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The antiferroelectric (Pb0.985Sm0.01) (Zr1-xTix)O3 (Ti-PSZO) thin films were synthesized on Pt(111)/Ti/SiO2/Si substrates using a chemical solution deposition method. The films were crystallized in the perovskite phase with a preferential orientation along (111) direction. With Ti doping in PSZO, a gradual transformation from antiferroelectric to ferroelectric phase transition was noticed at room temperature owing to the Ti doping induced lattice distortion. The phase transition has been confirmed through the P - E hysteresis loops, X-ray diffraction (peak shifting), capacitance-voltage measurements, and Raman scattering analysis. The thin film with Ti = 0.15 doping displayed a ferroelectric behavior with high dielectric constant and large dielectric tunability of about 62%. Also, Ti doping altered the Curie temperature (Tc) and enhanced the order of dielectric diffuseness. It is believed that Ti-doping in PSZO is an effective way to induce an antiferroelectric - ferroelectric phase transition and to tailor the electrical characteristics of PSZO thin films.

Excellent dielectric frequency, bias, and temperature stability of bismuth silicate (Bi2SiO5, BSO) thin films with a low dielectric loss has been obtained in this study. The thin films were prepared on Pt/Ti/SiO2/Si substrates by a chemical solution deposition method at a relatively low annealing temperature of 500 °C. The BSO films have a preferred growth along (200) orientation with dense fine-grained surface morphology. The dielectric constant and dielectric loss of the thin film annealed at 500 °C are 57 and 0.01, respectively, at 100 kHz, with little change between 1 kHz and 100 kHz and in the bias electric field range between −250 kV/cm and 250 kV/cm, indicating that the thin film exhibits a low dielectric loss as well as excellent frequency and bias field stability. The dielectric-temperature measurements confirmed that the BSO thin film annealed at 500 °C also has good temperature stability between 150 K and 450 K. Our results suggest that the BSO thin films have potential applications in the next-generation integrated capacitors.

Antiferroelectric Sm-doped PbZrO3 (PSZO) thin films were prepared on Pt(111)/Ti/SiO2/Si substrates using a chemical solution deposition method. The effects of Sm doping concentration on structural, morphology, dielectric, antiferroelectric, and energy storage characteristics of PSZO thin films were investigated. With Sm doping, all the thin films were crystallized in perovskite phase along with a strong (111)- preferential orientation. It is found that Sm doping significantly altered the Curie temperature (Tc) and electric field-induced phase switching of the films. The PSZO film with Sm = 0.01 exhibited a maximum polarization of 53.7 μC/cm2, an energy storage density of 17.1 J/cm3 at ~444 kV/cm, and a dielectric constant of 175 at 1 kHz. The improved energy storage performance was attributed to high (111) degree of preferred orientation and site occupation of Sm ions.

Orthorhombic Bi2SiO5 thin films were fabricated on Pt/Ti/SiO2/Si substrates by incorporating a NiO thin layer between Bi2SiO5 and bottom electrode. Compared with those bare Pt/Bi2SiO5/Pt devices, a remarkably improved uniformity of resistive switching parameters such as electroforming voltages, reset voltages, and a resistance ratio of low/high states was demonstrated in the Bi2SiO5 devices with an embedded NiO layer. This improvement was attributed to the formation of the partial conductive filaments resulted from sufficient oxygen vacancies at the interface. Our results provide a method for the optimization of the operation voltage control toward forefront applications in nonvolatile memory.

We report the coexistence of resistive switching and magnetism modulation in the Pt/Co3O4/Pt devices, where the effects of thermal annealing and film thickness on the resistive and magnetization switching were investigated. The sol-gel derived nanocrystalline Co3O4 thin films obtained crack-free surface and crystallized cubic spinel structure. The 110 nm Co3O4 film based device annealed at 600 °C exhibited optimum resistive switching parameters. From I–V curves fitting and temperature dependent resistance, the conduction mechanism in the high-voltage region of high resistance state was dominated by Schottky emission. Magnetization-magnetic field loops demonstrated the ferromagnetic behaviors of the Co3O4 thin films. Multilevel saturation magnetization of the Co3O4 thin films can be easily realized by tuning the resistance states. Physical resistive switching mechanism can be attributed to the rejuvenation and annihilation of conductive filament consisting of oxygen vacancies. Results suggest that Pt/Co3O4/Pt device shows promising applications in the multifunctional electromagnetic integrated devices.

Orthorhombic Bi2SiO5 thin films with dense surface were synthesized by using a chemical solution deposition method. The crystallized films were first utilized to implement resistive memory cells with Pt/Bi2SiO5/Pt sandwich architecture. It exhibited outstanding switching parameters including concentrated distributions of low and high resistance states, uniform switching voltages, cycling endurance, and long retention. Furthermore, the model of formation and rupture of conductive filaments consisted of oxygen vacancies was used to well explain resistive switching behavior. The results revealed that the solution-processed Bi2SiO5 thin film devices have great potential for forefront application in nonvolatile memory.

Structure, dielectric, ferroelectric, fatigue, and photoluminescent properties of Bi3.86−kSm0.14LakTi3O12 (BSLT) thin films synthesized by sol–gel method were investigated. The XRD analysis indicated that the BSLT thin films formed single phase orthorhombic structure, and orthorhombic distortion was found to increase with increasing lanthanum doping content. Raman spectra revealed that BSLT thin films have significantly structure distorted because of La3+ doping, which is consistent with XRD results. Increasing La substitution results in improvement in dielectric and ferroelectric properties of BSLT thin films due to distorted structure and defects reduction. The films show almost fatigue-free ferroelectric polarization behavior at room temperature. Besides, the BSLT thin films show orange-red color emission at 604 nm and long florescence lifetime (about 0.75 ms). This study indicates that the thin films with an appropriate doping concentration of Sm3+, La3+ ions may have potential applications in multifunctional optoelectronic devices.

