Comparison of Micro-Fabrication Routes for Magneto-Impedance Elements: Lift-Off and Wet-Etching

We compare two photolithographic methods to pattern magneto-impedance elements with micrometric dimensions, suitable to build magnetic microsensors. The magnetic material to be patterned is deposited by sputtering onto silicon wafers. It has a sandwiched structure where the outer magnetic layers are composed by a stack of permalloy and thin titanium layers and the central non-magnetic layer is made of copper. The total thickness is 1.31
$\mu{\rm m}$
. After preparation it displays an excellent magneto-impedance performance that is intended to be retained after the patterning procedure. For the lift-off method, a negative-type resist is deposited and patterned onto the silicon wafer prior to the material deposition. The undesired parts of the material are peeled off when removing the resist. Even for such a thick film, the quality of the obtained samples is quite good and the magneto-impedance response of the micro-shaped samples is great. In the wet-etching method, a positive-type resist is deposited and patterned onto the sputtered material. The parts that are not protected by the resist are etched using an acid solution. The different chemical behavior of the metals that constitute the sample severely challenges the wet-etching process. The results are poor, and the results compare unfavorably to those obtained by the lift-off process.