Paul Lippens

Control of crystallographic and magnetic texture in dc-magnetron sputtered Co–Cr on flexible PET substrate

Abstract The paper reports on hard-magnetic thin films on flexible PET substrates. The total coating stack is deposited in a roll-coater by dc-magnetron sputtering and includes a Cr underlayer, a Co–Cr magnetic layer, and an SiO 2 wear-resistant layer on top. The influence of various deposition parameters on crystallographic and magnetic properties has been investigated. The magnetic anisotropy direction in Co–Cr can be changed from perpendicular to in-plane by applying a (very thin) Cr underlayer. This in-plane anisotropy is directed in the machine direction, probably due to an anisotropic magnetostriction. No clear relation between coercivity and crystallinity or grain size is observed. The coercivity is mainly influenced by film thickness and substrate temperature. For Co–Cr without Cr underlayer, an increasing temperature results in increased coercivity and more distinct grains. For Co–Cr with Cr underlayer, an increasing temperature results in decreased coercivity and less distinct grains.

Soft-magnetic sputtered coatings on pet-substrate for electronic article surveillance

Abstract Thanks to the scaling up to large web widths and the introduction of rotatable cylindrical magnetron technology, D.C.-magnetron sputtering has also entered consumer markets such as electronic article surveillance (EAS). A very widely applied way of protecting goods in shops is the use of strip labels. Such labels have a rapidly solidified, cast, soft-magnetic strip as the active element. This strip consists of a complex alloy and has a quasi-amorphous microstructure. However, because of the finite thickness of the strip (typically 50 μm), the label is not perfectly flat and is considerably stiff. As a consequence, printing and fixing the label both have limitations. Therefore, strip labels are gradually being ruled out by soft-magnetic sputtered thin film labels. In order to yield a sufficiently high signal level in the detection gate of the EAS system, a relatively large thickness (up to 1 μm) combined with a high degree of amorphicity of the sputter-deposited soft-magnetic thin film are required. This has, of course, drastic consequences for the sputter process itself (cooling conditions, allowed working pressures, magnetic arrays, etc.). A major factor reducing production costs is the use of rotatable magnetrons: up to 90% of the magnetic material of the target can be sputtered. This is even more important since the magnetic material is an expensive, high-purity, quintary 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 that this problem can successfully be solved if know-how on target production is integrated in the coating plant.

Requirements for sputtering magnetic alloys on organic film

Deposition of magnetic thin films on organic substrates in large width roll coaters by DC-magnetron sputtering imposes specific requirements on the sputter coater in terms of magnetrons (configuration, targets, magnet arrays,...) and process conditions (substrate cooling, deposition pressure,...). This paper will discuss how the use of rotatable magnetrons and multilayer coatings can solve the technical problems for producing amorphous, soft-magnetic coatings. Integration of know-how on target manufacturing in the sputter plant has been a critical issue in reducing production costs so that the sputtered film can be used in electronic article surveillance tags. Although hard-magnetic coatings for recording applications show completely different features in terms of microstructure and thickness, the experience gained with soft-magnetic alloys has considerably helped the authors in the development of thin films with good recording characteristics (a.o. H c >40 kA m -1 ).