Ni-Cu ferrite (Ni1-xCuxFe2O4, x = 0, 0.05, 0.1, 0.15, 0.2, 0.25) thin films were synthesized on Pt/Ti/SiO2/Si substrates via sol-gel method. The influence of Cu2+ ions substitution on the resistive switching and magnetism of nickel ferrite thin films were investigated. The appropriate 0.2 Cu2+ ions substituted Pt/NFO/Pt device exhibited improved resistive switching parameters such as lower electroforming voltages, narrow distribution of SET/RESET voltages, good endurance (103 cycles), and long data retention upto 105 s at 25 °C and 85 °C, respectively. With increasing Cu2+ ions substitution, the saturation magnetization of Ni-Cu ferrite thin films decreased. The 0.2 Cu2+ ions substituted Pt/NFO/Pt device illustrated the controlling magnetism by accompanying with high saturation magnetization to switch into low saturation magnetization during the resistive switching process. The modulation of Cu2+ ions substitution on the magnetic properties was linked with magnetic moments and oxygen vacancies concentrations. Current transport conduction mechanisms were Ohmic behavior in low resistance state and Schottky emission in high field region of high resistance state. Moreover, temperature dependence of resistance revealed that origin of switching mechanism was related with the hybrid Cu mental and oxygen vacancies conducting filaments. Our results suggest that controlling the paths of hybrid conductive filaments is an effective strategy to modulate resistive switching performance and magnetism in ferrite based devices.

Sol-gel method was used to prepare the Pr3+ ions-doped (1-x)Na0.5Bi0.5TiO3-xCaTiO3 (Pr-NBT-xCTO) (x = 0, 0.04, 0.06, 0.08, 0.1, 0.12, and 0.16) thin films on Pt/Ti/SiO2/Si and fused silicon substrates. The structure phase of thin films was evolving from rhombohedral (R3c) to orthorhombic (Pnma) with increasing CTO content. Owing to the morphotropic phase boundary (MPB), the improved ferroelectric and dielectric properties were obtained at x = 0.06–0.1. The MPB was formed from the concomitant phase of rhombohedral (R3c) and orthorhombic (Pnma). The Pr-NBT-0.08CTO thin film showed the best ferroelectric and dielectric properties, as well as strong relaxor behavior (the diffusion factor is γ = 1.79). In addition, all the films exhibited strong red emission as excited by UV light, and wide optical band-gap (3.44–3.47 eV), which might be influenced by grain size and structural variation. Our results indicate that Pr-NBT-xCTO thin films may have potential applications in ferroelectric-luminescence multifunctional optoelectronic devices.

Spinel Co3O4 thin films were synthesized using a sol–gel technique to study the annealing atmosphere effect on resistive switching (RS) and magnetic modulation properties. Compared with oxygen and air annealed Pt/Co3O4/Pt stacks, the nitrogen annealed Pt/Co3O4/Pt stack shows optimal switching parameters such as a lower forming voltage, uniform distribution of switching voltages, excellent cycle-to-cycle endurance (>800 cycles), and good data retention. Improvement in switching parameters is ascribed to the formation of confined conducting filaments (CFs) which are composed of oxygen vacancies. From the analysis of current–voltage characteristics and their temperature dependence, the carrier transport mechanism in the high-field region of the high resistance state was dominated by Schottky emission. Besides, temperature dependent resistance and magnetization variations revealed that the physical mechanism of RS can be explained based on the formation and rupture of oxygen vacancy based CFs. In addition, multilevel saturation magnetization under different resistance states is attributed to the variation of oxygen vacancy concentration accompanied with the changes in the valence state of cations. Results suggested that using a nitrogen annealing atmosphere to anneal the thin films is a feasible approach to improve RS parameters and enhance the magnetic properties of Co3O4 thin film, which shows promising applications to design multifunctional electro-magnetic coupling nonvolatile memory devices.

This work examined carefully the electrical performance of Pt/InGaZnO/W memory device and found the co-existence of volatile and non-volatile resistive switching effects dependent on the electroforming process. The Pt/InGaZnO/W device exhibited stable and volatile switches without electroforming process, which were originated from electron trapping and detrapping in intrinsic defects of InGaZnO thin films. However, after electroforming process, the device showed non-volatile bipolar resistive switching properties with high reliability including long retention, good endurance and concentrated switching voltages. On the basis of the resistance temperature dependence and the change of chemical states, the non-volatile resistive switching effects were explained by the formation and rupture of oxygen vacancies related filament. This study provides new insights into the effects of electroforming process and defect types on resistive switching behaviours.

We report on the structure, dielectric, ferroelectric, and photoluminescent properties of Sm3+-doped Bi4Ti3O12 thin films which were prepared on fused silica and Pt/Ti/SiO2/Si substrates by sol-gel method. The X-ray diffraction analysis confirmed that the Bi4-xSmxTi3O12 (BSmT) thin films were well crystallized in layered perovskite structure without any secondary phase. Raman spectra indicated that the structure of BSmT thin films was significantly distorted because of the Sm3+ doping. An appropriate doping amount of Sm3+ ions leads to obvious enhancement in ferroelectric and dielectric properties of BSmT thin films due to structure distortion and reduction in defects. In addition, the BSmT thin films also show orange-red color emission at 601 nm and long florescence lifetime (> 0.6 ms). This study indicated that lead-free BSmT thin films, which are featuring good electrical and photoluminescent properties, may have potential applications in integrated optoelectronic devices.

In this work, we have fabricated the MgZnO thin films directly on low resistive silicon substrates by using a chemical solution deposition route. Besides the investigation of the structures, morphologies, chemical states, and photoluminescence properties of MgZnO thin films, the bipolar resistive switching behaviours have been evaluated in the simple Ag/MgZnO/Si structures. The self-compliance resistive switching characteristics simplify the device configuration and circuit design for practical applications. In addition, the multilevel storage capabilities have also been investigated by regulating different operation voltages or compliance currents, respectively. The four level storage capabilities show long retention time and good cycling performance. The resistive switching mechanism has been explicated by the formation and rupture of Ag filament based on the electrochemical metallization model. This work suggests that the Ag/MgZnO/Si structures have potential non-volatile multilevel memory applications.

