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Resistive Switching in Metal–Insulator–Metal Structures Based on Germanium Oxide and Stabilized Zirconia
Abstract
Bipolar resistive switching in metal-insulator-metal structures based on a double-layer insulator composed of a layer of yttria-stabilized zirconia (YSZ) containing 12 mol % Y2O3 and a layer of GeOx is studied. It is shown that the incorporation of an additional GeOx layer into the structure leads to a significant decrease in the variation of resistive switching parameters at both negative and positive voltages. Au/Zr/GeOx/YSZ/TiN structures exhibit a high stability of the resistance ratio in high-resistance and low-resistance states during cyclic switching. The studied structures can be used for designing next-generation nonvolatile memory elements.
... Memristive behavior was influenced by quite a lot of parameters, in particular, the materials from which the device is made, as well as the methods for synthesizing memristors. At the moment, the most popular methods include magnetron sputtering [3,4], atomic layer deposition [5], and pulsed laser deposition [6]. These memristive structures are compatible with the CMOS (complementary metal-oxide-semiconductor) process and are suitable for creating devices of nonvolatile resistive memory (resistive random-access memory-RRAM) and logical devices [7,8] because after the power is turned off, the specified resistive state can be stored for a long time. ...
... Here, the nonlinear element is presented by the Au/Zr/ZrO2(Y)/TiN/Ti memristor fabricated on the oxidized silicon substrate using magnetron sputtering. The details of technological operations can be found in other works [3,13,16,[35][36][37]. To study the struc- Here, the nonlinear element is presented by the Au/Zr/ZrO 2 (Y)/TiN/Ti memristor fabricated on the oxidized silicon substrate using magnetron sputtering. ...
... To study the struc- Here, the nonlinear element is presented by the Au/Zr/ZrO 2 (Y)/TiN/Ti memristor fabricated on the oxidized silicon substrate using magnetron sputtering. The details of technological operations can be found in other works [3,13,16,[35][36][37]. To study the structure of the element, we used the high-resolution cross-sectional transmission electron microscopy (XTEM) operating the Jeol JEM-2100F microscope («JEOL» company, Japan) with an acceleration voltage of 200 kV. ...
This article presents a mathematical and experimental model of a neuronal oscillator with memristor-based nonlinearity. The mathematical model describes the dynamics of an electronic circuit implementing the FitzHugh–Nagumo neuron model. A nonlinear component of this circuit is the Au/Zr/ZrO2(Y)/TiN/Ti memristive device. This device is fabricated on the oxidized silicon substrate using magnetron sputtering. The circuit with such nonlinearity is described by a three-dimensional ordinary differential equation system. The effect of the appearance of spontaneous self-oscillations is investigated. A bifurcation scenario based on supercritical Andronov–Hopf bifurcation is found. The dependence of the critical point on the system parameters, particularly on the size of the electrode area, is analyzed. The self-oscillating and excitable modes are experimentally demonstrated.
... Oxide layer in the studied Au/Zr/oxide/TiN/Ti thin-film nanostructure is represented by the ZrO 2 (Y) or SiO 2 film of various thickness. The first dielectric material is a transition metal oxide with predominantly ionic nature of chemical bond (also known as a solid-state electrolyte), in which the yttrium oxide (12 mol.%) doping agent stabilizes the cubic phase of zirconia and determines certain concentration of oxygen vacancies playing a key role in resistive switchingformation and local destruction of conductive channels (filaments) in oxide film [30][31][32]. The second kind of oxide is a "native" dielectric for CMOS-technology and is also known as intrinsic resistive switching material [33]. ...
... The switching dielectric layer is a ZrO 2 (Y) or SiO 2 film with a thickness of 40 or 60 nm, upper electrode -Au film (40 nm) with Zr adhesion sublayer (3 nm), bottom electrode -TiN film (25 nm) with Ti sublayer (25 nm). Details of technological operations can be found elsewhere [30][31][32][33]. Fig. 2a shows typical current-voltage characteristics of the Au/Zr/oxide/TiN/Ti nanostructures with different composition and thickness of oxide films, which demonstrate reproducible bipolar switching between the low-resistance state (LRS) and the high-resistance state (HRS) after electroforming performed by applying a negative bias to the top electrode without a current compliance [30][31][32][33]. ...
