Magnetic Field Sensors Based on the Direct Magneto-Electric Effect in Hexaferrite Thin Films and the Equivalent Circuit Model

Abstract

We propose the design, fabrication, experimental implementation, and equivalent circuit model of a magneto-electric (ME) sensing device for determining the magnitude and direction of low-frequency ac magnetic fields. The device consists of two capacitive ME thin-film sensors fabricated by means of the laser ablation technique inside a pulsed laser deposition (PLD) chamber. The films are grown on a 500-nm thick indium tin oxide layer on $1.5\times 1.5$ cm2 silicon substrates using two deposition methods, namely, single target (ST) and multiple target (MT). The proposed setup is used to detect ac magnetic fields generated from a solenoid coil located at a distance of 10 mm. The experimental results demonstrate that the proposed magnetic field sensing approach using the MT method can establish the magnitude and direction of external magnetic fields with detection errors below 8%. Based on the experimental observations, we also establish a mathematical expression describing the direct ME coupling effect observed in M-type strontium hexaferrite thin films. Subsequently, we develop an electrical circuit model that can accurately predict device behavior using circuit simulations. The differential output voltages at different field strengths are predicted for both ST and MT films by simulating this equivalent circuit using the LTspice software from Linear Technology. The simulation results are in good agreement with the experimental data both qualitatively and quantitatively, and the average difference between the two ranges from 5% to 19% in the worst case.