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Zhang, Yuanhao, Jibo Xu, Yahui Yu, Weijie Zheng, Zhiyu Xu, Lingzhi Lu, Ziyu Wang, Chaojing Lu i Zheng Wen. "Changeable electroresistance in Pt/Pb(Zr,Ti)O3/(La,Sr)MnO3 tunnel junctions and memristive properties for synaptic plasticity emulation". Applied Physics Letters 120, nr 20 (16.05.2022): 203501. http://dx.doi.org/10.1063/5.0093112.
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Ferroelectric tunnel junctions (FTJs) are promising candidates for the next-generation memory technologies. The electroresistance mechanism, however, has been reported not only from the polarization-modulation of barrier profiles. Electrical migration of charged defects has also been observed as a possible origin for the resistive switching. Here, we achieve two kinds of electroresistance behaviors in Pt/Pb(Zr,Ti)O3/(La,Sr)MnO3 tunnel junctions by introducing oxygen vacancies in the Pb(Zr,Ti)O3 barrier. The oxygen vacancies are observed by x-ray photoelectron spectroscopy, and their effects on the widely adopted piezoresponse force microscopy characterizations of ultrathin ferroelectric films have been analyzed by AC voltage-dependent hysteresis loops. For the Pt/Pb(Zr,Ti)O3/(La,Sr)MnO3 device that is modulated by the polarization reversal, a counterclockwise resistance–voltage ( R– V) relationship is observed due to the tunneling between high and low barriers, whereas the R– V hysteresis loop is changed to clockwise with the existence of oxygen vacancies, in which conductive filaments are formed in the Pb(Zr,Ti)O3 barrier. However, such an ionic electroresistance is not stable during repetitive switching. Further investigation on memristive behaviors is, thus, performed on the ferroelectric-controlled Pt/Pb(Zr,Ti)O3/(La,Sr)MnO3 tunnel junctions. An excellent linearity is achieved in continuous resistance change owing to the nucleation-limited-switching mode of domain switching in the Pb(Zr,Ti)O3 barrier, giving rise to spike-timing-dependent plasticity behaviors for the Hebbian rule of learning and memory. These results provide insight into the distinguishing of ferroelectric and ionic contributions in electroresistance of FTJ devices, facilitating deep understanding of nonvolatile resistive memories.
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YANG, JUN, KAI-MING JIANG, WEN YUAN WU i YAN CHUN GONG. "MAGNETIC SWITCHING EFFECT IN SPIN FIELD-EFFECT TRANSISTORS". International Journal of Modern Physics B 24, nr 23 (20.09.2010): 4501–7. http://dx.doi.org/10.1142/s0217979210056190.
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Taking account the presence of external magnetic field, we study the conductance properties in spin field-effect transistors (SFET). It is shown that the conductance of the SFET exhibits an excellent magnetic switching characteristic for high potential barriers, and it is more and more pronounced with the potential barrier strength increasing. According to the effect, we can switch the SFET on or off by tuning the strength of the magnetic field. We also study how the conductance of the SFET is manipulated by spin–orbit coupling strength and spin polarization in source and drain.
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DING, HANG-CHEN, SI-QI SHI, WEI-HUA TANG i CHUN-GANG DUAN. "FERROELECTRIC SWITCHING PATH IN MONODOMAIN RHOMBOHEDRAL BiFeO3 CRYSTAL: A FIRST-PRINCIPLES STUDY". Journal of Advanced Dielectrics 01, nr 02 (kwiecień 2011): 179–84. http://dx.doi.org/10.1142/s2010135x11000264.
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Based on density-functional calculations, we have studied possible ferroelectric switching path in monodomain single crystal of rhombohedral BiFeO3 , a prototypical multiferroic compound. By carefully studying the behaviors of FeO6 corner-sharing double-tetrahedrons, we find abrupt changes in total energy and oxygen atomic positions, and therefore polarizations, occur in the ferroelectric switching path of rhombohedral BiFeO3 . Detailed analyses suggest that such behavior might be caused by the frustrated magnetic ordering in the paraelectric phase of rhombohedral BiFeO3 , where three O atoms and the Bi atom are in the same plane perpendicular to the polarization direction. This is supported by the fact that the ferroelectric switching for paramagnetic BiFeO3 is smooth and has a much lower energy barrier than that of antiferromagnetic BiFeO3 .
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Sun, Yu, Zi-Lin Yuan, Qian-Ze Li, Cai-Xin Zhang, Ke-Qiu Chen i Li-Ming Tang. "Electrically controlled valley polarization in 2D buckled honeycomb structures". Modern Physics Letters B 35, nr 25 (3.08.2021): 2150390. http://dx.doi.org/10.1142/s0217984921503905.
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Generating and manipulating valley polarization in a controlled method is significant. The inherently broken centrosymmetry of the buckled honeycomb structures gives it both ferroelectricity and valley degree of freedom, which provides an opportunity to realize electrically controlled valley polarization. In the first step, we explored the origin of buckling. The hexagonal structure is polar due to buckling of the surface, but the degree of buckling and the energy barrier to switching electric polarization are determined not solely by the chemical composition. We combined the electronegativity difference, bond length and the distribution of charge density to describe quantificationally the polarity of chemical bonds. It shows the characteristics of relatively long bond-length but relatively small electronegativity-difference. For exploring the ferroelectricity of buckling structures and the behavior of ferroelectric (FE) control of the valley degree of freedom, the [Formula: see text]-GaP is used as a model system to elucidate the strain effect on FE behavior and the magnetic proximity effect on the polarization and switching of valley. We found that the spontaneous polarization is positively correlated with the electronegativity difference within a certain range, and the compression strain can effectively manipulate spontaneous polarization and switch barrier. A combination of the magnetic proximity effect and the inversion of electric polarization can generate and switch valley polarization effectively.
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Zhu, Yong Dan, Cheng Hu i An You Zuo. "Resistive Switching Behavior in Pt/La0.7Sr0.3MnO3/Nb0.05Bi0.95FeO3/Nb:SrTiO3 Ferroelectric Heterostructure". Advanced Materials Research 1061-1062 (grudzień 2014): 333–36. http://dx.doi.org/10.4028/www.scientific.net/amr.1061-1062.333.
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we report reproducible resistive switching performance and relevant physical mechanism of Pt/La0.7Sr0.3MnO3/Nb0.05Bi0.95FeO3/Nb:SrTiO3 ferroelectric heterostructure which was fabricated by pulsed laser deposition. This device exhibits a nonvolatile resistive switching with a resistance ratio of up to 60 under 2V/-3V pulse voltages at room temperature. Low voltage readout, reliable resistance switching reproducibility and good time retention, indicating promise for non-destructive readout nonvolatile memories. In this metal/p-semiconductor/ferroelectric/n-semiconductor heterostructure, the mechanism of resistive switching behavior would be attributed to the ferroelectric polarization enhanced field-induced charge redistribution at the semiconductor/ferroelectric interface, resulting in the modulation of the interface barrier height. Keywords: Resistive switching, Ferroelectric resistive switching, Ferroelectric field effect.
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Zhang, Qingtian, Zijing Lin i K. S. Chan. "Spin polarization switching in monolayer graphene through a Rashba multi-barrier structure". Applied Physics Letters 102, nr 14 (8.04.2013): 142407. http://dx.doi.org/10.1063/1.4801843.
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Wei, Wei, Guoqing Zhao, XuePeng Zhan, Weiqiang Zhang, Pengpeng Sang, Qianwen Wang, Lu Tai i in. "Switching pathway-dependent strain-effects on the ferroelectric properties and structural deformations in orthorhombic HfO2". Journal of Applied Physics 131, nr 15 (21.04.2022): 154101. http://dx.doi.org/10.1063/5.0084660.
