Hasegawa M.,FEMTO ST Institute |
Chutani R.K.,FEMTO ST Institute |
Boudot R.,FEMTO ST Institute |
Mauri L.,SAES Getters |
And 3 more authors.
Journal of Micromechanics and Microengineering | Year: 2013
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. © 2013 IOP Publishing Ltd.
Barrera N.,Polytechnic of Milan |
Biscari P.,Polytechnic of Milan |
Urbano M.F.,SAES Getters
European Journal of Mechanics, A/Solids | Year: 2014
We study a macroscopic homogenized model of shape memory alloys. Starting from the Souza-Auricchio model, we put forward some modifications fit to improve the capability of the model to predict and estimate the onset of functional fatigue in the material. More specifically, we consider the presence in the Helmholtz free-energy density of a macroscopic plastic term in order to represent the fact that microscopic plasticity involves macroscopic strains. We further introduce an evolution of the transformation domain, in order to represent the fact that the more plastic slips occur, the more limited is the phase space available for further microscopic phase transformations. We finally generalize the functional dependence of the rate of dissipation function in terms of the driving forces, in order to relax the previously introduced constraint that functional fatigue could arise if and only if microscopic phase transition occur. In this paper we discuss the constitutive consequence of the proposed modifications, we discuss the calibration of constitutive parameters by means of simple experiments, and evidence the qualitative agreement of the modeling predictions with the outcome of some reported experimental results. © 2013 Elsevier Masson SAS. All rights reserved.
Biscari P.,Polytechnic of Milan |
Urbano M.F.,SAES Getters |
Zanzottera A.,Polytechnic of Milan |
Zanzotto G.,University of Padua
Journal of Elasticity | Year: 2016
We develop a nonlinear, three-dimensional phase field model for crystal plasticity which accounts for the infinite and discrete symmetry group G of the underlying periodic lattice. This generates a complex energy landscape with countably-many G-related wells in strain space, whereon the material evolves by energy minimization under the loading through spontaneous slip processes inducing the creation and motion of dislocations without the need of auxiliary hypotheses. Multiple slips may be activated simultaneously, in domains separated by a priori unknown free boundaries. The wells visited by the strain at each position and time, are tracked by the evolution of a G-valued discrete plastic map, whose non-compatible discontinuities identify lattice dislocations. The main effects in the plasticity of crystalline materials at microscopic scales emerge in this framework, including the long-range elastic fields of possibly interacting dislocations, lattice friction, hardening, band-like vs. complex spatial distributions of dislocations. The main results concern the scale-free intermittency of the flow, with power-law exponents for the slip avalanche statistics which are significantly affected by the symmetry and the compatibility properties of the activated fundamental shears. © 2015, Springer Science+Business Media Dordrecht.
Paff J.,Spectra Materials Inc |
Urbano M.,SAES Getters
IEEE International Vacuum Electronics Conference, IVEC 2014 | Year: 2014
Cathodes were simulated in ANSYS, constructed and tested at Spectra-Mat, Inc. Goals of the simulation included development of parameters appropriate to cathode materials and development of an approach for fast warm-up (FWU) cathode simulation. Cathode model and simulation solutions will be presented and compared against the test results. © 2014 IEEE.
Attanasi G.,European Center for Training and Research in Earthquake Engineering |
Auricchio F.,University of Pavia |
Urbano M.,Saes Getters
Journal of Materials Engineering and Performance | Year: 2011
The mechanical behavior of superelastic springs is investigated in this study. The goal is to evaluate the device response and to exploit the material superelastic behavior, main concerns being material and geometrical response nonlinearity. The investigation is made of two parts, i.e., an experimental campaign and a numerical model proposal. Experimental tests have been performed on superelastic SMA coil springs considering load history in tension and compression for three different spring geometrical configurations. Tested specimens experience a maximum elongation larger than the original spring axis length. The response is not symmetric and under compression it is affected by buckling instability. Nevertheless, experimental results show a very good superelastic behavior with no damage and with negligible residual displacements. Numerical analyses have been performed to reproduce the experimental campaign results. A simple finite element model is proposed. Experimental and numerical result agreement is very good. The numerical model turns out to be a powerful design tool even for the very complex geometrical and material nonlinear conditions under investigation. Hence, it is proposed as a useful tool for spring design validation and response prediction. © ASM International.
Hasegawa M.,CNRS Femto ST Institute |
Chutani R.K.,CNRS Femto ST Institute |
Gorecki C.,CNRS Femto ST Institute |
Boudot R.,CNRS Femto ST Institute |
And 4 more authors.
Sensors and Actuators, A: Physical | Year: 2011
This paper reports on the Si-glass anodic bonding process to fill micro Cs vapor cells with a buffer gas (Ar or Ne) at a controlled pressure (up to 20 kPa), which is one of the technological key steps to fabricate Cs vapor cells for miniature atomic clocks. In the atmosphere of these gases, the applicable bonding voltage was not high enough to achieve strong bonding because of the electrical breakdown caused by ionization of the gas. To improve the bonding quality, an original two-step anodic bonding method was proposed. The first step of the anodic bonding, which intends to pre-seal the gas in microcells, is carried out in the presence of a buffer gas by applying a voltage lower than the breakdown voltage. Subsequently, the second bonding is performed in air at sufficiently high voltages to improve the sealing quality. By employing optical spectroscopy, it was demonstrated that the cells maintain the buffer gas at an appropriate pressure for atomic clock operation. The accelerated aging tests show that Cs vapor as well as the buffer gas remained in the cells without any significant change in the pressure, which allow us to estimate the lifetime of the cells to be at least 3 years. Further CPT experiments revealed that the buffer-gas pressure change is less than 6.13 × 10-4 kPa throughout the aging test at 125 °C for more than 3 weeks. These results show that these microcells are appropriate for applications to atomic frequency references. © 2011 Elsevier B.V. All rights reserved.