Deposition of Giant Magnetoresitance (GMR) Sensors on Large Areas

Magnetic field sensors are broadly applied to detect any type of motion including proximity, rotations or vibrations. Motion sensing is required in numerous applications from industrial robotics, through prosthetics to virtual and augmented reality appliances. When fabricated using thin film technologies (thin film deposition and lithographic patterning), magnetic field sensors relying on giant magnetoresistive (GMR) effect made major impact on our society via realization of high-capacity hard disk drives. This was the key enabler behind the development of cloud storage and social media. Magnetic thin films are used in read heads of hard disk drives or as information bits in magnetic random access memory (RAM) or as electronic compasses in our smartphones for navigation purposes.

The GMR technology puts stringent requirements on a deposition facility. Indeed, GMR stacks typically consisting of multilayers of about 1-nm-thick Co and Cu layers (see Fig. 1) require precision in the film thickness of better than 0.1 nm. Only in this case, it is possible to fabricate high-performance sensors revealing large changes of electrical resistance with magnetic field. To comply with these requirements on the deposition accuracy over large areas, conventionally, thin film based magnetic field sensors are fabricated on planar substrates like Si wafers and are thick and rigid.

The need to realize magnetic field sensing functionality for flexible and wearable electronics stimulated development of technologies to prepare high-performance GMR sensors on polymeric foils of different thickness ranging from 1 μm up to 150 μm. This trend concerned also the realization of mechanically flexible anisotropic magnetoresitance (AMR) sensors, tunneling magnetoresistive (TMR) sensors and giant magnetoimpedance (GMI) sensors.Lab scale demonstrations highlighted the application potential of flexible magnetoelectronic devices for Internet of Things (IoT), smart home and eMobility.

When prepared on ultrathin polymeric foils (about 1 μm thick), magnetic field sensors can be applied to human skin for the realization of magnetosensitive smart skins. They enable touchless interactivity with our surrounding based on the interaction with magnetic fields (geomagnetic fields or permanent magnets), which is relevant for human-machine interfaces for virtual and augmented reality.

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