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The polarization switching pathway plays a key role in deciding the magnitudes of the spontaneous polarization and the coercive electric field, which can be used to realize controllable ferroelectric properties. In this paper, by first-principles calculations, we reveal how the spontaneous polarization ( Ps) and the switching barrier ( Eb) of orthorhombic HfO2 ( o-HfO2) respond to various lattice strains depending on two kinds of switching pathways, i.e., the shift-across (SA) pathway and the shift-inside pathway. It is revealed that the existence of the two pathways is most likely dependent on the interface termination of o-HfO2, and the SA pathway exhibits higher critical values of both Ps and Eb. By applying lattice strains on o-HfO2 (001) and (010) planes, a ferroelectric–paraelectric phase transition from the polar Pca21 to the nonpolar Pbcn can be observed. Importantly, the variation trends of Ps and Eb under the same lattice strains are found to be highly different depending on the switching pathways. However, by carefully designing the interfacial tail atoms, strain engineering can efficiently improve Eb and Ps for both pathways in o-HfO2 films. Our work uncovers the mechanisms of the switching pathways and opens a new avenue for preparing high-performance ferroelectric devices using strain engineering.
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Hamouda, Wassim, Furqan Mehmood, Thomas Mikolajick, Uwe Schroeder, Tevfik Onur Mentes, Andrea Locatelli i Nick Barrett. "Oxygen vacancy concentration as a function of cycling and polarization state in TiN/Hf0.5Zr0.5O2/TiN ferroelectric capacitors studied by x-ray photoemission electron microscopy". Applied Physics Letters 120, nr 20 (16.05.2022): 202902. http://dx.doi.org/10.1063/5.0093125.
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We have studied the field cycling behavior of microscopic TiN/Hf0.5Zr0.5O2/TiN ferroelectric capacitors using synchrotron-based soft x-ray photoemission electron microscopy. The oxygen vacancy ([Formula: see text]) concentration near the top TiN/Hf0.5Zr0.5O2 interface is estimated from the reduction of Hf4+ to Hf3+ as measured in the Hf 4f core level spectra. The [Formula: see text] concentration increases with field cycling and redistributes under the effect of the internal field due to the polarization. Upward pointing polarization slightly depletes the concentration near the top interface, whereas downward polarization causes [Formula: see text] drift toward the top interface. The [Formula: see text] redistribution after wake-up is consistent with shifts in the I–V switching peak. The Schottky barrier height for electrons decreases systematically with cycling in polarization states, reflecting the overall increase in [Formula: see text].
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Chen, Rong, Zilian Qi, Yingfei Xiong, Yicheng Li, Xiaodong Zhang i Kun Cao. "Interface-mediated ferroelectricity in PMN-PT/PZT flexible bilayer via pulsed laser deposition". Journal of Vacuum Science & Technology A 41, nr 3 (maj 2023): 032702. http://dx.doi.org/10.1116/6.0002386.
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Ferroelectric thin-film bilayers of Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT)/PbZr0.52Ti0.48O3 (PZT) were grown on a flexible substrate of mica using pulsed laser deposition. Growth of the bilayer was induced with a thin film of LaNiO3 (LNO) single crystal, which was deposited on a mica substrate through van der Waals epitaxy. The LNO thin film also serves as the electrode for the bilayer device. The growth of the LNO thin film along the [Formula: see text] orientation adopts a “Stranski–Krastanov” mechanism, governed by the relaxation of elastic energy between LNO/mica. Compared with the single layers of PMN-PT or PZT, or the bilayer of PZT/PMN-PT, the PMN-PT/PZT bilayer exhibits enhanced ferroelectric properties, with remnant polarization up to 72 μC/cm2. In addition, polarization in the PMN-PT/PZT bilayer exhibits excellent resistance against mechanical bending fatigue over 108 switching cycles. Such improved performances are ascribed to spontaneous polarizations enhanced by the residual stress at the PMN-PT/PZT heterointerface, increased interfacial potential barrier against leakage, and suppressed diffusion of Nb or Mg across the interface.
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Chen, Feng, Robert Schafranek, André Wachau, Sergey Zhukov, Julia Glaum, Torsten Granzow, Heinz von Seggern i Andreas Klein. "Barrier heights, polarization switching, and electrical fatigue in Pb(Zr,Ti)O3 ceramics with different electrodes". Journal of Applied Physics 108, nr 10 (15.11.2010): 104106. http://dx.doi.org/10.1063/1.3512969.
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Liehr, Maximilian, Jubin Hazra, Karsten Beckmann, Vineetha Mukundan, Ioannis Alexandrou, Timothy Yeow, Joseph Race i in. "Implementation of high-performance and high-yield nanoscale hafnium zirconium oxide based ferroelectric tunnel junction devices on 300 mm wafer platform". Journal of Vacuum Science & Technology B 41, nr 1 (styczeń 2023): 012805. http://dx.doi.org/10.1116/6.0002097.
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In this work, hafnium zirconium oxide (HZO)-based 100 × 100 nm2 ferroelectric tunnel junction (FTJ) devices were implemented on a 300 mm wafer platform, using a baseline 65 nm CMOS process technology. FTJs consisting of TiN/HZO/TiN were integrated in between metal 1 (M1) and via 1 (V1) layers. Cross-sectional transmission electron microscopy and energy dispersive x-ray spectroscopy analysis confirmed the targeted thickness and composition of the FTJ film stack, while grazing incidence, in-plane x-ray diffraction analysis demonstrated the presence of orthorhombic phase Pca21 responsible for ferroelectric polarization observed in HZO films. Current measurement, as a function of voltage for both up- and down-polarization states, yielded a tunneling electroresistance (TER) ratio of 2.28. The device TER ratio and endurance behavior were further optimized by insertion of thin Al2O3 tunnel barrier layer between the bottom electrode (TiN) and ferroelectric switching layer (HZO) by tuning the band offset between HZO and TiN, facilitating on-state tunneling conduction and creating an additional barrier layer in off-state current conduction path. Investigation of current transport mechanism showed that the current in these FTJ devices is dominated by direct tunneling at low electric field ( E < 0.4 MV/cm) and by Fowler–Nordheim (F–N) tunneling at high electric field ( E > 0.4 MV/cm). The modified FTJ device stack (TiN/Al2O3/HZO/TiN) demonstrated an enhanced TER ratio of ∼5 (2.2× improvement) and endurance up to 106 switching cycles. Write voltage and pulse width dependent trade-off characteristics between TER ratio and maximum endurance cycles (Nc) were established that enabled optimal balance of FTJ switching metrics. The FTJ memory cells also showed multi-level-cell characteristics, i.e., 2 bits/cell storage capability. Based on full 300 mm wafer statistics, a switching yield of >80% was achieved for fabricated FTJ devices demonstrating robustness of fabrication and programming approach used for FTJ performance optimization. The realization of CMOS-compatible nanoscale FTJ devices on 300 mm wafer platform demonstrates the promising potential of high-volume large-scale industrial implementation of FTJ devices for various nonvolatile memory applications.
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Liang, Shiheng, Zhongwei Yu, Xavier Devaux, Anthony Ferri, Weichuan Huang, Huaiwen Yang, Rachel Desfeux i in. "Quenching of Spin Polarization Switching in Organic Multiferroic Tunnel Junctions by Ferroelectric “Ailing-Channel” in Organic Barrier". ACS Applied Materials & Interfaces 10, nr 36 (20.08.2018): 30614–22. http://dx.doi.org/10.1021/acsami.8b11437.
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Abramov, Alexander, Boris Slautin, Victoria Pryakhina, Vladimir Shur, Andrei Kholkin i Denis Alikin. "Spatially-Resolved Study of the Electronic Transport and Resistive Switching in Polycrystalline Bismuth Ferrite". Sensors 23, nr 1 (3.01.2023): 526. http://dx.doi.org/10.3390/s23010526.
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Ferroelectric materials attract much attention for applications in resistive memory devices due to the large current difference between insulating and conductive states and the ability of carefully controlling electronic transport via the polarization set-up. Bismuth ferrite films are of special interest due to the combination of high spontaneous polarization and antiferromagnetism, implying the possibility to provide multiple physical mechanisms for data storage and operations. Macroscopic conductivity measurements are often hampered to unambiguously characterize the electric transport, because of the strong influence of the diverse material microstructure. Here, we studied the electronic transport and resistive switching phenomena in polycrystalline bismuth ferrite using advanced conductive atomic force microscopy (CAFM) at different temperatures and electric fields. The new approach to the CAFM spectroscopy and corresponding data analysis are proposed, which allow deep insight into the material band structure at high lateral resolution. Contrary to many studies via macroscopic methods, postulating electromigration of the oxygen vacancies, we demonstrate resistive switching in bismuth ferrite to be caused by the pure electronic processes of trapping/releasing electrons and injection of the electrons by the scanning probe microscopy tip. The electronic transport was shown to be comprehensively described by the combination of the space charge limited current model, while a Schottky barrier at the interface is less important due to the presence of the built-in subsurface charge.