Effect of oxygen annealing on bipolar resistive switching (BRS) properties of TiN/ZnO/CeO2-x/Pt devices was investigated. Bilayer ZnO/CeO2-x thin films were fabricated by rf-magnetron sputtering. It was observed that the improvement in cycle-to-cycle endurance degradation and uniformity of the bilayer ZnO/CeO2-x thin film is optimum at 400 °C annealing temperature due to decrease in oxygen vacancies during annealing, as confirmed by x-ray photoelectron spectroscopy. The BRS could be caused by the formation of interfacial TiON layer, which is most likely to be accountable for creating an adequate quantity of oxygen vacancies necessary for the formation and rupture of conductive filaments. Smaller Gibbs free energy of the formation of interfacial TiON ( − 611 k J m o l − 1 ) layer as compared to bilayer film ZnO ( − 650 k J m o l − 1 ) and CeO2 ( − 1024 k J m o l − 1 ) results in an easier re-oxidation of the filaments through the oxygen exchange with TiN top electrode. The analysis of current–voltage characteristics shows that the charge transport mechanism is Schottky emission. Moreover, the temperature dependence of high resistance state (HRS) and low resistance state (LRS) revealed the physical origin of the RS mechanism, which entails the oxygen vacancies for the formation and rupture of conducting paths.

Nano-crystalline zinc ferrite (ZnFe2O4) magnetic thin film was prepared on Pt/Ti/SiO2/Si substrate by chemical solution deposition method though spin coating technique. Reproducible nonpolar resistive switching (RS) characteristics in Pt/ZnFe2O4/Pt devices are reported. By changing the magnitude and polarity of the applied electric bias, reversible transitions among all the four nonpolar RS modes can be realized. For each switching mode, I-V characteristics were measured in the temperature range of 200 K–340 K. Temperature dependent I-V characteristics of high resistance state (HRS) have been found to support the conduction mechanism across the metal/insulator/metal (MIM) systems to be Schottky emission. Associated parameters such as activation energy and effective height of Schottky barrier at zero biasing (ϕo) have been evaluated at different temperature and electric field. In addition, the increase in resistance of low resistance state (LRS) with temperature revealed that the conduction through ZnFe2O4 in LRS is metallic. Based on the temperature-dependent characteristics, the reversible switching among the four modes of nonpolar RS via formation and rupture of the conducting filaments has been attributed to the joint effect of field-induced migration of oxygen vacancies and metallic Zn atoms.

Lead-free ferroelectric Pr3+-doped (1-x)Na0.5Bi0.5TiO3-xSrTiO3 (x = 0–0.5) (hereafter abbreviated as Pr-NBT-xSTO) thin films were prepared on Pt/Ti/SiO2/Si and fused silica substrates by a chemical solution deposition method combined with a rapid thermal annealing process at 700 °C, and their structural phase transition, dielectric, ferroelectric, and photoluminescent properties were investigated as a function of STO content. Raman analysis shows that with increasing STO content, the phase structures evolve from rhombohedral phase to coexistence of rhombohedral and tetragonal phases (i.e. morphotropic phase boundary), and then to tetragonal phase. The structural phase transition behavior has been well confirmed by temperature- and frequency- dependent dielectric measurements. Meanwhile, the variation in photoluminescence intensity of Pr3+ ions with different STO content in the NBT-xSTO thin films also indicates that there exists a clear structural phase transition when the film composition is close to the morphotropic phase boundary. Superior dielectric and ferroelectric properties are obtained in the Pr-NBT-0.24STO thin films due to the formation of morphotropic phase boundary. Our study suggests that Pr-NBT-xSTO thin films be promising multifunctional materials for optoelectronic device applications.

Influence of Gd ion doping on resistive switching (RS) and magnetic properties of NiFe2O4 (NiFe2−xGdxO4, NFG-x) thin films prepared by chemical solution deposition method was investigated. The 0.075 Gd-doped NiFe2O4 based devices exhibited much reliable repeatability, endurance (>500 switching cycles), and good data retention (105 s at 25 and 100 °C) without any significant degradation in their RS performance. Dominant conduction mechanisms in devices were Ohmic conduction at low resistance state and at lower voltage region of high resistance state, while Schottky emission dominated at higher voltage region in high resistance state. The physical mechanism of resistive switching was linked with the formation and rupture of conducting filaments, and the improved stability of the switching parameters for Pt/NFG/Pt devices was attributed to appropriate concentration of oxygen vacancies which can easily minimize randomness for formation/rupture of conductive filaments. Due to variation in concentration of oxygen vacancies, saturation magnetization of the RS device at high resistance state was higher than those at virgin state and low resistance state, and changes of saturation magnetization maintained a stable value of 40% between HRS and LRS of Pt/NFG-0.075/Pt device. Our study indicates that doping rare earth element into ferrite thin films is a viable approach for enhancing resistance switching and magnetic properties.

Switching instability significantly affects the development of resistive random access memories. An enhanced resistive switching uniformity was developed by embedding well-ordered Pt/Au nanostructures (NSs) in Pt/NiFe2O4/Pt devices. The well-ordered Pt/Au NSs arrays were developed on Pt/Ti/SiO2/Si substrates using 2D colloidal crystals as the deposition templates. The NiFe2O4 (NFO) thin films were then deposited on the Pt/Au NSs array via a spin coating technique, followed by annealing treatment. The memory devices were fabricated via Pt top electrode sputtering on the NFO film surface. The embedded device showed more uniform SET and RESET voltages and lower forming voltage than the non-embedded device. Distortion of electric field and temperature gradient around the Pt/Au NSs suppresses the random development of conductive filaments (CFs). Furthermore, the temperature gradient near the Au NSs could be relatively high during the forming process than in Pt NSs since Au has high thermal conductivity, promoting oxygen vacancy migration. Therefore, CFs easily nucleate in HRS and develop near Au NSs under the same bias voltage, leading to better resistive switching properties in the Au NSs array device than in the Pt NSs array device. This study provides an effective path for enhancing the resistive switching performances of devices.

