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Realization of rectifying and resistive switching behaviors of mesoscopic niobium oxide-based structures
Materials Letters 136 (2014) 404–406
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Realization of rectifying and resistive switching behaviors of mesoscopic niobium oxide-based structures N.А. Tulina a,n, А.N. Rossolenko a, I.Yu. Borisenko c, I.М. Shmytko a, А.М. Ionov a, А.А. Ivanov b a
Institute of Solid State Physics RAS, 2 Akademika Ossipyana Str., Chernogolovka 142432, Russia National Research Nuclear University “MEPhI”, Moscow, Russia c Institute of Microelectronics Technology and High Purity Materials RAS, 6 Akademika Ossipyana str., Chernogolovka 142432, Russia b
art ic l e i nf o
a b s t r a c t
Article history: Received 19 July 2014 Accepted 14 August 2014 Available online 23 August 2014
We address bipolar resistive switching effects in structures based on oxides of transition metals which are promising for applications in modern memory devices. Mesoscopic niobium oxide film heterostrucures have been produced. The current–voltage characteristics of the heterostructures based on amorphous films of anodized niobium oxide show a diode character with a weak BRS effect that is more pronounced in structures based on crystalline niobium oxide films. Analysis of the conductivity mechanisms in the heterostructures obtained suggests that the diode behavior and the existence of bistable resistance states are related to modulation of a Schottky barrier formed by a niobium oxide layer with a variable resistance in the metal–oxide interface. & 2014 Elsevier B.V. All rights reserved.
Keywords: Interface structures Bipolar resistive switchings Metal oxides Schottky barrier diode Charge transport Oxygen vacancies
1. Introduction The bipolar resistive switching (BRS) effect in heterostructures based on various compounds is nowadays the subject of intensive nanotechnology research aimed at producing elements of a new generation of nonvolatile and dual head memory that is to conquer new efficiency frontiers of size and information rate [1–6]. The effect manifests itself in electric field-induced changes of the resistance state of normal metal–compound heterostructure reaching several orders of magnitude. The BRS effects depend on the sign of electric field applied to heterostructures, exhibit a memory effect [2] and are promising candidates for various applications. To reveal the BRS nature, we proposed BRS investigations on binary niobium oxides in mesoscopic film structures Si/Nb/NBOx/Ag(Al) as they are the most technologically efficient from the viewpoint of applications.
2. Experimental The niobium oxides were prepared by anodic oxidation (АО) and laser deposition. The first technique is known to be used for obtaining amorphous Nb2O5 films [7,8], the other allows producing epitaxial crystalline films of even complex compounds. As a n Corresponding author. Tel.: þ 7 496 52 44 478, þ 7 496 52 28 393; fax: þ7 496 522 8160. E-mail address: [email protected] (N.А. Tulina).
http://dx.doi.org/10.1016/j.matlet.2014.08.086 0167-577X/& 2014 Elsevier B.V. All rights reserved.
rule, anodic oxide films are mainly composed of absolute valence oxide Nb2O5. Thin Nb and NbOx films were obtained by pulsed laser deposition. The substrates were single crystal Si(100) wafers of size 5 10 mm2. NbOx crystalline films were deposited in oxidizing atmosphere (0.3–0.5Torr N2O or O2). The films obtained were calibrated by the methods of local x-ray spectroscopy and xray photoelectron spectroscopy. According to the data of x-ray structural analysis and stylus profiling, the crystalline metallic niobium films were about 150 nm thick and the niobium oxide films about 200 nm thick. The thickness of the anodic films was controlled by the anodizing voltage, h ¼kV, where k is the anodizing constant, for Nb k ¼2.3 nm/V [9]. The mesoscopic heterostructures were made by photolithography (see inset to Fig. 1). The Nb– NbOx–Ag structure had a contact window of size 50 50 μm2 or 10 50 μm2. The heterostructures were studied to detect resistive switching, and the current–voltage characteristics (CVC) were also measured. Positive bias voltage was applied to the top electrode (Ag or Al) while the niobium film was grounded. Three types of transition were studied: mesoscopic junctions in amorphous oxides, mesoscopic junctions in crystalline oxides and heterojunctions with an upper microcontact (point-contact) electrode.