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Liu, Zhijie, Xinyu Wang, Xingyue Ma, Yurong Yang i Di Wu. "Doping effects on the ferroelectric properties of wurtzite nitrides". Applied Physics Letters 122, nr 12 (20.03.2023): 122901. http://dx.doi.org/10.1063/5.0145818.
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Ferroelectric materials have been explored for a long time for easy integration with state-of-the-art semiconductor technologies. Doped wurtzite nitrides have been reported as promising candidates due to their high stability, compatibility, and scalability. We investigate doping effects on ferroelectric properties of Sc-doped AlN (AlScN) and B-doped AlN (AlBN) by first-principles methods. The energy barrier against polarization switching is observed to decrease with increasing doping concentration at low concentration ranges, which is the origin of the emerging ferroelectricity in doped AlN. Further increasing the doping concentration to a critical value, the ferroelectric wurtzite phase transforms into paraelectric phases (a rock salt phase for AlScN and a zinc blende phase for AlBN), making it invalid to decrease the coercivity by increasing the doping concentration. Furthermore, it is revealed that different nonpolar structures (a hexagonal phase for AlScN and a [Formula: see text]-BeO phase for AlBN) appear in the ferroelectric switching pathway, generating different switching features in doped AlN. Our results give a microscopic understanding of the ferroelectricity in doped wurtzite materials and broaden the route to improve their ferroelectric properties.
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Pirro, Michele, Xuanyi Zhao, Bernard Herrera, Pietro Simeoni i Matteo Rinaldi. "Effect of Substrate-RF on Sub-200 nm Al0.7Sc0.3N Thin Films". Micromachines 13, nr 6 (31.05.2022): 877. http://dx.doi.org/10.3390/mi13060877.
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Sc-doped aluminum nitride is emerging as a new piezoelectric material which can substitute undoped aluminum nitride (AlN) in radio-frequency MEMS applications, thanks to its demonstrated enhancement of the piezoelectric coefficients. Furthermore, the recent demonstration of the ferroelectric-switching capability of the material gives AlScN the possibility to integrate memory functionalities in RF components. However, its high-coercive field and high-leakage currents are limiting its applicability. Residual stress, growth on different substrates, and testing-temperature have already been demonstrated as possible knobs to flatten the energy barrier needed for switching, but no investigation has been reported yet on the whole impact on the dielectric and ferroelectric dynamic behavior of a single process parameter. In this context, we analyze the complete spectrum of variations induced by the applied substrate-RF, from deposition characteristics to dielectric and ferroelectric properties, proving its effect on all of the material attributes. In particular, we demonstrate the possibility of engineering the AlScN lattice cell to properly modify leakage, breakdown, and coercive fields, as well as polarization charge, without altering the crystallinity level, making substrate-RF an effective and efficient fabrication knob to ease the limitations the material is facing.
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Müller, Moritz L., Maximilian T. Becker, Nives Strkalj i Judith L. MacManus-Driscoll. "Schottky-to-Ohmic switching in ferroelectric memristors based on semiconducting Hf0.93Y0.07O2 thin films". Applied Physics Letters 121, nr 9 (29.08.2022): 093501. http://dx.doi.org/10.1063/5.0095762.
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We demonstrate resistive switching and memristive behavior in devices consisting of ultrathin (4.5 nm) semiconducting, epitaxial ferroelectric Hf0.93Y0.07O2 (YHO) films on La0.7Sr0.3MnO3-buffered, Nb-doped SrTiO3 single crystal substrates with Au top electrodes. Unlike the tunneling-driven current–voltage characteristics of ferroelectric tunnel junctions which utilize ultrathin insulating (fully depleted) ferroelectric films, the semiconducting nature of our YHO films, i.e., the presence of free charge carriers introduced by Y doping, results in radically different current–voltage characteristics. Current–voltage measurements indicate a polarization-modulated transition from Schottky-barrier-controlled charge transport to Ohmic conduction in the YHO devices, which results in a large on/off ratio of up to 540. Moreover, voltage pulse train measurements reveal a broad range of accessible resistance states, which indicates the memristive behavior of the devices. Our results represent an important step toward the development of future nonvolatile memory and brain-inspired neuromorphic computing applications based on ultrathin semiconducting ferroelectric films.
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KIM, HONG KOO, i NASIR ABDUL BASIT. "FERROELECTRIC NONVOLATILE MEMORY FIELD-EFFECT TRANSISTORS BASED ON A NOVEL BUFFER LAYER STRUCTURE". International Journal of High Speed Electronics and Systems 10, nr 01 (marzec 2000): 39–46. http://dx.doi.org/10.1142/s0129156400000076.
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We have proposed and developed a ferroelectric nonvolatile field-effect transistor that incorporates a thin MgO buffer layer between a ferroelectric film and an oxidized Si substrate. The use of an MgO/SiO2 buffer for a ferroelectric gate is based on the following findings. First, a thin MgO buffer serves well as a template layer allowing the growth of highly oriented ferroelectric films on amorphous substrates. Second, MgO works well as a diffusion barrier between a ferroelectric film and a substrate, protecting the silicon FET channel region from interdiffusion or reaction that may occur during device processing. Third, thermal oxidation of Si is known to be one of the best ways of passivating silicon surfaces, thus to reduce high quality FET channels. The fabricated devices show excellent performance in ferroelectric polarization switching, memory retention, and fatigue resistance. The devices also demonstrate scalability in device dimension and operating voltage, i.e., they are suitable for low voltage operation (3-5 V or below) showing a sufficient memory window (1-2 V).
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Mokhtarnejad, Mahshid, Morteza Asgari i Arash Sabatyan. "Investigating Optical Properties of One-Dimensional Photonic Crystals Containing Semiconductor Quantum Wells". International Journal of Optics 2017 (2017): 1–8. http://dx.doi.org/10.1155/2017/7280613.
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This study examined MQWs made of InGaAs/GaAs, InAlAs/InP, and InGaAs/InP in terms of their band structure and reflectivity. We also demonstrated that the reflectivity of MQWs under normal incident was at maximum, while both using a strong pump and changing incident angle reduced it. Reflectivity of the structure for a weak probe pulse depends on polarization, intensity of the pump pulse, and delay between the probe pulse and the pump pulse. So this system can be used as an ultrafast all-optical switch which is inspected by the transfer matrix method. After studying the band structure of the one-dimensional photonic crystal, the optical stark effect (OSE) was considered on it. Due to the OSE on virtual exciton levels, the switching time can be in the order of picoseconds. Moreover, it is demonstrated that, by introducing errors in width of barrier and well as well as by inserting defect, the reflectivity is reduced. Thus, by employing the mechanism of stark effect MQWs band-gaps can be easily controlled which is useful in designing MWQ based optical switches and filters. By comparing the results, we observe that the reflectivity of MWQ containing 200 periods of InAlAs/InP quantum wells shows the maximum reflectivity of 96%.
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Yoo, Jaewook, Hyeonjun Song, Hongseung Lee, Seongbin Lim, Soyeon Kim, Keun Heo i Hagyoul Bae. "Recent Research for HZO-Based Ferroelectric Memory towards In-Memory Computing Applications". Electronics 12, nr 10 (19.05.2023): 2297. http://dx.doi.org/10.3390/electronics12102297.
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The AI and IoT era requires software and hardware capable of efficiently processing massive amounts data quickly and at a low cost. However, there are bottlenecks in existing Von Neumann structures, including the difference in the operating speed of current-generation DRAM and Flash memory systems, the large voltage required to erase the charge of nonvolatile memory cells, and the limitations of scaled-down systems. Ferroelectric materials are one exciting means of breaking away from this structure, as Hf-based ferroelectric materials have a low operating voltage, excellent data retention qualities, and show fast switching speed, and can be used as non-volatile memory (NVM) if polarization characteristics are utilized. Moreover, adjusting their conductance enables diverse computing architectures, such as neuromorphic computing with analog characteristics or ‘logic-in-memory’ computing with digital characteristics, through high integration. Several types of ferroelectric memories, including two-terminal-based FTJs, three-terminal-based FeFETs using electric field effect, and FeRAMs using ferroelectric materials as capacitors, are currently being studied. In this review paper, we include these devices, as well as a Fe-diode with high on/off ratio properties, which has a similar structure to the FTJs but operate with the Schottky barrier modulation. After reviewing the operating principles and features of each structure, we conclude with a summary of recent applications that have incorporated them.
