Abstract
Resistive random access memories (RRAMs) can be programmed to discrete resistive levels on demand via voltage pulses with appropriate amplitude and widths. This tuneability enables the design of various emerging concepts, to name a few: neuromorphic applications and reconfigurable circuits. Despite the wide interest in RRAM technologies there is still room for improvement and the key lies with understanding better the underpinning mechanism responsible for resistive switching. This work presents a methodology that aids such efforts, by revealing the nature of the resistive switching through assessing the transport properties in the non-switching operation regimes, before and after switching occurs. Variation in the transport properties obtained by analysing the current-voltage characteristics at distinct temperatures provides experimental evidence for understanding the nature of the responsible mechanism. This study is performed on prototyped device stacks that possess common Au bottom electrodes, identical TiO2 active layers while employing three different top electrodes, Au, Ni and Pt. Our results support in all cases an interface controlled transport due to Schottky emission and suggest that the acquired gradual switching originates by the bias induced modification of the interfacial barrier. Throughout this study, the top electrode material was found to play a role in determining the electroforming requirements and thus indirectly the devices’ memristive characteristics whilst both the top and bottom metal/oxide interfaces are found to be modified as result of this process.
Highlights
Resistive Random Access Memories (RRAM) are two terminal devices that can support a multitude of resistive memory levels in a non-volatile fashion, triggered by an appropriate electrical stimulus[1,2]
If a more physics view is employed, RRAM technologies can be identified as (i) electrochemical metallisation cells (ECM) where resistive switching (RS) relies upon the dissolution of an active electrode typically Ag or Cu11, (ii) valence change memories (VCM) where redox reactions lead to changes in the conductivity of the metal-oxide (MO) film[11], (iii) thermochemical (TCM) in which RS is a result of a fuse/ anti-fuse process due to current-induced temperature variation[11] and (iv) interfacial, arising by the modification of the potential barrier at metal electrode/core film interface[12]
The present paper introduces a methodology for extracting the switching mechanism nature of TiO2 RRAM cells by analysing the temperature dependence of their I–V characteristics in their non-switching regime, just before a switching event takes place
Summary
Resistive Random Access Memories (RRAM) are two terminal devices that can support a multitude of resistive memory levels in a non-volatile fashion, triggered by an appropriate electrical stimulus[1,2] This unique feature, referred to as resistive switching (RS), along with the technogy’s potential to co-integrate RRAM cells with conventional semiconductor devices sparked a great interest in this field over the past decade. It is timely to study and develop in more depth techniques and methodologies that allow us shining more light in the physical mechanism underpinning RS effects. RS effects appear to depend upon various parameters including the active area material, the metal electrodes employed and the electroforming process that is typically required in most of the RRAM technologies reported to date. The electrode materials may affect even the post-electroforming[16] electrical response of the device is a parameter to be considered
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