Christophe Gorecki

French National Centre for Scientific Research, Lutetia Parisorum, Île-de-France, France

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Publications (131)53.57 Total impact

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    ABSTRACT: A process based on deep reactive ion etching (DRIE) has been developed and optimized for the fabrication of millimeter deep silicon cavities with smooth sidewalls. The process combines two approaches which involve an optimized etching process based on the classical Bosch process (Alcatel A601E equipment) followed by the use of an aqueous etchant solution of potassium hydroxide (KOH) to smooth the surface and remove the fluorocarbon contaminants remaining after the DRIE process. As DRIE highly depends on the opening size of the patterned etch mask, different opening sizes have been tested to completely etch through a 1.4 mm thick silicon wafer. Additionally, the effect of different etch-stop materials onto the sidewalls quality has also been characterized. Sidewall quality of etched-through cavities was characterized by scanning electron microscopy (SEM) and contact surface profilometry. This single-step DRIE etching followed by short exposure to KOH solution permits to smooth sidewalls and achieve a surface roughness as low as 50 nm, which is the roughness typically obtained with the Bosch process on standard depths.
    Sensors and Actuators A Physical 01/2014; · 1.84 Impact Factor
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    ABSTRACT: This letter reports on the development of an integrated micro-optical beam splitter that can be array-arranged. The proposed wafer-level fabrication, based on 45$^{circ}$ saw-dicing of glass substrates, allows rapid and low-cost processing. In particular, it leads to high compactness and possibility of wafer-level alignment/assembly, suitable for vertically integrated imaging micro-instruments. The device, including additional out-of plane reflection for extraction of sensing beam, can be as small as 1 ${rm mm}^{3}$.
    IEEE Photonics Technology Letters 01/2014; 26(1):100-103. · 2.04 Impact Factor
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    ABSTRACT: MicroElectroMechanical Systems (MEMS) represent an extraordinary technology that promises to transform whole industries and drive the next technological revolution. These devices can replace bulky actuators and sensors with micrometer scale equivalents that can be produced in large quantities by silicon micromachining. MEMS improved functionalities and potential capabilities have brought in range many different application fields, including optical communications, medicine, guidance and navigation systems, RF devices, weapons systems, biological and chemical agent detection, and data storage. Because the field of commercial MEMS is still in its infancy, there is nevertheless an important issue for new MEMS which still requires advanced research, i.e. MEMS reliability.
    09/2013;
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    ABSTRACT: VIAMOS benefits from advanced MOEMS technologies, enabling a new generation of miniature instruments. The challenge is to provide hand-held, low-cost, fully parallel spectral domain miniature OCT devices adapted for early diagnosis of cutaneous pathologies. VIAMOS will lean on the experience and results fostered from a previous European collaborative project, diffusing the technology to medical diagnostic applications. The consequence will be a significant upgrade by adding new features such as heterodyne detection and integrated swept source.
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    ABSTRACT: The wafer-level integration technique of PageWafer® (SAES Getters' solution for getter film integration into wafer to wafer bonded devices) has been tested in hermetically sealed miniature glass-Si-glass cells filled with Cs and Ne, e.g. for microelectromechanical systems (MEMS) atomic clock applications. Getter effects on the cell atmosphere are analyzed by quadruple mass spectroscopy and coherent population trapping (CPT) spectroscopy. The quadruple mass spectroscopy revealed that the residual gases (H2, O2, N2 and CO2) that are attributed to anodic bonding process are drastically reduced by the getter films while desirable gases such as Ne seem to remain unaffected. The impurity pressure in the getter-integrated cells was measured to be less than 4 × 10−2 mbar, i.e. pressure 50 times lower than the one measured in the cells without getter (2 mbar). Consequently, the atmosphere of the getter-integrated cells is much more pure than that of the getter-free cells. CPT signals obtained from the getter-integrated cells are stable and are, in addition, similar to each other within a cell batch, suggesting the strong potential of applications of this getter film and especially for its wafer-level integration to MEMS atomic clocks and magnetometers.