3. Results and discussion Fig. 1 shows typical CVC examples of the amorphous film structures with different thicknesses of the АО oxide. The X-ray diffraction pattern of Fig. 2 revealed three types of reflections: Si
N.А. Tulina et al. / Materials Letters 136 (2014) 404–406
substrate, Nb film and a set nonstoichiometric Nb oxides. Fig. 3 shows CVC examples of the polycrystalline film heterostructures. Fig. 4 shows CVC examples of the amorphous film structures subjected to annealing at 800 1С for 0.5 h (multiphase crystalline state). We believe that the effects observed in our BRS structures are related to the diode nature of current transfer in structures with Schottky barriers on heavily doped semiconductors and the presence of oxygen vacancies in the structural interfaces. As seen from Fig. 1, the mesoscopic structures based on anodized niobium oxide films have significant deviations from stoichiometric composition within the homogeneity region. Structural x-ray analysis (Fig. 2) revealed a set of nonstoichiometric oxides. The crystalline film-based structures show a pronounced switching effect. The latter can be controlled by varying the properties of the interface and creating an extra barrier by (socalled) post-metallization annealing (PMA) [10]. The PMA influence on switching is connected to formation of a high vacancy concentration region near the aluminum electrode owing to aluminum–oxygen gettering. This region is likely to determine the switching process in the structures in question. The СVС of heterocontacts demonstrate diodic, electron-type conductivity with a slight switching effect that is enhanced provided the upper electrode is aluminum and the structures are annealed at 800 1С for 0.5 h. Structural x-ray analysis revealed that the annealing transfers the amorphous film to the multiphase crystalline state (Fig. 2), the very wide reflections in the inset witness nanocrystalline state of constituent niobium oxides. It should be also noted that the most important feature of the
Fig. 1. The СVС examples for mesoscopic Nb/Nb2O5/Ag structures. The niobium oxide was obtained by the electrolytic technique. The red signs (circle) denote oxide thickness h ¼46 nm, blue signs (triangle) h ¼ 23 nm, and green signs (diamond) h ¼ 12 nm. The bottom electrode (Nb film) was grounded, and the top electrode was on the Ag film. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Fig. 2. The x-ray spectrum of structure Si/Nb/NbOx.
405
transition metal–oxygen interaction is mixed valence connected to the presence of an unfilled (open) d-shell. In oxygen compounds these metals exhibit a wide range of valence states forming a number of different phases. Most transition metal oxides characterized based on anodic films with resistive switching have generally a diode nature. It is assumed that the properties of oxide structures are largely influenced by the presence of oxygen (vacancy) defects serving as traps. The main mechanisms of charge transfer in such structures are a) space-charge-limited currents (SCLC) induced by thermionic emission over the barrier (Schottky emission); b) ionization of impurity centers in sufficiently strong electric fields, the Poole–Frenkel effect; and c) tunnel passage of electrons through a thin barrier. Reasoning from the diode nature of CVC of heterojunctions with a BRS effect, we assume that these are Schottky-like diodes and apply the transport theory [11,12]: I ¼ I 0 ½expððeV IRsp Þ=E0 Þ 1
ð1Þ
where E0 is the energy of carrier tunneling through the barrier, I0 is saturation current, and Rsp is the series spreading resistance. Approximating the experimental CVC data of the heterocontacts with the forward-transfer diode properties as related to (1), we determined the parameters of the contacts in question; the results are presented in Table 1. Fig. 4 shows the CVC approximation for the structures under investigation. It is seen that at large shifts the high resistivity СVС branches of the structures with resistive switching exhibit Poole– Frenkel-type current contributions (ln(I/V) V1/2)). Yet, the low resistivity СVС branch is linear in the logarithmic current–voltage coordinates which is typical of Schottky thermionic emission involving transition to dependence I ¼CVk (SCLC regime).
Fig. 3. СVС examples for heterostructures based on polycrystalline Si/Nb/NbOx/Ag films. The upper electrode is of the microcontact type. Silver spring loaded pointcontact was used for Si/Nb/NbOx film structures. The x-ray niobium oxide spectrum is in the upper left corner.
