a linear measurement between a gripping-tool and a target-part during the assembly process of hybrid micro systems.

In this paper we assess the replication of micro-optical structures through vacuum casting. To that aim we have replicated, besides optical components and structures fabricated with DLP a variety of other optical components: micro-jet lenses, glass gratings, glass lenses and hybrid integrated systems. Shrinkage is always present on the replicated elements and therefore must be compensated in the master element, if one wants to have correct final dimensions. Furthermore it is of great importance that the replica is crystal-clear and without flow lines or other distortions. This can be obtained by tuning the different process parameters and by working with different types and qualities of polyurethane. In this paper we will highlight our findings on the assessment of the vacuum casting technology with respect to shrinkage, replication quality and transmission efficiency.

We have extended the technology of fabrication of optical spherical mirrors by using single-mask bulk micromachining to fabricate highly-uniform spherical arrays of micro-mirrors and to mold polymer-on-glass microlenses. The arrays fabricated feature 100% optical fill factor and very high field uniformity of optical characteristics of individual micro-mirrors (lenses). The technology is specially suitable for the fabrication of uniform arrays of spherical mirrors with small numerical apertures for use in Hartmann-Shack wavefront sensors. Optical tests with the hexagonal array of molded microlenses with pitch of 300μm and focal length of ~30mm demonstrated that the contribution of microlens imperfections into the wavefront reconstruction error does not exceed λ/50 rms.

Moulding of plastics enables fluidic and optical features to be integrated into a single element. This is particularly an advantage for product designs that impose space and weight constraints. Therefore, the use of plastic for biomedical and non telecommunications orientated optical applications continues to grow as design engineers take advantage of the ease of fabrication and the material flexibility. LIGA presents itself as a method ideally suited for the production of moulds for the manufacture of plastic microcomponents. Although LIGA is synonymous for lithography using synchrotron radiation x-rays, many other lithography and non-lithography methods for master production have been developed in the last few years, offering cost effective solutions to template production. These include UV LIGA methods, where deep resists such as SU-8 and AZ 4562, are employed for the master production. In addition, excimer laser micromachining offers a cost effective and efficient method for master fabrication, which later forms a template for electroforming. Furthermore, the use of Advanced Silicon Etching methods to prestructure silicon templates for electroforming, allows to the production of stepped mould inserts, which are particularly useful for microfluidic applications. This paper provides an overview of the different technologies, emphasizing the strengths and application areas of the different master structuring technologies. Considerations for the electroforming of microstructured mould inserts are also presented.

Fabrication processes of microdevices and integrated microsystems are indispensable for the development of Micro-Electro-Mechanical Systems (MEMS). Reduction lithography becomes an important step in many new applications requiring ultra thick photolayers, large Critical Dimensions (CD) and tight control limits. For this market segment, the ASML SA 5200 reduction step-and-repeat system is a cost-effective tool for the manufacture of advanced microelectronics, MEMS, and Integrated Circuits (ICs). Along with this trend, manufacturing and development engineers, in order to better predict process interactions and better estimate process manufacturing, increasingly utilize modeling and numerical simulations. This paper discusses the simulated and experimental lithographic performance of an i-line step-and-repeat system by using photosensitive Durimides^TM a photopolymer developed and commercialized by Arch Chemicals. These photopolymers are negative acting self-priming Polyimide precursors with a high photosensitivity, which provide thick layer exposure solutions with a wide process window. The excellent adhesion of Durimide^TM films makes these materials suitable for MEMS, buffer-coat, and packaging applications. The range of film thicknesses used is from 6 μm up to 80 μm. Process windows for the different thicknesses are investigated and discussed in terms of Exposure Latitude (EL), Depth Of Focus (DOF), and Size linearity. The lithography simulator PROLITH/2 with thick resist option has been used for all modeling activities in this work. Also, an extensive comparison is made between simulated and experimental data.

Aiming at correcting chromatic aberrations in a far-infrared band, the fabrication of a hybrid microlens array with one-step lithography is proposed, by using a coding grey-level mask. The designed hybrid microlens consists of a refractive microlens and a diffractive microlens in physics. Its structure parameters, in order to achieve the best correction of chromatic aberrations, are evaluated and optimized with the software OSLO to design the layout the grey-level mask. Based on the theory of partial coherent light, the photoresist exposure model and development model, the profile of hybrid microlens in the photoresist have been simulated, the nonlinear errors in the lithography process can be pre-compensated by correcting the mask design. A hybrid microlens array is fabricated through use of the designed mask.