Au-doped nickel ferrite (NiFe2O4-Au, NFO-Au) magnetic thin films were prepared on Pt/Ti/SiO2/Si substrates by a chemical solution deposition method to explore the effect of Au doping on unipolar resistive switching (RS) behavior. Experimental results reveal that 1% Au doped NFO film demonstrated considerably optimum switching parameters such as lower electroforming voltage, narrow distribution of SET/RESET voltages, good cycle-to-cycle endurance (103 cycles) and long data retention (105 s at 125 °C) as compared to NFO and Au-(0.5% and 2%) doped NFO films. The improved performance is attributed to suppressing of randomness of oxygen vacancies based filament by Au doping. Current transport conduction mechanisms are found to be Ohmic in low resistance state and Schottky emission in high resistance state. Physical model concerns for the rupture and formation of Au atoms assisted conductive filament inside the Au-doped NFO films based on the thermal effect of oxygen vacancies. Magnetic properties correlated with RS were measured and analyzed. The variation of saturation magnetization with different resistance state may be attributed to Au-doping induced different oxygen vacancies concentrations and make the conversion of valence states of Fe3+ and Fe2+ ions in octahedral sites easier. Our results provide a pathway towards the applications in nonvolatile RS memory and magnetoelectronic coupling devices.

Pr-doped ZnO hexagonal structure thin films with c-axis preferred orientation were deposited on Pt/Ti/SiO 2 /Si substrates by chemical solution deposition technique. The effects of Pr doping amount on the resistive switching behavior of Pt/Zn 1−x Pr x O/Pt (x = 0, 0.01, 0.03, and 0.05) memory cells were investigated. The results showed that Pr-doping lowered the c-axis orientation degree of the ZnO thin films, but improved the resistive switching properties of Pt/Zn 1−x Pr x O/Pt devices. The resistive switching devices exhibited good endurance, long retention, and uniform switching voltages. I-V characteristics and their temperature dependence analysis indicated that the conduction mechanism of LRS was Ohmic behavior, and that of HRS at relatively higher voltage is trap-controlled space charge limited current. The physical origin of the resistive switching can be referred to the formation and rupture of the oxygen vacancies related filaments.

Ce-doping NiFe2O4 spinel ferrite thin films were prepared on Pt / Ti / SiO2 / Si substrates using a chemical solution deposition method. It has been observed that Ce-doping induced enhancement of unipolar resistive switching properties, such as uniform switching voltages, enlarged ON / OFF ratio, and long retention in Pt / NiFe2O4 / Pt memory devices. The dominant conduction mechanisms in the thin film devices were Ohmic conduction at low resistance state and lower voltage region of high resistance state, while Schottky emission dominated at higher voltage region in high resistance state. The physical mechanism of resistive switching is related to the formation and rupture of conducting filament. The improved stability of the switching parameters for the devices can be attributed to Ce-doping minimizing random formation and rupture of conductive filament. This study indicates that doping rare earth ions in ferrite thin films would be an effective approach for obtaining stable resistance switching memory devices.

c-Axis oriented Tm3+-Dy3+-Eu3+ tri-codoped Bi2VO5.5 ferroelectric thin films were prepared on fused silica and Pt(111)/Ti/SiO2/Si substrates by using chemical solution deposition method, and charac...

Bipolar resistive switching performance has been demonstrated in the sandwiched Pt/Ta2O5/TiN structures, including uniform set and reset voltages distributions, good endurance, long retention, and high operation speed. In addition, multi-level storage capability has been achieved through controlling different reset stop voltages and different compliance currents in direct current voltage sweeping modes and by means of different pulse erasing voltages in pulse programming/erasing modes. High speed electrical pulse induced multi-level storage capability shows good endurance and long retention of the four level resistance states. On the basis of the conducting filament model, the multi-level switching capability has been explained. This study suggests that the Pt/Ta2O5/TiN devices have potential application in nonvolatile high speed and multi-level resistive switching memory.

(Bi 1.90 Eu 0.10 )(V 1− z Mo z )O 5.5 ( z = 0, 0.05, 0.10, 0.15 and 0.20) thin films with c -axis oriented were prepared on Pt(111)/Ti/SiO 2 /Si substrates by using chemical solution deposition method. The effect of Mo 6+ concentration on the structure, luminescence properties and dielectric properties of the thin films were characterized systematically. X-ray diffraction data indicates that the thin films with low Mo 6+ -doping content can remain Bi 2 VO 5.5 structure. When the Mo 6+ -doping content z reaches to 0.15, the thin films are a mixture of diphase with the main phase Bi 2 VO 5.5 and secondary phase Bi 2 MoO 6 . Under UV irradiation, all the thin films emit a bright red or orange emission which origin from Eu 3+ . With increasing Mo 6+ -doping content z , the relative intensity of the Red and Orange emissions show obviously change. The value of Red/Orange ratio first decrease, and it reached minimum when z is 0.15, then it recover to the initial value. The variation trend of the Red/Orange ratio reflects the change of the lattice symmetry. Dielectric constant of the thin films increased with the increasing of the Mo 6+ concentration while dielectric loss decreased. The decrease of the quantities of oxygen vacancies and the generation of Bi 2 MoO 6 phase are responsible for the improvement of electric properties. These results explain that Eu 3+ ion can be used as an effective luminescent probe in (Bi 1.90 Eu 0.10 )(V 1− z Mo z )O 5.5 ( z = 0, 0.05, 0.10, 0.15 and 0.20) thin films, and the electric properties of the thin films can be improved by Mo 6+ doping.

Nanocrystalline bilayer composite MnO2/Co3O4 thin films were fabricated by a simple chemical solution deposition method to investigate the resistive and magnetization switching properties. Compared with pure Co3O4 thin films device, bilayer MnO2/Co3O4 thin films device exhibits enhancement in resistive switching (RS) and magnetization modulation, such as uniform SET and RESET voltages, stable cycle-to-cycle switching endurance (>2 × 103 cycles), good data retention time (>104 s), and RS induced magnetization switching (∼63%). Through the analysis of fitting current-voltage (I–V) curves and temperature-dependent resistance, it demonstrated that Schottky emission conduction is dominated at high resistance state of the devices. Enhancement in RS performance can be attributed to the growth and dissolution of confined conductive filaments which are composed of Mn atoms and oxygen vacancies, evidenced by temperature dependence and magnetization switching at different resistance states. The physical relevancy between RS and magnetic switching involves in the creation and annihilation of conductive filaments, associated with the reversible conversion of cation valence state (Co2+ and Co3+, Mn ions and Mn atoms). Results suggest that by introducing a thin MnO2 inserting layer, Co3O4 based device shows promising applications for nonvolatile RS memory and multifunctional electromagnetic coupling device.

