Stephan Menzel | Forschungszentrum Juelich (original) (raw)

Papers by Stephan Menzel

IEEE Transactions on Electron Devices

Frontiers in Neuroscience

With the arrival of the Internet of Things (IoT) and the challenges arising from Big Data, neurom... more With the arrival of the Internet of Things (IoT) and the challenges arising from Big Data, neuromorphic chip concepts are seen as key solutions for coping with the massive amount of unstructured data streams by moving the computation closer to the sensors, the so-called “edge computing.” Augmenting these chips with emerging memory technologies enables these edge devices with non-volatile and adaptive properties which are desirable for low power and online learning operations. However, an energy- and area-efficient realization of these systems requires disruptive hardware changes. Memristor-based solutions for these concepts are in the focus of research and industry due to their low-power and high-density online learning potential. Specifically, the filamentary-type valence change mechanism (VCM memories) have shown to be a promising candidate In consequence, physical models capturing a broad spectrum of experimentally observed features such as the pronounced cycle-to-cycle (c2c) and...

IEEE Transactions on Electron Devices

2021 IEEE International Symposium on Circuits and Systems (ISCAS)

ACS Applied Electronic Materials

Memristive devices are two-terminal devices that can change their resistance state upon applicati... more Memristive devices are two-terminal devices that can change their resistance state upon application of appropriate voltage stimuli. The resistance can be tuned over a wide resistance range enabling applications such as multibit data storage or analog computing-in-memory concepts. One of the most promising classes of memristive devices is based on the valence change mechanism in oxide-based devices. In these devices, a configurational change of oxygen defects, i.e. oxygen vacancies, leads to the change of the device resistance. A microscopic understanding of the conduction is necessary in order to design memristive devices with specific resistance properties. In this paper, we discuss the conduction mechanism proposed in the literature and propose a comprehensive, microscopic model of the conduction mechanism in this class of devices. To develop this microscopic picture of the conduction, ab initio simulation models are developed. These simulations suggest two different types of conduction, which are both limited by a tunneling through the Schottky barrier at the metal electrode contact. The difference between the two conduction mechanisms is the following: for the first type, the electrons tunnel into the conduction band and, in the second type, into the vacancy defect states. These two types of conduction differ in their current voltage relation, which has been detected experimentally. The origin of the resistive switching is identical for the two types of conduction and is based on a modification of the tunneling distance due to the oxygen vacancy induced screening of the Schottky barrier. This understanding may help to design optimized devices in terms of the dynamic resistance range for specific applications.

2014 IEEE International Symposium on Circuits and Systems (ISCAS)

ABSTRACT Highly predictive memristive models of resistive switches are required to simulate the b... more ABSTRACT Highly predictive memristive models of resistive switches are required to simulate the behavior of anti-serially connected resistive switches, so called complementary resistive switches (CRSs). As an emerging non-volatile device suited for ultra-dense memory architectures, CRS cells offer great potential also as content addressable memories. Here, we introduce a circuit model for TaOx-based resistive switches which we implemented in VerilogA. This model is capable of predicting CRS behavior correctly.

Advanced Intelligent Systems

ACM Journal on Emerging Technologies in Computing Systems

APL Materials

The utilization of bipolar-type memristive devices for the realization of synaptic connectivity i... more The utilization of bipolar-type memristive devices for the realization of synaptic connectivity in neural networks strongly depends on the ability of the devices for analog conductance modulation under application of electrical stimuli in the form of identical voltage pulses. Typically, filamentary valence change mechanism (VCM)-type devices show an abrupt SET and a gradual RESET switching behavior. Thus, it is challenging to achieve an analog conductance modulation during SET and RESET. Here, we show that analog as well as binary conductance modulation can be achieved in a Pt/HfO 2 /TiOx/Ti VCM cell by varying the operation conditions. By analyzing the switching dynamics over many orders of magnitude and comparing to a fully dynamic switching model, the origin of the two different switching modes is revealed. SET and RESET transition show a two-step switching process: a fast conductance change succeeds a slow conductance change. While the time for the fast conductance change, the transition time, turns out to be state-independent for a specific voltage, the time for the slow conductance change, the delay time, is highly state-dependent. Analog switching can be achieved if the pulse time is a fraction of the transition time. If the pulse time is larger than the transition time, the switching becomes probabilistic and binary. Considering the effect of the device state on the delay time in addition, a procedure is proposed to find the ideal operation conditions for analog switching.

