Nanoionics and Nanoscale Memristive Switching in Room
Temperature SrTiO3 Thin Films
Hussein Nili, Sumeet Walia, Madhu Bhaskaran, Sharath Sriram
Functional Materials and Microsystems Research Group, RMIT University,
Melbourne, Victoria 3001, Australia
e: sharath.sriram@gmail.com
The consistent search for alternative non-volatile memories has revealed
emerging memory technologies based on nanoscale phenomena in functional oxides
[1]. Among the contenders resistive random access memory based on two terminal
devices has emerged as a promising candidate due to its facile fabrication, high
speed, scaling potential and low energy operation. The resistive switching operation
of a prominent subset of these devices is based on redox reactions and nanoionics
transport processes in the functional oxide layers and interfaces [2]. A particularly
interesting resistive switching effect is the bipolar switching based on valence change
mechanism in transition metal oxides such as TiO2 and SrTiO3 (STO) which is
triggered by drift diffusion of oxygen vacancies along the extended defects [3].
STO is dubbed by many as the foundation of oxide electronics [4]; hence, the
study of RS effects in STO based devices is of great interest. This work presents a
CMOS-compatible realization of STO-based resistive switches with excellent
switching performance. Amorphous STO (a-STO) thin films with sub-100 nm
thicknesses were deposited on SiO2 substrates using RF magnetron sputtering at
room temperature. The oxygen deficiency content of these films can be controlled
through the control of oxygen partial pressure during the deposition. In effect, this
allows for the realization of engineered oxygen vacancy with a uniform distribution
through the thickness of a-STO thin films without the need for high temperature
processing. Moreover, the controlled low temperature deposition can be utilized to
realize multi-layered oxide stacks with distinct interfaces.
Switching performance of sputtered a-STO was tested in asymmetric Pt/Ti/aSTO/Pt MIM structures utilizing 100 nm oxide thin films. After an electroforming step
under a high voltage gradient, the devices show non-volatile bipolar resistive
switching characteristics. Engineering as-grown oxygen deficiencies in a-STO thin
films results in an impressive improvement of OFF/ON ratios to the range of 10 3-104.
Compositional analysis confirms the valence change mechanism nature of the
bipolar switching in a-STO devices where the concentration of oxygen vacancies
under the Ti electrode increases significantly after the electroforming step, facilitating
the valence change mechanism in subsequent switching events.
This presentation will give an overview of conduction and switching
mechanisms in memristive devices based on low-temperature deposited a-STO thin
films, along with in situ nanoscale electrical characterization results.
Authors acknowledge project and Fellowship support from the Australian Research
Council via Discovery Projects DP130100062, DP1092717, and DP110100262.
References
[1] J. Yang et al., Nat. Nano 8, 13 (2013).
[2] R. Waser et al., Nat. Materials 6, 833 (2007).
[3] D. Strukov et al., Nature 453, 80 (2008).
[4] A. Santander-Syro et al., Nature 469, 189 (2011).