... Details of technological operations can be found elsewhere [30][31][32][33]. Fig. 2a shows typical current-voltage characteristics of the Au/Zr/oxide/TiN/Ti nanostructures with different composition and thickness of oxide films, which demonstrate reproducible bipolar switching between the low-resistance state (LRS) and the high-resistance state (HRS) after electroforming performed by applying a negative bias to the top electrode without a current compliance [30][31][32][33]. It should be mentioned that the developed nanostructures demonstrate fast switching (as low as 100 ns) and high enough endurance to the repeated programming cycles (10 5 more) [20]. ...
Construction and training principles have been proposed and tested for an artificial neural network based on metal-oxide thin-film nanostructures possessing bipolar resistive switching (memristive) effect. Experimental electronic circuit of neural network is implemented as a double-layer perceptron with a weight matrix composed of 32 memristive devices. The network training algorithm takes into account technological variations of the parameters of memristive nanostructures. Despite the limited size of weight matrix the developed neural network model is well scalable and capable of solving nonlinear classification problems.
... Oxide layer in the studied Au/Zr/oxide/TiN/Ti thin-film nanostructure (see Fig. 1) is represented by the ZrO 2 (Y) or SiO 2 film of various thickness. The first dielectric material is a transition metal oxide with predominantly ionic nature of chemical bond (also known as a solid-state electrolyte), in which the yttrium oxide (12 mol.%) doping agent stabilizes the cubic phase of zirconia and determines certain concentration of oxygen vacancies playing a key role in RS -formation and local destruction of conductive channels (filaments) in oxide film [40]- [42]. The second kind of oxide is a "native" dielectric for CMOS-technology which is also known as intrinsic RS material [43]. ...
... All measurements were carried out at room temperature and in atmospheric conditions. Fig. 2(a) and (b) show the current-voltage (I-V) characteristics of the Au/Zr/oxide/TiN/Ti nanostructures with different composition of oxide films, which demonstrate reproducible bipolar RS between the low-resistance state (LRS) and the high-resistance state (HRS) [40]- [43]. The observed RS is caused by the partial oxidation and recovery of conducting channels (filaments) in the oxide film under voltage of various polarity [24]. ...
... The thickness of the working dielectric (SiO 2 or ZrO 2 (Y)) was 40 nm, the thickness of the upper Au electrode was 40 nm, and the thickness of the lower electrode TiN and Ti layers was 25 nm each. The detailed description of the technology is given in [12,13]. ...
... The current-voltage characteristics of the structures, demonstrating reproducible switching between the low resistance state (LRS) and the high resistance state (HRS) are shown in Fig. 1 [11,12]. Resistive switching is determined by the oxidation and recovery of segments of conducting channels (filaments) in the oxide film when voltage with different polarity is applied to it. ...
A physical model of synaptically coupled neuron-like generators interacting via a memristive device has been presented. The model simulates the synaptic transmission of pulsed signals between brain neurons. The action on the receiving generator has been performed via a memristive device that demonstrates adaptive behavior. It has been established that the proposed coupling channel provides the forced synchronization with the parameters depending on the memristive device sensitivity. Synchronization modes 1: 1 and 2: 1 have been experimentally observed.
... Zirconia is a ceramic material with high strength, hardness, and toughness at high temperatures [1], and good biocompatibility [2]. It has been used in various applications, such as bearing races [3], insulators [4], orthopedic scaffolds [5], and dental implants [6]. Traditionally, zirconia or zirconiabased composites can be fabricated via slip casting, gel casting, injection molding, etc. [7], followed by sintering and machining. ...
... YSZ (yttria-stabilized zirconia) resistive memory has great potential for use in hightemperature environments, such as the aerospace, automotive, energy, and petrochemical industries [1,2]. In these fields, electronic devices operating in high-temperature environments require high-temperature stability and reliability. ...