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Song, Rui, Bi-Li Wang, Kai Feng, Li Wang i Dan-Dan Liang. "Structural, magnetic and ferroelectric properties of VOBr<sub>2 </sub>monolayer: A first-principles study". Acta Physica Sinica 71, nr 3 (2022): 037101. http://dx.doi.org/10.7498/aps.71.20211516.
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On the basis of first-principles calculations, the structure, magnetism and ferroelectricity of VOBr<sub>2</sub> monolayer are studied systematically in the present work. The calculation results indicate that a spontaneous ferroelectric distortion takes place at low temperature, causing the structure of VOBr<sub>2</sub> to transform from a centrosymmetric paraelectric phase to a ferroelectric one. In contrast with its sister compound VOI<sub>2</sub>, the dimerization of V is unstable in VOBr<sub>2</sub> and may quench the local magnetic moment on V ions. Additionally, the easy magnetization axis of VOBr<sub>2</sub> monolayer is in-plane along the <i>a</i>-axis, and the magnetic coupling between adjacent local moments is antiferromagnetic both along the <i>a</i>-axis and along the <i>b</i>-axis. Moreover, the ferroelectric displacement of V ions occurs in the <i>a</i>-axis, along the V—O—V chains direction, resulting in a polarization of about 40 μC/cm<sup>2</sup>. Comparing with the ferro-to-paraelectric reversal pathway, the energy barrier can be effectively reduced for ferroelectric switching on partial or individual V—O—V chains. It is reasonable to believe that the dipole moment flipping on specific chain can be achieved through a moderate external field, thereby providing new direction for designing the low-energy-consumption and high-density ferroelectric memory device.
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Shields, Joe, Carlota Ruiz de Galarreta, Jacopo Bertolotti i C. David Wright. "Enhanced Performance and Diffusion Robustness of Phase-Change Metasurfaces via a Hybrid Dielectric/Plasmonic Approach". Nanomaterials 11, nr 2 (18.02.2021): 525. http://dx.doi.org/10.3390/nano11020525.
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Materials of which the refractive indices can be thermally tuned or switched, such as in chalcogenide phase-change alloys, offer a promising path towards the development of active optical metasurfaces for the control of the amplitude, phase, and polarization of light. However, for phase-change metasurfaces to be able to provide viable technology for active light control, in situ electrical switching via resistive heaters integral to or embedded in the metasurface itself is highly desirable. In this context, good electrical conductors (metals) with high melting points (i.e., significantly above the melting point of commonly used phase-change alloys) are required. In addition, such metals should ideally have low plasmonic losses, so as to not degrade metasurface optical performance. This essentially limits the choice to a few noble metals, namely, gold and silver, but these tend to diffuse quite readily into phase-change materials (particularly the archetypal Ge2Sb2Te5 alloy used here), and into dielectric resonators such as Si or Ge. In this work, we introduce a novel hybrid dielectric/plasmonic metasurface architecture, where we incorporated a thin Ge2Sb2Te5 layer into the body of a cubic silicon nanoresonator lying on metallic planes that simultaneously acted as high-efficiency reflectors and resistive heaters. Through systematic studies based on changing the configuration of the bottom metal plane between high-melting-point diffusive and low-melting-point nondiffusive metals (Au and Al, respectively), we explicitly show how thermally activated diffusion can catastrophically and irreversibly degrade the optical performance of chalcogenide phase-change metasurface devices, and how such degradation can be successfully overcome at the design stage via the incorporation of ultrathin Si3N4 barrier layers between the gold plane and the hybrid Si/Ge2Sb2Te5 resonators. Our work clarifies the importance of diffusion of noble metals in thermally tunable metasurfaces and how to overcome it, thus helping phase-change-based metasurface technology move a step closer towards the realization of real-world applications.
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Long, Xiao, Huan Tan, Florencio Sánchez, Ignasi Fina i Josep Fontcuberta. "Disentangling electronic and thermal contributions to light-induced resistance switching in BaTiO3 ferroelectric tunnel junction". Journal of Applied Physics 132, nr 21 (7.12.2022): 214103. http://dx.doi.org/10.1063/5.0125040.
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In the presence of asymmetric potential barriers, such as those created by imprint fields, ferroelectric polarization can be reversed by light due to the photoinduced suppression of polarization. Both thermal effects and photocarrier-induced polarization screening may agree with this experimental observation, challenging its understanding. Here, we explore light-induced ferroelectric polarization switching in BaTiO3 thin films. Time-dependent photocurrent and photoresistance experiments at different wavelengths indicate that the optical switch of polarization is mainly driven by photocarriers rather than thermal effects. The effect of light on sample polarization is found to be relatively slow and that an illumination period as long as ≈100 s is required to achieve complete switching when using a 405 nm light wavelength and 1.4 W/cm2 power density. It is shown that this response is governed by the concentration of photo-generated charges, which is low due to the reduced light absorption of BaTiO3 films at the explored wavelengths. Our conclusions can help us to better design optically switching devices based on ferroelectric materials.
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Diao, Zhitao, Dmytro Apalkov, Mahendra Pakala, Yunfei Ding, Alex Panchula i Yiming Huai. "Spin transfer switching and spin polarization in magnetic tunnel junctions with MgO and AlOx barriers". Applied Physics Letters 87, nr 23 (5.12.2005): 232502. http://dx.doi.org/10.1063/1.2139849.
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Khan, Aaliyah C., Autumn S. Cook, Joshua A. Leginze i Joseph W. Bennett. "Developing new antiferroelectric and ferroelectric oxides and chalcogenides within the A2BX3 family". Journal of Materials Research 37, nr 1 (28.10.2021): 346–59. http://dx.doi.org/10.1557/s43578-021-00410-3.
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Abstract Here, we employ first-principles methods to expand the set of functional materials known as ferroelectrics and antiferroelectrics. We use known compounds, whose properties have previously been overlooked, as the springboard for new materials. We first develop methodology to search for polar instabilities in known nonpolar and antipolar compounds and then use this technique to identify new members of the A2BX3 family. This methodology identities new Pb-free oxides and chalcogenides, with a wide range of band gaps, to be used as solid-state photovoltaics. Finally, we perform a cursory evaluation of how compositional tuning of oxide materials can adjust the difference in energy between ground and metastable states, to assess the likelihood of polarization switching. In total, we report on a targeted sets of new materials to synthesize and design routes to obtain ferroelectrics and antiferroelectrics with energetic barriers amenable to switching with an electric field. Graphic abstract
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Ren, Yangyang, Yaxin Gao, Tingting Zhong, Menghao Wu i Jun-Ming Liu. "Proton transfer in layered hydrogen-bonded system γ-MOOH (M = Al, Sc): Robust bi-mode ferroelectricity and 1D superionic conductivity". Applied Physics Letters 122, nr 4 (23.01.2023): 042901. http://dx.doi.org/10.1063/5.0136846.
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Layered γ-MOOH, such as synthetic boehmite γ-AlOOH and γ-ScOOH, has been explored for various applications since 1950s. In this paper, based on first-principles calculations, we show the evidence of two proton transfer modes in their hydrogen-bonded network that give rise to extraordinary properties: (1) they, respectively, result in two distinct types of ferroelectricity with different switching mechanisms and polarizations, while the exhibiting mode under an electric field depends on various factors, including the field intensity and direction, the existence of vacancies, and temperature; and (2) the combination of two modes can lead to ultra-high proton conductivity along 1D channels. Their proton migration barriers ensure high ferroelectric Curie temperature, while still much lower compared with current proton conductors, giving rise to 1D superionicity with unprecedented protonic conductivity over 24 mS/cm. Those light weight nontoxic layered materials with high polarizations, Curie temperature, and ultra-high protonic conductivity should provide vast opportunities for various applications.
