Tarik Bourouina

Self-aligned vertical mirror and V-grooves applied to an optical-switch: modeling and optimization of bi-stable operation by electromagnetic actuation

Abstract High performance silicon-based, micro-optical switches are being developed for application to optical networks. The mechanical part was fabricated in a one-level mask step by bulk micromachining of (1xa00xa00) monocrystalline silicon with KOH. The resulting structure was assembled with a 100xa0μm-thick Permalloy piece and then, it was associated to a small magnetic circuit for its electromagnetic actuation. In order to avoid power consumption while holding ON and OFF states, a bi-stable operation principle is proposed. The bi-stable behavior is obtained by using a stable mechanical position due to the cantilever stiffness and a second magnetic stable position due to a permanent magnet. Switching operation is provided by electrical currents in windings. The aim of this paper is to present a study on modeling and optimization of this system by means of Finite Element Modelling (FEM) simulations, using ANSYS software. Iterative magneto-mechanical simulations are performed. Optimization of dimensions and material properties is presented.

The vibroscanning method for the measurement of micro-hole profiles

In this paper, we present technologies for measuring inner dimensions of small holes. In the first method with a single probe system, the electrical contact between a vibrating probe and the inner surface of a hole is detected and the duty factor of the contact is measured. Through controlled scanning by a probe with a constant duty factor, data on the ups and downs of the surface profile are obtained. To characterize inside profiles of micro-holes regardless of materials, we developed a new technology with a twin-probe system. With a silicon-based micro-twin probe 3 mm in length, a micro-hole with a diameter of around 125 µm was measured and the estimated imprecision of measurement on this set-up is smaller than 0.5 µm.

Self-aligned micromachining process for large-scale, free-space optical cross-connects

A new micromachining process for large-scale optical cross-connects is presented. It satisfies the high-accuracy optical alignment required for free-space optics. A self-aligned batch-process allowing the simultaneous fabrication of vertical mirrors and fiber guides is performed with only one-mask. This process is based on bulk micromachining of [100] silicon. A first demonstration is performed on a 2/spl times/2 elementary cell then, it is extended to the fabrication of larger mirror arrays. Promising performances such as insertion loss lower than 0.5 dB, sub-millisecond switching time (0.3 ms) and reliable operation (more than 20 million cycles) are demonstrated on a bypass switch. An improved fabrication process, leading to an increase of integration density is also presented. It is based on the combination of deep dry-etching and anisotropic wet-etching.

A new characterization tool for vertical profile measurement of high-aspect-ratio microstructures

We have developed a system for the measurement of the inner profile of high-aspect-ratio microstructures. This system uses silicon micro-probes with a sharp tip at their end and an integrated piezoresistive force sensor. The probes are 1 mm long with a cross-sectional area of 20 × 20 μm2, which allowed characterization of narrow and deep micro-holes having a radius as small as 40 μm. The measurement procedure utilizes an original algorithm, which prevents it from many unwanted phenomena. It is entirely automated by using a computer control.

Integration of two degree-of-freedom magnetostrictive actuation and piezoresistive detection: application to a two-dimensional optical scanner

A novel two-dimensional (2-D) optical-scanner device is presented. This device incorporates a highly magnetostrictive thin film with anisotropic properties, so that it can produce 2-D-actuation corresponding to bending and torsion vibrations. The magnetostrictive material is a TbFe-CoFe multilayer film, which has optimized properties for micro-actuators operating at low excitation magnetic fields. The new scanner also integrates an original 2-D piezoresistive detector realized in an easy fabrication process using integrated circuit (IC)-compatible technology. The detectors are able to selectively measure bending and torsional vibrations. This new device enables the synchronization of actuation and sensing for 2-D position control.

