Resistive switching memories operating on ionic carriers are considered as next generation storage-class memories to replace electronic transistor memory technologies. Strain engineering is a relevant optimization route to introduce defects for resistive switching materials based on mixed ionic-electronic conducting oxides. Interfacial strain control of electrical conductivity [1] was reported for sideways-contacted Gd_0.1Ce_0.9O_2-δ|Er₂O₃ (GCO|ERO) microdot heterostructures with alternating monolayers of insulating ERO and mixed-conducting GCO, whose lattice mismatch yielded compressive strain in the GCO layers.

We use ionic heterostructures as strain-modulated memristive devices based on the model system GCO|ERO to tune the property of “memristance.” Modulation of interfacial strain and interface count is used to engineer the R_off/R_on ratio and the system’s persistence [2]. By employing Raman microscopy and TEM on heterostructures with a range of monolayer thickness down to 3-5 nm, we observed an evolution in the near-order crystal symmetry from a mostly relaxed isotropic structure—present in devices with ~100 nm monolayers, to predominantly anisotropic strain fields in devices with monolayers of several nm. Resistive switching in these model systems is discussed.

Via sideways contacting, unique model experiments isolate the impact of electroforming on a symmetric device, revealing that reversing the electroforming polarity mirrors the memristive response about zero volts without affecting memristance. In addition to GCO|ERO we explore alternative insulating straining oxides which impart varying degrees of tensile strain on GCO. Strain mapping via TEM precession-enhanced electron nanodiffraction resolves lattice distortion in these systems with nanometer spatial resolution, and strain data are correlated with interface composition and electronic structure measured by electron energy-loss spectroscopy, providing atomic-level insights regarding strained heterostructure design [3].

Acknowledgements

We acknowledge ScopeM at ETH Zürich and the John M. Cowley Center for High Resolution EM at ASU, and thank the staff for their support.

References

[1] S. Schweiger, M. Kubicek, F. Messerschmitt, F. Murer, J.L.M. Rupp. ACS Nano 8 (2014) 5032

[2] S. Schweiger, R. Pfenninger, W.J. Bowman, U. Aschuauer, J.L.M. Rupp. Adv. Mat. (In press)

[3] W.J. Bowman, S. Schweiger, E. Izadi, A.D. Darbal, J.L.M. Rupp, P.A. Crozier. (In preparation)