As artificial intelligence and big data become increasingly prevalent, resistive random-access memory (RRAM) has become one of the most promising alternatives for storing massive amounts of data. In this study, we emp...As artificial intelligence and big data become increasingly prevalent, resistive random-access memory (RRAM) has become one of the most promising alternatives for storing massive amounts of data. In this study, we employed high-quality crystalline TiN/Al_(2)O_(3)/BaTiO_(3)/Pt RRAM with an optimized thin Al_(2)O_(3) interlayer around 12 nm thick prepared using atomic layer deposition since the thickness of the interlayer affects the memory window size. After insertion of the Al_(2)O_(3) interlayer, the novel RRAM exhibited outstanding uniform resistive switching voltage and the ON/OFF memory window drastically increased from 10 to 103 without any discernible decline in performance. Moreover, the low-resistance state and high-resistance state operating current values decreased by almost one order and three orders of magnitude, respectively, thereby decreasing the power consumption for the RESET and SET processes by more than three and almost one order of magnitude, respectively. The device also exhibits multilevel resistive switching behavior when varying the applied voltage. Finally, we also developed a 6 6 crossbar array which demonstrated consistent and reliable resistive switching behavior with minimal variation. Hence, our approach holds great promise for producing state-of-the-art non-volatile resistive switching devices.展开更多
Cu metal and its oxides have attracted much attention for photocatalytic CO_(2)reduction reaction(CO_(2)RR),but the stability and effects of Cu oxidation states on CO_(2)RR are not fully understood.Cu^(x+)/Cu^(0)-load...Cu metal and its oxides have attracted much attention for photocatalytic CO_(2)reduction reaction(CO_(2)RR),but the stability and effects of Cu oxidation states on CO_(2)RR are not fully understood.Cu^(x+)/Cu^(0)-loaded graphitic carbon nitride(g-C_(3)N_(4))heterojunctions(Cu-CuO_(x)/g-C_(3)N_(4))are fabricated via a stepwise calcination method for efficient photocatalytic CO_(2)RR.Cu_(2)O is the main component of Cu-CuO_(x)and the mixed valence Cu includes Cu^(0),Cu^(+),and Cu^(2+),which play the role of charge trapping sites and redox catalytic centers during the photocatalytic CO_(2)RR process.The main products were CO and CH_(4)for the CO_(2)RR with production rates of 14.45 and 0.66μmol g^(-1)h^(-1)for CO and CH_(4),which were higher than those for g-C_(3)N_(4)and Cu-CuO_(x),respectively.This photocatalytic CO_(2)RR performance is attributed to the ultrafast switching of“Cu^(x+)−Cu^(0)”and e_(CB^(−))/h_(VB^(+))trapping transformation in Cu-CuO_(x)benefited from the built-in IEF between Cu-CuO_(x)and g-C_(3)N_(4),increasing the efficient photogenerated e_(CB^(−)),and enabling the stability of Cu-CuO_(x)/g-C_(3)N_(4).Cu^(x+)adsorbed by H_(2)O works as the electron trapping site to change to Cu^(0)and switch to the hole trapping site;Cu^(0)works as the hole trapping site to change to Cu^(x+)and switch to the electron trapping site,causing the CO_(2)RR of the adsorbed CO_(2).Moreover,the coordinated Cu^(0)and Cu^(+)species facilitate the activation of the adsorbed CO_(2)and^(∗)CO generation,these adsorbed^(∗)CO on Cu^(0)and Cu^(+)detected by in-situ DRIFTS quickly transformed to^(∗)CHO with a lower energy barrier benefited from the mixed Cu^(0)/Cu^(+)active sites during CORR to produce CH_(4).This finding provides a new insight into the influence of mixed valence Cu during photocatalytic CO_(2)RR.展开更多
Field-free spin-orbit torque(SOT)switching of perpendicular magnetization is essential for future spintronic devices.This study demonstrates the field-free switching of perpendicular magnetization in an HfO_(2)/Pt/Co/...Field-free spin-orbit torque(SOT)switching of perpendicular magnetization is essential for future spintronic devices.This study demonstrates the field-free switching of perpendicular magnetization in an HfO_(2)/Pt/Co/TaO_(x) structure,which is facilitated by a wedge-shaped HfO_(2)buffer layer.The field-free switching ratio varies with HfO_(2)thickness,reaching optimal performance at 25 nm.This phenomenon is attributed to the lateral anisotropy gradient of the Co layer,which is induced by the wedge-shaped HfO_(2)buffer layer.The thickness gradient of HfO_(2)along the wedge creates a corresponding lateral anisotropy gradient in the Co layer,correlating with the switching ratio.These findings indicate that field-free SOT switching can be achieved through designing buffer layer,offering a novel approach to innovating spin-orbit device.展开更多
