Study of Resistive Switching in Polycrystalline ErMnO₃ Films

Rare-earth hexagonal manganites h-<i>R</i>MnO₃ (<i>R</i>=Y, Er, Ho to Lu) have been widely studied as multiferroic compounds. Recently, resistive switching behavior has been reported in polycrystalline hexagonal YMnO₃ thin films with promising applications for neuromorphic devices [1]. The particular interest in h-RMnO₃ compounds for memristive devices lies in the potential use of their peculiar ferroelectric domain pattern, and especially of their vortex lines where six-fold domains merge.<br/>In this work, we report the evidence of resistive switching behavior in polycrystalline ErMnO₃ thin films. The films (~60 nm thickness) were prepared on Pt/Ti/SiO₂/Si substrates by room temperature RF sputtering and subsequent annealing at high temperature (700-900 °C). They were characterized at the macro and microscale by X-ray diffraction, scanning electron microscopy, and confocal Raman spectroscopy. Metal-ErMnO₃-metal devices were fabricated using Ti/Au top electrodes. The Au/Ti/ErMnO₃/Pt devices exhibit a bipolar resistive switching with a R_OFF/R_ON ratio larger than 10⁴ and an ultra-low resistance of only 10 Ω in the low resistance state (R_ON), which may result in potential applications such as CMOS circuitry with low power consumption [2] and RF power switches [3]. We investigated the impact of electrical programming operations on the performances of the devices to improve their repeatability and endurance. Furthermore, we quantitatively studied the amount of hexagonal and orthorhombic crystalline phases by Raman spectroscopy and conductive atomic force microscopy and addressed the effect of their simultaneous presence on the resistive switching behavior of the films. We will discuss the properties of the different ErMnO₃phases and the origin of the resistive switching mechanism in the stacks.<br/><br/><br/><b>References</b><br/>[1] Bogusz, A., et al. "Resistive switching in polycrystalline YMnO₃ thin films." AIP Advances 4.10 (2014): 107135<br/>[2] Cao, Haichao, and Hao Ren. "A 10-nm-thick silicon oxide based high switching speed conductive bridging random access memory with ultra-low operation voltage and ultra-low LRS resistance." Applied Physics Letters 120.13 (2022): 133502<br/>[3] Pi, Shuang, et al. "Memristors as radiofrequency switches." 2016 IEEE International Symposium on Circuits and Systems (ISCAS). IEEE, 2016