Fig. 4. The СVС examples for mesoscopic Si/Nb/NbOх/Ag structures. The niobium oxide was obtained by the electrolytic technique and crystallized by annealing. The dashed line denotes the approximation of the heteterocontact CVCs by relationship (3).
406
N.А. Tulina et al. / Materials Letters 136 (2014) 404–406
Table 1 Parameters of contacts investigated. Sample
h (nm)
I0 (A)
E0 (eV)
Rsp (Ω)
Current transfer mechanism
#1 Nb/Nb2O5/Ag #2 Nb/Nb2O5/Ag #3_1 Nb/NbOx/Al #3_2 Nb/NbOx/Al #4_1 Nb/NbOx/Al #4_2 Nb/NbOx/Al #5_1 Nb/NbOx/Al #5_2 Nb/NbOx/Al
46, 12, 23, 23, 46, 46, 69, 69,
9.8 E 8 1.93 E 5 2.68 E 5 3.04 E 7 2.46 E 5 5.3 E 5 6.89 E 6 1.05 E 5
0.67 0.22 0.64 0.3 0.48 0.44 0.29 0.12
572 254 270 47963 1245 423 631 757
SCLC SCLC Poole–Frenkel SCLC Poole–Frenkel SCLC Poole–Frenkel SCLC
Off On Off On Off On
state state state state state state
anodized anodized polyсrystalline polyсrystalline polyсrystalline polyсrystalline polyсrystalline polyсrystalline
h,oxide layer thickness; I0, saturation current; Eo, tunneling energy; Rsp, spreading resistance.
The Poole–Frenkel phenomenon observed upon current transfer suggests the existence of localized donor centers. It is believed that in oxide compounds they are oxygen vacancies that when activated by a sufficiently large electric field (105 V/cm), could create levels and small zones in the dielectric gap. In [13] the authors consider the resistive switching mechanism caused by electron transition which is due to collisional trap ionization by the Poole–Frenkel mechanism and semiconductor metallization as the carriers reach their critical concentration, the so-called concentration instability in semiconductors. Such large fields could also stimulate electrodiffusion of mobile defects of oxygen vacancies and, hence, modulate the barrier. As a result, there are two scenarios of the reversible switching process: electron transition and diffusion and barrier modulation owing to oxygen vacancy motion. The broad XRD peaks (Fig. 2) show that the samples are indeed nanograined and contain, therefore, very developed grain boundaries. It has been recently demonstrated [14] that physical properties of pure and doped nanograined oxides strongly depend on defects like interphase boundaries and grain boundaries and on the presence of doping atoms in the amorphous surficial, interfacial and intergranular layers [15]. Such structural heterogeneities promote creation of areas with increased electric field intensity, defects electrodiffusion and formation of percolation current paths in the process of resistive switchings [16–18]. Simulations are used in works [17,18] to study the influence of nonuniform electric field distribution at a point-contact interface on the effect of bipolar resistive switching in oxide compounds. The BRS effect in numerous similar compound structures is also reported in literature [19–22]. 4. Conclusion The influence of the barrier interface properties on the bipolar resistive switching effect in film niobium-oxide-based heterostructures has been investigated. It is shown that the CVC of the heterocontacts with switching effects exhibit a diode behavior with Schottky-like barriers in heavily doped semiconductors. The spatial inhomogeneity of carrier distribution is responsible for the field influence on the potential interface barrier in the heterostructures demonstrating the BRS effect.
Modulation of the Schottky barrier under the electric field formed by the oxide layer with a varying resistance Rsp in the metal–oxide interface is the most probable model that explains occurrence of resistive switching in niobium-oxide-based structures.