The polarization switching plays a crucial role in controlling the final products in the catalytic pro-cess.The effect of polarization orientation on nitrogen reduction was investigated by anchoring transition metal a...The polarization switching plays a crucial role in controlling the final products in the catalytic pro-cess.The effect of polarization orientation on nitrogen reduction was investigated by anchoring transition metal atoms to form active centers on ferroelectric material In_(2)Se_(3).During the polariza-tion switching process,the difference in surface electrostatic potential leads to a redistribution of electronic states.This affects the interaction strength between the adsorbed small molecules and the catalyst substrate,thereby altering the reaction barrier.In addition,the surface states must be considered to prevent the adsorption of other small molecules(such as *O,*OH,and *H).Further-more,the V@↓-In_(2)Se_(3) possesses excellent catalytic properties,high electrochemical and thermody-namic stability,which facilitates the catalytic process.Machine learning also helps us further ex-plore the underlying mechanisms.The systematic investigation provides novel insights into the design and application of two-dimensional switchable ferroelectric catalysts for various chemical processes.展开更多
BACKGROUND Glucagon-like peptide-1 receptor agonists(GLP-1RAs)play a key role in managing type 2 diabetes mellitus(T2DM).Transitioning between different GLP-1RA has been proposed as a treatment strategy.AIM To investi...BACKGROUND Glucagon-like peptide-1 receptor agonists(GLP-1RAs)play a key role in managing type 2 diabetes mellitus(T2DM).Transitioning between different GLP-1RA has been proposed as a treatment strategy.AIM To investigate switching patterns between GLP-1RA and their impact on glycemic control.METHODS A retrospective study involving patients with T2DM who initiated GLP-1RA therapy between 2009 and 2021 and transitioned to another GLP-1RA.Baseline glycated hemoglobin(HbA1c)was defined as the most recent measurement within 1 year prior to switching,and follow-up HbA1c was the first measurement recorded 4-15 months post-switch.RESULTS Among 70654 patients initiating GLP-1RA therapy,18047(25.5%)switched regimens.In the 13970 patients with available HbA1c,levels decreased from 8.5%±1.6%to 7.6%±1.4%(P<0.001).HbA1c decreased in 78.3%(10943/13970)of these patients,with the most frequent improvement observed in those switching from daily to weekly GLP-1RA(81%,5582/6890).CONCLUSION Switching between GLP-1RAs can serve as a practical alternative to treatment intensification for effectively managing T2DM.展开更多
Based on the nonlinear Mohr-Coulomb failure criterion and an associated flow rule,a kinematic admissible velocity field of failure mechanism of the 2-layer soil above a shallow horizontal strip anchor plate is constru...Based on the nonlinear Mohr-Coulomb failure criterion and an associated flow rule,a kinematic admissible velocity field of failure mechanism of the 2-layer soil above a shallow horizontal strip anchor plate is constructed.The ultimate pull-out force and its corresponding failure mechanism through the upper bound limit analysis according to a variation principle are deduced.When the 2-layer overlying soil is degraded into single-layer soil,the model of ultimate pullout force could also be degraded into the model of single-layer soil.And the comparison between results of single-layer soil variation method and those calculated by rigid limit analysis method proves the correctness of our method.Based on that,the influence of changes of geotechnical parameters on ultimate pullout forces and failure mechanism of a shallow horizontal strip anchor with the 2-layer soil above are analyzed.The results show that the ultimate pull-out force and failure mechanism of a shallow horizontal strip anchor with the 2-layer soil above are affected by the nonlinear geotechnical parameters greatly.Thus,it is very important to obtain the accurate geotechnical parameters of 2-layer soil for the evaluation of the ultimate pullout capacity of the anchor plate.展开更多
This paper investigates L2-gain analysis and anti-windup compensation gains design for a class of discrete-time switched systems with saturating actuators and L2 bounded disturbances by using the switched Lyapunov fun...This paper investigates L2-gain analysis and anti-windup compensation gains design for a class of discrete-time switched systems with saturating actuators and L2 bounded disturbances by using the switched Lyapunov function approach.For a given set of anti-windup compensation gains,we firstly give a sufficient condition on tolerable disturbances under which the state trajectory starting from the origin will remain inside a bounded set for the corresponding closed-loop switched system subject to L2 bounded disturbances.Then,the upper bound on the restricted L2-gain is obtained over the set of tolerable disturbances.Furthermore,the antiwindup compensation gains aiming to determine the largest disturbance tolerance level and the smallest upper bound of the restricted L2-gain are presented by solving a convex optimization problem with linear matrix inequality(LMI) constraints.A numerical example is given to illustrate the effectiveness of the proposed design method.展开更多