Nanoscale

A detailed study of the electrical transport in TaOx thin films with x ∼ 1 provides an insight in... more A detailed study of the electrical transport in TaOx thin films with x ∼ 1 provides an insight into the conduction in conductive filaments inside Ta2O5-based resistive switching devices.

Applied Surface Science

At the end of a rush lasting over half a century, in which CMOS technology has been experiencing ... more At the end of a rush lasting over half a century, in which CMOS technology has been experiencing a constant and breathtaking increase of device speed and density, Moore's law is approaching the insurmountable barrier given by the ultimate atomic nature of matter. A major challenge for 21st century scientists is finding novel strategies, concepts and materials for replacing silicon-based CMOS semiconductor technologies and guaranteeing a continued and steady technological progress in next decades. Among the materials classes candidate to contribute to this momentous challenge, oxide films and heterostructures are a particularly appealing hunting ground. The vastity, intended in pure chemical terms, of this class of compounds, the complexity of their correlated behaviour, and the wealth of functional properties they display, has already made these systems the subject of choice, worldwide, of a strongly networked, dynamic and interdisciplinary research community. Oxide science and technology has been the target of a wide four-year project, named Towards Oxide-Based Electronics (TO-BE), that has been recently running in Europe and has involved as participants several hundred scientists from 29 EU countries. In this review and perspective paper, published as a final deliverable of the TO-BE Action, the opportunities of oxides as future electronic materials for Information and Communication Technologies ICT and Energy are discussed. The paper is organized as a set of contributions, all selected and ordered as individual building blocks of a wider general scheme. After a brief preface by the editors and an introductory contribution, two sections follow. The first is mainly devoted to providing a perspective on the latest theoretical and experimental methods that are employed to investigate oxides and to produce oxide-based films, heterostructures and devices. In the second, all contributions are dedicated to different specific fields of applications of oxide thin films and heterostructures, in sectors as data storage and computing, optics and plasmonics, magnonics, energy conversion and harvesting, and power electronics. M. Cuoco and J. van den Brink 3. Perspectives for applications of ultimate (atomic) control of oxide films using PLD G. Koster, M. Huijben, G. Rijnders 4. Oxide MBE and the path to creating and comprehending artificial quantum materials D. G. Schlom and K.M. Shen 5. Nanoscale patterning of complex-oxide materials A. Kalaboukhov and H. Boschker 6. Epitaxial oxide films on semiconductor substrates F. Sánchez and M. Spreitzer 7. Recent achievements and challenges in atomic layer deposition of complex oxides for heterostructures M. Napari and J.L. Macmanus-Driscoll 8. Structure solving and refining, and strain gradients mapping in epitaxial thin films by X-ray diffraction techniques C. Frontera 9. Characterization of point defects in functional oxide thin films D.J. Keeble 10. Developments in electron microscopy of exotic states at oxide interfaces: cryogenic imaging and advanced detectors I. El Baggari and L.F. Kourkoutis Applications 11. Resistive switching oxides for data storage R. Dittmann 12. Oxides for data storage and processing: Ferroelectric tunnel junctions V. Garcia and M. Bibes 13. Oxides for data storage: Ferroelectric RAMs U. Schröeder and T. Mikolajick 14. Alternative logic concepts using oxide-based electronic devices S. Menzel and A. Siemon 15. High-k dielectrics for CMOS and emerging logic devices M. Fanciulli 16. Oxide nano-electronics for neuromorphic computing J. Grollier 17. Possible future quantum technologies based on correlated nanoelectronics G. Cheng and J. Levy 18. Epitaxial oxide barriers for magnetic tunnel junctions H. Sukegawa and K. Hono 19. Magnetically ordered insulators for advanced spintronics M. Althammer, S.T.B. Goennenwein and R. Gross 20. Functional oxides in photonic integrated devices G. Herranz and P. Sanchis 21. Recent concepts and future opportunities for oxides in solar cells A. Hagfeldt and M. Lira-Cantu 22. All-oxide heterojunction solar cells R. Tamayo and A. Calleja 23. Photoferroelectrics I. Fina, C. Paillard and B. Dkhil 24. Progress of indium-free transparent conducting oxides S. Panigrahi, R. Martins and E. Fortunato 25. Electrochromic and thermochromic oxide materials G.A. Niklasson and C.G. Granqvist 26. Ionotronics and nanoionics in energy devices: current status and future of μ-SOFC S. Sanna and N.