Acknowledgment The work was supported by the programs of the Division of Physical Sciences RAS “Physics of Novel Materials and Structures” and “Quantum Mesoscopic and Disordered Structures” and the RFBR, Grant no. 14-07-00951. References [1] Waser R, Aono M. Nat Mater 2007;6:833. [2] Tulina NA. Phys Usp 2007;50:1171. [3] Karg SF, Meijer GI, Bednorz JG, Rettner CT, Schrott AG, Joseph EA, et al. J Res Dev 2008;52:481. [4] Yang JJ, Pickett MD, Li X, Ohlberg DAA, Stewart DR, Williams RS, et al. Nat Nanotechnol 2008;3:429. [5] Meijer GI. Science 2008;319:1625. [6] Pershin YV, Di Ventra M. Adv Phys 2011;60:145. [7] Daly CM, Keil RG. J Electrochem Soc 1975;122:350. [8] Pergament AL, Stefanovich GB. Thin Solid Films 1998;322:33. [9] Nakada D, Berggren KK, Macedo E, Liberman V, Orlando TP. IEEE Trans Appl Supercond 2003;13:111. [10] Wang J, Jian D, Ye Y, Chang L, Lai C. J Phys D: Appl Phys 2013;46:275103. [11] Rhoderiсk EH. Metal–semiconductor contacts. Oxford: Oxford University Press; 1978. [12] Schroeder D. Adv Solid State Phys 1996;36:265. [13] Sandomirskii VB, Sukhanov AA, Zdan AG. Sov Phys JETP 1970;31:902. [14] Straumal BB, Protasova SG, Mazilkin AA, Tietze T, Goering E, Schütz G, et al. Beilstein J Nanotechnol 2013;4:361. [15] Straumal BB, Mazilkin AA, Protasova SG, Straumal PB, Myatiev AA, Schütz G, et al. Phys Met. Metallogr 2012;113:1244. [16] Rozenberg MJ, Sánchez MJ, Weht R, Acha C, Gomez-Marlasca F, Levy P. Phys Rev B 2010;81:115101. [17] Tulina NA, Sirotkin VV. Physica C 2004;400:105. [18] Tulina NA, Sirotkin VV, Yu. I, Borisenko, Ivanov AA. Bull Russ acade sci:Phys. 2013;77:265. [19] Nian YB, Strozier J, Wu M, Chen X, Igenative A. Phys Rev Lett 2007;98:146403. [20] Tulina NA, Borisenko IYu, Shmytko IM, Ionov AM, Kolesnikov NN, Borisenko DN. Phys Lett A 2012;376:3398. [21] Plecenik T, Tomášek M, Belogolovskii M, Truchly M, Gregor M, Noskovič J, et al. J Appl Phys 2012;111:056106. [22] Tulina NA, Borisenko IYu, Sirotkin VV. Solid State Commun 2013;170:48.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Realization of rectifying and resistive switching behaviors of mesoscopic niobium oxide-based structures N.А. Tulina a,n, А.N. Rossolenko a, I.Yu. Borisenko c, I.М. Shmytko a, А.М. Ionov a, А.А. Ivanov b a
Institute of Solid State Physics RAS, 2 Akademika Ossipyana Str., Chernogolovka 142432, Russia National Research Nuclear University “MEPhI”, Moscow, Russia c Institute of Microelectronics Technology and High Purity Materials RAS, 6 Akademika Ossipyana str., Chernogolovka 142432, Russia b
art ic l e i nf o
a b s t r a c t
Article history: Received 19 July 2014 Accepted 14 August 2014 Available online 23 August 2014
We address bipolar resistive switching effects in structures based on oxides of transition metals which are promising for applications in modern memory devices. Mesoscopic niobium oxide film heterostrucures have been produced. The current–voltage characteristics of the heterostructures based on amorphous films of anodized niobium oxide show a diode character with a weak BRS effect that is more pronounced in structures based on crystalline niobium oxide films. Analysis of the conductivity mechanisms in the heterostructures obtained suggests that the diode behavior and the existence of bistable resistance states are related to modulation of a Schottky barrier formed by a niobium oxide layer with a variable resistance in the metal–oxide interface. & 2014 Elsevier B.V. All rights reserved.
Keywords: Interface structures Bipolar resistive switchings Metal oxides Schottky barrier diode Charge transport Oxygen vacancies
1. Introduction The bipolar resistive switching (BRS) effect in heterostructures based on various compounds is nowadays the subject of intensive nanotechnology research aimed at producing elements of a new generation of nonvolatile and dual head memory that is to conquer new efficiency frontiers of size and information rate [1–6]. The effect manifests itself in electric field-induced changes of the resistance state of normal metal–compound heterostructure reaching several orders of magnitude. The BRS effects depend on the sign of electric field applied to heterostructures, exhibit a memory effect [2] and are promising candidates for various applications. To reveal the BRS nature, we proposed BRS investigations on binary niobium oxides in mesoscopic film structures Si/Nb/NBOx/Ag(Al) as they are the most technologically efficient from the viewpoint of applications.
