Resistive switching in Cu:TCNQ thin films

Recently there has been a growing interest in alternative non-volatile memory technology concepts for massive data storage, which have the potential to eventually replace Flash in future CMOS generations. Resistive switching materials, which can be incorporated in simple metal-isolator-metal (MIM) structure, are especially promising due to their auspicious scaling properties. Various different materials are studied in terms of their compatibility to standard CMOS processes, and their switching characteristics. In order to asses the potential of the various concepts, a principal understanding of the underlying mechanisms is necessary. The charge transfer (CT) complex Cu:TCNQ, which consists of copper as the metallic donor and Teracyanoquinodimethane as organic acceptor, is studied within the scope of this thesis. An established and widely accepted theory to the switching mechanisms in Cu:TCNQ has still been missing, despite published work of several groups on this topic. The main aim of this study is therefore the improvement of the physical understanding of the resistive switching effect in Cu:TCNQ thin films. In a first step, the design and construction of a high vacuum chamber is presented, which is customized for the deposition of Cu:TCNQ thin films. The development of two different thermal evaporation routes allows for the first time the fabrication of functional test structure with Cu:TCNQ layer thicknesses below 100 nm. The electrical characterization of these simple memory cells displays promising results. Among other things, the switching threshold voltages are reduced to the lowest reported values (< 2.5 V) for Cu:TCNQ memory cells to date. Above all, valuable contributions regarding the physical origins of the switching mechanism could be extracted from the results of the electrical and physical characterization. It could be demonstrated for the first time, that the electrical characteristics of the reference cells were dominated by an interface layer to the Al top electrode. This interface could be identified as a thin, naturally formed aluminum oxide/-hydroxide layer. Impedance spectroscopic measurements in off– and on–state could be fitted accurately by means of equivalent circuit models, which are introduced for the Cu:TCNQ memory cells. Comparison samples without a Cu:TCNQ layer (Al/AlOx/Cu) are prepared in this context for the first time, and show remarkably similar current voltage characteristics. A new theory explaining the resistive switching in standard Cu:TCNQ memory cells is presented under consideration of all obtained results. It is suggested, that in devices with Al top electrodes, a naturally formed aluminum oxide interface layer acts as a solid electrolyte which mediates a Cu ion based electrochemical switching. The Cu:TCNQ layer appears to be a suitable spacer, which possibly stabilizes the reversible switching by acting as a Cu ion buffer.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2009

Author dc:creator

• Kever, Thorsten

Contributors dc:contributor

• Waser, Rainer

• info:eu-repo/classification/ddc/620
• CMOS-Speicher
• Charge-transfer-Komplexe
• PVD-Verfahren
• Ingenieurwissenschaften
• resistive Speicher
• RRAM
• resistive switching

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

eng

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-113546%22

OAI record oai:identifier

https://publications.rwth-aachen.de/oai2d?verb=GetRecord&metadataPrefix=oai_dc&identifier=oai%3Apublications.rwth-aachen.de%3A51234