Atomic Peening Effect Research Articles

Linear Stiffness Tuning in MEMS Devices via Prestress Introduced by TiN Thin Films

Stiffness tuning is crucial for micro/nanoscale devices to achieve advanced functionalities such as bistability, which enables efficient energy harvesting, large motion actuation, and programmable mechanical properties. Prestress implemented by thin films is one of the effective approaches for stiffness control; however, it is rarely used in practice because of the poor controllability in traditional thin film materials. Here, we demonstrate robust stiffness tuning on a microelectromechanical system (MEMS) sensor by using prestress in titanium nitride (TiN) thin films. Benefiting from the atomic peening effect, TiN exhibits linearly controllable prestress, which provides direct access to zero and negative stiffness in the mechanical device, resulting in multiple functionalities, including significantly enhanced sensitivity near zero-stiffness and bistable snapping behavior as stiffness becomes negative. The demonstrated technique can be a powerful tool to manipulate mechanical behaviors and facilitate exceptional sensing and actuating functionalities for micro/nanoscale devices.

Sputtered chromium nitride films with finely tuned intra- and intercolumnar porosities as pseudocapacitive electrode for supercapacitors

The thin-film electrode for supercapacitors has broad prospects for providing high energy storage capacity. However, the microstructure of dense film resulting in poor ion access limits its capacitance still far below the theoretical value. Here, CrN thin film electrodes with good cycle performance can be prepared by tuning the porosity of the film at the nanoscale level. The atomic diffusion process and atomic peening effect that occur during the sputtering process of chromium nitride are the pivotal parameters for generating porosity and high specific surface area. During the controlled sputtering process, an increase in the nitrogen flow rate causes an increase in the porosity in each column (intracolumnar porosity), while an increase in temperature controlling the gap between two columns (intercolumnar porosity). When the nitrogen flow rate is 10 sccm and the deposition temperature is 250 °C the CrN film has the areal capacitance of 41.7 mF cm−2, 10 mV s−1 at the thickness of 950 nm. In addition, the CrN film has good electrochemical cycling stability, the capacity retention rate is still as high as 93.2% after 20,000 cycles. Therefore, the CrN film electrode has a promising application prospects in energy storage systems such as supercapacitors.

Residual stress reduction in piezoelectric Sc0.4Al0.6N films by variable-pressure sputtering from 0.4 to 1.0 Pa

Scandium aluminum nitride (ScAlN) films are promising piezoelectric materials for various microelectromechanical systems. However, residual stress in ScAlN films is a serious problem. In this study, Sc0.4Al0.6N films were deposited on silicon (100) substrates by using a reactive magnetron sputtering system. The total gas pressure during the latter stage of film deposition was increased to a high pressure (1.0 Pa) without quenching the plasma and was initiated subsequent to the deposition of an adequate-quality piezoelectric underlayer at a lower pressure (0.4 Pa). The final film is 2.3 μm thick and exhibits a piezoelectric response of 20.1 pC⋅N−1, and its residual compressive stress is about 25% that of a film deposited solely at 0.4 Pa. The result is due to two effects: 1) good crystalline quality of the Sc0.4Al0.6N underlayer due to the atomic peening effect at the low pressure and 2) inherited (002)w growth that is attributed to layer-by-layer selective adsorption of atoms which had lower energies at the higher gas pressure.

Preparation of Cu-W film by ion beam sputtering and characterization

This works aims at exploring the effects of dual ion beam sputtering-assembled W-rich copper-tungsten films. The film characterization was performed by means of X-ray diffraction and magnetic coating thickness testing. Our results indicate a gradual change in the tungsten structure—from approximately metastable and amorphous to crystalline—as the Ar+ ion energy increases during the sputtering process. Due to the reflection effect, an increase in film thickness was also observed with increasing energy. At lower energies, the film deposition become very difficult due to the atomic shot peening effect.