Advanced Electronic Materials

Physical Review Materials

The generation of anti-Frenkel pairs (oxygen vacancies and oxygen interstitials) in monoclinic an... more The generation of anti-Frenkel pairs (oxygen vacancies and oxygen interstitials) in monoclinic and cubic HfO 2 under an applied electric field is examined. A thermodynamic model is used to derive an expression for the critical field strength required to generate an anti-Frenkel pair. The critical field strength of E cr aF ∼ 10 1 GVm −1 obtained for HfO 2 exceeds substantially the field strengths routinely employed in the forming and switching operations of resistive switching HfO 2 devices, suggesting that field-enhanced defect generation is negligible. Atomistic simulations with molecular static (MS) and molecular dynamic (MD) approaches support this finding. The MS calculations indicated a high formation energy of E aF ≈ 8 eV for the infinitely separated anti-Frenkel pair, and only a decrease to E aF ≈ 6 eV for the adjacent anti-Frenkel pair. The MD simulations showed no defect generation in either phase for E < 3 GVm −1 , and only sporadic defect generation in the monoclinic phase (at E = 3 GVm −1) with fast (t rec < 4 ps) recombination. At even higher E but below E cr aF both monoclinic and cubic structures became unstable as a result of field-induced deformation of the ionic potential wells. Further MD investigations starting with preexisting anti-Frenkel pairs revealed recombination of all pairs within t rec < 1 ps, even for the case of neutral vacancies and charged interstitials, for which formally there is no electrostatic attraction between the defects. In conclusion, we find no physically reasonable route to generating point-defects in HfO 2 by an applied field.

AIP Advances

The interface between a metal and a semiconductor is known as Schottky contact and a key factor i... more The interface between a metal and a semiconductor is known as Schottky contact and a key factor in semiconductor technologies. Those interfaces normally build an energetic barrier, which is responsible for the exponential current voltage dependence. Analytical models often describe the right trend for the description of the Schottky barrier height, but fail to predict the barrier properties quantitatively correct. To overcome this problem atomistic and quantum mechanical approaches are required such as the here applied density functional theory combined with the non-equilibrium Greens function method. So far, these methods have rarely been applied to wide band gap metal oxides, which leads to a lack in the understanding of oxide electronics. The presented study deals with the image force induced Schottky barrier lowering of a SrTiO 3 /Pt interface as a model system for wide band gap metal-oxide Schottky contacts. The Schottky barrier lowering is investigated for the case of different doping concentrations/positions and for different voltages. From a defect chemical point of view, oxygen vacancies act as donors in many metal oxides and dominate the electronic conduction in oxide electronics. Consequently, we investigated the Schottky barrier lowering induced by oxygen vacancies. The second doping mechanism is achieved in the sense of classical doping using Nb impurities, which form a conventional n-type donor. The atomistic simulation reveals the Schottky barrier lowering effect for both type of dopants. The results are compared to a standard analytical model regarding the Schottky barrier lowering.

IEEE Transactions on Electron Devices

Advanced Electronic Materials

Faraday Discussions

In this work, the ultimate switching speed limit of redox-based resistive switching devices is di... more In this work, the ultimate switching speed limit of redox-based resistive switching devices is discussed. Based on a theoretical analysis of the underlying physical processes, it is derived that the switching speed is limited by the phonon frequency.

Advanced materials (Deerfield Beach, Fla.), Jan 7, 2018

Resistive switching based on transition metal oxide memristive devices is suspected to be caused ... more Resistive switching based on transition metal oxide memristive devices is suspected to be caused by the electric-field-driven motion and internal redistribution of oxygen vacancies. Deriving the detailed mechanistic picture of the switching process is complicated, however, by the frequently observed influence of the surrounding atmosphere. Specifically, the presence or absence of water vapor in the atmosphere has a strong impact on the switching properties, but the redox reactions between water and the active layer have yet to be clarified. To investigate the role of oxygen and water species during resistive switching in greater detail, isotope labeling experiments in a N /H O tracer gas atmosphere combined with time-of-flight secondary-ion mass spectrometry are used. It is explicitly demonstrated that during the RESET operation in resistive switching SrTiO -based memristive devices, oxygen is incorporated directly from water molecules or oxygen molecules into the active layer. In h...