In this work, large-area ferrite thin films of ferromagnetic yttrium iron garnet (Y3Fe5O12, YIG) were synthesized on Pt/Ti/SiO2/Si (Pt) substrates by a sol-gel method to investigate the resistive and magnetization switching properties. The synthesized YIG thin films acquire a single garnet structure. The Pt/YIG/Pt stack illustrates unipolar resistive switching behavior with excellent switching uniformity, large memory window (102), stable cycle-to-cycle endurance, and good data storage retention (104 s). The ~46% saturation magnetization variation could be realized via the conversion between high and low resistance states by manipulating the electric field. Schottky emission is governed in the high-field region for the high resistance state. Temperature dependence of resistance and magnetization variation confirms that oxygen vacancies conductive filament model and valence state change (Fe2+ and Fe3+) are responsible for the resistive and magnetization switching mechanisms. These results indicate that YIG ferrite based stack is suitable to design the electro-magnetic coupling multifunctional nonvolatile memory devices.

Pr3+-doped Na0.5Bi0.5TiO3 (Pr-NBT) thin films with different preferred orientations including random, (100), and (110) orientations were prepared on Pt/Ti/SiO2/Si substrates by a chemical solution deposition method combining with a rapid thermal annealing. Effects of the crystallographic orientation on the ferroelectric and dielectric properties of Pr-NBT thin films were investigated. XRD patterns revealed that the preferential orientation degrees of (100)- and (110)-oriented Pr-NBT thin films were 97% and 69%, respectively. The (100)-oriented Pr-NBT thin film has a higher dielectric constant of 1035 compared to the (110)- and randomly oriented ones. Furthermore, a large remnant polarization (2Pr = 31 µC/cm2) was obtained from the highly (100)-oriented Pr-NBT thin film, which is 1.55 times larger than that of the randomly oriented film. The quantitative relationship in dielectric constants between the (100)-, (110)-oriented, and randomly oriented Pr-NBT thin films was calculated using the dipole azimuth model. The calculated result was consistent with experimental measurements. The optimal dielectric tunable property (tunability = 40.8%, FoM = 10.2) is obtained from (100)-oriented films. The highly (100)-oriented Pr-NBT lead-free thin film is promising for use in integrated microelectronic devices.

Au nanoparticles loaded c-axis oriented Bi2VO5.5 (BVO) porous thin films were prepared by using a simple spin-coating technique. The porous structures were formed through the hydrolysis of bismuth nitrate, Bi(NO3)3, one of the raw materials for synthesizing the BVO precursor solutions. The optimal photocatalytic rate of the porous thin film is three times more than that of pure BVO thin film. The enhancement of photocatalytic activity can be attributed to the Schottky barrier in the intimate interface between Au nanoparticles and BVO grains and the increase of absorption of light caused by surface plasmon resonance effect of gold nanoparticles. The possible degradation mechanism of Au–BVO-Methylene Blue system has been discussed based on the energy band structure and further trapping experiments. This study provides a simple method to prepare bismuth-containing oxide porous thin films without any pore-forming reagents, and the results suggest that the Au nanoparticles loaded BVO thin film is a promising candidate material for water or air treatment.

Eu 3+ -doped Bi 2 Ti 2 O 7 pyrochlore structure thin films were prepared by a chemical solution deposition method. The red-orange photoluminescence and dielectric relaxation of Bi 2− x Eu x Ti 2 O 7 thin films have been investigated in terms of Eu 3+ doping content ( x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6) and annealing temperature. The crystallinity and surface morphology of the thin films were evaluated by X-ray diffractometer and field emission scanning electron microscopy. It was shown that the thin films annealed at 600 °C were well crystallized in pyrochlore structure without other impurity phases. Intense visible red-orange photoluminescence, originated from doubly split electric-dipole 5 D 0 → 7 F 2 and magnetic-dipole 5 D 0 → 7 F 1 transitions of Eu 3+ ions, could be observed under ultraviolet excitation. The quenching concentration for photoluminescence of Bi 2− x Eu x Ti 2 O 7 thin films is about x = 0.5. In addition, the Bi 2− x Eu x Ti 2 O 7 thin films had a relatively low dielectric loss and a high dielectric constant as well as highly stable bias electric field properties. Meanwhile, the thin films exhibited dielectric relaxation based on the temperature and frequency dependence of dielectric properties. Our study suggested that Eu 3+ -doped Bi 2 Ti 2 O 7 thin films have potential applications in new multifunctional optoelectronic thin-film devices.

Eu 3+ -doped Bi 12 TiO 20 thin films were prepared on Pt/Ti/SiO 2 /Si and fused silica substrates by a chemical solution deposition method. The thin films annealed at 600 °C crystallized in a sillenite structure with a uniform thickness. After an electroforming process, the resistive switching properties were observed in the thin films sandwiched with top and bottom Pt electrodes. The dominant conduction mechanisms in Pt/Bi 10.8 Eu 1.2 TiO 20 /Pt devices were Ohmic conduction at low resistance state and lower-voltage region of high resistance state, and Schottky emission at higher-voltage region in high resistance state. The dielectric and photoluminescent properties of the thin films have also been investigated. With increasing Eu 3+ content, the dielectric constant increased and dielectric loss decreased due to improved crystallization of the thin films. Under 350 nm excitation, the thin films on fused silica substrates exhibited the visible emissions assigned to the transitions 5 D 0 → 7 F 1,2 of Eu 3+ ions. The results indicate that Eu 3+ -doped Bi 12 TiO 20 thin films are potential multifunctional materials which could be applied to optoelectronic thin film devices.

Eu3+-doped Ba0.7Sr0.3TiO3 thin films were prepared by a chemical solution deposition method and characterized by X-ray diffraction, field emission scanning electron microscopy, photoluminescence and dielectric measurements. The thin films were well crystallized with a pure perovskite structure. A contraction of the unit cell was observed upon incorporation of Eu3+ ions below 2 mol%, while an expansion occurred as the Eu3+ concentration was further increased above 2 mol%, indicating that Eu3+ ions with different concentrations occupied different lattice sites. Photoluminescence spectra showed two prominent transitions of Eu3+ ions at 594 nm (5D0 → 7F1) and 618 nm (5D0 → 7F2) upon excitation at 395 nm (7F0 → 5L6). There existed two quenching concentrations at 2 mol% and 4 mol% due to different lattice sites of the Eu3+ ions. We also investigated the dielectric properties of the thin films. Our study suggests that Eu3+-doped Ba0.7Sr0.3TiO3 thin films have potential applications in multifunctional optoelectronic devices.

