Printable giant magnetoresistive sensors with high sensitivity at small magnetic fields

• Applicants: Professor Dr.-Ing. Christoph Leyens; Dr. Denys Makarov
• Subject Area: Synthesis and Properties of Functional Materials
• Term: from 2018 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 407555984

Printed electronics are about to revolutionize the field of conventional electronics offering low-cost, large area and high-throughput production. By adding a magneto-sensitive element to the family of printable electronics, we envision the realization of energy efficient contactless switches for intelligent packaging or postcards as well as smart and protective clothes (e.g., for firefighters, athletes) offering the in-cloth integrated navigation and position tracking modules. Although highly demanded, high-performance printable magnetic field sensors relying on giant magnetoresistive (GMR) effect are not available manly due to the lack in the fundamental understanding of the magnetoresistive effects in a GMR powder mixed with a polymeric binder solution.First proof-of-concept realizations of printable GMR sensors are reported by us. However, the optimization of the sensors is based on empirical approaches, which do not allow us to achieve strong sensor responses in the range of small magnetic fields, e.g. <10 mT as needed for the application in consumer electronics and wearables. It can well be that the performance of printed sensors in the small fields region is fundamentally limited by the randomization effects due to the electron transport through percolated GMR flakes. Alternatively, it can be that we do not understand the role of the size of the GMR flakes on the GMR response of printed sensors. Is there a limitation on the flake size when the GMR response will disappear due to the mechanical impact upon ball milling? What is the impact of the ball milling on the magnetic properties of the GMR powder? In this project we address these important fundamental issues, aiming to boost the performance of printed GMR sensors further. Our preliminary work indicates that the magnetron sputter deposition used to fabricate the GMR powder might be not optimal to achieve sensitivity at small magnetic fields. In this project, we will prepare GMR powder using complementary approaches: (i) magnetron sputter deposition and (ii) ion beam sputtering. In contrast to the magnetron sputter deposition, the ion beam sputtering allows to produce GMR multilayers revealing (i) the absence of hysteresis and (ii) superior linearity even at small magnetic fields. This performance is very attractive for the realization of high-performance flexible and printable magnetic field sensors. The fabrication of GMR stacks using ion beam sputtering is not as well established as using magnetron sputter deposition. Therefore, the fundamental understanding of the magnetization processes in ion-beam sputtered magnetic/nonmagnetic sandwiches is still lacking. We will close this gap and investigate what is the physical reason behind the experimentally observed remarkable linearity and absence of hysteresis of the GMR response down to small magnetic fields of GMR stacks prepared by ion-beam sputtering.

• DFG Programme: Research Grants