Zr, V and Zr-V films were evaporated on silicon substrates for evaluating their gettering properties for microelectromechanical systems (MEMS) packaging. The film microstructure was characterized by scanning electron microscope, atomic force microscope, transmission electron microscopy, X-ray diffraction and electrical measurements. Films are amorphous or nanocrystallized according to their composition. Film samples were then activated at various temperatures under argon atmosphere at low pressure of oxidizing species. After annealing, oxygen sorption by the samples was measured by ion beam analysis. Finally, getter films were integrated inside MEMS vacuum packages with a maximum temperature of 300°C. An optimal gettering performance was obtained with the Zr85V15 alloy composition which is close to the limit of the amorphous zone in the phase diagram. For the amorphous films, no correlation is found between oxygen diffusivity and getter performance. The role of grain boundaries in the activation performance of Zr-V getter films was emphasized, by showing that increasing the density of grain boundary enhances the getter performance of the film until an optimum, above which a further increase becomes detrimental to the getter sorption properties. Below this optimum, the enhancement of getter performance by the increasing of grain boundary density can be modelled and allows to predict the getter performance of a Zr-V film knowing its microstructure.

Pd/Y bilayers have a high hydrogen sorption ability suitable for their use as low temperature hydrogen getter for vacuum packaging and for hydrogen sensing applications. Pd/Y bilayers with variable Pd thicknesses in the 4-40 nm range were e-beam evaporated on silicon in ultrahigh vacuum. Deposition rate of the Pd ultrathin films was calibrated by grazing incidence X-Ray reflectivity measurements on films deposited on silicon. Sheet resistance measurements of the Pd/Y bilayers were performed as function of temperature in high vacuum, under a low partial pressure of deuterium, and under a low partial pressure of oxygen. Results show that Pd thicknesses above 15 nm efficiently passivate the yttrium surface against oxidation up to at least 250 degrees C and that the onset temperature of formation of yttrium dihydride does not vary significantly with Pd overlayer thickness. For thinner Pd films, because of Pd film discontinuity allowing yttrium oxidation, yttrium hydrogenation is slowed down.

Ti, Zr, V, Zr-Ti, Zr-V, Ti-V and Ti-Zr-V alloy thin films were co-evaporated under UHV. Their composition was characterized by Rutherford Backscattering Spectrometry while their microstructure was characterized directly by X-ray diffraction and scanning electronic microscopy, and indirectly by electrical measurements. Depending on their composition, films are polycrystalline or amorphous and have a resistivity ranging from 60 to 160 mu S2 cm. Amorphous films exhibit resistivities higher than 150 mu S2 cm and negative TCRs, in accordance with Mooij rule. No bulk oxidation in ambient air was detected by electrical measurements over a period as long as 2 years. After deposition, films were activated during a thermal annealing at 5 degrees C/min up to 400 degrees C under 10-7mbar vacuum or 10-3 mbar of H2. An in situ sheet resistance monitoring of the films during annealing allowed to detect their hydrogenation and thus to compare their activation temperatures. Films with amorphous microstructure (ZrV, TiZrV) have lower activation temperatures than single element films and nanocrystalline ZrTi and TiV films. TiZrV has the lowest activation temperature, while single metal films have the highest activation temperatures.

We investigated the sorption of hydrogen by yttrium-based getters for their application to vacuum wafer-level packaging of microelectromechanical systems. Thin alloy films were co-evaporated under ultra-high vacuum on silicon wafers. Getters were activated by annealing during 1 h under inert argon atmosphere with traces of oxidizing species, at temperatures ranging from 200 degrees C to 400 degrees C. Three complementary techniques of ion beam analysis were performed on the samples: Rutherford Backscattering Spectrometry (RBS), Nuclear Reaction Analysis (NRA) and Elastic Recoil Detection Analysis (ERDA), to quantify metal, oxygen and hydrogen contents, and their in-depth distributions. The results show that oxidation occurs during annealing and prevents or not hydrogen sorption depending on the film composition. Due to its fast diffusion, hydrogen tends to accumulate near the film/substrate interface and starts to diffuse into the substrate as well. The different compositions of getter films are compared in terms of oxygen and hydrogen absorptions.