Highly uniform resistive switching performance has been demonstrated in amorphous Bi2O3 thin films. The thin films were prepared by using a low-temperature photochemical solution deposition method simply combining chemical solution deposition and ultraviolet irradiation treatment. The Pt/Bi2O3/Pt memory devices exhibit reproducible resistive switching performance, uniform switching voltage, concentralized distribution of high and low resistance states, and good endurance. The conduction mechanisms of the thin films were discussed on the basis of analysis of current–voltage characteristics. The excellent resistive switching performance of the amorphous Bi2O3 thin films can be attributed to the reduction of –OH groups and the formation of enhanced Bi–O bonding under UV irradiation treatment, based on X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and field-emission scanning electron microscopy analysis. Our study suggests that amorphous Bi2O3 thin films have potential applications in resistive memory, and the UV irradiation treatment is an effective method for low-temperature fabrication of some amorphous oxide thin films with good resistive switching properties, especially for flexible electronic devices.

Cerium oxide (CeO2−x) film was deposited on Pt/Ti/SiO2/Si substrate by rf magnetron sputtering at room temperature. Resistive switching characteristics of these ceria films have been improved by increasing oxygen content during deposition process. Endurance and statistical analyses indicate that the operating stability of CeO2−x-based memory is highly dependent on the oxygen content. Results indicate that CeO2−x film-based RRAM devices exhibit optimum performance when fabricated at an argon/oxygen ratio of 6:24. An increase in the oxygen content introduced during CeO2−x film deposition not only stabilizes the conventional bipolar RS but also improves excellent switching uniformity such as large ON/OFF ratio (102), excellent switching device-to-device uniformity and good sweep endurance over ~ 500 repeated RS cycles. Conduction in the low-resistance state (LRS) as well as in the low bias field region in the high-resistance state (HRS) is found to be Ohmic and thus supports the conductive filament (CF) theory. In the high voltage region of HRS, space charge limited conduction (SCLC) and Schottky emission are found to be the dominant conduction mechanisms. A feasible filamentary RS mechanism based on the movement of oxygen ions/vacancies under the bias voltage has been discussed.

Eu-doped Ba1−xSrxTiO3 (x = 0, 0.2, 0.3, and 0.4) thin films with Eu-doping content of 1 mol% have been prepared on fused silica substrates by a chemical solution deposition method and characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), optical and photoluminescence measurements. XRD analysis showed that the films were well crystallized with a pure perovskite structure in the annealing temperature range from 650 to 750 °C. AFM observation indicated that the films were dense and smooth. The band-gap energies of the thin films were also investigated. The more the Sr content in the thin films, the narrower the energy gap of the thin films. Photoluminescence spectra of the thin films showed two prominent transitions of Eu3+ ions at 594 nm (5D0 → 7F1) and 618 nm (5D0 → 7F2) upon excitation at 395 nm (7F0 → 5L6). The observed changes of luminescence spectra by the decrease of the intensity ratio R, which was defined as the ratio of the integrated emission intensity of 5D0 → 7F2 transition to that of 5D0 → 7F1 transition, were associated with the increase of the inversion symmetry of Eu3+ sites when Sr content increased. Lifetime study of photoluminescence indicated that the average lifetime of the thin films was approximately 0.7 ms.

Oxygen vacancies derived resistive and magnetic switching, was demonstrated in facile solution-processed Au-Co3O4 nanocomposite thin films, in terms of optimum Au content. The metal element introduced is a unique way to create the optimum amount of oxygen vacancies in the dielectric films even in the absence of electrochemically active electrodes. Compared with pure Co3O4 based device, the RRAM device with Au additives showed bipolar switching behavior with uniform Set/Reset voltages, enhanced endurance of >103 cycles, and stable time-dependent resistances up to 104 s. The introduction of Au nanoparticles caused the oxygen vacancies based confined filament growth for optimum switching uniformity and stability. Results showed that Ohmic conduction was dominant at LRS and Schottky emission was dominated at HRS of the devices. Temperature dependence and magnetization change of various resistance states revealed that resistive and magnetic switching was due to the formation and rupture of conductive filaments of Au atoms confined oxygen vacancies with the conversion of cation valence states (Co2+ and Co3+). The present study suggests that Au-Co3O4 nanocomposite thin films have a potential for future multifunctional electromagnetic integrated device applications.

Highly c-axis oriented Bi2−xEuxVO5.5 (x = 0, 0.05, 0.10, 0.15, and 0.20) thin films were prepared on Pt(111)/Ti/SiO2/Si and fused silica substrates by using chemical solution deposition method, and characterized by X-ray diffraction, scanning electron microscopy, and optical and electrical measurements. Under 356 nm UV irradiation, a bright red photoluminescence can be observed in the thin films with x = 0.10, 0.15, and 0.20. The emission spectra included two strong peaks which originated from 5D0 → 7F1 (595 nm) and 5D0 → 7F2 (619 nm) transitions of Eu3+ ions. With increasing Eu3+-doping content x, the dielectric dispersion weakened, and dielectric loss decreased. Eu3+ doping can also decrease the leakage current of the thin films. These results demonstrate that Bi2−xEuxVO5.5 thin films are a kind of multifunctional material with potential applications in luminescent ferroelectric devices.

(200)-oriented Eu-doped cerium oxide thin films were fabricated, on fused silica substrates by a chemical solution deposition method. The thin films obtained were characterized by X-ray diffraction, field emission scanning electron microscopy, X-ray photoelectron spectroscopy, and photoluminescence measurements. Ce with valence state 4 + is confirmed to be predominant in Eu-doped CeO2 thin films. All the thin films were dense and crack-free, and showed bright orange-red emissions under ultraviolet light excitation, originated from the 5D0 → 7F1 and 5D0 → 7F2 transitions of Eu3 + ions. Structure distortions induced by Eu-doping affected the light emission of electric dipole transition 5D0 → 7F2. The strongest photoluminescent intensity was observed in the thin films with a Eu-doping content x of 0.08, indicating the existence of concentration quenching effect of photoluminescence. Lifetime study of photoluminescence indicated that the decrease of lifetime was originated from augmented pathway for deactivating excited Eu3 + ions. Our study suggests that Eu3 +-doped CeO2 thin films have potential applications in optoelectronic devices.

