Speaker
Description
Extraordinary magnetoresistance (EMR) sensors are geometry-dependent 4-terminal devices based on high-conductivity semiconductors and metal inclusions, that can achieve over $10^6\,\%$ magnetoresistance ratios [1,2]. The origin of such effect can be explained by Lorentz force, rewriting the conductivity tensor of the semiconductor with a magnetic field dependence. Deviations of the current path result in charge accumulation in the semiconductor, giving rise to incredibly high voltage differences.
In this work, this effect is employed for passive current limiting applications with a 2-terminal device. With the possibility to integrate a magnetic circuit in the current path, the rise in current will create a field on the EMR device, in turn increasing its resistance and thus limiting the current overshoot and its plateau levels [3]. Investigations of the analytical model of such device shows that the maximum achievable MR ratio is $\mu^{2}B^{2}$, where $\mu$ is the charge-carrier mobility of the semiconductor and $B$ is the magnitude of the applied magnetic field. Contrary to the 4-terminal sensor, metal inclusions do not improve the current limiter performance, and charge-accumulation at the edges degrades the obtained MR. The model indicates that this can be mitigated by engineering the geometry of the device, increasing the dimension parallel to the deviated current path. To approach the theoretical limit, the length of the device must be $\mu B$ times its thickness. We also present another solution to avoid charge-accumulation by short-circuiting the semiconductor edges, improving the MR without changing the device geometry. Another known negative influence on MR is the contact resistivity between the semiconductor and the metal electrodes [4]. The present work also proposes a way of minimizing this by tweaking the device geometry.
In current limiter applications, it is the current of the main circuit itself that passes through the device, and not a small bias current as it is the case in sensor applications. Electric current levels can reach units of amperes, and as high current passes through the EMR element, resistive power dissipation becomes relevant. Electric and thermal simulations with finite element method (COMSOL) in 3D for different device sizes corroborate the analytical model and are used to investigate resistance variations and Joule heating.
Acknowledgements
This work has been jointly supported by Eaton and Silicon Austria Labs, owned by the Republic of Austria, the Styrian Business Promotion Agency, the federal state of Carinthia, the Upper Austrian Research and the Austrian Association for the Electric and Electronics Industry.
References
[1] S. A. Solin, T. Thio, D. R. Hines, and J. J. Heremans, “Enhanced Room-Temperature Geometric Magnetoresistance in Inhomogeneous Narrow-Gap Semiconductors,” Science, vol. 289, no. 5484. American Association for the Advancement of Science (AAAS), pp. 1530–1532, Sep. 2000. doi: 10.1126/science.289.5484.1530.
[2] J. Sun and J. Kosel, “Extraordinary Magnetoresistance in Semiconductor/Metal Hybrids: A Review,” Materials, vol. 6, no. 2. MDPI AG, pp. 500–516, Feb. 13, 2013. doi: 10.3390/ma6020500.
[3] P. Kopejtko, “Current controlling element based on saturation of a magnetic circuit”, EP Patent EP3 961 925A1, Mar,. 2022
[4] J. Sun and J. Kosel, “Finite Element Analysis on the Influence of Contact Resistivity in an Extraordinary Magnetoresistance Magnetic Field Micro Sensor,” Journal of Superconductivity and Novel Magnetism, vol. 25, no. 8. Springer Science and Business Media LLC, pp. 2749–2752, Aug. 06, 2011. doi: 10.1007/s10948-011-1256-8.