Titanium, zirconium, and Zr-Ti alloy thin films were evaporated under UHV. AFM, TEM and SEM observations showed that grain size at the surface of the films varies with their thickness and composition. The single-metal films exhibit larger grain than alloy films. The highest density of grain boundaries is found for Zr-Ti film with a balanced content in Zr and Ti. For the three types of films, the grain boundary density at the surface decreases when increasing the film thickness. The gettering properties of the films were studied by activation annealing in the range of 200 degrees C-400 degrees C by in situ sheet resistance monitoring and by integrating them into MEMS packages sealed at 300 degrees C. In both cases, the sorption of gases was found to increase with the surface density of grain boundaries. In the specific activation conditions of MEMS packaging, it is shown that reducing the film thickness from 400 nm to 50 nm enhances gas sorption by the Zr-Ti getter and for the first time, the activation of a getter film thinner than 100 nm integrated in a MEMS package was demonstrated.

Films of Zr and Zr-V were evaporated on silicon substrates and their gettering properties were evaluated for MEMS packaging. Their microstructure was determined by SEM and TEM. The films were then activated at different temperatures at low pressure of oxidizing species under argon atmosphere. The oxygen sorption was measured after annealing by ion-beam analyses. Finally, integrations of getter films with various compositions were realized inside hermetic MEMS packages sealed at 300 °C. All the results showed an optimal performance for the alloy with composition Zr 85 V 15 having a nanocrystallized structure. This work emphasizes the role of grain boundaries in the activation performance of getter films, showing that increasing the density of grain boundary enhances the getter performance until a point where an excess of grain boundaries like in a quasi-amorphous film becomes detrimental to the getter effect.

This paper presents a resonating quartz MEMS magnetometer exploiting the torque induced by the external magnetic field on a stack of ferromagnetic and antiferromagnetic materials and the differential measurement of the resonance frequencies of two DETFs. It is targeted for applications such as magneto-inertial navigation. This sensor was fabricated using a wet HF/NH4F etching process and its working principle was proven correct with a magnetic sensitivity of 770 Hz/T.

Many microsensors need to operate in medium vacuum, which is obtained by low temperature vacuum packaging integrating a getter film. By a thermal activation during the sealing process, the getter film aims to compensate the outgassing of the inner surfaces of the micro-cavity and also leaks after sealing. Thin films of getter alloys were coevaporated under ultra-high vacuum on silicon wafers. They were activated by annealing at temperatures ranging from 225°C to 400°C, during one hour under Argon atmosphere with traces of oxidizing species. Three complementary ion beam analysis techniques were performed to obtain depth profiles and to quantify the number of atoms of the different gaseous species absorbed by the getter films: Rutherford Backscattering Spectrometry (RBS), Nuclear Reaction Analysis (NRA) and Elastic Recoil Detection Analysis (ERDA). The results show that both oxygen and hydrogen diffuse inside the getter films. However, hydrogen tends to accumulate near the interface between film and substrate and starts to diffuse inside substrate as well. We demonstrated that the sorption of hydrogen by an yttrium-based getter film is tailored by its composition and depends on its degree of oxidation.