Long-term stability test of Mo/HZSM-5-N catalysts（HZSM-5-N stands for nano-sized HZSM-5） in methane dehydroaromatization（MDA）reaction has been performed with periodic CH4-H2 switch at 1033-1073 K for more than 100...Long-term stability test of Mo/HZSM-5-N catalysts（HZSM-5-N stands for nano-sized HZSM-5） in methane dehydroaromatization（MDA）reaction has been performed with periodic CH4-H2 switch at 1033-1073 K for more than 1000 h.During this test,methane conversion ranges from 13% to 16%,and mean yield to aromatics（i.e.benzene and naphthalene） exceeds 10%.N2-physisorption,XRD,NMR and TPO measurements were performed for the used Mo/HZSM-5 catalysts and coke deposition,and the results revealed that the periodic hydrogenation can effectively suppress coke deposition by removing the inert aromatic-type coke,thus ensuring Mo/HZSM-5 partly maintained its activity even in the presence of large amount of coke deposition.The effect of zeolite particle size on the catalytic activity was also explored,and the results showed that the nano-sized zeolite with low diffusion resistance performed better.It is recognized that the size effect was enhanced by reaction time,and it became more remarkable in a long-term MDA reaction even at a low space velocity.展开更多
The resistive switching characteristics of TiO_2 nanowire networks directly grown on Ti foil by a single-step hydrothermal technique are discussed in this paper. The Ti foil serves as the supply of Ti atoms for growth...The resistive switching characteristics of TiO_2 nanowire networks directly grown on Ti foil by a single-step hydrothermal technique are discussed in this paper. The Ti foil serves as the supply of Ti atoms for growth of the TiO_2 nanowires, making the preparation straightforward. It also acts as a bottom electrode for the device. A top Al electrode was fabricated by e-beam evaporation process. The Al/TiO_2 nanowire networks/Ti device fabricated in this way displayed a highly repeatable and electroforming-free bipolar resistive behavior with retention for more than 10~4 s and an OFF/ON ratio of approximately 70. The switching mechanism of this Al/TiO_2 nanowire networks/Ti device is suggested to arise from the migration of oxygen vacancies under applied electric field. This provides a facile way to obtain metal oxide nanowire-based Re RAM device in the future.展开更多
In this study,resistive random-access memory(RRAM)-based crossbar arrays with a memristor W/TiO_(2)/HfO_(2)/TaN structure were fabricated through atomic layer deposition(ALD)to investigate synaptic plasticity and resi...In this study,resistive random-access memory(RRAM)-based crossbar arrays with a memristor W/TiO_(2)/HfO_(2)/TaN structure were fabricated through atomic layer deposition(ALD)to investigate synaptic plasticity and resistive switching(RS)characteristics for bioinspired neuromorphic computing.X-ray photoelectron spectroscopy(XPS)was employed to explore oxygen vacancy concentrations in bilayer TiO_(2)/HfO_(2)films.Gaussian fitting for O1s peaks confirmed that the HfO_(2)layer contained a larger number of oxygen vacancies than the TiO_(2)layer.In addition,HfO_(2)had lower Gibbs free energy(ΔG°=-1010.8 kJ/mol)than the TiO_(2)layer(ΔG°=-924.0 kJ/mol),resulting in more oxygen vacancies in the HfO_(2)layer.XPS results andΔG°magnitudes confirmed that formation/disruption of oxygen-based conductive filaments took place in the TiO_(2)layer.The W/TiO_(2)/HfO_(2)/TaN memristive device exhibited excellent and repeatable RS characteristics,including superb 10^(3) dc switching cycles,outstanding 107 pulse endurance,and high-thermal stability(10^(4) s at 125℃)important for digital computing systems.Furthermore,some essential biological synaptic characteristics such as potentiation-depression plasticity,paired-pulse facilitation(PPF),and spike-timing-dependent plasticity(STDP,asymmetric Hebbian and asymmetric anti-Hebbian)were successfully mimicked herein using the crossbar-array memristive device.Based on experimental results,a migration and diffusion of oxygen vacancy based physical model is proposed to describe the synaptic plasticity and RS mechanism.This study demonstrates that the proposed W/TiO_(2)/HfO_(2)/TaN memristor crossbar-array has a significant potential for applications in non-volatile memory(NVM)and bioinspired neuromorphic systems.展开更多
基金supported by the National Research Foundation of Korea funded by the Korean Government(grant No.RS-2023-00208801).