Sputtered Titanium Carbide Thick Film for High Areal Energy on Chip Carbon‐Based Micro‐Supercapacitors

The areal energy density of on‐chip micro‐supercapacitors should be improved in order to obtain autonomous smart miniaturized sensors. To reach this goal, high surface capacitance electrode (>100 mF cm−2) has to be produced while keeping low the footprint area. For carbide‐derived carbon (CDC) micro‐supercapacitors, the properties of the metal carbide precursor have to be fine‐tuned to fabricate thick electrodes. The ad‐atoms diffusion process and atomic peening effect occurring during the titanium carbide sputtering process are shown to be the key parameters to produce low stress, highly conductive, and thick TiC films. The sputtered TiC at 10−3 mbar exhibits a high stress level, limiting the thickness of the TiC‐CDC electrode to 1.5 µm with an areal capacitance that is less than 55 mF cm−2 in aqueous electrolyte. The pressure increase up to 10−2 mbar induces a clear reduction of the stress level while the layer thickness increases without any degradation of the TiC electronic conductivity. The volumetric capacitance of the TiC‐CDC electrodes is equal to 350 F cm−3 regardless of the level of pressure. High values of areal capacitance (>100 mF cm−2) are achieved, whereas the TiC layer is relatively thick, which paves the way toward high‐performance micro‐supercapacitors.

Effects of oxygen gas flow rates and Ga contents on structural properties of Ga-doped ZnO films prepared by ion-plating with a DC arc discharge

Structural properties of highly c-axis oriented polycrystalline Ga-doped ZnO (GZO) films prepared by ion-plating with a DC arc discharge were studied in terms of the oxygen gas flow rate (FO2) introduced into the chamber during the deposition process and the Ga2O3 content in the GZO sintered pellet. The X-ray diffraction (XRD) measurements revealed that the GZO films have the residual compressive stress along the a-axis direction (in-plane) and the tensile stress along the c-axis direction (out-of-plane). The increase in FO2 or the increase in Ga2O3 content was effective for relaxing the in-plane compressive stress induced by the so-called atomic peening effect. The positive correlation between the carrier concentration (n) and the primitive cell volume (V) would be due to the incorporation of Ga atoms substituting Zn sites (GaZns) together with the generation of n-type intrinsic defects or complex defects.

Tailoring the nanostructure of Ti–Si–N thin films by HiPIMS in deep oscillation magnetron sputtering (DOMS) mode

Nanocomposite TiSiN films consist of nano-sized TiN crystallites surrounded by an amorphous Si–N matrix. Many works have shown that the hardness of nanostructured TiSiN films increases with increasing silicon content up to an optimal concentration. However, energetic ion bombardment of the growing film also influences the hardness and structure of TiSiN films. The main objective of the present work was to tailor the nanostructure of TiSiN films by using the highly ionized fluxes of sputtered material generated in a HiPIMS discharge. For this purpose TiSiN films were deposited by DOMS (deep oscillation magnetron sputtering) mode. The energetic ion bombardment of the growing films was controlled by changing the peak power.The crystal structure of TiSiN films was analyzed by X-ray diffraction (XRD) with a parallel beam in both θ–2θ and GIXRD geometries. EDS and XPS were used to elucidate the chemical composition of the films and the nature of the chemical bonding, respectively. The microstructure of the films was characterized by SEM while their mechanical properties were measured by nanoindentation.All the films deposited by DOMS have a nanocomposite microstructure consisting of two phases: f.c.c TiN and a-SiN. Although similar amounts of SiN were detected in the films, both the phase distribution and the properties of the f.c.c phase depend on the peak power. Two deposition regimes were identified. At low peak power (up to 44kW) the growing film is bombarded with a high flux of low energy ionized sputtered species promoting the surface mobility of the ad-atoms and avoiding the atomic peening effect. At high peak power the energetic species impinging on the substrate are able to penetrate in the sub-surface of the growing film, resulting in an intense atomic peening effect which ultimately leads to secondary nucleation due to the high number of defects.

Nanocolumnar zinc oxide as a transparent conductive oxide film for a blue InGaN-based light emitting diode

A comprehensive study of ZnO nanocolumnar structure has been conducted through x-ray diffraction spectroscopy, atomic force microscopy, field emission scanning electron microscopy and UV-visible spectroscopy measurements. This study involves the development of an efficient ZnO transparent conductive oxide film fabricated by RF magnetron sputtering for use in a blue indium gallium nitride based light emitting diode. FESEM measurements revealed that a maximum growth temperature of 500°C induced the formation of a nanocolumnar structure. The XRD measurements revealed that the stress reduction in the film also contributed to a superior ZnO nanocolumnar structure. In addition, the reduction of the oxygen percentage during deposition resulted in significant improvement of the structure. The reduced atomic peening effect yielded lower stress in the film. Thus, a dense, uniform-thickness, fine nanocolumnar ZnO of lateral size measuring 30 to 60nm was successfully fabricated at the lowest oxygen percentage of 7%. This film also exhibited good transparency at the blue region with 78% optical transmission.