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Stoleriu, Laurentiu, Cristina Ciomaga, Fabio Fochi, Pilar Ochoa, José Fernández, Carmen Galassi, Vincenzo Buscaglia, Paolo Nanni i Liliana Mitoseriu. "Mechanically clamped PZT ceramics investigated by First-Order Reversal Curves diagram". Processing and Application of Ceramics 4, nr 3 (2010): 209–14. http://dx.doi.org/10.2298/pac1003209s.
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The First Order Reversal Curves (FORC) diagrams method was developed for characterizing the switching properties of ferroelectrics. In the present paper, the FORC method was applied for hard Pb(Zr,Ti)O3 ceramics with symmetric and asymmetric clamping. An ideal high-oriented single-crystalline ferroelectric with rectangular P(E) loop would be characterised by a delta-function FORC distribution, while real ferroelectrics and mostly the polycrystalline ceramics show dispersed FORC distributions. All the investigated ceramics show FORC distributions with non-Gaussian shape, slightly elongated along the coercitive axis, meaning a high dispersion of the energy barriers separating the two bi-stable polarizations ?P. The degree of dispersion is enhanced by clamping. The maximum FORC coercivity is located at ~ (1.9-2) MV/m for all the hard ceramics. The FORC cycling experiment causes the reversal of the initial poling and result in a positive/negative bias on the FORC diagrams. According to the observed features, it results that FORC coercivity is more related to the nature of the material, while the bias field is more sensitive to the electrical and mechanical boundary conditions in which the ferroelectric ceramics evolves while switching.
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Yu, Qisheng, Jiawei Huang, Changming Ke, Zhuang Qian, Liyang Ma i Shi Liu. "Semiconducting nonperovskite ferroelectric oxynitride designed ab initio". Applied Physics Letters 122, nr 14 (3.04.2023): 142902. http://dx.doi.org/10.1063/5.0141987.
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The recent discovery of HfO2-based and nitride-based ferroelectrics that are compatible to the semiconductor manufacturing process has revitalized the field of ferroelectric-based nanoelectronics. Guided by a simple design principle of charge compensation and density functional theory calculations, we discover that HfO2-like mixed-anion materials, TaON and NbON, can crystallize in the polar [Formula: see text] phase with a strong thermodynamic driving force to adopt anion ordering spontaneously. Both oxynitrides possess large remnant polarization, low switching barriers, and unconventional negative piezoelectric effect, making them promising piezoelectrics and ferroelectrics. Distinct from HfO2 that has a wide bandgap, both TaON and NbON can absorb visible light and have high charge carrier mobilities, suitable for ferroelectric photovoltaic and photocatalytic applications. This class of multifunctional nonperovskite oxynitride containing economical and environmentally benign elements offers a platform to design and optimize high-performing ferroelectric semiconductors for integrated systems.
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Ye, Fan, Xin-Gui Tang, Jia-Ying Chen, Wen-Min Zhong, Li Zhang, Yan-Ping Jiang i Qiu-Xiang Liu. "Neurosynaptic-like behavior of Ce-doped BaTiO3 ferroelectric thin film diodes for visual recognition applications". Applied Physics Letters 121, nr 17 (24.10.2022): 171901. http://dx.doi.org/10.1063/5.0120159.
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Brain-like neuromorphic computing networks based on the human brain information processing model are gradually breaking down the memory barriers caused by traditional computing frameworks. The brain-like neural system consists of electronic synapses and neurons. The multiple ferroelectric polarization switching modulated by the external electric field is well suited to simulate artificial neural synaptic weights. Therefore, ferroelectric diodes' (FDs) synapses have great advantages in building highly reliable and energy-efficient artificial neural networks. In this paper, we demonstrate the FDs synapse, which is based on rare-earth metal-doped BaTiO3 ferroelectric dielectric layer materials. This performs short-term and long-term synaptic plasticity behaviors by modulating synaptic weights using pulsed stimuli to polarize or flip ferroelectric films. In addition, convolutional neural networks were constructed on the MNIST dataset and the Fashion-MNIST dataset to check the feasibility of the device in simulating bio-visual recognition. The results expand the application of FDs' devices in the intersection of artificial intelligence and bioscience.
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Abbasi, Pedram, David P. Fenning i Tod A. Pascal. "Electrocatalytic Hydrogen Evolution on Ferroelectric Perovskite Heterostructures". ECS Meeting Abstracts MA2022-01, nr 38 (7.07.2022): 1691. http://dx.doi.org/10.1149/ma2022-01381691mtgabs.
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Ferroelectric perovskites have recently attracted interest for a wide range of photocatalytic and electrochemical applications1 due to their intrinsic properties for light adsorption2, electron–hole pair separation3–5 and a hypothesized enhancement of catalytic activity by polarization switching6–8. However, most of the well-known ferroelectric perovskites e.g., BaTiO3 and Pb (Zr, Ti)O3 are known to have limited activity toward electrocatalytic reactions e.g. hydrogen evolution (HER) and water splitting.2 In this work, we demonstrate that introducing only a few mono layers of SrRuO3, a metallic oxide from perovskite family, can significantly enhance the catalytic activity of BaTiO3 toward HER. Using a combination of first principle DFT+U calculations and experiments on thin films grown by molecular beam epitaxy, we investigated the activity of heterostructures of different thicknesses toward HER in an alkaline electrolyte. Computational results show that the Gibbs free energy barrier of H* adsorption on one monolayer of SrRuO3 atop ferroelectric BaTiO3 is at least two times smaller than BaTiO3, depending on the adsorption site or the direction of ferroelectric polarization. In line with the findings from our DFT calculations, our experimental results confirm significantly higher current density and lower charge transfer resistance toward hydrogen evolution for SrRuO3/BaTiO3 heterostructures compared to bare BaTiO3 surfaces. Harnessing oxide heterostructures, as demonstrated here, opens the door to leveraging the unique properties of ferroelectrics as supports to promote electrocatalytic activity.
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Hofstetter, Daniel, Cynthia Aku-Leh, Hans Beck i David P. Bour. "AlGaN-Based 1.55 µm Phototransistor as a Crucial Building Block for Optical Computers". Crystals 11, nr 11 (22.11.2021): 1431. http://dx.doi.org/10.3390/cryst11111431.
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An optically activated, enhancement mode heterostructure field effect transistor is proposed and analytically studied. A particular feature of this device is its gate region, which is made of a photovoltaic GaN/AlN-based superlattice detector for a wavelength of 1.55 µm. Since the inter-subband transition in this superlattice does normally not interact with TE-polarized (or vertically incoming) radiation, a metallic second-order diffraction grating on the transistor gate results in a re-orientation of the light into the horizontal direction—thus providing the desired TM-polarization. Upon illumination of this gate, efficient inter-subband absorption lifts electrons from the ground to the first excited quantized state. Due to partial screening of the strong internal polarization fields between GaN quantum wells and AlN barriers, this slightly diagonal transition generates an optical rectification voltage. Added to a constant electrical bias, this optically produced gate voltage leads to a noticeable increase of the transistor’s source-drain current. The magnitude of the bias voltage is chosen to result in maximal transconductance. Since such a phototransistor based on high-bandgap material is a device involving only fast majority carriers, very low dark and leakage currents are expected. The most important advantage of such a device, however, is the expected switching speed and, hence, its predicted use as an optical logic gate for photonic computing. In the absence of a p-n-junction and thus of both a carrier-induced space charge region, and the parasitic capacitances resulting thereof, operation frequencies of appropriately designed, sufficiently small phototransistors reaching 100 GHz are envisaged.
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Xue, Fei, Xin He, Yinchang Ma, Dongxing Zheng, Chenhui Zhang, Lain-Jong Li, Jr-Hau He, Bin Yu i Xixiang Zhang. "Unraveling the origin of ferroelectric resistance switching through the interfacial engineering of layered ferroelectric-metal junctions". Nature Communications 12, nr 1 (grudzień 2021). http://dx.doi.org/10.1038/s41467-021-27617-6.