    Journal of Micromechanics and Microengineering 04/2013; 23(5):055022. · 1.79 Impact Factor
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    ABSTRACT: We present the preliminary design, construction and technology of a microoptical, millimeter-size 3-D microlens scanner, which is a key-component for a number of optical on-chip microscopes with emphasis on the architecture of confocal microscope. The construction of the device relies on the vertical integration of micromachined building blocks: top glass lid, silicon electrostatic comb-drive X-Y and Z microactuators with integrated scanning microlenses, ceramic LTCC spacer, and bottom lid with focusing microlens. All components are connected on the wafer level only by sequential anodic bonding. The technology of through wafer vias is applied to create electrical connections through a stack of wafers. More generally, the presented bonding/connection technologies are also of a great importance for the development of various silicon-based devices based on vertical integration scheme. This approach offers a space-effective integration of complex MOEMS devices and an effective integration of various heterogeneous technologies.
    Proc SPIE 03/2013;
  • Physical Review A 02/2013; 87(2). · 3.04 Impact Factor
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    ABSTRACT: We report on a theoretical study and experimental characterization of coherent population trapping (CPT) resonances in buffer gas-filled vapor cells with push-pull optical pumping (PPOP) on Cs D1 line. We point out that the push-pull interaction scheme is identical to the so-called lin per lin polarization scheme. Expressions of the relevant dark states, as well as of absorption, are reported. The experimental setup is based on the combination of a distributed feedback (DFB) diode laser, a pigtailed intensity Mach-Zehnder electro-optic modulator (MZ EOM) for optical sidebands generation and a Michelson-like interferometer. A microwave technique to stabilize the transfer function operating point of the MZ EOM is implemented for proper operation. A CPT resonance contrast as high as 78% is reported in a cm-scale cell for the magnetic-field insensitive clock transition. The impact of the laser intensity on the CPT clock signal key parameters (linewidth - contrast - linewidth/contrast ratio) is reported for three different cells with various dimensions and buffer gas contents. The potential of the PPOP technique for the development of high-performance atomic vapor cell clocks is discussed.
    Physical Review A 02/2013; 87(1). · 3.04 Impact Factor
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    ABSTRACT: This work presents the development of an integrated micro-optical beam splitter that can be arranged in array, and based on saw-dicing of glass substrates. The latter allows a rapid and rather low-cost processing, and in addition leads to high compactness and possibility of wafer level alignments, suitable for vertically integrated imaging microinstruments. The device allowing additional out-of plane reflection for extraction of sensing beam can be as small as 1mm3.
    Solid-State Sensors, Actuators and Microsystems (TRANSDUCERS & EUROSENSORS XXVII), 2013 Transducers & Eurosensors XXVII: The 17th International Conference on; 01/2013
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    ABSTRACT: This paper reports on a compact table-top Cs clock based on coherent population trapping (CPT) with advanced frequency stability performance. The heart of the clock is a single buffer gas Cs-Ne microfabricated cell. Using a distributed feedback (DFB) laser resonant with the Cs D1 line, the contrast of the CPT signal is found to be maximized around 80°C, a value for which the temperature dependence of the Cs clock frequency is canceled. Advanced techniques are implemented to actively stabilize the clock operation on a zero-light-shift point. The clock frequency stability is measured to be 3.8 × 10¿(11) at 1 s and well below 10¿(11) until 50 000 s. These results demonstrate the possibility to develop highperformance chip-scale atomic clocks using vapor cells containing a single buffer gas.
