Enhanced Soft Magnetic Properties of [NiFe/Ta]<italic>n</italic> Laminated Films for Flux Amplification in Magnetic Sensors

Abstract

The soft magnetic properties of single-layer NiFe and multilayer [NiFe/Ta] n thin films were investigated and presented in this paper. The NiFe films were prepared by RF sputtering method on thermally oxidized Si substrates at room temperature. The thickness dependence of coercivity ( $H_{c}$ ) of single-layer NiFe was revealed by the fact that the $H_{c}$ increased with the thicker films of 25, 50, 100, and 200 nm. In order to enhance the softness of the NiFe films, the non-magnetic spacer tantalum (1 nm) was introduced in the laminated structures leading to a decrease in $H_{c}$ with increase in the number of separated layers ( $n$ ). Notably, with the tantalum spacer of 1 nm at $n = 3$ , $H_{c}$ decreased dramatically from 35 down to 0.3 Oe. A minimum $H_{c}$ of 0.14 Oe was achieved at $n = 3$ and the Ta thickness of 3 nm. A possible application for the designing flux concentrator (FC) in magnetic sensor was simulated using the finite-element method. The obtained favorable results of the multilayer structures envisaged that the microfabrication of laminated [NiFe/Ta] n films would be appropriately used in magnetic sensor applications, such as the flux guide films, FC parts, and the integrated core of fluxgate sensors.