2. Experimental The niobium oxides were prepared by anodic oxidation (АО) and laser deposition. The first technique is known to be used for obtaining amorphous Nb2O5 films [7,8], the other allows producing epitaxial crystalline films of even complex compounds. As a n Corresponding author. Tel.: þ 7 496 52 44 478, þ 7 496 52 28 393; fax: þ7 496 522 8160. E-mail address: [email protected] (N.А. Tulina).
http://dx.doi.org/10.1016/j.matlet.2014.08.086 0167-577X/& 2014 Elsevier B.V. All rights reserved.
rule, anodic oxide films are mainly composed of absolute valence oxide Nb2O5. Thin Nb and NbOx films were obtained by pulsed laser deposition. The substrates were single crystal Si(100) wafers of size 5 10 mm2. NbOx crystalline films were deposited in oxidizing atmosphere (0.3–0.5Torr N2O or O2). The films obtained were calibrated by the methods of local x-ray spectroscopy and xray photoelectron spectroscopy. According to the data of x-ray structural analysis and stylus profiling, the crystalline metallic niobium films were about 150 nm thick and the niobium oxide films about 200 nm thick. The thickness of the anodic films was controlled by the anodizing voltage, h ¼kV, where k is the anodizing constant, for Nb k ¼2.3 nm/V [9]. The mesoscopic heterostructures were made by photolithography (see inset to Fig. 1). The Nb– NbOx–Ag structure had a contact window of size 50 50 μm2 or 10 50 μm2. The heterostructures were studied to detect resistive switching, and the current–voltage characteristics (CVC) were also measured. Positive bias voltage was applied to the top electrode (Ag or Al) while the niobium film was grounded. Three types of transition were studied: mesoscopic junctions in amorphous oxides, mesoscopic junctions in crystalline oxides and heterojunctions with an upper microcontact (point-contact) electrode.
3. Results and discussion Fig. 1 shows typical CVC examples of the amorphous film structures with different thicknesses of the АО oxide. The X-ray diffraction pattern of Fig. 2 revealed three types of reflections: Si
N.А. Tulina et al. / Materials Letters 136 (2014) 404–406
substrate, Nb film and a set nonstoichiometric Nb oxides. Fig. 3 shows CVC examples of the polycrystalline film heterostructures. Fig. 4 shows CVC examples of the amorphous film structures subjected to annealing at 800 1С for 0.5 h (multiphase crystalline state). We believe that the effects observed in our BRS structures are related to the diode nature of current transfer in structures with Schottky barriers on heavily doped semiconductors and the presence of oxygen vacancies in the structural interfaces. As seen from Fig. 1, the mesoscopic structures based on anodized niobium oxide films have significant deviations from stoichiometric composition within the homogeneity region. Structural x-ray analysis (Fig. 2) revealed a set of nonstoichiometric oxides. The crystalline film-based structures show a pronounced switching effect. The latter can be controlled by varying the properties of the interface and creating an extra barrier by (socalled) post-metallization annealing (PMA) [10]. The PMA influence on switching is connected to formation of a high vacancy concentration region near the aluminum electrode owing to aluminum–oxygen gettering. This region is likely to determine the switching process in the structures in question. The СVС of heterocontacts demonstrate diodic, electron-type conductivity with a slight switching effect that is enhanced provided the upper electrode is aluminum and the structures are annealed at 800 1С for 0.5 h. Structural x-ray analysis revealed that the annealing transfers the amorphous film to the multiphase crystalline state (Fig. 2), the very wide reflections in the inset witness nanocrystalline state of constituent niobium oxides. It should be also noted that the most important feature of the
Fig. 1. The СVС examples for mesoscopic Nb/Nb2O5/Ag structures. The niobium oxide was obtained by the electrolytic technique. The red signs (circle) denote oxide thickness h ¼46 nm, blue signs (triangle) h ¼ 23 nm, and green signs (diamond) h ¼ 12 nm. The bottom electrode (Nb film) was grounded, and the top electrode was on the Ag film. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Fig. 2. The x-ray spectrum of structure Si/Nb/NbOx.