    IEEE transactions on ultrasonics, ferroelectrics, and frequency control 11/2012; 59(11):2584-7. · 1.80 Impact Factor
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    ABSTRACT: This paper reports a batch-fabrication technique based on micromachining of silicon molds to create, after replication, arrays of microlenses characterized by high fill factors. The technique for single microlens generation (compatible with various types of replication or integration so that microlenses made of plastics or glass can be generated) was reported previously and showed its potential in terms of range of shapes and cost. However, subtleties of chemical etching makes more difficult the generation of high fill factor matrices when microlenses size overcomes several tenth of microns. Thus, in this paper, we describe the analysis of the chemical etching process and the corresponding adaptation of the mask design to achieve 100% fill factors arrays of microlenses. The process to fabricate arrays of microlens, with hexagonal footprints and element sizing from 30 to 270 microns and having NA from 0.2 to 0.4, is described. The hexagonal footprint shape of the elements in the arrays leads to 100% geometrical fill factor of fabricated structures. Isotropic etching used for the molds fabrication preserves the spherical profile of the resulting microlenses.
    Proc SPIE 05/2012;
  • Christophe Gorecki, Katarzyna Krupa, Michał Józwik
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    ABSTRACT: Micro-electro-mechanical systems are exposed to a variety of environmental stimuli, making a prediction of operational reliability difficult. Here, we investigate environmental effects on properties of piezoelectrically actuated microcantilevers, where AlN is used as actuation material. The environmental effects to be considered include thermal and humid cycling, as well as harsh electrical loading performed under normal conditions. Investigated properties are defined for the static and dynamic behavior of microcantilevers. A Twyman-Green interferometer, operating in both stroboscopic regime and time-average interferometry mode, is used as a metrology tool. The initial deflection and frequency changes of the first resonance mode of the microcantilevers are monitored during accelerated thermal aging tests, humidity tests, as well as harsh electrical loading and fatigue tests. Finally, the resonant fatigue tests accelerated by application of a high voltage are accomplished to evaluate a lifetime of microcantilevers. Monitoring the micromechanical behaviors of devices driven by AlN during the lifetime tests assists monitoring of their long-term stability. FEM calculation is used to identify critical areas of stress concentration in the cantilever structure and to further explain various failure mechanisms.
    Proc SPIE 05/2012;
  • Christophe Gorecki, Anand K. Asundi, Wolfgang Osten
    Proc SPIE 05/2012;
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    ABSTRACT: This paper reports the characterization of compact Cs CPT clocks based on a single buffer gas Cs-Ne microcell. Two different experimental set-ups are tested. The first set-up uses an externally-modulated 895 nm Distributed Feedback (DFB) laser source while the second one uses a directly-modulated custom-designed 895 nm Vertical Cavity Surface Emitting Laser (VCSEL) source. Using the DFB set-up, through reduction of the temperature-dependent collisional frequency shift and an active light shift suppression technique, a clock frequency stability of 3.8 × 10-11 at 1 s and greatly better than 10-11 at 60000 s is demonstrated. This proves the potential of single buffer gas Cs-Ne microfabricated cells for the development of miniature atomic clocks. Preliminar characterization of CPT resonances are reported with the VCSEL-based setup. It is expected that similar clock stability performances are achievable in this case.
    European Frequency and Time Forum (EFTF), 2012; 01/2012
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    ABSTRACT: The construction of optical micro systems imposes new challenges on assembly technologies. These include the handling of multiple heterogeneous substrates, low thermal budget for the establishment of bonding connections, the accurate alignment of the substrates during wafer stacking and the integration of special components such as discrete optical lenses. In order to address these problems, a hierarchic wafer/component bonding process is proposed for the assembly of a 3-axis confocal scanning microscope. Experiment results indicate that the 9 constitutive components of the microscope, which are made from materials with different thermal expansion coefficients, can be joined together at less than 400°C global temperature. The strength of the achieved bonding is comparable to standard anodic or fusion bonding and can withstand diverse back-end-of-line processes such as dicing or grinding. Besides, the hermeticity of the developed bonding process is validated by monitoring the static deformation of a leak-indicating membrane.