IEEE Transactions on Electron Devices

Frontiers in Neuroscience

With the arrival of the Internet of Things (IoT) and the challenges arising from Big Data, neurom... more With the arrival of the Internet of Things (IoT) and the challenges arising from Big Data, neuromorphic chip concepts are seen as key solutions for coping with the massive amount of unstructured data streams by moving the computation closer to the sensors, the so-called “edge computing.” Augmenting these chips with emerging memory technologies enables these edge devices with non-volatile and adaptive properties which are desirable for low power and online learning operations. However, an energy- and area-efficient realization of these systems requires disruptive hardware changes. Memristor-based solutions for these concepts are in the focus of research and industry due to their low-power and high-density online learning potential. Specifically, the filamentary-type valence change mechanism (VCM memories) have shown to be a promising candidate In consequence, physical models capturing a broad spectrum of experimentally observed features such as the pronounced cycle-to-cycle (c2c) and...

IEEE Transactions on Electron Devices

2021 IEEE International Symposium on Circuits and Systems (ISCAS)

ACS Applied Electronic Materials

Memristive devices are two-terminal devices that can change their resistance state upon applicati... more Memristive devices are two-terminal devices that can change their resistance state upon application of appropriate voltage stimuli. The resistance can be tuned over a wide resistance range enabling applications such as multibit data storage or analog computing-in-memory concepts. One of the most promising classes of memristive devices is based on the valence change mechanism in oxide-based devices. In these devices, a configurational change of oxygen defects, i.e. oxygen vacancies, leads to the change of the device resistance. A microscopic understanding of the conduction is necessary in order to design memristive devices with specific resistance properties. In this paper, we discuss the conduction mechanism proposed in the literature and propose a comprehensive, microscopic model of the conduction mechanism in this class of devices. To develop this microscopic picture of the conduction, ab initio simulation models are developed. These simulations suggest two different types of conduction, which are both limited by a tunneling through the Schottky barrier at the metal electrode contact. The difference between the two conduction mechanisms is the following: for the first type, the electrons tunnel into the conduction band and, in the second type, into the vacancy defect states. These two types of conduction differ in their current voltage relation, which has been detected experimentally. The origin of the resistive switching is identical for the two types of conduction and is based on a modification of the tunneling distance due to the oxygen vacancy induced screening of the Schottky barrier. This understanding may help to design optimized devices in terms of the dynamic resistance range for specific applications.

2014 IEEE International Symposium on Circuits and Systems (ISCAS)

ABSTRACT Highly predictive memristive models of resistive switches are required to simulate the b... more ABSTRACT Highly predictive memristive models of resistive switches are required to simulate the behavior of anti-serially connected resistive switches, so called complementary resistive switches (CRSs). As an emerging non-volatile device suited for ultra-dense memory architectures, CRS cells offer great potential also as content addressable memories. Here, we introduce a circuit model for TaOx-based resistive switches which we implemented in VerilogA. This model is capable of predicting CRS behavior correctly.

Advanced Intelligent Systems

ACM Journal on Emerging Technologies in Computing Systems

APL Materials

The utilization of bipolar-type memristive devices for the realization of synaptic connectivity i... more The utilization of bipolar-type memristive devices for the realization of synaptic connectivity in neural networks strongly depends on the ability of the devices for analog conductance modulation under application of electrical stimuli in the form of identical voltage pulses. Typically, filamentary valence change mechanism (VCM)-type devices show an abrupt SET and a gradual RESET switching behavior. Thus, it is challenging to achieve an analog conductance modulation during SET and RESET. Here, we show that analog as well as binary conductance modulation can be achieved in a Pt/HfO 2 /TiOx/Ti VCM cell by varying the operation conditions. By analyzing the switching dynamics over many orders of magnitude and comparing to a fully dynamic switching model, the origin of the two different switching modes is revealed. SET and RESET transition show a two-step switching process: a fast conductance change succeeds a slow conductance change. While the time for the fast conductance change, the transition time, turns out to be state-independent for a specific voltage, the time for the slow conductance change, the delay time, is highly state-dependent. Analog switching can be achieved if the pulse time is a fraction of the transition time. If the pulse time is larger than the transition time, the switching becomes probabilistic and binary. Considering the effect of the device state on the delay time in addition, a procedure is proposed to find the ideal operation conditions for analog switching.