YSZ is a promising material for resistive memory devices due to its high concentration of oxygen vacancies, which provide the high anion migration rates crucial for the manifestation of resistance switching in metal oxides. Therefore, investigating the ionic conductivity of YSZ is an important issue. The ionic conductivity and thermal stability of 8 mol% YSZ were studied using the theories and methods of solid-state physics and physical chemistry. The impact of anomalous atomic vibrations on the material was also explored, and the variation in the ion vibration frequency, electrical conductivity, and thermal stability coefficient of electrical conductivity with temperature was obtained. The results show that the ion conductivity of an 8 mol% YSZ solid electrolyte increases nonlinearly with temperature, with a smaller increase at lower temperatures and a larger increase at higher temperatures. Considering the anharmonic effect of ion vibrations, the electrolyte conductivity is higher than the result of the harmonic approximation, and the anharmonic effect becomes more significant at higher temperatures. Our research fills the gap in the current literature regarding the theoretical non-harmonic exploration of the ion conductivity and thermal stability factor of YSZ solid electrolytes. These results provide valuable theoretical guidance for the development and application of high-performance YSZ resistive memory devices in high-temperature environments.
... The thin-film nanostructures of a metal-oxide-metal type were used to fabricate the memristive devices. Typical crosssection electron microscopy image of the Au/ZrO 2 (Y)/TiN/Ti structure is shown in Figure 2. The I-V characteristics of the structure demonstrate reproducible switching between the low resistance state (LRS) and the high resistance state (HRS) [13,14]. Resistive switching is determined by the oxidation and recovery of segments of conducting channels (filaments) in the oxide film when voltage with different polarity is applied to it. ...
... It should be noted that the observed switching requires less energy than the similar MOM memristive structures with the same electrode area [24]. ...
It is shown that self-forming GeSi nanoislands built into the dielectric-semiconductor interface in the Si(001)-based metal-oxide-semiconductor (MOS) structures with the SiOx and ZrO2(Y) dielectric layers obtained by magnetron sputtering initiate bipolar resistive switching without preliminary electroform-ing. The I-V characteristics and electrical parameters of the MOS structures in the high-and low-resistance states have been investigated. The change in the charge incorporated in the dielectric at the dielectric-semiconductor interface during resistive switching has been established, which is related to the formation and destruction of conducting filaments. The optically stimulated switching of the MOS structures with the ZrO2(Y) dielectric layer from the high-to low-resistance state has been observed, which is caused by an increase in the conductivity of the space charge region in the Si substrate due to the interband optical absorption in Si leading to the voltage redistribution between Si and ZrO2(Y). A difference between the shapes of the low-signal photovoltage spectra of the MOS structures in the spectral region of the Si intrinsic photosensitivity in the high-and low-resistance states related to the leakage of photoexcited carriers from Si into a metal electrode through filaments has been found.
... Следует отметить, что наблюдаемое переключение требует меньших затрат энергии по сравнению с аналогичными мемристивными структурами МОМ с такой же площадью электродов [24]. ...
The self-assembled GeSi nanoislands built into the semiconductor-insulator interface of the MOS-structures based on Si(001) with SiOx and ZrO2(Y) oxide layers deposited by magnetron sputtering have been shown to initiate bipolar resistive switching without preliminary electroforming. The current-voltage curves and electrical parameters of the MOS-structures in the high-resistance state and in the low-resistance state have been studied. A change in the built-in charge in the dielectric near the insulator-semiconductor interface during resistive switching is established and associated with the formation and destruction of conductive filaments. The light-stimulated resistive switching of MOS-structures with ZrO2(Y) layer from the high-resistance to the low-resistance state is observed, which is associated with an increase in the conductivity of the space-charge region in the Si substrate due to interband optical absorption in Si, which causes a voltage redistribution between Si and ZrO2(Y) layer. A difference in the shape of the small signal photo-voltage spectra of MOS-structures is found in the spectral region of intrinsic photosensitivity of Si in the high and low resistance states due to the leakage of photo-excited charge carriers from Si to the metal electrode through filaments.
... The device structure of RRAM is a capacitor like configuration with a metal-insulator-metal (M-I-M) structure. It is observed that the resistive switching occurring in the M-I-M structure can be changed by an electrical signal applied to it [8]. Recent reports on memory arrays are focused on the metal oxide-based RRAM due to the ease of the materials and exceptional compatibility with the fabri-cation procedure of CMOS. ...
