Forming-free threshold switching in polycrystalline ErMnO₃ films for neuromorphic applications

Rare-earth hexagonal manganites, h-RMnO₃ (R=Y, Er, Ho to Lu), are promising candidates for memristive devices owing to their peculiar ferroelectric domain pattern, especially the vortex lines where six-fold domains merge [1]. Studies in this regard have led to the demonstration of non-volatile resistive switching behavior in polycrystalline hexagonal YMnO₃ [2]. In this work, we report the first demonstration of forming-free threshold switching behavior in polycrystalline ErMnO₃ thin films, which is a result of volatile resistive switching. ErMnO₃ thin films of 60 nm were deposited on Pt by RF sputtering with subsequent post-deposition annealing to crystallize them. The Pt/ErMnO₃/Pt devices were fabricated by patterning Pt electrodes on ErMnO₃ through photolithography. The devices show a repeatable unipolar threshold switching behavior. As this electrical behavior was hitherto not reported in ErMnO₃, a detailed structural study (XRD, Raman, XPS, SEM, AFM) and extensive electrical measurements (IV, VI, IV-T) were performed to gain a clear understanding of the physical origin of the threshold switching. Based on the structural and electrical measurements a trap-assisted and thermally-activated Poole-Frenkel conduction model is hypothesized to explain the threshold switching effect and the current controlled negative-differential resistance characteristics in ErMnO₃ based filamentary switching devices. The devices exhibit very good performances with high endurance (>1000 cycles) and low variability. This original behavior offers an interesting perspective in the field of neuromorphic applications where it can be used as a scalable selector device conjointly with non-volatile memories [3].

References

[1] H. Schmidt, Appl. Phys. Lett. 118, 140502 (2021), doi: 10.1063/5.0032988.

[2] V. R. Rayapati et al., J. Appl. Phys. 126 (2019), doi:10.1063/1.5094748.

[3] X. Liu et al., IEEE Electron Device Lett. 33, 236–238 (2012), doi: 10.1109/LED.2011.2174452.