Transient creep in free-standing thin polycrystalline aluminum films

Kalkman, A. J.; Verbruggen, A. H.; Janssen, G. C. A. M.; Radelaar, S.

doi:10.1063/1.1509099

Cited by 20 publications

(12 citation statements)

References 41 publications

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“…invoked by the distribution of the densities of geometrically necessary dislocations or by surface constraints like passivation layers [11]. Thin film materials are also reported to be prone to time dependent deformations such as creep [12][13][14][15][16] and anelasticity [12,[17][18][19][20][21][22]. Creep, accumulating plastic deformation under a constant load over time, is also observed in bulk materials, where it is a relatively well studied phenomenon, see [23,24] and the references therein.…”

Section: Introductionmentioning

confidence: 99%

“…Additionally, some anelasticity was observed in the response, which was attributed to grain boundary sliding. After a correction for the anelastic relaxation, the experimental results were reproduced reasonably well by a material model based on dislocation glide [12]. Quasi-static micro-tensile stress relaxation tests on free-standing Al and Al-Ti thin films at stress levels below the yield strength were performed by [17,18].…”

Section: Introductionmentioning

confidence: 99%

“…In these experiments, it was observed that after an initial elastic spring back upon unloading, an additional strain recovery occurs over time and almost no permanent deformation remains. The bulge tests and stress dip tests by [12] on free-standing polycrystalline Al films with thicknesses between 220 and 550 nm showed that thinner beams are more resistant to creep deformations. Moreover, at about the same stress levels, creep strains in thin film samples were at least three orders of magnitude smaller than that of the material in bulk form.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Crystal plasticity based modeling of time and scale dependent behavior of thin films

Ertürk¹,

Gao²,

Bielen³

et al. 2013

GAMM-Mitteilungen

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The micro and sub-micro scale dimensions of the components of modern high-tech products pose challenging engineering problems that require advanced tools to tackle them. An example hereof is time dependent strain recovery, here referred to as anelasticity, which is observed in metallic thin film components of RF-MEMS switches. Moreover, it is now well known that the properties of a thin film material strongly depend on its geometrical dimensions through so-called size effects. A strain gradient crystal plasticity formulation (SGCP) was recently proposed [1][2][3][4], involving a back stress in terms of strain gradients capturing the lattice curvature effect. In the present work, the SGCP model is used in a realistic simulation of electrostatic bending of a free standing thin film beam made of either a pure fcc metal or a particle strengthened Al-Cu alloy. The model capabilities to describe the anelastic and plastic behavior of metallic thin films in comparison with experimentally available data are thereby assessed. Simulation results show that the SGCP model is able to predict a macroscopic strain recovery over time following the load removal. The amount of the anelastic relaxation and the accompanying relaxation times result from the rate dependent modeling approach, the basis of which is phenomenological only. The SGCP model is not fully capable of describing the permanent deformations in an alloy thin beam as observed in electrostatic experiments. Hence, to incorporate realistic time constants and the influence of the microstructure into the mechanical behavior of the thin film material, an improved constitutive law for crystallographic slip is necessary within the SGCP formulation.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Crystal plasticity based modeling of time and scale dependent behavior of thin films

Ertürk¹,

Gao²,

Bielen³

et al. 2013

GAMM-Mitteilungen

View full text Add to dashboard Cite

show abstract

“…The physical micro-mechanisms of creep in these free-standing microbeams are, however, poorly understood, let alone implemented in models. In the literature some reports can be found discussing creep and relaxation effects in thin aluminum films [6][7][8][9][10][11].…”

Section: Figure 1: Scanning Electron Micrograph Of An Rf-mems Switch mentioning

confidence: 99%

Mechanically probing time-dependent mechanics in metallic MEMS

Hoefnagels

Bergers

Delhey

et al. 2011

MEMS and Nanotechnology, Volume 2

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The reliability of metallic micro-electromechanical systems (MEMS) depends on time-dependent deformation such as creep. To this end, a purely mechanical experimental methodology for studying the time-dependent deformation of free-standing microbeams has been developed. It is found most suitable for the investigation of creep due to the simplicity of sample handling and preparation and setup design, whilst maximizing long term stability and displacement resolution. The methodology entails the application of a constant deflection to a μm-sized free-standing aluminum cantilever beam for a prolonged period of time. After this load is removed, the deformation evolution is immediately recorded by acquiring surface height profiles through confocal optical profilometry. Image correlation and an algorithm based on elastic beam theory are applied to the full-field beam profiles to yield the tip deflection as a function of time. The methodology yields the tip deflection as function of time with ~3 nm precision.

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“…The physical micro-mechanisms of creep are, however, not nearly understood, let alone implemented in models. In the literature some reports can be found discussing creep and relaxation effects in thin aluminum films [3][4][5][6][7][8]. However, specifically for free-standing thin films not much research has focused on determining size-effects in time-dependent material behavior [9].…”

Section: Introductionmentioning

confidence: 99%

Creep measurements in free-standing thin metal film micro-cantilever bending

Bergers

Hoefnagels

Geers

2011

MEMS and Nanotechnology, Volume 4

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Creep is a time-dependent deformation mechanism that affects the reliability of metallic MEMS. Examples of metallic MEMS are RF-MEMS capacitors/switches, found in wireless/RF applications. Proper modeling of this mechanism is yet to be achieved, because size-effects that play a role in MEMS are not well understood. To understand this better, a methodology is setup to study creep in Al-Cu alloy thin film micro-cantilevers micro-fabricated in the same MEMS fabrication process as actual RF-MEMS devices. The methodology entails the measurement of time-dependent deflection recovery after maintaining cantilevers at a constant deflection for a prolonged period. Confocal profilometry and a simple mechanical setup with minimal sample handling are applied to control and measure the deformation. Digital image correlation, leveling and kinematics-based averaging algorithms are applied to the measured surface profiles to correct for various errors and improve the precision to yield a precision <7% of the surface roughness. A set of measurements is presented in which alloy microstructure length scales at the micrometer-level are varied to probe the nature of this creep behavior.

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Transient creep in free-standing thin polycrystalline aluminum films

Cited by 20 publications

References 41 publications

Crystal plasticity based modeling of time and scale dependent behavior of thin films

Crystal plasticity based modeling of time and scale dependent behavior of thin films

Mechanically probing time-dependent mechanics in metallic MEMS

Creep measurements in free-standing thin metal film micro-cantilever bending

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