SOFT-MAGNETIC SPUTTERED COATINGS ON PET-SUBSTRATE FOR ELECTRONIC ARTICLE SURVEILLANCE

Thanks to the scaling up to large web widths and the introduction of r otatable cylindrical magnetron technology, D.C.-magnetron sputtering h as also entered consumer markets such as electronic article surveillan ce (EAS). A very widely applied way of protecting goods in shops is th e use of strip labels. Such labels have a rapidly solidified, cast, so ft-magnetic strip as the active element. This strip consists of a comp lex alloy and has a quasi-amorphous microstructure. However, because o f the finite thickness of the strip (typically 50 mu m), the label is not perfectly flat and is considerably stiff. As a consequence, printi ng and fixing the label both have limitations. Therefore, strip labels are gradually being ruled out by soft-magnetic sputtered thin film la bels. In order to yield a sufficiently high signal level in the detect ion gate of the EAS system, a relatively large thickness (up to 1 mu m ) combined with a high degree of amorphicity of the sputter-deposited soft-magnetic thin film are required. This has, of course, drastic con sequences for the sputter process itself (cooling conditions, allowed working pressures, magnetic arrays, etc.). A major factor reducing pro duction costs is the use of rotatable magnetrons: up to 90% of the mag netic material of the target can be sputtered. This is even more impor tant since the magnetic material is an expensive, high-purity, quintar y Co alloy. A drawback, however, is the fact that such targets are not readily available on the market. In the following, it will be shown t hat this problem can successfully be solved if know-how on target prod uction is integrated in the coating plant. (C) 1997 Elsevier Science S .A.