文摘As artificial intelligence and big data become increasingly prevalent, resistive random-access memory (RRAM) has become one of the most promising alternatives for storing massive amounts of data. In this study, we employed high-quality crystalline TiN/Al_(2)O_(3)/BaTiO_(3)/Pt RRAM with an optimized thin Al_(2)O_(3) interlayer around 12 nm thick prepared using atomic layer deposition since the thickness of the interlayer affects the memory window size. After insertion of the Al_(2)O_(3) interlayer, the novel RRAM exhibited outstanding uniform resistive switching voltage and the ON/OFF memory window drastically increased from 10 to 103 without any discernible decline in performance. Moreover, the low-resistance state and high-resistance state operating current values decreased by almost one order and three orders of magnitude, respectively, thereby decreasing the power consumption for the RESET and SET processes by more than three and almost one order of magnitude, respectively. The device also exhibits multilevel resistive switching behavior when varying the applied voltage. Finally, we also developed a 6 6 crossbar array which demonstrated consistent and reliable resistive switching behavior with minimal variation. Hence, our approach holds great promise for producing state-of-the-art non-volatile resistive switching devices.
基金support of the National Natu-ral Science Foundation of China(No.62004143,22476058,and 22076052)the Key R&D Program of Hubei Province(No.2022BAA084).
文摘Cu metal and its oxides have attracted much attention for photocatalytic CO_(2)reduction reaction(CO_(2)RR),but the stability and effects of Cu oxidation states on CO_(2)RR are not fully understood.Cu^(x+)/Cu^(0)-loaded graphitic carbon nitride(g-C_(3)N_(4))heterojunctions(Cu-CuO_(x)/g-C_(3)N_(4))are fabricated via a stepwise calcination method for efficient photocatalytic CO_(2)RR.Cu_(2)O is the main component of Cu-CuO_(x)and the mixed valence Cu includes Cu^(0),Cu^(+),and Cu^(2+),which play the role of charge trapping sites and redox catalytic centers during the photocatalytic CO_(2)RR process.The main products were CO and CH_(4)for the CO_(2)RR with production rates of 14.45 and 0.66μmol g^(-1)h^(-1)for CO and CH_(4),which were higher than those for g-C_(3)N_(4)and Cu-CuO_(x),respectively.This photocatalytic CO_(2)RR performance is attributed to the ultrafast switching of“Cu^(x+)−Cu^(0)”and e_(CB^(−))/h_(VB^(+))trapping transformation in Cu-CuO_(x)benefited from the built-in IEF between Cu-CuO_(x)and g-C_(3)N_(4),increasing the efficient photogenerated e_(CB^(−)),and enabling the stability of Cu-CuO_(x)/g-C_(3)N_(4).Cu^(x+)adsorbed by H_(2)O works as the electron trapping site to change to Cu^(0)and switch to the hole trapping site;Cu^(0)works as the hole trapping site to change to Cu^(x+)and switch to the electron trapping site,causing the CO_(2)RR of the adsorbed CO_(2).Moreover,the coordinated Cu^(0)and Cu^(+)species facilitate the activation of the adsorbed CO_(2)and^(∗)CO generation,these adsorbed^(∗)CO on Cu^(0)and Cu^(+)detected by in-situ DRIFTS quickly transformed to^(∗)CHO with a lower energy barrier benefited from the mixed Cu^(0)/Cu^(+)active sites during CORR to produce CH_(4).This finding provides a new insight into the influence of mixed valence Cu during photocatalytic CO_(2)RR.
基金Project supported by the National Natural Science Foundation of China (Grant No.12274108)the Natural Science Foundation of Zhejiang Province,China (Grant Nos.LY23A040008 and LY23A040008)the Basic Scientific Research Project of Wenzhou,China (Grant No.G20220025)。
文摘Field-free spin-orbit torque(SOT)switching of perpendicular magnetization is essential for future spintronic devices.This study demonstrates the field-free switching of perpendicular magnetization in an HfO_(2)/Pt/Co/TaO_(x) structure,which is facilitated by a wedge-shaped HfO_(2)buffer layer.The field-free switching ratio varies with HfO_(2)thickness,reaching optimal performance at 25 nm.This phenomenon is attributed to the lateral anisotropy gradient of the Co layer,which is induced by the wedge-shaped HfO_(2)buffer layer.The thickness gradient of HfO_(2)along the wedge creates a corresponding lateral anisotropy gradient in the Co layer,correlating with the switching ratio.These findings indicate that field-free SOT switching can be achieved through designing buffer layer,offering a novel approach to innovating spin-orbit device.