405
transition metal–oxygen interaction is mixed valence connected to the presence of an unfilled (open) d-shell. In oxygen compounds these metals exhibit a wide range of valence states forming a number of different phases. Most transition metal oxides characterized based on anodic films with resistive switching have generally a diode nature. It is assumed that the properties of oxide structures are largely influenced by the presence of oxygen (vacancy) defects serving as traps. The main mechanisms of charge transfer in such structures are a) space-charge-limited currents (SCLC) induced by thermionic emission over the barrier (Schottky emission); b) ionization of impurity centers in sufficiently strong electric fields, the Poole–Frenkel effect; and c) tunnel passage of electrons through a thin barrier. Reasoning from the diode nature of CVC of heterojunctions with a BRS effect, we assume that these are Schottky-like diodes and apply the transport theory [11,12]: I ¼ I 0 ½expððeV IRsp Þ=E0 Þ 1
ð1Þ
where E0 is the energy of carrier tunneling through the barrier, I0 is saturation current, and Rsp is the series spreading resistance. Approximating the experimental CVC data of the heterocontacts with the forward-transfer diode properties as related to (1), we determined the parameters of the contacts in question; the results are presented in Table 1. Fig. 4 shows the CVC approximation for the structures under investigation. It is seen that at large shifts the high resistivity СVС branches of the structures with resistive switching exhibit Poole– Frenkel-type current contributions (ln(I/V) V1/2)). Yet, the low resistivity СVС branch is linear in the logarithmic current–voltage coordinates which is typical of Schottky thermionic emission involving transition to dependence I ¼CVk (SCLC regime).
Fig. 3. СVС examples for heterostructures based on polycrystalline Si/Nb/NbOx/Ag films. The upper electrode is of the microcontact type. Silver spring loaded pointcontact was used for Si/Nb/NbOx film structures. The x-ray niobium oxide spectrum is in the upper left corner.
Fig. 4. The СVС examples for mesoscopic Si/Nb/NbOх/Ag structures. The niobium oxide was obtained by the electrolytic technique and crystallized by annealing. The dashed line denotes the approximation of the heteterocontact CVCs by relationship (3).
406
N.А. Tulina et al. / Materials Letters 136 (2014) 404–406
Table 1 Parameters of contacts investigated. Sample
h (nm)
I0 (A)
E0 (eV)
Rsp (Ω)
Current transfer mechanism
#1 Nb/Nb2O5/Ag #2 Nb/Nb2O5/Ag #3_1 Nb/NbOx/Al #3_2 Nb/NbOx/Al #4_1 Nb/NbOx/Al #4_2 Nb/NbOx/Al #5_1 Nb/NbOx/Al #5_2 Nb/NbOx/Al
46, 12, 23, 23, 46, 46, 69, 69,
9.8 E 8 1.93 E 5 2.68 E 5 3.04 E 7 2.46 E 5 5.3 E 5 6.89 E 6 1.05 E 5
0.67 0.22 0.64 0.3 0.48 0.44 0.29 0.12
572 254 270 47963 1245 423 631 757
SCLC SCLC Poole–Frenkel SCLC Poole–Frenkel SCLC Poole–Frenkel SCLC
Off On Off On Off On
state state state state state state
anodized anodized polyсrystalline polyсrystalline polyсrystalline polyсrystalline polyсrystalline polyсrystalline
h,oxide layer thickness; I0, saturation current; Eo, tunneling energy; Rsp, spreading resistance.
