Speaker
Description
Anisotropic Magnetoresistive (AMR) sensors provide a straightforward, low cost and low power consumption solution for magnetic field sensing applications [1]. Despite being a mature technology, a vertical sensor packing strategy in parallel electrical connection can be beneficial for AMR devices, by reducing their electrical noise without increasing the device footprint. These advantages were already demonstrated for other xMR architectures [2].
In this work we study the influence of surface roughness on microfabricated sensors in a vertically packed structure, insulated with a non-conductive spacer layer (Fig. 1a). Each AMR element was measured at different packing levels (from N=1 to N=4) allowing the correlation of topography and roughness on each sensing layer with changes in key parameters of the $R(H)$ curves - Fig. 1b) -, such as $\Delta R/R$, $R$ and Magnetic Saturation Field ($H_{Sat}$). Overall, an increase in $R$ is observed, leading to a slight decrease in AMR (e.g. from 2.4 $\%$ to 2.2 $\%$); magnetically, a linear increase in $H_{Sat}$ is found (e.g. from $\approx$2 mT to $\approx$8 mT). For the electrical noise characterization, four different designs were patterned to obtain similar resistance values ($\approx$1 k$\Omega$) at each number of packed levels, thus providing a comparable baseline for noise measurements (Fig. 1c). Interlevel coupling will also be studied as a function of the non-conductive layer thickness used to separate different levels.
The specific contributions of surface roughness [3] and interlevel coupling will be discussed, aiming towards low noise AMR sensor tailoring. Additionally, key parameters for sensor performance are also evaluated at each number of vertically packed levels, including Hooge parameter for noise characterization.
Fig. 1 a) Schematic representation of vertically packed AMR sensors in parallel electrical connection. b) Representative $\Delta R/R$ curves of AMR sensors with increasing vertically packed levels. c) Resistance values of microfabricated designs for noise measurements with a 1 k$\Omega$ resistance baseline.
Acknowledgements
The authors acknowledge BASE (UIDB/0536/2020), PROGRAMATICO (UIDP/0536/2020) Programs and grant PD/BD/150391/2019.
References
[1] M. A. Khan, J. Sun, B. Li, A. Przybysz, and J. Kosel, “Magnetic sensors-A review and recent technologies,” Engineering Research Express, vol. 3, no. 2. IOP Publishing, p. 022005, Jun. 01, 2021. doi: 10.1088/2631-8695/ac0838.
[2] M. Silva, F. Franco, D. C. Leitao, S. Cardoso, and P. P. Freitas, “Two-dimensional arrays of vertically packed spin-valves with picoTesla sensitivity at room temperature,” Scientific Reports, vol. 11, no. 1. Springer Science and Business Media LLC, Jan. 08, 2021. doi: 10.1038/s41598-020-79856-0.
[3] H. Liu, T. Škereň, A. Volodin, K. Temst, A. Vantomme, and C. Van Haesendonck, “Tailoring the magnetic anisotropy, magnetization reversal, and anisotropic magnetoresistance of Ni films by ion sputtering,” Physical Review B, vol. 91, no. 10. American Physical Society (APS), Mar. 05, 2015. doi: 10.1103/physrevb.91.104403.
