Coating technology enables customized magnetic sensors

Coating technology enables customized magnetic sensors

Technology News |
By Jean-Pierre Joosting

Magnetic sensors are ubiquitous today. They measure the rotation speed of the wheels in our cars for the anti-lock system, they read the data from fixed disks and detect micro cracks in metal components. The wealth of possible applications requires individual sensor designs and dimensioning for all these applications.

The sensors consist of micro-structured stacks of alternating magnetic and non-magnetic layers, with each layer having a thickness of just a few nanometers. Under the influence of external magnetic fields, the electric resistance of these stacks is changing. Though the giant magneto-resistance effect has revolutionized the sensors, one problem remains: The magnetic field strength at which the sensors are switching from one state to the other one is more or less a fixed value.

DESY scientists now have developed a manufacturing technique that makes it possible to control the magnetic properties of the sensor layers. With the process, it is possible to “adjust” the magnetic field strength required to switch in each single layer of the stack. In addition, the preferred magnetic orientation of each layer can be adapted to the needs of the respective design. This makes it possible to implement a large variety of sensors with individual properties. “Hitherto it was necessary to adapt the application to the properties of the sensor. Now we can customize the sensor to the needs of the application,” explains DESY researcher Kai Schlange who authored the study in which he reveals the results of the research project.

The basis for the new sensor technology is the Oblique Incidence Deposition (OID). The OID process, already known for single layers, makes it possible to shape any magnetic material on any substrate. By varying the deposition angle, technologists can determine if a magnetic layer should switch at an external magnetic field of, for example 0.5 millitesla or only at a field strength a hundred times higher.

The researchers noted that the application of this technique is not only possible for single layers but also for stacks with a high number of layers. The production of such multi-layer systems has been carried out at under vacuum. Through experiments with an X-ray source, the physicists were able to exactly survey the magnetic properties of each single layer in such a multi-layer stack. Thus they could prove that OID makes it possible to implant magnetic structures of any desired complexity and at high exactness into extended stacks. “This technique enables manufacturing magnetic sensors whose signals are much more precise and contain more information than ever before”, explained Ralf Röhlsberger who headed the research team. “It significantly increase the precision of measuring rotational movements, leading to substantially better safety of motors, drive systems and engine controls, in particular if these engines are operated under extreme conditions”.

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