Magnetic actuation of bending and torsional vibrations for 2D optical-scanner application

Abstract This paper deals with a magnetically actuated microresonator as a test device for light deflection applications (optical scanners). 2D scanning of a laser spot was achieved with this device and an optical scanning window of nearly 24° was attained. Giant magnetostrictive thin films are used. They present the novel feature to produce wireless actuation in both bending and torsional modes, which can be decoupled at the corresponding resonance frequencies. In addition, depending on working conditions (bias field, magnetization orientation), the ratio between bending and torsional responses can be adjusted over a very large scale. We show how this ratio can be fixed by two methods: (i) by an appropriate choice of the initial state of the magnetic thin film during its deposition, and (ii) by a DC magnetic field, which is applied during the device operation. The mechanical characterization of the cantilever is presented. Anharmonic behavior due to large deflections was obtained. This nonlinear behavior is lessened with a folded-type mechanical structure. Torsional deflections up to 23 μm, corresponding to mechanical rotations of ±5.9° angles have been attained at a field as low as 3.5 mT, corresponding to only 2% of the anisotropy field. Bending deflection can be twice in similar conditions.

Application of a multilayered magnetostrictive film to a micromachined 2-D optical scanner

A novel two-dimensional (2-D) optical scanner has been designed, manufactured and characterized. This scanner features a large mirror (8/spl times/6 mm) and is therefore suitable for industrial applications where cheap optical sources and lenses are requested. This scanner uses a multilayer film for its actuation. This film is well known for its high magnetostriction. The mechanical design has been optimized using conventional mechanical considerations as well as finite-element simulations. The device has been characterized in two configurations. Depending on the direction of the applied magnetic field, the magnetostrictive properties of the active film or the electromagnetic force are selectively used. Using this last, total optical deflection angles of 32/spl deg/ and 11/spl deg/ for an applied magnetic field of 0.3 mT are obtained. The ratio of the corresponding resonant frequencies is around 4.5, allowing a nice scanning pattern. Compared to our previous prototype on the same project , the mechanical-magnetic sensitivity has been improved by about a factor 24 when the magnetostriction is used, and by about a factor 75 when the electromagnetic force is used.

Effect of direct current bias field and alternating current excitation field on vibration amplitudes and resonance frequencies of a magnetostrictively actuated bimorph microresonator

The dynamic behavior of magnetomechanical bimorph microresonators is analyzed. These resonators are composed of a sputter-deposited TbDy(CoFe)2 thin film on silicon cantilevers. This film has giant magnetostrictive properties. It is made anisotropic by postdeposition annealing under magnetic field. We prepared two samples with different orientations of the easy axis: along the cantilever width axis and with an orientation of 22°, respectively. Both bending and torsion modes of vibration can be excited by proper combination of external magnetic field and the direction of the easy axis. Vibration amplitudes and resonance frequencies are studied in those modes. Several experimental conditions are investigated. The dependence of vibration amplitudes on a magnetic dc bias field applied either along the hard axis or along the easy axis is studied. The bending/torsion vibration amplitude ratio was shown to be tunable over a very wide range, offering interesting practical applications. In addition, the dependence...

Mechanical nonlinearities in a magnetically actuated resonator

This paper presents mechanical characteristics of a silicon-based magnetic micro-actuator - a test device, which was developed for optical-scanner applications. A magneto-elastic bimorph is used for the actuation. Deflections over 20 µm have been measured in a torsion mode, for an excitation field of 3 mT. The effect of large deflections generated anharmonic behavior of the mechanical structure working near resonance. Experimental results are analyzed with reference to a theoretical model and by a comparison with FEM simulations.

Magnetostrictive Microactuators and Application to Two-Dimensional Optical Scanners

We have fabricated and studied magnetostrictive (MS) bimorph microresonators. They consist of silicon cantilevers coated with a sputter-deposited TbDyCoFe alloy thin film. This material has giant magnetostrictive properties and it also has strong anisotropy. As a consequence, the resonators exhibit a unique behavior, that is, they are capable of vibrating in both bending and torsional modes with only one excitation field. This unique property was used to build a novel two-dimensional (2D) optical scanner. This device operates at high frequencies (10–61 kHz) and exhibits an optical deflection angle of ±12° at an excitation field of 4 mT; this is only 2% of the saturation field of the MS material. Moreover, the contactless magnetic actuation enabled an easy wireless vacuum encapsulation that resulted in Q-factors of up to 1400 and improved the vibration amplitude to four times more than that in air.