    01/2012;
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    ABSTRACT: This paper describes the thermal analysis of LTCC packaged Cs vapour cell for MEMS atomic clock. Aim is to maintain the temperature of the inner cell trapping the Cs vapour, which is a critical parameter for stable MEMS atomic clock.
    01/2012;
  • [show abstract] [hide abstract]
    ABSTRACT: Micro-electro-mechanical systems are exposed to a variety of environmental stimuli, making a prediction of operational reliability difficult. Here, we investigate environmental effects on properties of piezoelectrically actuated microcantilevers, where aluminum nitride is used as actuation material. The environmental effects to be considered include thermal and humid cycling, as well as harsh electrical loading performed under normal conditions. Investigated properties are defined for the static and dynamic behavior of microcantilevers. A Twyman–Green interferometer, operating in both stroboscopic regime and time-average interferometry mode, is used as a metrology tool. The initial deflection and frequency changes of the first resonance mode of the microcantilevers are monitored during accelerated thermal aging tests, humidity tests, as well as harsh electrical loading and fatigue tests. Finally, the resonant fatigue tests accelerated by application of a high voltage are accomplished to evaluate a lifetime of microcantilevers. Monitoring the micromechanical behaviors of devices driven by aluminum nitride during the lifetime tests assists monitoring of their long-term stability. Finite Element Modeling is used to identify critical areas of stress concentration in the cantilever structure and to further explain various failure mechanisms.
    Sensors and Actuators A: Physical. 11/2011; 171(2):306–316.
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    ABSTRACT: The paper presents the novel approach to an interferometric, quantitative, massive parallel inspection of MicroElectroMechanicalSystems (MEMS), MicroOptoElectroMechanical Systems (MOEMS) and microoptics arrays. The basic idea is to adapt a micro-optical probing wafer to the M(O)EMS wafer under test. The probing wafer is exchangeable and contains one of the micro-optical interferometer arrays based on: (1) a low coherent interferometer array based on a Mirau configuration or (2) a laser interferometer array based on a Twyman-Green configuration. The optical, mechanical, and electro-optical design of the system and data analysis concept based on this approach is presented. The interferometer arrays are developed and integrated at a standard test station for micro-fabrication together with the illumination and imaging modules and special mechanics which includes scanning and electrostatic excitation systems. The smart-pixel approach is applied for massive parallel electro-optical detection and data reduction. The first results of functional tests of the system are presented. The concept is discussed in reference to the future M(O)EMS and microoptics manufacturers needs and requirements.
    Proc SPIE 08/2011;
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    ABSTRACT: We report the characterization of Coherent Population Trapping (CPT) resonances in Cs vapor microcells filled with Neon (Ne) buffer gas. The impact on the atomic hyperfine resonance of some external parameters such as laser intensity and cell temperature is studied. We show the suppression of the first-order light shift by proper choice of the microwave power. The temperature dependence of the Cs ground state hyperfine resonance frequency is shown to be canceled in the 77-80°C range for various Ne buffer gas pressures. We preliminary demonstrate a 852 nm VCSEL-modulated based CPT atomic clock exhibiting a short term fractional frequency instability σ<sub>y</sub>(τ) = 1.5×10<sup>-10</sup> τ<sup>-1/2</sup> until 200 s.
    Frequency Control and the European Frequency and Time Forum (FCS), 2011 Joint Conference of the IEEE International; 06/2011
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    ABSTRACT: We report on the measurement of the dependence on temperature of the Cs clock frequency in microfabricated vapor cells filled with a mixture of Ne and Ar through the detection of Coherent Population Trapping (CPT) resonances. The temperature-dependence reduction of the Cs clock frequency is demonstrated in various cells. The inversion temperature at which the Cs clock frequency sensitivity is greatly reduced is found to be only dependent on the partial pressure of buffer gases and is measured to be lower than 80°C as expected with simple theoretical calculations.
    Frequency Control and the European Frequency and Time Forum (FCS), 2011 Joint Conference of the IEEE International; 06/2011