Our work in the field of magnetic sensors, from fundamental to applied research, involves developing high performance magnetic sensors of giant magnetoresistance, tunnel or inductive types, for a wide variety of applications. These developments are based on an understanding of physical phenomena (magnetic couplings, properties of thin-film materials, spin electronics, transport, noise, electronics, etc.), control of structural deposits to optimize and adapt stacks for specific applications, electrical and magnetic characterizations to measure sensor performance, and modeling with macrospin or micromagnetic simulations. These sensors can be developed all the way to systems by integrating them into setups/demonstrators using the electronics, manufacturing and packaging tools developed at the LNO.
Fundamental studies in the framework of magnetic sensing
[Coll. LAF]
Sensitivity and noise are two important parameters for magnetic sensors: they define the detectivity, i.e. the minimum field that can be detected at a certain frequency. We thus investigate these parameters improvement methods: stabilization of the magnetic sensing layer with a pinning field (by an external field, internal to the stack or by shape anisotropy)[1], vertical stacking of several giant magnetoresistance stacks[2] and driving the dynamics of the magnetic sensing layer by spin transfer torque or by external RF excitation[3]. Another study, linked to the ANR STORM and the ADAGE project within the PEPR SPIN framework, has been launched to integrate Spin Orbit Torque as an additional degree of freedom in the TMR sensor, so as to be able to electrically shift the magnetization of the reference layer or the free layer on demand. This would make for more versatile and adaptable sensors, capable, for example, of changing field range or directivity during operation, or correcting offsets
[2] 10.1103/PhysRevApplied.13.034031
Characterization tools of the magnetic properties at the local scale
[Coll. CEA/ LIST/DISC – GET- Elytmax (INSA Lyon) and Laboratoire Ampere – Laboratoire de Physique des Solides, Orsay]
The characterization of the magnetic properties of materials at the local scale is important for applications such as in fundamental research, in-situ monitoring, non-destructive testing or nanometrology. In this way, we used MR sensors whose size could be reduced down to the µm scale while keeping a good detectivity of the order of nT/. We investigate in the lab several examples.
Two scanning MR systems have been developed at two length scales, submillimeter and submicrometer: the 3D scanner and the MR-SPM (scanning probe microscope), and have been validated on samples furnished by collaborators.
An innovative solution to measure local magnetic properties, adapted to real-time monitoring and magnetic circuit evaluation, composed by GMR sensors has also been developed.
A probe designed to investigate 2D mesoscopic systems (graphene[1] and Moiré[2]) has been successfully used to detect the orbital moments, and will be adapted to other topological systems (ANR TireDHel, starting 2024).
[2] 10.1103/physrevlett.131.116201
Biological and medical applications
Coll. CEA/JOLIOT/SPI/LERI, SPEC/LETS, Service de Bactériologie-Hygiène, Hôpital Antoine Béclère AP-HP Paris Saclay, Hôpital Robert Debré Paris, CEA-Biomaps et Neurospin, INSA Lyon, Tohoku University, Japan – Ernst Strüngmann Institute-Frankfurt, Germany]
The development of early diagnosis techniques transportable to the patient’s bedside is a challenge not only for healthcare, but also for defense and the environment. We have patented a specific, very sensitive and easy to use GMR sensor-based biochip[1],[2] that can robustly detect magnetically labelled biological targets of various size (cancer cells, bacteria) in complex matrices (culture medium, plasma etc…).
Ultra sensitive magnetic sensors (detectivity below 0.1fT/sqrt(Hz) have also been optimized to develop a realistic very low field MRI. Two systems have been mounted, a brain MRI system functioning at 10 mT and installed at Neurospin and an MRI system for premature babies (ANR VLFMRI) which will be installed at Robert Debré hospital.
Locating catheters in the human body is also of great interest and we have started this activity by inserting GMRs or TMRs sensors at the tip of catheters in a controlled field environment to track their movement during vascular surgery without patient exposure to irradiation.
Finally, the Magnetrodes program, intended to measure magnetic signals of neurons in vivo with very thin pointed probes with GMR[3], has allowed to extract single neurons signatures[4].
[1]https://doi.org/10.3390/bios9030105
[2] https://doi.org/10.1039/D2LC00353H
[3] 10.1021/acssensors.0c01578
Figure 1: a) Typical reconfigurable sensor combining SOT line and TMR pillar b) GMR sensor-based biochip for early diagnosis test c) Example of 3D GMR probe for magnetic cartography d) MRI image of a phantom acquired on the baby system in 15 minutes. The voxel size is 8 mm3, the largest structures are 10 mm in diameter.
Industrial applications
Coll. Allegro Microsystems, CST, CMPhy, Michelin, Airbus Defense and Space, Schlumberger, Dassault, Orano
Based on its long-term knowledge of magnetic sensing and on its fabrication and characterization tools, the LNO team is very active in industrial partnerships to propose innovative and robust solutions in the industrial, consumer or automotive field.
The collaboration with Crivasense technologies (founded in 2014 with CEA) and Allegro Microsystems, a world leader in magnetic sensors for automotive and consumer applications, has led to launching many products, based on GMR and TMR, such as current sensor, position sensor or angle sensors. This collaboration and the related common laboratory have ended at the beginning of 2024 by decision of the industrial partner.
Other partnerships with industrials have been launched during the period, for non-destructive testing (CMPhy, Michelin), oil prospection (Schlumberger), current sensors (Airbus), nuclear fuel analysis (CEA-DES and Orano)…
Regular Industrial contracts for magnetic characterization or deposition services are performed, showing their interest in the laboratory’s expertise.
Perspectives : Fundamental aspects of the research, in particular related to spin-orbit torque effects and the use of magnetic textures, will be studied both in terms of fundamental understanding and to provide the building blocks for future magnetic sensing devices. These aspects are developed for the next years in the ANR STORM project and the ADAGE project in the SPIN PEPR.
Today, GMR devices have been optimized in terms of signal to noise and the focus is now on Tunnel magneto-resistance (TMR) structures where low frequency noise is still a strong limitation. Their optimization will be pursued for applications in spin waves detection and 2D systems investigation. They will be also the basis for the next generation of ultra-sensitive magnetometers, with the integration of different types of concentrators.
Regarding medical and biological applications, very low field MRI will reach the end of the laboratory development with the implementation of first devices in hospitals in the next period and the technology will be transferred to an existing or a new company.
In the context of IHU Prometheus (Paris-Saclay), the sensor-based biochip will be adapted and evaluated for the detection of bacteria responsible for sepsis, to enable early treatment of patients.
Finally, the dynamics of integrating the team’s research towards solutions dedicated to industrial challenges will be pursued within the framework of various types of industrial partnerships.