4.7 Article

Conditioning Circuits for Nanoscale Perpendicular Spin Transfer Torque Magnetic Tunnel Junctions as Magnetic Sensors

Journal

IEEE SENSORS JOURNAL
Volume 23, Issue 6, Pages 5670-5680

Publisher

IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
DOI: 10.1109/JSEN.2023.3241967

Keywords

Magnetic sensor; magnetic tunnel junction (MTJ); nanometer scale; spin transfer torque (STT); STTmagnetic; random access memories (MRAM); STT-MTJ

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This article presents a new type of magnetic sensor using a perpendicular spin transfer torque magnetic tunnel junction (MTJ). The sensor has a cylindrical shape with a diameter of 50 nm, making it one of the smallest ever reported. The article describes the principle of operation, signal processing electronics, and compares its performance with commercially available sensors. The developed sensor has a sensitivity of 1.28 V/T, a dynamic range of 80 mT, and a noise level of 21.8 μT/√Hz. The sensor and its electronics are compatible with existing fabrication processes, allowing for mass production in various markets.
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 21.8 mu T/root 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.

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