文摘The polarization switching plays a crucial role in controlling the final products in the catalytic pro-cess.The effect of polarization orientation on nitrogen reduction was investigated by anchoring transition metal atoms to form active centers on ferroelectric material In_(2)Se_(3).During the polariza-tion switching process,the difference in surface electrostatic potential leads to a redistribution of electronic states.This affects the interaction strength between the adsorbed small molecules and the catalyst substrate,thereby altering the reaction barrier.In addition,the surface states must be considered to prevent the adsorption of other small molecules(such as *O,*OH,and *H).Further-more,the V@↓-In_(2)Se_(3) possesses excellent catalytic properties,high electrochemical and thermody-namic stability,which facilitates the catalytic process.Machine learning also helps us further ex-plore the underlying mechanisms.The systematic investigation provides novel insights into the design and application of two-dimensional switchable ferroelectric catalysts for various chemical processes.
文摘BACKGROUND Glucagon-like peptide-1 receptor agonists(GLP-1RAs)play a key role in managing type 2 diabetes mellitus(T2DM).Transitioning between different GLP-1RA has been proposed as a treatment strategy.AIM To investigate switching patterns between GLP-1RA and their impact on glycemic control.METHODS A retrospective study involving patients with T2DM who initiated GLP-1RA therapy between 2009 and 2021 and transitioned to another GLP-1RA.Baseline glycated hemoglobin(HbA1c)was defined as the most recent measurement within 1 year prior to switching,and follow-up HbA1c was the first measurement recorded 4-15 months post-switch.RESULTS Among 70654 patients initiating GLP-1RA therapy,18047(25.5%)switched regimens.In the 13970 patients with available HbA1c,levels decreased from 8.5%±1.6%to 7.6%±1.4%(P<0.001).HbA1c decreased in 78.3%(10943/13970)of these patients,with the most frequent improvement observed in those switching from daily to weekly GLP-1RA(81%,5582/6890).CONCLUSION Switching between GLP-1RAs can serve as a practical alternative to treatment intensification for effectively managing T2DM.
基金Project (51478477) supported by the National Natural Science Foundation of ChinaProject (2016CX012) supported by the Innovation-Driven Project of Central South University,ChinaProject (2014122006) supported by the Guizhou Provincial Department of Transportation Foundation,China
文摘Based on the nonlinear Mohr-Coulomb failure criterion and an associated flow rule,a kinematic admissible velocity field of failure mechanism of the 2-layer soil above a shallow horizontal strip anchor plate is constructed.The ultimate pull-out force and its corresponding failure mechanism through the upper bound limit analysis according to a variation principle are deduced.When the 2-layer overlying soil is degraded into single-layer soil,the model of ultimate pullout force could also be degraded into the model of single-layer soil.And the comparison between results of single-layer soil variation method and those calculated by rigid limit analysis method proves the correctness of our method.Based on that,the influence of changes of geotechnical parameters on ultimate pullout forces and failure mechanism of a shallow horizontal strip anchor with the 2-layer soil above are analyzed.The results show that the ultimate pull-out force and failure mechanism of a shallow horizontal strip anchor with the 2-layer soil above are affected by the nonlinear geotechnical parameters greatly.Thus,it is very important to obtain the accurate geotechnical parameters of 2-layer soil for the evaluation of the ultimate pullout capacity of the anchor plate.
基金supported by National Natural Science Foundation of China (Nos.61174073 and 90816028)
文摘This paper investigates L2-gain analysis and anti-windup compensation gains design for a class of discrete-time switched systems with saturating actuators and L2 bounded disturbances by using the switched Lyapunov function approach.For a given set of anti-windup compensation gains,we firstly give a sufficient condition on tolerable disturbances under which the state trajectory starting from the origin will remain inside a bounded set for the corresponding closed-loop switched system subject to L2 bounded disturbances.Then,the upper bound on the restricted L2-gain is obtained over the set of tolerable disturbances.Furthermore,the antiwindup compensation gains aiming to determine the largest disturbance tolerance level and the smallest upper bound of the restricted L2-gain are presented by solving a convex optimization problem with linear matrix inequality(LMI) constraints.A numerical example is given to illustrate the effectiveness of the proposed design method.
