Printed magnetoresistive sensors for contactless switching

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Printed electronics are a key technology in many industrial sectors. In collaboration with the Group of Dr. Denys Makarov, Helmholtz-Zentrum Dresden-Rossendorf HZDR, IKTS researchers are now demonstrating considerable progress in development and thus opening up a new type of application: Using low-cost, readily available materials and industrially relevant high-throughput processes, they are able to print flexible magnetoresistive sensors for contactless switching.

© Fraunhofer IKTS
Flexible magneto-resistive sensor with contacts.

Contactless switches are currently based on optical, capacitive or magnetic devices, the latter mostly on so-called reed elements. While optical switches cannot be used in dusty or foggy environments, capacitive ones reach their limits under water. Reed switches are fragile during installation and operation, offer only limited miniaturization and are rigid. These disadvantages prevent installation in flexible electronics. The novel printed switches could soon be a marketable solution that would enable exactly this and be flexibly applicable both in harsh environments and under ionizing radiation, e.g. in medical diagnostics and therapy.


Potential replacement of reed sensors


Since printed magnetoresistive (MR) sensors do not have mechanically moving parts, they unlike reed sensors, have proven to be robust against mechanical influences: “That's why our solution has the potential to replace reed sensors in many areas. Possible applications for human-machine interaction under previously unimaginable conditions are also conceivable. This could be of particular relevance to the workflows of medical and security personnel, for example,“ explains Dr. Mykola Vinnichenko, who has validated a novel process combination for the printing of MR sensors at Fraunhofer IKTS. The characterization and proof of the magnetoresistive properties was carried out at HZDR.


Combination of screen printing and diode laser sintering


By combining material-efficient screen printing and post-processing via diode laser sintering, flexible, robust MR sensors with individual designs can be produced within a few seconds as the basis for contactless switching applications. “Diode laser sintering is the enabling technology here when readily available materials must be functionalized magneto-resistively. The combined process is relatively easy to upscale and thus suitable for mass production. Hundreds of millions of flexible MR sensors can be easily produced,“ adds the physicist, pointing out the potentially low cost of less than a cent per sensor with an easy integration into portable electronics or smart textiles.


Technology transfer


The technology was demonstrated on a laboratory scale. Currently, the researchers at IKTS and HZDR are looking for industrial partners for joint further development, transfer projects and upscaling.

Demonstration of the functional principle of the printed switch. The permanent magnet approaches the sensor, an increasing magnetic field leads to an increasing electrical resistance. Using electronic threshold logic, the changing resistance is then converted into an on-off signal. The latter serves to switch the light source on and off (© HZDR ).