Micro-spectroscopic investigation of valence change processes in resistive switching SrTiO3 thin films
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Due to physical limitations of the currently used ash memory in terms of writing speed and scalability, new concepts for data storage attract great interest. A possible alternative with promising characteristics are so-called „Resistive Random Access Memories“ (ReRAM). These memory devices are based on the resistive switching eect where the electrical resistance of a metal-insulator-metal (MIM) structure can be switched reversibly by a current or voltage pulse. Although this eect attracted wide scientic as well as commercial interest, up to now the it is not fully understood on a microscopic scale. Consequently, in this work the chemical and physical modications caused by the resistive switching process are studied by spectroscopic techniques. As most switching models predict a strongly localized rather than a homogeneous eect, advanced microspectroscopy techniques are employed where additionally the lateral structure of the sample is imaged. In this work Fe-doped SrTiO3 lms are used as model material due to the thorough understanding of their defect chemistry. The epitaxial thin lms are prepared by pulsed laser deposition. In a rst approach, transmission X-ray microscopy is employed to study the bulk properties of ReRAM devices. At rst, a new procedure for sample preparation based on a selective etching process is developed in order to realize photon-transparent samples. Investigations of switched devices reveal a signicant contribution of Ti3+ states within growth defects. In contrast to the indirect evidence in previous studies, this observation directly conrms that the resistance change is based on a local redox-process. The localization of the switching process within the growth defects is explained by a selfaccelerating process due to Joule heating within the pre-reduced defects. In a second approach, after removal of the top electrode the chemical and electronic structure of the former interface between the oxide lm and the electrode is investigated by photoemission electron microscopy. Within this work devices with dierent thickness of the oxide layer are studied. While the results for thicker lms can be explained by a localization of the switching eect within growth defects, for lms with a lower oxide thickness we observe a considerable modication of the chemical structure up to phase formation on an extended lateral scale. In particular, we detect the formation of a new, Sr-rich phase which can be modeled by a special Ruddlesden-Popper phase using ab-initio theory. While most switching models assume only the diusion of oxygen vacancies, our experiments clearly reveal that (at least) during forming diusion is also enabled within the cation sublattice.
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Micro-spectroscopic investigation of valence change processes in resistive switching SrTiO3 thin films, Annemarie Köhl
- Sprache
- Erscheinungsdatum
- 2014
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- Titel
- Micro-spectroscopic investigation of valence change processes in resistive switching SrTiO3 thin films
- Sprache
- Englisch
- Autor*innen
- Annemarie Köhl
- Erscheinungsdatum
- 2014
- ISBN10
- 3893369880
- ISBN13
- 9783893369881
- Kategorie
- Skripten & Universitätslehrbücher
- Beschreibung
- Due to physical limitations of the currently used ash memory in terms of writing speed and scalability, new concepts for data storage attract great interest. A possible alternative with promising characteristics are so-called „Resistive Random Access Memories“ (ReRAM). These memory devices are based on the resistive switching eect where the electrical resistance of a metal-insulator-metal (MIM) structure can be switched reversibly by a current or voltage pulse. Although this eect attracted wide scientic as well as commercial interest, up to now the it is not fully understood on a microscopic scale. Consequently, in this work the chemical and physical modications caused by the resistive switching process are studied by spectroscopic techniques. As most switching models predict a strongly localized rather than a homogeneous eect, advanced microspectroscopy techniques are employed where additionally the lateral structure of the sample is imaged. In this work Fe-doped SrTiO3 lms are used as model material due to the thorough understanding of their defect chemistry. The epitaxial thin lms are prepared by pulsed laser deposition. In a rst approach, transmission X-ray microscopy is employed to study the bulk properties of ReRAM devices. At rst, a new procedure for sample preparation based on a selective etching process is developed in order to realize photon-transparent samples. Investigations of switched devices reveal a signicant contribution of Ti3+ states within growth defects. In contrast to the indirect evidence in previous studies, this observation directly conrms that the resistance change is based on a local redox-process. The localization of the switching process within the growth defects is explained by a selfaccelerating process due to Joule heating within the pre-reduced defects. In a second approach, after removal of the top electrode the chemical and electronic structure of the former interface between the oxide lm and the electrode is investigated by photoemission electron microscopy. Within this work devices with dierent thickness of the oxide layer are studied. While the results for thicker lms can be explained by a localization of the switching eect within growth defects, for lms with a lower oxide thickness we observe a considerable modication of the chemical structure up to phase formation on an extended lateral scale. In particular, we detect the formation of a new, Sr-rich phase which can be modeled by a special Ruddlesden-Popper phase using ab-initio theory. While most switching models assume only the diusion of oxygen vacancies, our experiments clearly reveal that (at least) during forming diusion is also enabled within the cation sublattice.