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AbstractFerroelectric memristors have found extensive applications as a type of nonvolatile resistance switching memories in information storage, neuromorphic computing, and image recognition. Their resistance switching mechanisms are phenomenally postulated as the modulation of carrier transport by polarization control over Schottky barriers. However, for over a decade, obtaining direct, comprehensive experimental evidence has remained scarce. Here, we report an approach to experimentally demonstrate the origin of ferroelectric resistance switching using planar van der Waals ferroelectric α-In2Se3 memristors. Through rational interfacial engineering, their initial Schottky barrier heights and polarization screening charges at both terminals can be delicately manipulated. This enables us to find that ferroelectric resistance switching is determined by three independent variables: ferroelectric polarization, Schottky barrier variation, and initial barrier height, as opposed to the generally reported explanation. Inspired by these findings, we demonstrate volatile and nonvolatile ferroelectric memristors with large on/off ratios above 104. Our work can be extended to other planar long-channel and vertical ultrashort-channel ferroelectric memristors to reveal their ferroelectric resistance switching regimes and improve their performances.
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Wang, Hao-Chen, Zhi-Hao Wang, Xuan-Yan Chen, Su-Huai Wei, Wenguang Zhu i Xie Zhang. "Competition between stepwise polarization switching and chirality coupling in ferroelectric GeS nanotubes". Chinese Physics Letters, 13.03.2023. http://dx.doi.org/10.1088/0256-307x/40/4/047701.
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Abstract The ferroelectricity of group-IV chalcogenides $MX$ ($M$=Ge, Sn; $X$=Se, S) monolayers has been extensively investigated, but how the ferroelectricity evolves in their one-dimensional nanotubes remains largely unclear. Employing an accurate deep-learning interatomic potential of first-principles precision, we uncover a general stepwise mechanism for polarization switching in zigzag and chiral GeS nanotubes, which has an energy barrier that is substantially lower than the one associated with the conventional one-step switching mechanism. The switching barrier (per atom) gradually decreases as increasing the number of intermediate steps and converges to a value that is almost independent of the tube diameter.
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Wei, Yingfen, Sylvia Matzen, Cynthia P. Quinteros, Thomas Maroutian, Guillaume Agnus, Philippe Lecoeur i Beatriz Noheda. "Magneto-ionic control of spin polarization in multiferroic tunnel junctions". npj Quantum Materials 4, nr 1 (grudzień 2019). http://dx.doi.org/10.1038/s41535-019-0201-0.
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AbstractMultiferroic tunnel junctions (MFTJs) with Hf0.5Zr0.5O2 barriers are reported to show both tunneling magnetoresistance effect (TMR) and tunneling electroresistance effect (TER), displaying four resistance states by magnetic and electric field switching. Here we show that, under electric field cycling of large enough magnitude, the TER can reach values as large as 106%. Moreover, concomitant with this TER enhancement, the devices develop electrical control of spin polarization, with sign reversal of the TMR effect. Currently, this intermediate state exists for a limited number of cycles and understanding the origin of these phenomena is key to improve its stability. The experiments presented here point to the magneto-ionic effect as the origin of the large TER and strong magneto-electric coupling, showing that ferroelectric polarization switching of the tunnel barrier is not the main contribution.
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Bernacki, Stephen E. "Polarization Dependent Conductivity in Thin Film Pzt Capacitors". MRS Proceedings 243 (1991). http://dx.doi.org/10.1557/proc-243-135.
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AbstractPolarization dependent conductivity is a dependence of the low field non switching steady state conduction current through a metal ferroelectric metal (MFM) thin film capacitor on the remanent polarization state of the capacitor. This paper proposes a simple theoretical model based on Schottky barrier formation due to PZT-platinum work function differences and barrier height modulation due to remanent polarization. The model predicts a conduction current dependence on both remanent polarization state and electrode material. Finally, we present experimental data in qualitative agreement with the model.
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Lee, Kyoungjun, Kunwoo Park, Hyun-Jae Lee, Myeong Seop Song, Kyu Cheol Lee, Jin Namkung, Jun Hee Lee, Jungwon Park i Seung Chul Chae. "Enhanced ferroelectric switching speed of Si-doped HfO2 thin film tailored by oxygen deficiency". Scientific Reports 11, nr 1 (18.03.2021). http://dx.doi.org/10.1038/s41598-021-85773-7.
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AbstractInvestigations concerning oxygen deficiency will increase our understanding of those factors that govern the overall material properties. Various studies have examined the relationship between oxygen deficiency and the phase transformation from a nonpolar phase to a polar phase in HfO2 thin films. However, there are few reports on the effects of oxygen deficiencies on the switching dynamics of the ferroelectric phase itself. Herein, we report the oxygen- deficiency induced enhancement of ferroelectric switching properties of Si-doped HfO2 thin films. By controlling the annealing conditions, we controlled the oxygen deficiency concentration in the ferroelectric orthorhombic HfO2 phase. Rapid high-temperature (800 °C) annealing of the HfO2 film accelerated the characteristic switching speed compared to low-temperature (600 °C) annealing. Scanning transmission electron microscopy and electron energy-loss spectroscopy (EELS) revealed that thermal annealing increased oxygen deficiencies, and first-principles calculations demonstrated a reduction of the energy barrier of the polarization flip with increased oxygen deficiency. A Monte Carlo simulation for the variation in the energy barrier of the polarization flipping confirmed the increase of characteristic switching speed.
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Huang, Biaohong, Xuefeng Zhao, Xiaoqi Li, Lingli Li, Zhongshuai Xie, Di Wang, Dingshuai Feng i in. "Schottky Barrier Control of Self-Polarization for a Colossal Ferroelectric Resistive Switching". ACS Nano, 26.06.2023. http://dx.doi.org/10.1021/acsnano.3c01548.
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Xia, Feng, i Q. M. Zhang. "Influence of Metal Electrodes on the Ferroelectric Responses of Poly(vinylidene fluoride-trifluoroethylene) Copolymer Thin Films". MRS Proceedings 734 (2002). http://dx.doi.org/10.1557/proc-734-b9.20.
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ABSTRACTFerroelectric polymer thin films have been investigated for applications such as sensors, MEMS, and memory devices, just name a few. In these thin film devices, it is anticipated that the interface effect will play an important role in determining the device performance. In this paper, we present the results of a recent study on the influence of metal electrodes on ferroelectric switching behavior of poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) polymer thin films. The results show that the influence of metal electrodes on the polarization response can be divided into two effects, the bulk effect and interface effect. The bulk effect manifests itself as the built-in bias field when metal electrodes with different work functions were used on the two surfaces of the P(VDF-TrFE) film. The interface effect is more complicated but is directly related to the metal work function. For a metal I/insulator (ferroelectric film)/metal II (MIM) sandwich structure in which the metal I and metal II possess different work functions, the low frequency polarization hysteresis loop shows asymmetric response (different switching fields). The polarization switching time also depends on whether the applied voltage is in parallel or anti-parallel to the built-in bias field. In the fast polarization switching process, it was observed that the interface effect plays a dominating role and the switching time is mainly limited by the charge injection from metal electrodes to the polymer film. For metal electrodes with higher work function, higher injection currents and hence faster polarization switching were observed. The results from I-V studies also show that the charge injection process is a Schottky type and the barrier height estimated from the temperature dependence of the I-V curves is consistent with the metal work functions used.
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Zhu Mao-Cong, Shao Ya-Jie, Zhou Jing, Chen Wen, Wang Zhi-Qing i Tian Jing. "Niobium-doped lead zirconate titanate ferroelectric films improve the resistive properties of CuInS<sub>2</sub> QDs". Acta Physica Sinica, 2022, 0. http://dx.doi.org/10.7498/aps.71.20220911.
