Electrical and mechanical properties of layered gold–chromium thin films for ohmic contacts in RF-MEMS switches

Mulloni, Viviana; Bartali, Ruben; Colpo, S.; Giacomozzi, F.; Laidani, N.; Margesin, B.

doi:10.1016/j.mseb.2009.06.004

Cited by 9 publications

(8 citation statements)

References 16 publications

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“…The data presented in tables 2 and 3 deserve some comments. Young's modulus of bulk gold is 80 GPa, while the value normally used for MEMS structures modeling is around 75 MPa [22,23], even though higher or lower values have been reported for thin films [8,[24][25][26] and for electrodeposited gold [11,27,28]. The values found with the method reported in this paper are then well within the acceptable range and the differences found among the different arrays investigated are probably justified by the experimental inhomogeneities and modeling approximations.…”

Section: Resultssupporting

confidence: 51%

A simple analytical method for residual stress measurement on suspended MEM structures using surface profilometry

Mulloni¹,

Colpo²,

Faes³

et al. 2013

J. Micromech. Microeng.

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This paper presents an analytical method to calculate residual stress and Young's modulus in clamped-clamped beams. These types of structures are a typical building block of many MEMS devices, and this guarantees accurate transferability of the measured parameters. The method is based on the determination of beam bending as a function of applied load by means of a surface profiler, and as a function of beam length. By modeling analytically both the elastic and the stress contribution to beam bending, it is possible to obtain both the stress value and Young's modulus by a simple fitting of the experimental data. Results are presented for electrodeposited gold beam arrays of different widths, but the method is in principle exploitable for every type of suspended film where the residual stress strongly influences the material properties. Accuracy and limitations of the method are also discussed.

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Section: Resultssupporting

confidence: 51%

A simple analytical method for residual stress measurement on suspended MEM structures using surface profilometry

Mulloni¹,

Colpo²,

Faes³

et al. 2013

J. Micromech. Microeng.

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“…The thermal treatments described in the Experimental Section were performed in order to promote some metalgold interdiffusion to have some alloying of the two metals, coupled with some preserved layering structure that should lead to the highest hardness possible. From a previous study (Mulloni et al 2009) it was already clear that the optimum value is however limited also by resistivity increase, metal oxidation, and fabrication constraints that limit the optimum temperature to about 200-250°C, being the treatment at 200°C the more indicative for a normal fabrication process, while the treatment at 350°C can be interpreted as the upper limit of realistic process compatibility. The alloying metal layers have been deposited close but not directly on the surface of the multimetal layer, with the purpose of increasing the hardness where the material is more subjected to wear, but trying also to avoid contamination and oxidation phenomena due to direct exposition of the alloying metal to ambient atmosphere.…”

Section: Resultsmentioning

confidence: 99%

“…On this basis, a trade-off between different separate layers and partial alloying promoted by controlled thermal treatments can lead to an increased value of hardness which preserves the main desirable characteristics of gold, because this metal can be left on the external surface. In a previous study (Mulloni et al 2009) chromium has been investigated as promising alloying metal, showing good results in terms of material hardening, but also a strong tendency to oxidation and therefore limited compatibility with real switch production.…”

Section: Introductionmentioning

confidence: 99%

Gold-based thin multilayers for ohmic contacts in RF-MEMS switches

et al. 2012

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In RF-MEMS switches many reliability issues are related to the metal contacts in the switching area. The quality of this contact strongly influences switching failures due to wear, adhesion and stiction. Gold is widely used as contact material, but is a soft metal. Contact hardness can be improved preserving good conductivity and chemical inertness alternating gold layers with thin layers of other metals. A detailed study of mechanical, electrical and morphological properties of gold-chromium, gold-platinum and gold-palladium multilayers is presented and discussed. Annealing treatments modify hardness values, but a careful choice of the alloying metal is essential because hardness is reduced upon exposure to plasma ashing, a very frequent microfabrication process. This treatment also increases contact roughness, deteriorating the contact surface. Platinum is the only metal tested that is unaffected by plasma oxidation, and it also reduces the diffusion of chromium adhesion layer on the contact surface.

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“…It is known that Cr tends to diffuse and react with the substrate during processing, depending upon the choice of substrate and other combined materials. For example, in NEMS/MEMS [2,3] or CMOS structures [4], the behavior of the Cr interlayers during the processing steps is of fundamental importance [5][6][7]. Recently, it was shown that thermionic emission properties can be improved by employing chromium silicide (Cr 5 Si 3 ) as an electrical nanocontact material, as it facilitates charge transfer through the Si/Au interface by lowering the Schottky barrier [8].…”

Section: Introductionmentioning

confidence: 99%