Micromechanical characterization of electroplated permalloy films for MEMS

Abstract

In order to improve the reliability of MEMS designs, evaluating the mechanical properties of soft magnetic materials is needed. In this paper, we present a tensile testing method to characterize the mechanical properties of microscale electroplated permalloy (80 wt% Ni, 20 wt% Fe) films. The gauge section of the specimen is 50 lm wide, 100 lm long and 5 lm thick. The measured Young's modulus of permalloy films is 96.4 GPa, and the tensile strength is 1.61 GPa. The fracture strain measured by the images of specimens is about 2%.

Nanocrystalline Electroplated Cu–Ni: Metallic Thin Films with Enhanced Mechanical Properties and Tunable Magnetic Behavior

“…Interestingly, although the hardness values of nanocrystalline Cu–Ni are slightly lower than for Si, the latter exhibits a Young's modulus of 130 GPa,7 hence lower than for the metallic films investigated here. In turn, the measured Young's modulus of permalloy (96.4 GPa)—one of the typical alloys used for soft magnetic MEMS—is also much lower than for Cu–Ni 10. If one assumes a Poisson's ratio for Cu–Ni of 0.34,48 the real Young's modulus of the Cu 1– x Ni x nanocrystalline films would vary between 180.2 and 204 GPa for x = 0.45 and 0.87, respectively.…”

“…From a magnetic point of view, pure Ni, Ni 19 Fe 81 (permalloy) and CoFe‐based alloys have received attention due to their soft magnetic character 9. However, some of their mechanical properties (e.g., hardness in fine‐grained Ni or Young's modulus in Ni 19 Fe 81 thin films) are worse than those of silicon 10, 11. Most of these detrimental issues could be overcome by advanced routes to nc‐metallic thin films that combine ferromagnetic behavior with good mechanical properties and low surface roughness.…”

Magnetic Microstructure of Rolled‐Up Single‐Layer Ferromagnetic Nanomembranes

“…By using these values, we have estimated the compressive strains in the deposition direction as ε P = (9 ± 3) ‰ and ε T = (7 ± 2) ‰. To calculate the strain, the equation for the magnetostrictive anisotropy K = 3/2 λε Y is applied, with the magnetostriction constant λ = 5 × 10 −6 and the Young's modulus Y = 100 GPa for electroplated Py . Interestingly, the coercive field of the rolled‐up nanomembrane measured in the easy‐axis direction, H C,T = (6.1 ± 0.2) kA m –1 , was found to be smaller than that of the reference planar film, H C,P = (10.0 ± 0.2) kA m –1 .…”

The Use of Test Structures to Perform Chip Level Characterization Studies of Ni and NiFe Electrochemical Deposition

“…Xin Zing et al [22] introduced another variant of microrotating sensor with improved sensitivity though notches. In particular, when the magnitude of the residual stress was small, the micro-rotating structures could still make the measurement with a high accuracy of ±1 MPa [22,23]. Another approach [24] uses a load lever, a pair of torsion bars, supported by a 15×15mm frame and is based upon a two-step bulk micromachining process.…”