... The traditional approaches to control the reproducibility of resistive switching include the formation of special electric field concentrators [11][12][13] and appropriate selection of materials/interfaces in memristive device structure. In the latter case, bilayer or multilayer structures are formed, in which the switching oxide alternates with a barrier/buffer layer (layers) to control the migration of oxygen vacancies, [14,15] with a layer of low dielectric constant [16,17] to obtain nonlinear currentvoltage (I-V) characteristics, or with a layer of higher/lower thermal conductivity [18,19] for the removal/retention of heat in the switching area and to achieve analog switching character. To tune the resistive states with given accuracy, regardless of ...
Variability of resistive switching is a key problem for application of memristive devices in emerging information‐computing systems. Achieving a stable switching between the nonlinear resistive states is an important task on the way to implementation of large memristive cross‐bar arrays and solving the related sneak‐path‐current problem. A promising approach is the fabrication of memristive structures with appropriate interfaces by combining the materials of electrodes with certain oxygen affinity and different dielectric layers. In the present work, such approach allows the demonstration of stabilized resistive switching in a multilayer device structure based on ZrO2(Y) and Ta2O5 films. It is established for the large‐area devices that the switching is stabilized after several hundreds of cycles. A possible scenario of the stabilization is proposed taking into account experimental data on the presence of grain boundaries in ZrO2(Y) as the preferred sites for nucleation of filaments, self‐organization of Ta nanocrystals as the electric field concentrators in Ta2O5 film, as well as oxygen exchange between oxide layers and interface with bottom TiN electrode. The robust resistive switching between nonlinear states is implemented in microscale cross‐point devices without numerous cycling before stabilization promising for the fabrication of programmable memristive weights in passively integrated cross‐bar arrays.
... Some of them are shown to be scalable in cross-bar architecture and applicable in neuromorphic hardware [23][24][25][26]. Among the metal-oxide memristive structures, the yttria stabilized zirconia (ZrO 2 (Y), YSZ) has emerged as a promising candidate for the functional oxide layer in memristive devices [27,28]. On the one hand, the YSZ is quite appropriate for the realization and computer simulation of resistive switching because the concentration of oxygen vacancies in YSZ that define the processes of electroforming and resistive switching can be well controlled by the yttrium doping level. ...
... Yttria stabilized zirconia (YSZ) ZrO 2 (Y) is a promising material for the memristor devices [10][11][12][13]. It is featured by a high concentration of oxygen vacancies that provides the high anion mobility [14]. ...
We report the investigations of the ion migration polarization in the yttria stabilized zirconia (YSZ) thin films in the Metal-Oxide-Metal (MOM) and Metal-Oxide-Semiconductor (MOS) stacks due to the drift of the oxygen vacancies under the external bias voltage applied between the electrodes. The parameters characterizing the drift of the oxygen vacancies in YSZ such as the ion drift activation energy, mobile ion concentration, and the drift mobility have been determined in the temperature range 300–500 K. These data are important for deeper understanding of the fundamental mechanisms of the electroforming and resistive switching in the YSZ-based MOM and MOS stacks, which are promising for the Resistive Random Access Memory (RRAM) and other memristor device applications.
... 22 A few research groups attempted to use Y-doped ZrO 2 as a high-k dielectric for metal-insulator-semiconductor (MIS) capacitors in CMOS devices and a switching material for MIM capacitors in resistive random access memory (RRAM) devices. [28][29][30][31][32][33] ...
With accelerated shrinking of integrated circuit, the fabrication of metal-insulator-metal (MIM) capacitors having a high capacitance density and low leakage current for dynamic random access memory (DRAM) has become a challenge. In this study, we investigated Y-stabilized ZrO2 as a novel high-k material for DRAM capacitors. We used atomic layer deposition (ALD) to produce Y-stabilized ZrO2; this technique enables easy control of the Y concentration by changing the ratio of ZrO2 to Y2O3 ALD cycles. This technique is suitable for future DRAM capacitors, as it provides superior thickness controllability and conformality. Y doping into ZrO2 increases the oxygen vacancy content in the films and transforms the ZrO2 crystal structure from monoclinic to cubic. As a result, the dielectric constant is significantly increased from 19.1 to 30.2. Moreover, Y doping shifts the defect level into the conduction band rather than the energy bandgap, resulting in about 60 times lower leakage current density for Y-doped ZrO2 compared to undoped ZrO2. It is notable that the dielectric properties and the leakage current density are simultaneously enhanced, indicating that Y-doped ZrO2 is a promising candidate to satisfy the requirements of future DRAM capacitors.
