Piezoresistance characteristics of some magnetic and non-magnetic metal films

Abstract

We have measured the strain–resistance characteristics of some non-magnetic and magnetic metal films. In order to suit to the objective of this article, we have chosen the Pd film as an example for the non-magnetic film, the Fe 21Ni 79 film for the magnetic film with a positive magnetostriction ( λ s>0), and the Co 20Ni 80 film for the magnetic film with λ s<0. The thickness t f of the films ranged from 40 to 1500 Å. The strain gauge factor γ of the Pd film was obtained from the linear strain–resistance plot. Then, γ is expressed as a function of the sheet resistivity R sq. For the magnetic films, only when the film is saturated either longitudinally (∥) or transversely (⊥) by an external field, is the strain–resistance plot linear. While in a zero-field, the strain–resistance plot becomes non-linear. From the former, we could obtain γ ∥ or γ ⊥, and from the latter, we could obtain γ ap. γ ∥ or γ ⊥ is of the same order of magnitude as γ. However, γ ap is abnormally large, due to the magnetoelastic and the anisotropic magnetoresistance effects. In addition to the piezoresistance data, we also found the critical thickness ( t fc) for the electrical coalescence and that ( t fm) for the magnetic coalescence. Usually, for the same magnetic material, t fm> t fc. The coalescence ability is the best for the Co 20Ni 80 films, and the worst for the Pd films.