Sensors and Actuators A 106 (2003) 26–29 Magnetic field sensors based on thin film multi-layer structures P.I. Nikitin a,∗ , S.I. Kasatkin b , A.M. Muravjov b , P.M. Vetoshko a , M.V. Valeiko a , V.I. Konov a , T. Meydan c a General Physics Institute, Academy of Sciences of Russia, 38 Vavilov Street, Moscow 119991, Russia b Institute of Control Sciences, Academy of Sciences of Russia, 85 Profsoyuznaya Street, Moscow 117806, Russia c Wolfson Centre, School of Engineering, Cardiff University, Wales Newport Road, P.O. Box 687, Cardiff CF2 3TD, UK Abstract Thin film multi-layer structures were deposited and optimised for various low noise magnetic field sensors. Original bridge schemes have been tested for the magnetoresitive sensors, which are sensitive not only to amplitude but also to the magnetic field direction. Double-layer anisotropic magnetoresistive sensors have showed decreased hysteresis and lower influence of previous measurements. Deposited spin-dependent structures with antiferromagnetic fixing layer of Fe 50 Mn 50 had 30% magnetoresistive effect. © 2003 Elsevier B.V. All rights reserved. Keywords: Magnetic films; Sandwiched structures; Sensors 1. Introduction Multi-layer structures of thin magnetic films are exten- sively studied now and successfully used in many mag- netic sensors. Among them, giant magnetoresistive sensors (GMR) based on the spin-tunnelling and spin-valve effects should be mentioned first of all [1,2]. It is possible to pro- duce low noise magnetic samples for high sensitive mag- netometers, which use uniform rotation of magnetisation in a single domain sample [3], with multi-layer structures of traditional permalloy films, each thin layer being sepa- rated by low conducting or dielectric films. In many cases, the multi-layer magnetic structures can improve properties of traditional sensors such as anisotropic magnetoresistive sensors (AMR), which are mainly produced using single magnetic films. This is due to several effects. For example, in a double-layer structure a closure of a demagnetisation magnetic field can be realised, which decreases hysteresis and influence of previous measurements (residual magneti- sation or the “memory” effect). To decrease these effects, a single-layer AMR sensor KMZ51 (Philips Semiconductor) is integrated with a planar coil, and short current pulses of different polarity and rather big amplitude are passed before each measurement. Another prospective way to improve per- formance of the AMR sensors is deposition of a second soft magnetic layer on the top of the control current conductor. ∗ Corresponding author. Tel.: +7-095-135-0376; fax: +7-095-135-0376. E-mail address: nikitin@kapella.gpi.ru (P.I. Nikitin). Magnetisation of this layer will increase the magnetic field acting on the AMR structure. This paper is devoted to the optimisation of multi-layer magnetic structures for sensor applications as well as bridge schemes for the AMR and GMR sensors. 2. Deposition procedures Amorphous magnetic FeCoNiSiB films were fabricated on silicon, glass and ceramic substrates by means of pulsed UV excimer (XeCl) and IR (CO 2 ) laser deposition as well as RF sputtering. Besides, polycrystalline soft ferromag- netic materials that have high saturation magnetisation, such as Ni 81 Fe 19 (permalloy) and zero-magnetostriction Ni 60 Co 30 Fe 10 , were deposited onto various substrates and used in sandwiched structures. The films were examined by the X-ray diffraction, X-ray specular reflectivity, X-ray pho- toelectron spectroscopy, transmission electron microscopy, profilometry, and ellipsometry. As was previously shown in [4,5], high power laser abla- tion of an amorphous magnetic target is capable to provide congruent composition transfer to a growing film and pro- duce good magnetic properties of the film. The laser-deposited films on glass and Si substrates ap- peared to be very hard and mirror-like. Microscopy and profilometry revealed high optical quality of their surfaces. A number of droplets on the surfaces were observed, but it was substantially reduced by proper adjustment of the 0924-4247/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0924-4247(03)00098-0