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As a new type of non-volatile memory, quantum dots resistive random access memory (RRAM) has attracted much attention for its simplicity of preparation, fast responding time, high storage density, and smaller device size. CuInS<sub>2</sub> quantum dots (CuInS<sub>2</sub> QDs) are a kind of excellent resistive functional material with abundant electron capture sites, high optical absorption coefficient, and high carrier mobility. In this paper, CuInS<sub>2</sub> QDs/PNZT films were prepared by spin-coating CuInS<sub>2</sub> QDs on PNZT films. The results show that the resistive properties of CuInS<sub>2</sub> QDs RRAMs can be effectively improved by introducing PNZT films and can be controlled by altering the polarization direction. The CuInS<sub>2</sub> QDs/PNZT film in the negative polarization state promotes the interfacial electrons flowing to the PNZT film, which will reduce the height of the interfacial barrier and the thickness of the interfacial depletion region. And it will reduce the resistance of the composite film at the LRS. Compared to the switching voltage and resistive switching ratio of the pure CuInS<sub>2</sub> QDs film (10<sup>3</sup>), the switching voltage of the device is reduced to -4.1/3.4 V and the resistive switching ratio is increased to 10<sup>6</sup>. Furthermore, it maintains good stability in the 10<sup>3</sup> cycle durability test. In contrast, the CuInS<sub>2</sub> QDs/PNZT film interface has a larger barrier height and depletion-layer thickness when the PNZT is in the positive polarization state, which increases the resistance of the composite film in the LRS state. As a result, the switching voltage of the device increases to -6.4/5.7 V with a resistive switching ratio of 104. The resistive properties of the CuInS<sub>2</sub> QDs/PNZT film can be tuned by changing the polarization direction, as the polarization direction of the PNZT changes the interfacial energy band structure and affects the conduction mechanism. This work reveals the feasibility of using ferroelectric thin films to improve the resistive properties of quantum dots RRAMs and providing further opportunities for the development of RRAMs.
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Wolf, R. M., J. F. M. Cillessen, J. B. Giesbers, E. Pastoor, G. Miiller, K. O. Grosse-Holz i P. W. M. Blom. "Oxidic Field Effect Structures with Memory". MRS Proceedings 401 (1995). http://dx.doi.org/10.1557/proc-401-163.
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Two types of switching memory devices have been made by integrating a ferroelectric layer in a device. A Schottky diode consisting of a ferroelectric semiconductor and a high work function metal was found to show a bistable I-V behaviour. Experimentally an On/Off current ratio of two orders of magnitude was found in a structure consisting of a semiconducting PbTiO3 layer with a gold top contact, grown on a La0.5Sr0.5CoO3 bottom contact layer. The ferroelectric polarization parallel or antiparallel to the internal field of the diode gives rise to a change in the Schottky barrier height and depletion width. This will, depending on the polarization direction of the ferroelectric layer, enhance or diminish the tunnel probability of charge carriers through the Schottky barrier and thereby increase or decrease the current through the device. In the Ferroelectric Field Effect Transistor an insulating ferroelectric gate oxide was brought in close contact to a gated n-type Sb-doped SnO2 semiconducting channel layer. A maximum On/Off Source-Drain current (IsD) ratio at zero gate voltage of 5.7 was found. Gate pulse measurements showed retention of IsD after polarisation reversal of the ferroelectric gate oxide in both polarization directions. After more than 104 switching cycles the device shows a gradual decrease in ISD both in the On and Off state.
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Park, Jaehong, In Won Yeu, Gyuseung Han, Cheol Seong Hwang i Jung-Hae Choi. "Ferroelectric switching in bilayer 3R MoS2 via interlayer shear mode driven by nonlinear phononics". Scientific Reports 9, nr 1 (17.10.2019). http://dx.doi.org/10.1038/s41598-019-50293-y.
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Abstract We theoretically investigate the mechanism of ferroelectric switching via interlayer shear in 3R MoS2 using first principles and lattice dynamics calculations. First principle calculations show the prominent anharmonic coupling of the infrared inactive interlayer shear and the infrared active phonons. The nonlinear coupling terms generates an effective anharmonic force which drives the interlayer shear mode and lowers the ferroelectric switching barrier depending on the amplitude and polarization of infrared mode. Lattice dynamics simulations show that the interlayer shear mode can be coherently excited to the switching threshold by a train of infrared pulses polarized along the zigzag axis of MoS2. The results of this study indicate the possibility of ultrafast ferroelectricity in stacked two-dimensional materials from the control of stacking sequence.
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Li, Yue, Xing-peng Liu, Tang-you Sun, Fa-bi Zhang, Tao Fu, Pei-hua Wang-yang, Hai-ou Li i Yong-he Chen. "Impact of Al x Ga1-x N barrier thickness and Al composition on the electrical properties of ferroelectric HfZrO/Al2O3/AlGaN/GaN MFSHEMTs". Chinese Physics B, 22.06.2022. http://dx.doi.org/10.1088/1674-1056/ac7b1a.
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Abstract Ferroelectric (FE) HfZrO/Al2O3 gate stack AlGaN/GaN metal-FE-semiconductor heterostructure field-effect transistors (MFSHEMTs) with varying Al x Ga1-x N barrier thickness and Al composition are investigated and compared by TCAD simulation with non-FE HfO2/Al2O3 gate stack metal-insulator-semiconductor heterostructure field-effect transistors (MISHFETs). Results show that the decrease of the two-dimensional electron gas density with decreasing AlGaN barrier thickness is more effectively suppressed in MFSHEMTs than that in MISHFETs due to the enhanced FE polarization switching efficiency. The electrical characteristics of MFSHEMTs, including transconductance, subthreshold swing, and on-state current, effectively improve with decreasing AlGaN thickness in MFSHEMTs. High Al composition in AlGaN barrier layers that are under 3 nm thickness plays a great role in enhancing the two-dimensional electron gas density and FE polarization in MFSHEMTs, improving the transconductance and the on-state current. The subthreshold swing and threshold voltage can be reduced by decreasing the AlGaN thickness and Al composition in MFSHEMTs, affording favorable conditions for further enhancing the device.
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Mehling, V., Ch Tsakmakis i D. Gross. "Fully Coupled 3-D Modelling of Ferroelectric Polycrystalline Material Behavior". MRS Proceedings 881 (2005). http://dx.doi.org/10.1557/proc-881-cc4.9.
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AbstractA thermodynamically consistent phenomenological model for the material behavior of polycrystalline ferroelectric ceramics is presented. The internal state of the material is described by two internal state variables. The first one is a second-order texture tensor, determining a simple orientation distribution function (ODF) for the axes of the crystal unit cells. The second is the vector of relative irreversible polarization. The irreversible strains are derived from the ODF by volume averaging. The polarization saturation states are calculated by summing up the possible contributions of all cells to the overall polarization. An invariant formulation of the piezoelectric law is applied. Analogous to the thermodynamical framework of rate-independent plasticity, driving forces and evolution laws for the internal state variables are established. Saturation and coupling of the switching behavior are governed by energy barrier functions introduced in the electric enthalpy function. Numerical examples illustrate the models capabilities.
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Li, Dong, Pengyu Liu, Ruiman He, Yihang Bai, Chang Liu, Bing Wang i Guanwei Jia. "Intrinsic multiferroicity and magnetoelectric coupling in VSI2 monolayer". Applied Physics Letters 123, nr 5 (31.07.2023). http://dx.doi.org/10.1063/5.0155960.
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Two dimensional (2D) multiferroic materials have great potential for miniaturized electronic and high-density multi-states data storage devices due to the coexistence of electric and spin polarization. Because the origins of magnetism and ferroelectricity are mutually exclusive and difficult to coexist, there are still rare to date 2D multiferroic semiconductors with good performance. Here, we propose a 2D multiferroic material, VSI2 monolayer, which has both ferromagnetic and ferroelectric properties by first principles calculation. It shows robust ferroelectricity with an appropriate switching barrier (∼140 meV), and the in-plane ferroelectric polarization is 1.44 × 10−10 C/m. At the same time, the VSI2 monolayer magnetic easy axis is along the b-axis direction and owns a large magnetic anisotropy energy (MAE) (512 μeV/V-ion). Based on Monte Carlo simulations of the Heisenberg model, the Curie temperature (TC) is calculated to be approximately 92 K. In addition, biaxial strain can significantly change the MAE, and the in-plane magnetic easy axis can be switched to the out-of-plane direction by 5% biaxial tensile strain. In particular, we can change the magnetic moment at the two ends of VSI2 nanoribbons by switching the direction of electric polarization, providing an opportunity for the application of magnetic-electric control and memory devices. Our theoretical prediction provides a good platform for studying the 2D multiferroic effects and spintronic properties.
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Lee, Kwang B., S. Tirumala, Y. Song, Sang O. Ryu i Seshu B. Desu. "Simple Electrode-Barrier Structure Using Ir for Integration of PZT-Based High-Density Nonvolatile Memories". MRS Proceedings 541 (1998). http://dx.doi.org/10.1557/proc-541-197.