... In this study, we analyze the effect of electroforming and switching in capacitors based on SiO x (Au/SiO x /TiN/Ti) and exhibiting the memristive phenomenon both on the I–V characteristics and on the parameters of the immitance depending on fre- quency. 1. EXPERIMENTAL Thin-film capacitor structures with the resistive switching phenomenon were formed on an oxidized silicon substrate with metallization (TiN (25 nm)/Ti (20 nm)/SiO 2 (30 nm)/Si) obtained by magnetron sputtering [17, 18]. The SiO x films with thicknesses of 20, 40, and 60 nm were deposited by radio-frequency magnetron sputtering of quartz on the MagSputt 3G-2 (Torr International) setup in the argon–oxygen gas measured using ellipsometry was 1.46, indicating a nearly stoichiometric composition of the film (x ≈ 2). ...
The change of the immitance of the metal–insulator–metal memristive structures based on SiOx, which is observed during electroforming and resistive switching, confirms the formation of conducting channels (filaments) in the insulator during forming and their rupture upon a transition of the structure to a highresistance state. The observed switching of the differential capacitance and conductivity synchronously with the switching of current (resistance) can substantially extend the functional applications of memristive devices of this type.
... The SiO x dielectric film with a thickness of 40 nm was deposited by the rf-magnetron sputtering of fused silica target using the MagSputt 3G-2 machine (Torr International) in the argon-oxygen gas mixture (30% oxygen content) at the pressure of 5.6·10 −3 Torr and substrate temperature of 400 • C. The optical refractive index of oxide film was 1.46 according to the data of spectroscopic ellipsometry. Top Au electrodes (40 nm) with the Zr underlayer (3 nm) and area of 8.4·10 −3 cm −2 or 1.2·10 −3 cm −2 were deposited through the mask by the method of dc-magnetron sputtering in an argon atmosphere at the pressure of 5·10 −3 Torr and substrate temperature of 200 • C. The Zr underlayer was introduced to improve the adhesion of the top electrode material to the oxide film by analogy with the previously studied Au/Zr/ZrO 2 /TiN/Ti structures [22]. ...
Resistive memories are outstanding electron devices that have displayed a large potential in a plethora of applications such as nonvolatile data storage, neuromorphic computing, hardware cryptography, etc. Their fabrication control and performance have been notably improved in the last few years to cope with the requirements of massive industrial production. However, the most important hurdle to progress in their development is the so‐called cycle‐to‐cycle variability, which is inherently rooted in the resistive switching mechanism behind the operational principle of these devices. In order to achieve the whole picture, variability must be assessed from different viewpoints going from the experimental characterization to the adequation of modeling and simulation techniques. Herein, special emphasis is put on the modeling part because the accurate representation of the phenomenon is critical for circuit designers. In this respect, a number of approaches are used to the date: stochastic, behavioral, mesoscopic..., each of them covering particular aspects of the electron and ion transport mechanisms occurring within the switching material. These subjects are dealt with in this review, with the aim of presenting the most recent advancements in the treatment of variability in resistive memories.
In this letter, the conduction and bipolar switching mechanism of the ultrathin AlOx(3 nm)/TaOx(5 nm) memristor are investigated through the electrical characterization and elemental analysis. The AlOx/TaOx memristor exhibits high uniformity and excellent analog property after initial reset process. The following experiments and analyses demonstrate that the switching behavior could take place over the whole area of TaOx/Pt interface and is dominated by the tunneling barrier modulation induced by oxygen ions migration.
Formation-free multi-level resistive switching characteristics by using 10 nm-thick polycrystalline GeOx film in a simple W/GeOx/W structure and understanding of switching mechanism through redox reaction in H2O2/sarcosine sensing (or changing Ge°/Ge⁴⁺ oxidation states under external bias) have been reported for the first time. Oxidation states of Ge⁰/Ge⁴⁺ are confirmed by both XPS and H2O2 sensing of GeOx membrane in electrolyte-insulator-semiconductor structure. Highly repeatable 1000 dc cycles and stable program/erase (P/E) endurance of >10⁶ cycles at a small pulse width of 100 ns are achieved at a low operation current of 0.1 µA. The thickness of GeOx layer is found to be increased to 12.5 nm with the reduction of polycrystalline grain size of <7 nm after P/E of 10⁶ cycles, which is observed by high-resolution TEM. The switching mechanism is explored through redox reaction in GeOx membrane by sensing 1 nM H2O2, which is owing to the change of oxidation states from Ge⁰ to Ge⁴⁺ because of the enhanced O²⁻ ions migration in memory device under external bias. In addition, sarcosine as a prostate cancer biomarker with low concentration of 50 pM to 10 µM is also detected.