Nanoscale

A detailed study of the electrical transport in TaOx thin films with x ∼ 1 provides an insight in... more A detailed study of the electrical transport in TaOx thin films with x ∼ 1 provides an insight into the conduction in conductive filaments inside Ta2O5-based resistive switching devices.

Applied Surface Science

At the end of a rush lasting over half a century, in which CMOS technology has been experiencing ... more At the end of a rush lasting over half a century, in which CMOS technology has been experiencing a constant and breathtaking increase of device speed and density, Moore's law is approaching the insurmountable barrier given by the ultimate atomic nature of matter. A major challenge for 21st century scientists is finding novel strategies, concepts and materials for replacing silicon-based CMOS semiconductor technologies and guaranteeing a continued and steady technological progress in next decades. Among the materials classes candidate to contribute to this momentous challenge, oxide films and heterostructures are a particularly appealing hunting ground. The vastity, intended in pure chemical terms, of this class of compounds, the complexity of their correlated behaviour, and the wealth of functional properties they display, has already made these systems the subject of choice, worldwide, of a strongly networked, dynamic and interdisciplinary research community. Oxide science and technology has been the target of a wide four-year project, named Towards Oxide-Based Electronics (TO-BE), that has been recently running in Europe and has involved as participants several hundred scientists from 29 EU countries. In this review and perspective paper, published as a final deliverable of the TO-BE Action, the opportunities of oxides as future electronic materials for Information and Communication Technologies ICT and Energy are discussed. The paper is organized as a set of contributions, all selected and ordered as individual building blocks of a wider general scheme. After a brief preface by the editors and an introductory contribution, two sections follow. The first is mainly devoted to providing a perspective on the latest theoretical and experimental methods that are employed to investigate oxides and to produce oxide-based films, heterostructures and devices. In the second, all contributions are dedicated to different specific fields of applications of oxide thin films and heterostructures, in sectors as data storage and computing, optics and plasmonics, magnonics, energy conversion and harvesting, and power electronics. M. Cuoco and J. van den Brink 3. Perspectives for applications of ultimate (atomic) control of oxide films using PLD G. Koster, M. Huijben, G. Rijnders 4. Oxide MBE and the path to creating and comprehending artificial quantum materials D. G. Schlom and K.M. Shen 5. Nanoscale patterning of complex-oxide materials A. Kalaboukhov and H. Boschker 6. Epitaxial oxide films on semiconductor substrates F. Sánchez and M. Spreitzer 7. Recent achievements and challenges in atomic layer deposition of complex oxides for heterostructures M. Napari and J.L. Macmanus-Driscoll 8. Structure solving and refining, and strain gradients mapping in epitaxial thin films by X-ray diffraction techniques C. Frontera 9. Characterization of point defects in functional oxide thin films D.J. Keeble 10. Developments in electron microscopy of exotic states at oxide interfaces: cryogenic imaging and advanced detectors I. El Baggari and L.F. Kourkoutis Applications 11. Resistive switching oxides for data storage R. Dittmann 12. Oxides for data storage and processing: Ferroelectric tunnel junctions V. Garcia and M. Bibes 13. Oxides for data storage: Ferroelectric RAMs U. Schröeder and T. Mikolajick 14. Alternative logic concepts using oxide-based electronic devices S. Menzel and A. Siemon 15. High-k dielectrics for CMOS and emerging logic devices M. Fanciulli 16. Oxide nano-electronics for neuromorphic computing J. Grollier 17. Possible future quantum technologies based on correlated nanoelectronics G. Cheng and J. Levy 18. Epitaxial oxide barriers for magnetic tunnel junctions H. Sukegawa and K. Hono 19. Magnetically ordered insulators for advanced spintronics M. Althammer, S.T.B. Goennenwein and R. Gross 20. Functional oxides in photonic integrated devices G. Herranz and P. Sanchis 21. Recent concepts and future opportunities for oxides in solar cells A. Hagfeldt and M. Lira-Cantu 22. All-oxide heterojunction solar cells R. Tamayo and A. Calleja 23. Photoferroelectrics I. Fina, C. Paillard and B. Dkhil 24. Progress of indium-free transparent conducting oxides S. Panigrahi, R. Martins and E. Fortunato 25. Electrochromic and thermochromic oxide materials G.A. Niklasson and C.G. Granqvist 26. Ionotronics and nanoionics in energy devices: current status and future of μ-SOFC S. Sanna and N.