MEMS actuators rely on the deformation of silicon structures. Using dimensions smaller than dozens of micrometers reveals that the micro-electro-mechanical systems (MEMS) actuators are affected by fabrication inaccuracies, leading to hardly predictable forces and/or actuation results. In this paper, MEMS bistable buckled beam actuators are presented. A series of structures based on pre-shaped buckled beams of lengths ranging from 2 to 4 mm, constant width of 5 μm and actuation stroke ranging from 20 to 100 μm was fabricated. Experimental data show a significant difference with predictions from a conventional analytical model. The model commonly used for buckled beams design assumes a rectangular beam section, but it is not the case of the fabricated beams. Furthermore, only symmetric buckling modes (mode 1, mode 3…) are supposed to exist during snap-through. In this paper, new analytical models have been developed on the basis of the models of the literature to consider the effective beam shape. The first improved analytical model enabled prediction of the MEMS buckled beams mechanical behavior in a 30% margin on the whole range of operation. A second model has been introduced to consider both the effective shape of the beam and centro-symmetric buckling modes. This refined model exhibits the partial suppression of buckling mode 2 by a central shuttle. Therefore, mode 2 and mode 3 coexist at the beginning and the end of snap-through, while mode 3 quickly vanishes due to increasing rotation of the central shuttle to leave exclusive presence of mode 2 near the mid-stroke. With this refined model, the effective force-displacement curve can be predicted in a margin reduced to a few percentages in the center zone of the response curve, allowing the accurate prediction of the position switch force. In addition, the proposed model allows accurate results to be reached with very small calculation time.

• CoFe/NiMn stack sputtered on a quartz substrate. • Influence of the annealing procedure on the exchange coupling. • Influence of the thickness of CoFe and NiMn on the exchange coupling. • Influence of shape anisotropy on the hysteresis loop.

This paper presents an innovative 1D MEMS resonating magnetometer exploiting the torque induced by the external magnetic field on a stack of ferromagnetic and antiferromagnetic materials. It is targeted for applications such as magneto-inertial navigation. The sensor was successfully fabricated using a wet chemical process and its working principle was proven correct. The experimental results showed a sensitivity of 1500 Hz/T and an estimated resolution of 7.3 nT.

Yttrium, titanium, and yttrium-titanium getter thin films were elaborated on silicon by coevaporation in ultrahigh vacuum. Y-Ti films exhibit nanometric crystallites size (18–35 nm) leading to a very high grain boundary density, which is a favorable microstructure for activation at low temperature. The yttrium content in Y-Ti alloys influences grain size, resistance against room temperature oxidation, and gettering performance for oxygen. Y-Ti films with an yttrium content higher than 30% show strong oxygen sorption during annealing at low temperature (<300 °C). After 1 h of annealing at 250 °C, it was estimated that the yttrium-based getter films can trap between 0.2 and 0.5 μmol of oxygen per cm2, while no oxygen sorption was detected for a single metal titanium film. This makes Y-Ti getter alloys attractive candidates for the packaging of MEMS under vacuum with a low bonding temperature.

Sheet resistance of transition metal-based getter films was recorded during 1 h 15 min of activation at 250 °C by in situ 4-probes measurement under vacuum. Co-evaporated alloys of Zr–Ti, Zr–V and Zr–Co with different compositions were studied. Results show that resistivity and temperature coefficient of resistance (TCR) are linked and follow the Mooij rule. A gradual disorder in the structure was deduced from the less disordered—pure metals then Zr–Ti then Zr–V—to the highest, i.e. Zr–Co. A specific study of Zr–Ti showed that the grain size directly impacts TCR and resistivity of as-deposited film, and oxygen content after activation at 250 °C. For Zr–V and Zr–Co, the amorphous structure has to be taken into account and it has been shown that too much disorder in the structure is detrimental for sorption ability. The most oxidized films no longer follow the Mooij rule after annealing.

Buckled beam-based bistable actuators are the key for contactless digital actuation. In this paper, the design, fabrication and characterization of bistable buckled beams is presented. A series of structures based on pre-shaped buckled beams of lengths ranging from 2 to 4 mm, a constant width of 5 um and an actuation stroke ranging from 20 to 100 um was fabricated. Experimental data show a significant difference with classical model predictions, mainly because the actuation method results in a displacement which is a combination of several buckling modes. Thus the model commonly used for buckled beams design has then been modified in order to take into account the beam shape effectively fabricated and experimental results. An accurate model was obtained, enabling good prediction of the experimental switching behavior of microfabricated buckled beams.