Crystal defects and related stress inY2O3thin films: Origin, modeling, and consequence on the stability of theC-type structure

We study the impact that the crystal defects have on the $C$-type structure of rare earth sesquioxide thin films grown by ion-beam sputtering, through the example of ${\mathrm{Y}}_{2}$O${}_{3}$. By monitoring the energy of the argon beam used in the sputter deposition process (between 600 and 1200 eV), we show that it is possible to control the microstructure (defects concentration, stress state and phase) in the oxide layer. Two main types of defects, ascribed to the ``atomic peening effect'', are evidenced by high-resolution transmission electron microscopy, Rutherford backscattering spectroscopy, and nuclear reaction analysis experiments: anti-Frenkel pairs, leading to a disorder on the oxygen-vacancy network, and oxygen-vacancy dislocations loops, to accommodate the strong nonstoichiometry. From a macroscopic measurement of the residual stresses in the as-deposited and the annealed layers, through x-ray diffraction and the $\mathrm{sin}{}^{2}\ensuremath{\Psi}$ method, we have modeled the related stress state using an enhanced triaxial stress model. In the as-grown films, we evidence the coexistence of a biaxial and a hydrostatic stress, due to inclusions of atomic size defects. Quantitative information of the concentration and the nature of each type of defect (size effect) have also been determined, in good agreement with experiments. Interestingly, in the most energetic growth conditions corresponding to the highest degree of disorder on the oxygen-vacancy network and to the highest stress field in the film, we demonstrate that it is possible to stabilize an unexpected and metastable non equilibrium fluorite-like phase (X-type).

In situ stress evolution during magnetron sputtering of transition metal nitride thin films

Stress evolution during reactive magnetron sputtering of TiN, ZrN, and TiZrN layers was studied using real-time wafer curvature measurements. The presence of stress gradients is revealed, as the result of two kinetically competing stress generation mechanisms: atomic peening effect, inducing compressive stress, and void formation, leading to a tensile stress regime predominant at higher film thickness. No stress relaxation is detected during growth interrupt in both regimes. A change from compressive to tensile stress is evidenced with increasing film thickness, Ti content, sputtering pressure, and decreasing bias voltage.

Structural evolution and electrochemical performance of LiFePO 4/C thin films deposited by ionized magnetron sputtering

Thin films of carbon mixed LiFePO 4 were prepared by ionized magnetron sputter deposition (IMSD) and post anneal. The IMSD technique uses a built-in radio frequency coil to generate an inductively coupled plasma (ICP) confined close to the substrate. Therefore, the films were deposited under concurrent ion bombardment, which resulted in an atomic-peening effect during film growth. The evolution of film structures and surface morphologies under different ICP plasma conditions was investigated. The deposited LiFePO 4/C thin films were tested as cathodes for lithium ion batteries. The performances of these thin film cathodes can be related to the modified film structures and surface morphologies. All the films showed a typical discharge voltage of LiFePO 4 at 3.5–3.4 V, except for the 600 °C annealed films. The thin film cathodes deposited under suitable ICP plasma powers exhibited higher specific capacity.

Structure and Internal Stress of Tin-Doped Indium Oxide and Indium–Zinc Oxide Films Deposited by DC Magnetron Sputtering

Representative transparent conductive oxide films, such as tin-doped indium oxide (ITO) and indium–zinc oxide (IZO) films, were deposited by dc magnetron sputtering using corresponding oxide targets under various total gas pressures (Ptot) ranging from 0.3 to 3.0 Pa. The ITO films deposited at a Ptot lower than 0.7 Pa were polycrystalline and were found to have a large compressive stress of about 1.5 ×109 Pa, whereas the ITO films deposited at 1.5–3.0 Pa were amorphous and had a low tensile stress. In contrast, all the IZO films deposited at a Ptot range of 0.3–3.0 Pa showed an entirely amorphous structure, where the compressive stress in the IZO films deposited at a Ptot lower than 1.5 Pa was lower than that in the ITO films. Such compressive stress was considered to be generated by the atomic peening effect of high-energy neutrals (Ar0) recoiled from the target or high-energy negative ions (O-) accelerated in the cathode sheath toward the film surface.