We have studied light-induced resistive switching in metal–insulator–semiconductor structures based on silicon covered with a tunneling-thin SiO2 layer and nanometer-thick layer of antimony. The role of an insulator was played by yttria-stabilized zirconia.
We have studied Au/SiOx
/TiN/Ti memristive structures obtained by magnetron sputtering, which exhibit a reproducible resistive switching effect. The influence of the thickness and stoichiometry of SiOx
layer and the area of Au electrode on the parameters of switching has been analyzed. The obtained results show evidence in favor of the filament model of resistive switching in SiOx
films.
Specific features (abrupt changes in current caused by voltage variation) of nonequilibrium depletion in metal–insulator–semiconductor structures based on gallium arsenide and silicon with a 40-nm-thick film of yttria-stabilized zirconia were revealed. These features may help extend the range of application of the nonequilibrium depletion effect in microelectronics.
High resolution transmission microscopy and optical absorption spectroscopy have been used to
examine how metallic nanocrystals (NCs) are formed in the course of implantation of Au ions into thin films of yttria stabilized zirconia (YSZ) and subsequent thermal annealing. It was found that, under certain implantation conditions, Au4Zr NCs are formed in addition to Au NCs in the YSZ matrix. The conditions in which Au4Zr NCs are formed in the course of implantation and decompose under the subsequent annealing were determined.
We have studied bipolar resistive switching (BRS) with memory in a binary oxide structure Si–
SiO2–V2O5–Au manufactured by reactive magnetron sputtering. A physical model is proposed that explains
the formation of a BRS structure with a nanosized silicon channel in SiO2 and reversible modulation of con�
ductivity in thin V2O5 layer at the channel boundary. The radius of this silicon channel is found from calcu�
lations based on the heat equation and atomic force microscopy data.
Using as an example metal-insulator-semiconductor structures based on GaAs with stabilized (by yttrium oxide) zirconium dioxide, which show the effect of resistive-switching random-access memory, the possibility is considered of controlling phenomena associated with the forming process in the insulator and on the insulator-semiconductor interface, as well as in the semiconductor, by measuring the response of the semiconductor.
The effect of the layer thickness of the TiO
x
/TiO2 heterostructure on its memristor properties is investigated. The dependence of the stoichiometry index of the prepared layers on their thickness is analyzed using Auger spectroscopy. The dependence of ratio R
off/R
on of the resistances in the high- and low-resistance states of a memristor element on the thickness of its layers is nonmonotonic. The highest value of R
off/R
on = 200 was attained for identical thickness of the TiO
x
and TiO2 layers, equal to 30 nm.
Memristive properties of the pulsed laser deposited Pt/TiOx/TiO2/Pt heterostructures with different layer thicknesses are studied. It was found that the memristor device provides nonmonotonic dependence of the ratio of its resistance in low and high conductive states Roff/Ron on layers thickness. The maximum value of the ratio Roff/Ron = 200 is obtained when the thickness of both TiOx and TiO2 layers is 30 nm. The dependence of the stoichiometry index of deposited layers from their thicknesses is studied by means of Auger spectroscopy measurements. The nonmonotonic behaviour of the ratio Roff/Ron on layer thickness is discussed in terms of wide stoichiometry distribution through the amorphous TiOx/TiO2 structure. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
The resistance switching mechanism of a metal/CuO/metal sandwich with a planar device structure has been studied. We report the direct observation of a conducting bridge within the CuO channel of the device, which is formed upon the initial voltage application (forming process). It is found that the resistance switching phenomenon only occurs when just a single bridge is formed during a soft dielectric breakdown. We argue that the reduction and oxidation of this conducting bridge by the action of an applied field and/or current gives rise to a novel nonvolatile memory effect.