To have better understanding of the effects of using different epoxies as the encapsulation and/or underfill epoxies on the fatigue life of flip chip packages, finite element analysis was conducted. The finite element analysis software, ANSYS, was used to model flip chip packages with and without underfill and encapsulation and to run thermal testing simulations. The results revealed that the package with the longest fatigue life was the one with the underfill epoxy only. Packages with both underfill and encapsulation epoxies had shorter fatigue life, while packages with the encapsulation epoxy only had the shortest fatigue life. The use of the underfill epoxy with higher Young’s Modulus and lower viscosity and CTE reduces the thermal shear stress experienced by the solder joint, thus lengthening its fatigue life.

Ag filled isotropic conductive adhesives (ICAs) have been investigated as promising alternatives for lead-containing solders in surface mount technology (SMT) application. However, one serious concern is the electro-migration of the silver filled in the ICAs, especially when used in high density interconnection assembly. In the present study, electro-migration resistance and contact resistance of ICAs containing Ag-Sn alloys as conductive fillers were investigated. It was found that electro-migration resistance depended on the Ag-Sn ratio and that Ag-Sn alloys containing 25 - 75 mol% of Sn had excellent electro-migration resistance though their contact resistance was rather high, compared with silver. To improve their contact resistance, a mixture of Ag-Sn alloy and Sn-Bi alloy was also investigated. The mixture effectively combined electro-migration resistance with lower contact resistance. These new ICAs and conventional ICAs (as reference) were evaluated for SMT, using chip components with several kinds of terminations for their stability in both contact resistance and adhesion strength during reliability tests. From the test results, it can be concluded that the new ICA is potential material for SMT application.

The test procedures and experimental results for calibration of a 2-D piezoresistive stress sensor using a four-point bending (4PB) fixture are reported. Focuses have been made on the (100) silicon test chip due to the fact that it is the most commonly used in the current microelectronics industry. The sensors on the (100) test chips were able to accurately measure plane stress components in a temperature compensated manner. The resistance of stress sensors was found to vary linearly with the applied stress. The piezoresistive coefficients were calculated and found to coincide with the reported values for silicon. A further study of the thermally induced stresses is also included in this paper to determine the resistance change that varies linearly with temperature.

This paper is dealing with the field simulation problems of MEMS structures. Both thermal and electro-static fields are considered. Two simulation algorithms are investigated in details: the Fourier transformation method applied to multi-layer structures and the successive node reduction algorithm belonging to the family of FDM methods. Extensions of these methods are discussed, e.g. the application of the Fourier method to mixed lateral boundary conditions and methods for physical level/network model level co-simulation.

The design of a novel mounting substrate for high power diode laser bars is presented. This substrate is combining the high thermal conductivity of diamond with the property of being able to adjust its coefficient of thermal expansion (CTE) to that of the laser material GaAs. Such a unique feature has become possible by attributing to the hard material diamond an artificial ductility by laser cutting of stress relieving openings in the diamond substrates. Combining two of these substrates in a sandwich with a middle layer of copper, one is able to realize a desired CTE just by choosing the right copper layer thickness. Based on the results of 3D-FEM calculations, some of these diamond-copper-diamond substrates have been produced with different copper thicknesses. The technique of electronic speckle pattern interferometry (ESPI) has been employed to measure the average CTE of these substrates. For diamond thicknesses of 0,3 mm, a copper foil thickness of 0,05 mm enabled a CTE-match with GaAs. A nearly stress free state in the laser bars mounted on these substrates has been demonstrated by photocurrent spectroscopy.

For optical parallel fibre modules (PFM), efficient cooling is vital in order to fulfil reliability and performance requirements. The environment where these devices are to be used typically exhibits a wide variation in temperature, airflow and available space. Using optional external heat sinks attached on this device is a simple method to achieve a satisfactory cooling from a thermal and fabrication point of view. A selection of external heat sinks with cooling elements consisting of pins, flanges and foils have been evaluated experimentally on this device for varying air velocity (0-5 m/s). The thermal conductance of the device with attached external heat sinks is found depend essentially only on the thermal conductance of the bare module and the airflow exposed heat sink area. In addition, the attachment of heat sinks using adhesive films and the internal thermal properties of this type of devices are discussed.

The interfacial behavior of a flip chip structure under thermal testing was investigated using real-time moire interferometry. The maximum shear strain occurred at the silicon-epoxy interface. The shear strain variation increased significantly along the interface, with the maximum shear concentration occurring at the edge of the specimen. The creep effect was more dominant in the FR4-epoxy interface. To characterize the behavior of the interfacial crack, stress intensity factors and the strain energy release rate in the vicinity of the crack tip were used to conduct a qualitative study. A sharp strain gradient occurred at the crack tip. The stress intensity factors were dependent on temperature.