基金financially supported by the"Strategic Priority Research Program"of Chinese Academy of Sciences(No.XDA09030101)the National Natural Science Foundation of China(No.21103181 and 21473185)+1 种基金DICP Fundamental Research Program for Clean Energy(DICP M201301)Shaanxi Yanchang Petroleum Group Co.Ltd
文摘Long-term stability test of Mo/HZSM-5-N catalysts（HZSM-5-N stands for nano-sized HZSM-5） in methane dehydroaromatization（MDA）reaction has been performed with periodic CH4-H2 switch at 1033-1073 K for more than 1000 h.During this test,methane conversion ranges from 13% to 16%,and mean yield to aromatics（i.e.benzene and naphthalene） exceeds 10%.N2-physisorption,XRD,NMR and TPO measurements were performed for the used Mo/HZSM-5 catalysts and coke deposition,and the results revealed that the periodic hydrogenation can effectively suppress coke deposition by removing the inert aromatic-type coke,thus ensuring Mo/HZSM-5 partly maintained its activity even in the presence of large amount of coke deposition.The effect of zeolite particle size on the catalytic activity was also explored,and the results showed that the nano-sized zeolite with low diffusion resistance performed better.It is recognized that the size effect was enhanced by reaction time,and it became more remarkable in a long-term MDA reaction even at a low space velocity.
基金supported by the Natural Sciences and Engineering Research Council(NSERC)of CanadaThe financial support of the State Scholarship Fund of China(No.201506160061)
文摘The resistive switching characteristics of TiO_2 nanowire networks directly grown on Ti foil by a single-step hydrothermal technique are discussed in this paper. The Ti foil serves as the supply of Ti atoms for growth of the TiO_2 nanowires, making the preparation straightforward. It also acts as a bottom electrode for the device. A top Al electrode was fabricated by e-beam evaporation process. The Al/TiO_2 nanowire networks/Ti device fabricated in this way displayed a highly repeatable and electroforming-free bipolar resistive behavior with retention for more than 10~4 s and an OFF/ON ratio of approximately 70. The switching mechanism of this Al/TiO_2 nanowire networks/Ti device is suggested to arise from the migration of oxygen vacancies under applied electric field. This provides a facile way to obtain metal oxide nanowire-based Re RAM device in the future.
基金financially supported in part by a grant(2021R1C1C1004422)of the National Research Foundation(NRF)grant funded by the Korean government(MSIP)。
文摘In this study,resistive random-access memory(RRAM)-based crossbar arrays with a memristor W/TiO_(2)/HfO_(2)/TaN structure were fabricated through atomic layer deposition(ALD)to investigate synaptic plasticity and resistive switching(RS)characteristics for bioinspired neuromorphic computing.X-ray photoelectron spectroscopy(XPS)was employed to explore oxygen vacancy concentrations in bilayer TiO_(2)/HfO_(2)films.Gaussian fitting for O1s peaks confirmed that the HfO_(2)layer contained a larger number of oxygen vacancies than the TiO_(2)layer.In addition,HfO_(2)had lower Gibbs free energy(ΔG°=-1010.8 kJ/mol)than the TiO_(2)layer(ΔG°=-924.0 kJ/mol),resulting in more oxygen vacancies in the HfO_(2)layer.XPS results andΔG°magnitudes confirmed that formation/disruption of oxygen-based conductive filaments took place in the TiO_(2)layer.The W/TiO_(2)/HfO_(2)/TaN memristive device exhibited excellent and repeatable RS characteristics,including superb 10^(3) dc switching cycles,outstanding 107 pulse endurance,and high-thermal stability(10^(4) s at 125℃)important for digital computing systems.Furthermore,some essential biological synaptic characteristics such as potentiation-depression plasticity,paired-pulse facilitation(PPF),and spike-timing-dependent plasticity(STDP,asymmetric Hebbian and asymmetric anti-Hebbian)were successfully mimicked herein using the crossbar-array memristive device.Based on experimental results,a migration and diffusion of oxygen vacancy based physical model is proposed to describe the synaptic plasticity and RS mechanism.This study demonstrates that the proposed W/TiO_(2)/HfO_(2)/TaN memristor crossbar-array has a significant potential for applications in non-volatile memory(NVM)and bioinspired neuromorphic systems.