Compressive stress, preferred orientation and film composition in Ti-based coatings developed by plasma immersion ion implantation-assisted deposition

Plasma immersion ion implantation-assisted deposition has been employed to develop Ti based coatings in the presence or absence of a reactive nitrogen environment. When TiN coatings have been developed on Al alloys, it has been observed that a large compressive stress develops in the coating, which can be reduced when the substrate bias is increased. The formation of stress is attributed to atomic peening effect that densifies a coating, whereas thermal spikes generated at high substrate bias reduce the stress. For TiAl coatings delivered from an alloy plasma source, the Al content decreases with increasing negative substrate bias. This is in agreement with the results of TRIDYN ballistic computer simulations, which confirm that the film composition is significantly influenced by preferential sputtering. The results indicate that time-averaged substrate bias is an ill-defined parameter to describe coating properties deposited by the above technique.

Compressive stress, preferred orientation and film composition in Ti-based coatings developed by plasma immersion ion implantation-assisted deposition

Plasma immersion ion implantation-assisted deposition has been employed to develop Ti based coatings in the presence or absence of a reactive nitrogen environment. When TiN coatings have been developed on Al alloys, it has been observed that a large compressive stress develops in the coating, which can be reduced when the substrate bias is increased. The formation of stress is attributed to atomic peening effect that densifies a coating, whereas thermal spikes generated at high substrate bias reduce the stress. For TiAl coatings delivered from an alloy plasma source, the Al content decreases with increasing negative substrate bias. This is in agreement with the results of TRIDYN ballistic computer simulations, which confirm that the film composition is significantly influenced by preferential sputtering. The results indicate that time-averaged substrate bias is an ill-defined parameter to describe coating properties deposited by the above technique.

Annealing effects on the structure and mechanical properties of r.f.-sputtered Cr–B hard thin films

Cr–B thin films were synthesized by an r.f. plasma-assisted magnetron sputtering method using pure CrB 2 target on quartz glass, glass ceramic, NaCl single crystal and silicon wafer substrates. After the sputtering process, the as-deposited Cr–B thin films were annealed at 773, 973 and 1173 K for 5 h. The influence of annealing temperature on the structure and properties of Cr–B thin films was investigated. Although the films were deposited at low temperature ( T S/ T M<0.1) in this study, X-ray diffraction and transmission electron microscopy observation results indicate that fine crystalline grains are still formed in these films. With increasing annealing temperature, the grain size increased gradually from 10 to 30 nm. The compressive stress in the Cr–B films is rather small due to the long target–substrate distance of this apparatus which reduces the atomic peening effect. The hardness decreased scarcely with increasing annealing temperature from about 21 GPa for as deposited to about 19 GPa for 1173 K owing to the grain growth and relaxation of residual stress. The present study shows that Cr–B thin films can be used below 1200 K with stable structure and high hardness.

Atomic Peening Effect of Ambient Gas on Platinum Films Grown on Amorphous Substrates by Pulsed Laser Deposition

The effects of substrate temperatures and ambient gas pressures on the preferred orientation of platinum films deposited on amorphous SiO2/Si(100) substrates by the pulsed laser deposition method were studied. Even at room temperature, platinum films could be grown under vacuum with (111) preferred orientation. The increase of substrate temperature to 600°C induced the additional (100) orientation. While the presence of ambient oxygen or nitrogen gas suppressed (111) orientation at room temperature, it had the opposite effect of enhancing (111) orientation and suppressing (100) orientation at 600°C. The effect of ambient gas pressure at high temperatures on the selective enhancement of platinum film crystallinity on SiO2 is proposed to be due to the atomic peening effect of gas molecules.