High-performance resistive switching Pt/TiO2/Pt memory cells were fabricated. The amorphous TiO2 active layer was prepared by using a low-temperature photochemical solution deposition method—a simple preparation process combining first chemical solution deposition of the TiO2 film layer and subsequent ultraviolet (UV) irradiation treatment. The obtained Pt/TiO2/Pt memory cells exhibited excellent resistive switching parameters, such as centralized distribution of set and reset voltages, stable current values at high and low resistance states, and long retention time. The conductive mechanisms of high resistance state and low resistance state were Schottky emission and Ohmic conduction, respectively. The X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and scanning electron microscopy characterization of the TiO2 thin films indicated that the UV irradiation treatment can lead to decomposition of the residual organics and the formation of enhanced metal-oxide bonds in the thin films. On the basis of the analysis of current–voltage characteristics and the temperature dependence of resistance, we explained the resistive switching phenomenon for Pt/TiO2/Pt devices by using the model of formation/rupture of conductive filaments. Our study also suggested that the simple photochemical solution deposition method can be used for preparing some other oxide thin films with good resistive switching properties at low processing temperature which is promising to be extended to flexible resistive switching devices.

We report on highly uniform resistive switching properties of amorphous InGaZnO (a-IGZO) thin films. The thin films were fabricated by a low temperature photochemical solution deposition method, a simple process combining chemical solution deposition and ultraviolet (UV) irradiation treatment. The a-IGZO based resistive switching devices exhibit long retention, good endurance, uniform switching voltages, and stable distribution of low and high resistance states. Electrical conduction mechanisms were also discussed on the basis of the current-voltage characteristics and their temperature dependence. The excellent resistive switching properties can be attributed to the reduction of organic- and hydrogen-based elements and the formation of enhanced metal-oxide bonding and metal-hydroxide bonding networks by hydrogen bonding due to UV irradiation, based on Fourier-transform-infrared spectroscopy, X-ray photoelectron spectroscopy, and Field emission scanning electron microscopy analysis of the thin films. This study suggests that a-IGZO thin films have potential applications in resistive random access memory and the low temperature photochemical solution deposition method can find the opportunity for further achieving system on panel applications if the a-IGZO resistive switching cells were integrated with a-IGZO thin film transistors.

The photoluminescent and dielectric properties of Eu3+/Gd3+ co-doped Bi2Ti2O7 ((Bi1.5-xGdxEu0.5)Ti2O7, BGET) pyrochlore thin films, with Gd content varying in the full range of 0 ≤ x ≤ 1.5, have been investigated. The thin films were synthesized by a conventional chemical solution deposition method. The typical intra-4f transitions of Eu3+ ions can be excited by UV radiation. The close correlation between the excitation spectra and the optical band-gap energy of the BGET thin films indicates the essential role of host sensitization in the excitation of Eu3+ luminescence. The host sensitization mechanism can be explained by a resonant energy transfer between host fundamental emission and Eu–O bond absorption. A two-step charge transfer (CT) process is proposed based on the energy band structure determined by XPS technique and spectral analysis. The maximum PLE efficiency can be obtained when the greatest overlap between host emission and Eu→O CT absorption spectra is achieved. The essential role of the host energy-band structure is confirmed by these results.

Photoluminescent (PL) and dielectric properties of La 1− x Eu x AlO 3 thin films were investigated in terms of Eu doping content ( x = 0, 0.02, 0.04, 0.06, 0.08, and 0.1) and annealing temperature. The La 1− x Eu x AlO 3 thin films were prepared by a chemical solution deposition method and characterized by X-ray diffraction, field emission scanning electron microscopy, photoluminescence and dielectric measurement. The thin films were dense with a uniform thickness, and showed bright red-orange emissions, originated from the 5 D 0 → 7 F 2 and 5 D 0 → 7 F 1 transitions of Eu 3+ ions. A stronger emission of 5 D 0 → 7 F 2 than that of 5 D 0 → 7 F 1 was attributed to Eu 3+ -doping induced structural distortion. The strongest PL intensity was observed in the thin films with a Eu 3+ -doping content x of 0.06, indicating the existence of concentration quenching effect of photoluminescence. Further lifetime study of photoluminescence indicated that the concentration quenching effect was due to the lifetime decrease of 5 D 0 → 7 F 1 and 5 D 0 → 7 F 2 transitions when Eu 3+ -doping content x increased. In addition, highly stable dielectric-bias electric field properties of Eu 3+ -doped LaAlO 3 thin films have been confirmed. Our study suggests that Eu 3+ -doped LaAlO 3 thin films have potential applications in integrated thin-film optoelectronic devices.

We report on an effective combination of good dielectric properties with bright red emission in Y 3+ /Eu 3+ -codoped ZrO 2 thin films. The thin films were deposited on fused silica and Pt/TiO 2 /SiO 2 /Si substrates using a chemical solution deposition method. The crystal structure, surface morphology, electrical and optical properties of the thin films were investigated in terms of annealing temperature, and Y 3+ /Eu 3+ doping content. The 5%Eu 2 O 3 –3%Y 2 O 3 –92%ZrO 2 thin film with 400 nm thickness annealed at 700 °C exhibits optimal photoluminescent properties and excellent electrical properties. Under excitation by 396 nm light, the thin film on fused silica substrate shows bright red emission bands centered at 593 nm and 609 nm, which can be attributed to the transitions of Eu 3+ ions. Dielectric constant and dissipation factor of the thin films at 1 kHz are 30 and 0.01, respectively, and the capacitance density is about 65.5 nf/cm 2 when the bias electric field is less than 500 kV/cm. The thin films also exhibit a low leakage current density and a high optical transmittance with a large band gap.

