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.

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.

Herein, we study the crystallization of undoped and nitrogen doped amorphous GeTe thin films (slightly rich in Ge) obtained by sputtering using substrate curvature measurements to understand the underlying mechanisms controlling stress evolution in the film throughout the phase transformation. At temperatures below crystalli-zation temperature, amorphous films showed stress relaxation and the stress gradually became tensile with annealing time. The GeTe samples show a two-step crystallization wherein amorphous GeTe crystallized first (at the crystallization temperature Tx) followed by crystallization of excess Ge (Ge precipitation) at -Tx+50 degrees C. Upon GeTe crystallization, a sharp increase in the tensile stress is explained using a coalescence mechanism. This interpretation resolves the issue of the discrepancy between the measured stress buildup reported by several authors and the predicted stress jump from elastic accommodation of density change. The precipitation of excess Ge (from amorphous to crystalline) along grain boundaries in GeTe leads to compressive stress build-up. Ni-trogen doping affects both the GeTe and Ge crystallization events leading to lesser tensile and compressive stress. The models for stress relaxation in the amorphous phase, stress build-up due to GeTe, and excess Ge crystalli-zation are discussed.

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.

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.

fast and reliable data storage is and Computing being is the global next-generation data an annual of non-volatile data their properties, p hase change materials (PCMs) can the PCMs can be reversibly switched between an amorphous and a crystalline phase through controlled (local) heating, e,g, by lasers or by an electrical current PCMs the to Phase Change Random Access Memories (PCRAM), very alternative to replace flash technology In this contribution investigations on the PCM GST-theta a Ge-rich material within the Ge-Sb-Te ternary system GST-theta crystallization temperatures above 350°C , is in automotive applications In a previous study on 50 nm thick of GST-theta we that the

In this work, we reexamine Ge rejection in Ge-rich GeTe thin films with a slight deviation from stoichiometry using a unique combination of in situ measurements: curvature and x-ray diffraction as well as electrical resistance and x-ray diffraction and reflectivity during annealing. This unique combination of several experiments performed simultaneously on a synchrotron beamline allows to monitor in situ, during the crystallization and phase transformation, the microstructure, the strain and the stress changes, as well as electrical properties of GeTe films. Structural, electrical and thermomechanical evolutions of the GeTe thin films upon annealing are shown to follow three different steps. Stage I, before crystallization, is characterized by a tensile stress variation and a small decrease of the mass density. Stage II corresponds to the rhombohedral alpha GeTe phase crystallization leading to an abrupt tensile stress jump (+72 MPa), a mass density increase, and followed by a slight compressive stress evolution. During stage III, Ge crystallization is observed leading to a compressive stress jump (similar to 54 MPa), an abrupt increase in alpha GeTe lattice spacing and diffracted intensity, whereas alpha GeTe diffraction peak widths decrease. During cooling a thermoelastic behavior is observed. A detailed analysis of stage III (Ge precipitation and crystallization) is performed and discussed regarding structural, stress, microstrain, electrical and thermomechanical properties. In particular, this study reveals that crystalline Ge precipitation results in important changes (volume of the unit cell, homogeneity of lattice spacing, average stress...) in the surrounding GeTe matrix. Different scenarios are proposed to understand these results. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Phase change materials are attractive materials for non-volatile memories because of their ability to switch reversibly between an amorphous and a crystal phase. The volume change upon crystallization induces mechanical stress that needs to be understood and controlled. In this work, we monitor stress evolution during crystallization in thin GeTe films capped with SiOx, using optical curvature measurements. A 150 MPa tensile stress buildup is measured when the 100 nm thick film crystallizes. Stress evolution is a result of viscosity increase with time and a tentative model is proposed that renders qualitatively the observed features.

Stress changes in GeTe thin films on silicon have been studied in situ as a function of temperature by optical curvature measurements. Crystallization of the initially amorphous layers is evidenced by a steep tensile stress buildup. The crystallization temperature is shown to be thickness-dependent for the thinner films. Various annealing conditions, such as cooling/re-heating steps and isothermal stages, allow exploring the thermo-mechanical behavior of the films. A non-thermoelastic temperature-dependent behavior is observed in the amorphous phase before crystallization.

A complementary suite of in situ synchrotron X-ray techniques is used to investigate both structural and chemical evolution during ZnO growth by atomic layer deposition. Focusing on the first 10 cycles of growth, we observe that the structure formed during the coalescence stage largely determines the overall microstructure of the film. Furthermore, by comparing ZnO growth on silicon with a native oxide with that on Al2O3(001), we find that even with lattice-mismatched substrates and low deposition temperatures, the crystalline texture of the films is dependent strongly on the nature of the interfacial bonds.

Phase change materials (PCMs) such as Ge2Sb2Te5 (GST) undergo a reversible amorphous-to-crystal transition that is the basis of their interest for next generation non-volatile memories. The large density change upon crystallization raises important issues because of the large mechanical stresses occurring during memory cycling. In order to investigate the intimate relationship between stress buildup and microstructure evolution we have built a dedicated setup, which allows combining X-ray diffraction and curvature measurements on DiffAbs beamline at SOLEIL synchrotron. Using a thin (30nm) GST film deposited on Si we show that this setup yields a wealth of interesting results. A clear correlation is observed between phase transition and stress buildup. Detailed information is obtained on the thermomechanical behavior of the different phases. Systematic investigation of PCMs with this original setup will help understanding the thermomechanical behavior of PCM thin films and nanostructures.

Texture evolution is an important issue in materials and nanosciences. Understanding it is fundamental for controlling the final orientation, which in fine controls the desired properties of nanodevices. Here, we reveal the formation of a peculiar texture during the silicidation of nanoscale Pd thin films. We demonstrate that the crystallographic relationship observed between the silicide and the Si(001) substrate, named gyroaxy, evolves continuously and collectively during silicidation. This continuous rotation of the nanosized grains over a wide angular range is proposed to be associated with a diffusional mechanism.