Advanced Electronic Materials

Physical Review Materials

The generation of anti-Frenkel pairs (oxygen vacancies and oxygen interstitials) in monoclinic an... more The generation of anti-Frenkel pairs (oxygen vacancies and oxygen interstitials) in monoclinic and cubic HfO 2 under an applied electric field is examined. A thermodynamic model is used to derive an expression for the critical field strength required to generate an anti-Frenkel pair. The critical field strength of E cr aF ∼ 10 1 GVm −1 obtained for HfO 2 exceeds substantially the field strengths routinely employed in the forming and switching operations of resistive switching HfO 2 devices, suggesting that field-enhanced defect generation is negligible. Atomistic simulations with molecular static (MS) and molecular dynamic (MD) approaches support this finding. The MS calculations indicated a high formation energy of E aF ≈ 8 eV for the infinitely separated anti-Frenkel pair, and only a decrease to E aF ≈ 6 eV for the adjacent anti-Frenkel pair. The MD simulations showed no defect generation in either phase for E < 3 GVm −1 , and only sporadic defect generation in the monoclinic phase (at E = 3 GVm −1) with fast (t rec < 4 ps) recombination. At even higher E but below E cr aF both monoclinic and cubic structures became unstable as a result of field-induced deformation of the ionic potential wells. Further MD investigations starting with preexisting anti-Frenkel pairs revealed recombination of all pairs within t rec < 1 ps, even for the case of neutral vacancies and charged interstitials, for which formally there is no electrostatic attraction between the defects. In conclusion, we find no physically reasonable route to generating point-defects in HfO 2 by an applied field.

AIP Advances

The interface between a metal and a semiconductor is known as Schottky contact and a key factor i... more The interface between a metal and a semiconductor is known as Schottky contact and a key factor in semiconductor technologies. Those interfaces normally build an energetic barrier, which is responsible for the exponential current voltage dependence. Analytical models often describe the right trend for the description of the Schottky barrier height, but fail to predict the barrier properties quantitatively correct. To overcome this problem atomistic and quantum mechanical approaches are required such as the here applied density functional theory combined with the non-equilibrium Greens function method. So far, these methods have rarely been applied to wide band gap metal oxides, which leads to a lack in the understanding of oxide electronics. The presented study deals with the image force induced Schottky barrier lowering of a SrTiO 3 /Pt interface as a model system for wide band gap metal-oxide Schottky contacts. The Schottky barrier lowering is investigated for the case of different doping concentrations/positions and for different voltages. From a defect chemical point of view, oxygen vacancies act as donors in many metal oxides and dominate the electronic conduction in oxide electronics. Consequently, we investigated the Schottky barrier lowering induced by oxygen vacancies. The second doping mechanism is achieved in the sense of classical doping using Nb impurities, which form a conventional n-type donor. The atomistic simulation reveals the Schottky barrier lowering effect for both type of dopants. The results are compared to a standard analytical model regarding the Schottky barrier lowering.

IEEE Transactions on Electron Devices

Advanced Electronic Materials

Faraday Discussions

In this work, the ultimate switching speed limit of redox-based resistive switching devices is di... more In this work, the ultimate switching speed limit of redox-based resistive switching devices is discussed. Based on a theoretical analysis of the underlying physical processes, it is derived that the switching speed is limited by the phonon frequency.

Advanced materials (Deerfield Beach, Fla.), Jan 7, 2018

Resistive switching based on transition metal oxide memristive devices is suspected to be caused ... more Resistive switching based on transition metal oxide memristive devices is suspected to be caused by the electric-field-driven motion and internal redistribution of oxygen vacancies. Deriving the detailed mechanistic picture of the switching process is complicated, however, by the frequently observed influence of the surrounding atmosphere. Specifically, the presence or absence of water vapor in the atmosphere has a strong impact on the switching properties, but the redox reactions between water and the active layer have yet to be clarified. To investigate the role of oxygen and water species during resistive switching in greater detail, isotope labeling experiments in a N /H O tracer gas atmosphere combined with time-of-flight secondary-ion mass spectrometry are used. It is explicitly demonstrated that during the RESET operation in resistive switching SrTiO -based memristive devices, oxygen is incorporated directly from water molecules or oxygen molecules into the active layer. In h...