The color-tunable up-conversion (UC) emission and infrared photoluminescence and dielectric relaxation of Er3+/Yb3+ co-doped Bi2Ti2O7 pyrochlore thin films prepared by a chemical solution deposition method have been investigated. The pyrochlore phase structure of Bi2Ti2O7 can be stabilized by Er3+/Yb3+ co-doping. Intense color-tunable UC emission and infrared photoluminescence can be detected on the thin films excited by a 980 nm diode laser. Two UC emission bands centered at 548 and 660 nm in the spectra can be assigned to 2H11/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions of Er3+ ions, respectively. A Stokes infrared emission centered at 1530 nm is due to 4I13/2 → 4I15/2 transition of Er3+ ions. The dependence of UC emission intensity on pumping power indicates that the UC emission of the thin films is a two-photon process. The thin films also exhibit a relatively high dielectric constant and a low dissipation factor as well as a good bias voltage stability. Temperature- and frequency-dependent dielectric relaxation has been confirmed. This study suggests that Er3+/Yb3+ co-doped Bi2Ti2O7 thin films can be applied to new multifunctional photoluminescence dielectric thin-film devices.

Conducting atomic force microscopy (C-AFM) is used to observe the formation and removal of conducting filaments of Mg0.6Zn0.4O thin film at a nanoscale in order to study the mechanisms of resistive switching. C-AFM probe with Pt coating is used as a movable top electrode for measuring local I-V and for C-AFM imaging. Writing and reading of micro-bits on the resistive switching thin film are demonstrated. The local I-V behavior is similar to the macroscopic behavior of the resistive switching thin film. However, the probability for successful in situ detection of resistive switching of formation in the current experiment is only one quarter, much less than that with a macroscopic top electrode. Experimental results are explained using the filament model which illustrates the switching mechanism of the thin film. The current work would be useful for the improvement of resistive switching thin films and their applications.

Bi3.95Er0.05Ti3O12 (BErT) thin films were prepared on Pt/Ti/SiO2/Si and indium-tin-oxide (ITO)-coated glass substrates at room temperature by pulsed laser deposition. These thin films were amorphous with uniform thickness. Excellent dielectric characteristics have been confirmed. The amorphous BErT thin films deposited on the Pt/Ti/SiO2/Si and ITO-coated glass substrates exhibited almost the same dielectric constant of 52 with a low dielectric loss of less than 0.02 at 1 kHz. Meanwhile, the dielectric properties of the thin films had an excellent bias voltage stability and thermal stability. The amorphous BErT thin films might have potential applications in microelectronic and optoelectronic devices.

High-sensitive visible-light photodetectors based on α-Fe2O3 thin films on p-Si substrates with a responsivity as high as 2 × 103 A/W have been fabricated and characterized. The solution-processed devices exhibit a rapid rise/decay time (

Temperature dependence of dielectric properties of (1−x)Ba(Zr0.2Ti0.8)O3–x(Ba0.7Ca0.3)TiO3 (x=0.15, 0.30, and 0.50) (BZT–xBCT) thin films prepared by a sol–gel method has been investigated. The results show that there is a broad dielectric maximum near T m and the diffuse parameter γ is close to 2, indicating a nearly complete diffuse phase transition in BZT–xBCT thin films. The dielectric relaxor behaviors of the thin films well follow Vogel–Fulcher relation. The thin films show a high dielectric tunability up to 65 %, with a small variation in the temperature range from 248.15 to 373.15 K. This study indicates that the thin films, especially for x=0.50, are promising candidates for tunable device applications with good temperature stability.

We reported the effects of Mn doping on the structure and dielectric properties of (Ba0.835Ca0.165)(Zr0.09Ti0.91)O3 (BCZT) thin films prepared by sol–gel method. The (Ba0.835Ca0.165)Mnx(Zr0.09Ti0.91)1 − xO3 (x = 0, 0.002, 0.005, and 0.01) thin films exhibited a pure pseudo-cubic perovskite structure with random orientation. Scanning electron microscopy and atomic force microscopy observation showed that increasing Mn-doping amount caused a decrease in particle size and a cluster of the particles, while the film surface remained smooth and crack-free. Compared with the undoped film, Mn doped BCZT thin films exhibited smaller dielectric constant and lower dielectric loss. The figure of merit reached the maximum value of 16.7 with a tunability of 53.6% for the film with 0.5 mol % Mn doping, when a bias electric field of 400 kV/cm was applied at 100 kHz. The results indicated that the Mn doped BCZT thin films are suitable for tunable microwave device applications.

Bi4-xEuxTi3O12 (BEuT) ferroelectric thin films were prepared on fused silica substrates by using chemical solution deposition technique. The attained samples had a polycrystalline bismuth-layered perovskite structure, and their optical properties were composition dependent. The thin film samples had good optical transmittance above 500 nm wavelength. A blue shift of the optical absorption edge was observed in the BEuT thin films with increasing Eu3+ concentration. The optical band gaps of BEuT thin films were estimated to be about 3.57, 3.60, 3.61, 3.63, and 3.69 eV for the samples with x = 0.25, 0.40, 0.55, 0.70, and 0.85, respectively. Photoluminescence measurements showed that two emission peaks of BEuT thin films originated from two transitions of 5 D 0 → 7 F 1 (594 nm) and 5 D 0 → 7 F 2 (617 nm) had maximum intensities when Eu3+ concentration was x = 0.40. The relatively high quenching concentration of Eu3+ content was thought to be related to the layered structure of BEuT thin films. These results suggested that multifunctional BEuT thin film materials could have promising applications in optoelectronic devices.

Bi 3.95 Er 0.05 Ti 3 O 12 (BErT) thin films were prepared on flexible polyimide (PI) substrates at room temperature by pulsed laser deposition. These BErT thin films deposited under low oxygen pressures are dense, uniform, and crack-free with an amorphous structure. The highly flexible thin film with a thickness of about 160 nm deposited under 3 Pa oxygen pressure shows excellent dielectric characteristics, such as a dielectric constant of 51 and a dielectric loss of 0.025, and a maximum capacitance density of 237 nF/cm 2 at 1 kHz. When it is curved at different curvature radii (by applying external deformation), the thin film still remains superior dielectric performance. In addition, the thin film also shows good dielectric aging characteristic (or thermal stability) and high optical transparency. BErT thin films can find applications in flexible optoelectronic devices and embedded capacitors.