Microstructural changes in GeSbTe film during repetitious overwriting in phase-change optical recording

Microstructural changes that occur in a GeSbTe film during repetitious overwriting in phase-change optical recording were investigated. The GeSbTe active layer was melted by a focused laser diode (LD) beam during each overwriting process over amorphous mark formation. The repetitious solidification and liquefaction process in such a short time as 50–200 ns resulted in microstructural changes in the active layer: a segregation, sink, and void formations. The sink was formed in the low-density active layer due to the shrinking of the volume during the resolidification process. Sink formation could be suppressed when a high-density active layer, having more than 80% of the bulk density, was used. Such a high-density GeSbTe film, however, resulted in a void formation of the size of 0.1 μm. The voids were thought to be nucleated by residual vacancies and Ar precipitation, since the active layer contained a high concentration of Ar impurities, due to the atomic peening effect. The subsequent void coalescence and migration processes across the beam scanning direction could result in the formation of thermally discontinuous grooves at the edges of the written marks. The voids could also migrate along the LD beam scanning direction, accompanied by a material flow of the active layer in the opposite direction. These phenomena were also found to depend on the material used to fabricate the protective layers which sandwiched the active layer. A TaOx protective layer enhanced the void migration across the track, resulting in the removal of voids from the center of the track. Use of the ZnS:SiO2 compound protective layer confined voids to the center of the track. The ZnS:SiO2 protective layer also promoted the formation of thermally discontinuous grooves at the edges of amorphous marks. The material flow along the track resulted in a thicker active layer at the start of the consecutive LD irradiation, and also in a high void density region at the final edge of the irradiation having a length on the order of 10 μm. This tendency was found for both the ZnS:SiO2 and TaOx sandwiching media.

Effects of Film Thickness and Annealing Temperature on the Stress in Amorphous Gd-Fe Alloy Thin Films

ABSTRACTGd-Fe films were deposited by magnetron sputtering on glass substrates. The results shoved that the stress is compressive in most cases, and a larger compressive stress exists at the film-substrate interface. The stress is independent on the film thickness when the film thickness is greater than 0.20 μm. The stress becomes tensile only when the annealing temperature attains 400ºC. Therefore, the interfacial stress and the growth stress coexist in the Gd-Fe films, and the former will not be dominant when the film thickness is greater than 0. 2μm. The interfacial stress may originate from the inhomogeneous distribution of film composition at the interface, and the origin of growth stress can be explained by the atomic peening effect. The relation between the stress and the annealing temperature can be comprehended with the amorphous structure model.

The Origin of Stress in Co-Cr Alloy Thin Films Deposited by Magnetron Sputtering

ABSTRACTCo-Cr alloy thin films are considered as an applicable perpendicular magnetic recording medium, and their mechanical properties such as internal stress can not be neglected. In this experiment, Co-Cr films are deposited on glass substrates by D. C planar magnetron sputtering, and the effects of film thickness, Ni-Fe underlayer as well as substrate temperature on the stress are studied respectively. The stresses are all tensile in all cases, and the stress existing at the film-substrate interface is very small. According to the above experimental results and the structure analysis of the films, the atomic peening effect produced by the rebounded working gas atoms can be negligible, and the stress is thought to originate from the film growth process but not from the inter-facial effect. Therefore, the structural defect elimination model is proposed (here the defects mainly include vacancies and grain boundaries). With this model, the origin of the tensile stress as well as the relations between the stress and the deposition conditions are explained qualitatively.

Stresses in Amorphous Gd-Fe Alloy Thin Films Deposited by Magnetron Sputtering

ABSTRACTAmorphous Gd-Fe alloy thin films were made by D.C. planar magnetron sputtering under various deposition conditions (e.g., film thickness, composition, working pressure of Ar, negative bias voltage and deposition rate). The stress, the film composition and the content of entrapped Ar in the films were measured respectively. The experimental results showed that in this case the working pressure of Ar and the negative bias voltage did not change the composition of the films, and the stresses were all compressive except for the films deposited in a very high working pressure of Ar. The origin of the compressive stress can be attributed to the atomic peening effect produced by fast neutral working gas atoms rebounded from the sputtering target. The magnitude of the compressive stress depends not only on the amount of Ar atoms incorporated in the films but also on the film microstructure such as the packing density.