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.