The Poole–Frenkel phenomenon observed upon current transfer suggests the existence of localized donor centers. It is believed that in oxide compounds they are oxygen vacancies that when activated by a sufficiently large electric field (105 V/cm), could create levels and small zones in the dielectric gap. In [13] the authors consider the resistive switching mechanism caused by electron transition which is due to collisional trap ionization by the Poole–Frenkel mechanism and semiconductor metallization as the carriers reach their critical concentration, the so-called concentration instability in semiconductors. Such large fields could also stimulate electrodiffusion of mobile defects of oxygen vacancies and, hence, modulate the barrier. As a result, there are two scenarios of the reversible switching process: electron transition and diffusion and barrier modulation owing to oxygen vacancy motion. The broad XRD peaks (Fig. 2) show that the samples are indeed nanograined and contain, therefore, very developed grain boundaries. It has been recently demonstrated [14] that physical properties of pure and doped nanograined oxides strongly depend on defects like interphase boundaries and grain boundaries and on the presence of doping atoms in the amorphous surficial, interfacial and intergranular layers [15]. Such structural heterogeneities promote creation of areas with increased electric field intensity, defects electrodiffusion and formation of percolation current paths in the process of resistive switchings [16–18]. Simulations are used in works [17,18] to study the influence of nonuniform electric field distribution at a point-contact interface on the effect of bipolar resistive switching in oxide compounds. The BRS effect in numerous similar compound structures is also reported in literature [19–22]. 4. Conclusion The influence of the barrier interface properties on the bipolar resistive switching effect in film niobium-oxide-based heterostructures has been investigated. It is shown that the CVC of the heterocontacts with switching effects exhibit a diode behavior with Schottky-like barriers in heavily doped semiconductors. The spatial inhomogeneity of carrier distribution is responsible for the field influence on the potential interface barrier in the heterostructures demonstrating the BRS effect.
Modulation of the Schottky barrier under the electric field formed by the oxide layer with a varying resistance Rsp in the metal–oxide interface is the most probable model that explains occurrence of resistive switching in niobium-oxide-based structures.
Acknowledgment The work was supported by the programs of the Division of Physical Sciences RAS “Physics of Novel Materials and Structures” and “Quantum Mesoscopic and Disordered Structures” and the RFBR, Grant no. 14-07-00951. References [1] Waser R, Aono M. Nat Mater 2007;6:833. [2] Tulina NA. Phys Usp 2007;50:1171. [3] Karg SF, Meijer GI, Bednorz JG, Rettner CT, Schrott AG, Joseph EA, et al. J Res Dev 2008;52:481. [4] Yang JJ, Pickett MD, Li X, Ohlberg DAA, Stewart DR, Williams RS, et al. Nat Nanotechnol 2008;3:429. [5] Meijer GI. Science 2008;319:1625. [6] Pershin YV, Di Ventra M. Adv Phys 2011;60:145. [7] Daly CM, Keil RG. J Electrochem Soc 1975;122:350. [8] Pergament AL, Stefanovich GB. Thin Solid Films 1998;322:33. [9] Nakada D, Berggren KK, Macedo E, Liberman V, Orlando TP. IEEE Trans Appl Supercond 2003;13:111. [10] Wang J, Jian D, Ye Y, Chang L, Lai C. J Phys D: Appl Phys 2013;46:275103. [11] Rhoderiсk EH. Metal–semiconductor contacts. Oxford: Oxford University Press; 1978. [12] Schroeder D. Adv Solid State Phys 1996;36:265. [13] Sandomirskii VB, Sukhanov AA, Zdan AG. Sov Phys JETP 1970;31:902. [14] Straumal BB, Protasova SG, Mazilkin AA, Tietze T, Goering E, Schütz G, et al. Beilstein J Nanotechnol 2013;4:361. [15] Straumal BB, Mazilkin AA, Protasova SG, Straumal PB, Myatiev AA, Schütz G, et al. Phys Met. Metallogr 2012;113:1244. [16] Rozenberg MJ, Sánchez MJ, Weht R, Acha C, Gomez-Marlasca F, Levy P. Phys Rev B 2010;81:115101. [17] Tulina NA, Sirotkin VV. Physica C 2004;400:105. [18] Tulina NA, Sirotkin VV, Yu. I, Borisenko, Ivanov AA. Bull Russ acade sci:Phys. 2013;77:265. [19] Nian YB, Strozier J, Wu M, Chen X, Igenative A. Phys Rev Lett 2007;98:146403. [20] Tulina NA, Borisenko IYu, Shmytko IM, Ionov AM, Kolesnikov NN, Borisenko DN. Phys Lett A 2012;376:3398. [21] Plecenik T, Tomášek M, Belogolovskii M, Truchly M, Gregor M, Noskovič J, et al. J Appl Phys 2012;111:056106. [22] Tulina NA, Borisenko IYu, Sirotkin VV. Solid State Commun 2013;170:48.