Reversible counter-clockwise and clockwise resistive switching in a TiN/TiO2/TiN structure was studied by different polarities of bias voltage. The nature of the bipolar switching phenomenon is related to the creation and annihilation of filament paths caused by redox reactions at locally confined interfaces between the TiO2 layer and TiN electrode. The analysis of electron energy loss spectroscopy (EELS) confirmed the formation of interfacial TiOxN1−x layer between the TiO2 and TiN bottom electrode. The TiOxN1−x layer reduces current levels of ON and OFF states by partially blocking oxygen ion drift to the TiN bottom electrode.
We report a high performance and low-power operated resistive memory. Using stacked covalent-bond-dielectric GeO x on metal-oxide SrTiO x to form the cost-effective Ni/ GeO x / SrTiO x / TaN resistive random access memory, ultralow set power of small 1 W 0.9 A at 1.2 V, reset power of 13 pW 0.13 nA at 0.1 V, fast 50 ns switching time and good 10 6 cycling endurance are realized. © 2011 American Institute of Physics. doi:10.1063/1.3549689 The resistive random access memory RRAM 1–18 based on a metal-insulator-metal MIM structure provides a potential solution for down scaling beyond MONOS nonvolatile memory. 19,20 To reach resistive bistability of RRAM, the nonstoichiometric transition metal-oxides TMO have been used, but these devices usually suffer the high set/reset currents. Several physical mechanisms have been applied to reach RRAM functions, such as conductive filaments, 12,13 valence change mechanism, 14 oxygen vacancies, 15,16 electric-field enhanced migration of oxygen vacancies, 17 and Schottky interface modulation. 18 Although low switching current down to 25 A was reported in TiN/ TiO x / HfO x / TiN RRAM, 14 this device is operated in bipolar mode and requires a transistor to deliver the opposite polarity currents. The diode-driven unipolar-type RRAM such as NiO 1 is preferred to bipolar one due to simple con-stituents and three-dimensional cell integration; unfortu-nately, the poor endurance, small resistance ratio of high-to low-resistance state HRS/LRS, high current compliance re-lated large size transistor, and high forming power are other challenges. In this letter we report an ultralow power RRAM with only setting power of 1 A and 1.1 V to LRS. The device can be reset to HRS at even smaller 0.12 nA and 0.13 V that can be driven by a diode under reverse bias. Excellent en-durance up to 10 6 cycles is also reached with a fast 50 ns switching time. Such record high performance is achieved using covalent-bond-dielectric/metal-oxide of GeO x / SrTiO x , where no metallic filament is available in covalent-bond GeO x . The MIM capacitors were fabricated on standard Si wa-fers. To permit VLSI backend integration, the process began with depositing a 200-nm-thick SiO 2 isolation layer on the Si substrates. Then 100 nm TaN was deposited and patterned as the bottom electrode. After that, the 12 nm thick SrTiO x STO were deposited by sputtering. Sequentially, two thick-nesses of 5 and 8 nm GeO x were deposited. Finally, the 25 nm Ni top electrode was deposited and patterned by a metal mask. The device size 11304 m 2 of GeO and GeO/STO RRAMs is the same for comparison. Figure 1a shows the swept I-V curves of Ni/ GeO x / TaN device with different GeO x thickness. The GeO 2 has been used as the gate dielectric for Ge metal-oxide-semiconductor field-effect transistor MOSFET, 21 which has smaller energy bandgap E G of 5.6 eV and weaker bond enthalpy of 659 kJ/mol than the 9 eV and 800 kJ/mol values of SiO 2 . The GeO 2 forms oxygen vacancy at low temperature to degrade the GeO 2 / Ge MOSFET, 21 but such oxygen vacancy is useful for RRAM. 15–17 In Ni/ GeO x / TaN device, small set current of 0.25 A at 4 V 1 W and ultralow reset current of 20 pA at 0.66 V 13 pW were achieved in the 8 nm GeO x devices with a bipolar-mode operation. Because there is no metal in GeO x to form the conductive metallic filaments, the RRAM behavior in GeO x may be related to electron injection created defects in covalent-bond GeO x from lower work function TaN 4.6 eV than top Ni 5.1 eV. This was supported from the much
The influence of Ti top electrode material on the resistive switching properties of ZrO 2 -based memory film using Pt as bottom electrode was investigated in the present study. When Ti is used as top electrode, the resistive switching behavior becomes dependent on bias polarity and no current compliance is needed during switching into high conducting state. This phenomenon is attributed to the fact that a series resistance between Ti and ZrO 2 film, composed of a TiO x layer, a ZrO y layer, and even the contact resistance, imposed a current compliance on the memory device. Besides, our experimental results imply that switching the device into high conducting state is a field driven process while switching back into low conducting state is a current driven process. © 2007 American Institute of Physics.