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AbstractWe have investigated the electrode-barrier properties of Ir for PZT-based nonvolatile memories. Ir layer was rf-sputtered onto a poly-Si coated Si wafer. PZT thin films were deposited on Ir/poly-Si/SiO2/Si by means of sol-gel spin coating. Highly c-axis oriented perovskite PZT thin films were obtained, which might be due to the interface-controlled growth. We found that Ir in itself acted as an oxygen barrier, which was confirmed from the measurement of P-E hysteresis loops with the electrical contact between top-electrode and bottom-poly-Si. Remanent polarization and coercive field of 1rO2/PZT/Ir/poly-Si capacitor were 20 μC/cm2and 30 kV/cm, respectively and the capacitor showed negligible polarization fatigue up to 1011 switching repetitions. However, the leakage current density at the field of larger than 80 kV/cm was high, which was believed to be related to the unknown phase in PZT caused by the reaction of PbO with bottom-Ir. Such high leakage current behavior could be successively improved by the insertion of vacuum-annealed IrOx buffer layer between PZT/Ir. The electrical properties of IrOx/PZT/annealed-IrO2Ir/poly-Si capacitors are also discussed.
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Guo, Fei, Yaping Liu, Rui Liu, Siyuan Guo, Haojie Xu, Yang Li, Bo Yang i Shifeng Zhao. "The evolution between ferroelectric photovoltaic effect and resistance switching behavior engineered by the polarization field and barrier characteristics". Optics Express, 22.06.2023. http://dx.doi.org/10.1364/oe.493183.
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Ryu, Hojoon, Haonan Wu, Fubo Rao i Wenjuan Zhu. "Ferroelectric Tunneling Junctions Based on Aluminum Oxide/ Zirconium-Doped Hafnium Oxide for Neuromorphic Computing". Scientific Reports 9, nr 1 (grudzień 2019). http://dx.doi.org/10.1038/s41598-019-56816-x.
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AbstractFerroelectric tunneling junctions (FTJs) with tunable tunneling electroresistance (TER) are promising for many emerging applications, including non-volatile memories and neurosynaptic computing. One of the key challenges in FTJs is the balance between the polarization value and the tunneling current. In order to achieve a sizable on-current, the thickness of the ferroelectric layer needs to be scaled down below 5 nm. However, the polarization in these ultra-thin ferroelectric layers is very small, which leads to a low tunneling electroresistance (TER) ratio. In this paper, we propose and demonstrate a new type of FTJ based on metal/Al2O3/Zr-doped HfO2/Si structure. The interfacial Al2O3 layer and silicon substrate enable sizable TERs even when the thickness of Zr-doped HfO2 (HZO) is above 10 nm. We found that F-N tunneling dominates at read voltages and that the polarization switching in HZO can alter the effective tunneling barrier height and tune the tunneling resistance. The FTJ synapses based on Al2O3/HZO stacks show symmetric potentiation/depression characteristics and widely tunable conductance. We also show that spike-timing-dependent plasticity (STDP) can be harnessed from HZO based FTJs. These novel FTJs will have high potential in non-volatile memories and neural network applications.
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Hu, Yuzhong, Kaushik Parida, Hao Zhang, Xin Wang, Yongxin Li, Xinran Zhou, Samuel Alexander Morris i in. "Bond engineering of molecular ferroelectrics renders soft and high-performance piezoelectric energy harvesting materials". Nature Communications 13, nr 1 (24.09.2022). http://dx.doi.org/10.1038/s41467-022-33325-6.
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AbstractPiezoelectric materials convert mechanical stress to electrical energy and thus are widely used in energy harvesting and wearable devices. However, in the piezoelectric family, there are two pairs of properties that improving one of them will generally compromises the other, which limits their applications. The first pair is piezoelectric strain and voltage constant, and the second is piezoelectric performance and mechanical softness. Here, we report a molecular bond weakening strategy to mitigate these issues in organic-inorganic hybrid piezoelectrics. By introduction of large-size halide elements, the metal-halide bonds can be effectively weakened, leading to a softening effect on bond strength and reduction in polarization switching barrier. The obtained solid solution C6H5N(CH3)3CdBr2Cl0.75I0.25 exhibits excellent piezoelectric constants (d33 = 367 pm/V, g33 = 3595 × 10−3 Vm/N), energy harvesting property (power density is 11 W/m2), and superior mechanical softness (0.8 GPa), promising this hybrid as high-performance soft piezoelectrics.
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Yan, Shuo, Xueli Hu, Xiaomei Lu, Junting Zhang, Xiaofan Shen i Fengzhen Huang. "Self-organization of ferroelectric domains induced by water and reinforced via ultrasonic vibration". Communications Materials 4, nr 1 (26.05.2023). http://dx.doi.org/10.1038/s43246-023-00371-6.
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AbstractPattern formation caused by self-organization is a fascinating phenomenon that appears in biological, chemical, and physical systems. In ferroelectrics, although a variety of domain patterns have been reported at different scales and dimensions, the self-organization process of ferroelectric domains was rarely investigated. Here, in 0.72Pb(Mg1/3Nb2/3)O3−0.28PbTiO3 bulk crystals exposed to water, the self-organized formation process of domain structures is observed and reinforced by ultrasonic vibration. By combining experimental observations and theoretical analysis, we find that adsorbed H+/OH− ions on the sample surface act as screening charges to induce the coarsening of the ferroelectric domains. Meanwhile, interactions among dipoles determine the ordering of the domain configuration, while ultrasonic vibration reduces the barrier height for polarization switching. The process of domain evolution deviates from that of the non-conservative dynamic system, and instead fits a percolation model with a clear transition point. This work demonstrates the self-organization of ferroelectric domains induced by water, which is of value for understanding domain dynamics and for the development of high-performance ferroelectric materials.
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Rehman, Majeed Ur, i Zhenhua Qiao. "MX family: An efficient platform for topological spintronics based on Rashba and Zeeman-like spin splittings". Journal of Physics: Condensed Matter, 24.10.2022. http://dx.doi.org/10.1088/1361-648x/ac9d15.
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Abstract Taking various combinations of M = (Mo, W) and X = (C, S, Se) as examples, we propose that MX (M = transition metals, X = IV,V or VI elements) family can establish an excellent platform for both conventional and topological spintronics applications based on anisotropic Rashba-like and non-magnetic Zeeman-type spin splittings with electrically tunable nature. In particular, we observe sizeable Zeeman-like and Rashba-like spin splittings with an anisotropic nature. Meanwhile, they exhibit Rashba-like and topologically robust helical edge states when grown in ferroelectric and paraelectric phases, respectively. These MX monolayers are realized to be valley Hall insulators due to valley contrasting Berry curvatures. The carriers in these MX monolayers can be selectively excited from opposite valleys depending on the polarity of circularly polarized light. Most promisingly, the Berry curvature peaks at the two valleys can be inverted by switching the polarization direction from +P to −P , enabling the MX family to be efficient for applications based on the valley spin valve effect. The amplitude of the spin splitting can be further tuned by applying external means such as strain, electric field or polarization direction. Furthermore, considering graphene/WC as a prototype example via interfacial engineering, we show that these MX monolayers can boost the relativistic effect by coupling with the systems exhibiting extremely weak spin-orbit coupling. Depending on the polarization state, graphene/WC junction passes through the transformation from the semiconducting junction to the Shotcky barrier-free contact. Finally, we reveal that these MX monolayers could also be grown on the substrates such as WS2(001) and GaTe (001) with type-II band alignment, where electron and hole become layer splitting across the interface. Our analysis should be fairly applied to other systems with same geometry, such as WN, TaN, ZrTe, MoP, MoN, NbN, and NbS.
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Li, Yun-Qin, Xin-Yu Wang, Shi-Yu Zhu, Dai-Song Tang, Qi-Wen He i Xiao-Chun Wang. "Enhanced vertical polarization and ultra-low polarization switching barriers of two-dimensional SnS/SnSSe ferroelectric heterostructures". Journal of Materials Chemistry C, 2022. http://dx.doi.org/10.1039/d2tc02721f.
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Switching polarization via inter-layer sliding or heterostructural inversion in two-dimensional SnS/SnSSe ferroelectric heterostructures with enhanced vertical polarization and ultra-low switching barriers.