2023-09, Nicolas, Hugo, Sousa, Ricardo C., Mora-Hernández, Ariam, Prejbeanu, Ioan-Lucian, Hebrard, Luc, Kammerer, Jean-Baptiste, Pascal, Joris

This paper presents the use of the spin transfer torque effect in perpendicular magnetic tunnel junctions to operate the devices as magnetic sensors. The junctions, specifically designed for sensing applications exhibit close to low-coercivity, allowing the sensitivity to be as high as 25 mV/mT for a large dynamic range of 20 mT. In addition, the junctions have diameters ranging from 20 to 100 nanometers, making them among the smallest magnetic sensing elements ever reported to our knowledge. A single operational amplifier operates the junction and outputs a voltage proportional to the external magnetic field. This paper opens the way to a monolithic integration of both the conditioning electronics and the perpendicular magnetic tunnel junction.

2023, Nicolas, Hugo, Sousa, Ricardo C., Mora-Hernández, Ariam, Prejbeanu, Ioan-Lucian, Hebrard, Luc, Kammerer, Jean-Baptiste, Pascal, Joris

This article demonstrates a new type of magnetic sensor using a perpendicular spin transfer torque magnetic tunnel junction (MTJ). The sensing element has a cylindrical shape of 50 nm in diameter and is to our knowledge among the smallest magnetic sensor ever reported. This article describes the principle of operation of the sensing element and the associated signal processing electronics, which delivers a signal proportional to the external magnetic field. Experimental results are detailed and compared to the state-of-the-art commercially available integrated magnetic sensors as well as published magnetoresistive sensors based on MTJs with comparable size. The measured sensitivity of the developed sensor is 1.28 V/T, and its dynamic range reaches 80 mT. The measured noise level is 21.8μT/√ Hz. Two different operating principles of the proposed sensor are described and compared, one based on a time-to-digital converter and one based on a pulsewidth-modulated (PWM) signal. Both methods require only standard microelectronics components, which are suitable for monolithic integration of the sensing element with its conditioning electronics. Subsequent improvements of the sensing element as well as conditioning electronics are required to further lower the noise level. The sensing element and its conditioning electronics are compatible with fabrication processes already used in magnetic random access memory fabrication. This opens the way to mass production and addresses various markets, such as consumer electronics, automotive, industrial sensing, physics experiments, or medical devices.

2023-02, Vergne, Céline, Féry, Corentin, Quirin, Thomas, Nicolas, Hugo, Madec, Morgan, Hemm-Ode, Simone, Pascal, Joris

2022-06, Quirin, Thomas, Vergne, Céline, Féry, Corentin, Badertscher, Patrick, Nicolas, Hugo, Mannhart, Diego, Osswald, Stefan, Kuhne, Michael, Sticherling, Christian, Madec, Morgan, Hébrard, Luc, Knecht, Sven, Pascal, Joris

2023, Vergne, Céline, Nicolas, Hugo, Madec, Morgan, Hemm-Ode, Simone, Guzman, Raphael, Pascal, Joris

On-chip magnetometers are already integrated within long-term implants such as cardiac implantable electronic devices. They are also good candidates to be integrated within the next generations of brain stimulation electrodes to provide their position and orientation. In all cases, long-term implants are expected to be at least certified as MRI conditional. We investigated the resilience to the exposure to 3 T and 7 T of an anisotropic magnetoresistive sensor integrating a set/reset function. The sensitivity, non-linearity, and offset of a batch of 63 identical sensors were not affected by the exposure. These preliminary results provide new insights on the usability of magnetoresistive sensors for biomedical applications requiring MRI conditionality.

2022, Nicolas, Hugo, Pascal, Joris, Hebrard, Luc, Kammerer, Jean-Baptiste, Sousa, Ricardo C., Mora-Hernandez, Ariam, Prejbeanu, Ioan-Lucian