We introduce a model that accounts for the bipolar resistive switching
phenomenom observed in transition metal oxides. It qualitatively describes the
electric field-enhanced migration of oxygen vacancies at the nano-scale. The
numerical study of the model predicts that strong electric fields develop in
the highly resistive dielectric-electrode interfaces, leading to a spatially
inhomogeneous oxygen vacancies distribution and a concomitant resistive
switching effect. The theoretical results qualitatively reproduce non-trivial
resistance hysteresis experiments that we also report, providing key validation
to our model.
This paper studies the effects of both the positive and negative forming processes on the resistive switching characteristics of a Pt/Yb2O3/TiN RRAM device. The polarity of the forming process can determine the transition mechanism, either bipolar or unipolar. Bipolar behavior exists after the positive forming process, while unipolar behavior exists after the negative forming process. Furthermore, the bipolar switching characteristics of the Pt/Yb2O3/TiN device can be affected by using a reverse polarity forming treatment, which not only reduces the set and reset voltage, but also improves the on/off ratio.
TiO2 (oxygen rich, region 1)/TiO2−x (oxygen poor, region 2) multilayer homojunctions were studied as alternative resistive switching structures for both high and low resistance transitions. Stable bipolar resistive switching characteristics, including stable switching speeds (microseconds) and endurance behaviors, as well as long retention times (>104 s) were demonstrated. The nature of the resistive switching phenomenon in multilayer structures seems to be a combination of the conduction path and the redox reaction, resulting from the oxygen ions drifting between the oxygen rich and poor regions of the multilayer structures. A possible conduction sketch for bipolar switching behaviors is also discussed.
The main results of the computer simulation of the oxygen vacancy in pure silicon dioxide are presented. The semi-empirical method, MNDO from the MOPAC package, is used. Silicon dioxide is simulated by molecular clusters of different sizes and structures. Calculated positions of the absorption and luminescence bands of the neutral oxygen vacancy are in satisfactory agreement with those of the oxygen-deficient center observed in pure silicon dioxide. The absorption and luminescence bands of the vacancy correspond to the dipole allowed one-electron transitions between two localized states with the levels in the energy gap of SiO2. The lower level is doubly occupied; the upper one is empty, resulting from the bonding and antibonding combination of sp orbitals of two silicon atoms adjacent to the vacant site, respectively.
Electric-pulse induced resistance hysteresis switching loops for Pr0.7Ca0.3MnO3 perovskite oxide films were found to exhibit an additional sharp "shuttle tail" peak around the negative pulse maximum for films deposited in an oxygen-deficient ambient. The resistance relaxation in time of this "shuttle tail" peak as well as resistance relaxation in the transition regions of the resistance hysteresis loop show evidence of oxygen diffusion under electric pulsing, and support a proposed oxygen diffusion model with oxygen vacancy pileup at the metal electrode interface region as the active process for the nonvolatile resistance switching effect in transition-metal oxides.
Many metal-insulator-metal systems show electrically induced resistive switching effects and have therefore been proposed as the basis for future non-volatile memories. They combine the advantages of Flash and DRAM (dynamic random access memories) while avoiding their drawbacks, and they might be highly scalable. Here we propose a coarse-grained classification into primarily thermal, electrical or ion-migration-induced switching mechanisms. The ion-migration effects are coupled to redox processes which cause the change in resistance. They are subdivided into cation-migration cells, based on the electrochemical growth and dissolution of metallic filaments, and anion-migration cells, typically realized with transition metal oxides as the insulator, in which electronically conducting paths of sub-oxides are formed and removed by local redox processes. From this insight, we take a brief look into molecular switching systems. Finally, we discuss chip architecture and scaling issues.
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