Abstract
In recent years, several materials and metal-insulator-metal devices are being intensively studied as prospective non-volatile memories due to their resistive switching effect. In this work, thickness-dependent resistive switching polarity was observed in TiN/Ti/HfO2/Pt structures as the sign of the voltages at which SET and RESET occur depended on the film thickness. A thorough revision of the previous literature on bipolar resistive switching polarity changes is made in order to condense previous knowledge of the subject in a brief and comprehensible way and explain the experimental measurements. The different resistive switching polarities occur in a similar voltage range, which is a new finding when compared to precedent research on the subject. A hypothesis is proposed to explain the change in resistive switching polarity, based on the assumption that polarity change is due to filament disruption occurring at different interfaces.
Highlights
Non-volatile resistive random-access memories (RRAM) based on the resistive switching (RS) effect are of increasing interest due to their characteristics, such as small cell size and low operating voltages, as well as simple device structure composed of metal-insulatormetal (MIM) junctions
A thorough investigation of foregoing reported cases and studies on reversible and irreversible CW—CCW RS changes leads to the hypothesis that polarity change is due to filament disruption occurring at different interfaces
The thinner sample presents a Ti cap layer thicker than the HfO2 which ensures its role as an oxygen reservoir, creating an oxygen vacancy-rich zone in the HfO2 near the interface
Summary
The RS effect occurs when conductive filaments (CF) grow in a dielectric film between two metal electrodes by applying an electric field. After these CFs are formed for the first time (electroforming process), certain voltage values can be applied to either break (RESET process) or form the CFs again (SET process) [1,2,3,4,5]. In the case of MIM devices where the dielectric is an oxide and none of the metal electrodes is electrochemically active, the filament is formed by oxygen vacancies (valence change mechanism or VCM), otherwise the filament would be formed by migration of metal cations
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