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Theses

Etude de la fiabilité de MEMS à fonctionnement électrostatique

Abstract : This thesis summarizes the work concerning reliability testing of electrostatic capacitive- and ohmic-type RF MEMS switches developed by the CEA-Leti. In the first chapter the measurement of stiffness by the nanoindentation technique on real MEMS switches are completed by AFM, SEM and FIB observations in order to explain the electrical behavior of different wafers of the ohmic-type switches. The second chapter presents the results of the characterization of the structural and physical properties of the dielectrics, which are typically used in our ohmic- and capacitive-type RF MEMS switches. Elemental analyses confirm that all SiNx and SiO2 samples fabricated by the PECVD technique have inferior quality compared to their high-temperature counterparts.The conduction mechanism are identified in PECVD SiNx and SiO2 by measuring I-V curves on MIM capacitors. For both SiNx materials, that is deposited in high- (HF) and mixed-frequency (MF) mode, the conduction process is controlled by Poole-Frenkel mechanism. For the MF SiO2 the conduction mechanism is most likely to be controlled by Schottky emission. The I-V measurements reveal, that all these materials are prone to trapping parasitic charge, which is observed as hysteresis between the ramp-up and ramp-down parts of the I-V curve.For studying the kinetics of charge trapping the MIM capacitors are used. To identify the trapping properties the constant current injection technique is used. The PECVD SiNx dielectric turns out to show logarithmic dependence of the trapping kinetics, while the SiO2 shows an exponential dependence. The total concentration of traps shows no field-dependence for the HF SiNx and MF SiO2 or weak field dependence for the MF SiNx sample. The capture cross section is field dependent for both samples with SiNx, which is consistent with the repulsive trapping model. For the SiO2, where the first order trapping model was used, the capture cross-section is not field dependent.In the chapter 4, experimental voltage drifts are measured during constant voltage stress tests for different voltage stress levels. In the following part we propose an original approach to modeling of the voltage drifts based on the identified conduction mechanism and trapping properties of the dielectrics. We demonstrate that thanks to our model it is possible to explain the measured voltage drifts in terms of the identified dielectric properties. The simulated results are in good agreement with experimental ones for all investigated materials and it allows to predict the voltage drift for any aging conditions. In the next step, we use our model to study the effect of the dielectric properties and the switch design on the long term behavior of RF MEMS switches.
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Adam Koszewski. Etude de la fiabilité de MEMS à fonctionnement électrostatique. Autre. Université de Grenoble, 2011. Français. ⟨NNT : 2011GRENT063⟩. ⟨tel-00858495⟩

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