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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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

We report high dielectric tunabilities of (1 − x)Ba(Zr 0.2 Ti 0.8 )O 3 − x(Ba 0.7 Ca 0.3 )TiO 3 (BZT–xBCT) (x = 0.15, 0.30, 0.40, 0.45, 0.50, and 0.55) thin films prepared by a sol–gel method. The films show a pure perovskite structure with random orientation. They have moderate dielectric constant ranging from 350 to 500 and low dielectric loss near 3.0% at 1 kHz with 0 V bias at room temperature. The dielectric tunability of the BZT–0.55BCT thin films is up to 65% at 400 kV/cm and 100 kHz. The films exhibit a high optical transmission in the range of 420 nm–1500 nm. Their optical band gap energies are about 3.90 eV.

Structural, photoluminescence, dielectric, and ferroelectric properties of lead-free perovskite Pr3+-doped xK0.5Bi0.5TiO3–(1−x)Na0.5Bi0.5TiO3 (x = 0–1.0) thin films were studied. The thin films were prepared by a chemical solution deposition method combined with a rapid thermal annealing process at 700°C. We observed that the thin film with x = 0.15, corresponding to the morphotropic phase boundary in the solid solution ceramics or single crystal bulk counterparts, showed a very large dielectric constant and a high remanent polarization, as well as a strong red emission at 611 nm assigned to 1D23H4 transitions of the Pr3+ ions. In addition, this study also indicates that the morphotropic phase boundary in xK0.5Bi0.5TiO3–(1−x)Na0.5Bi0.5TiO3 thin films might be probed by photoluminescence probe of Pr3+ ions because the photoluminescence of Pr3+ ions is very sensitive to the phase structure changes.

Strong upconversion photoluminescence and large ferroelectric polarization were observed for the first time in layered structure Er3+–Yb3+–W6+ triply substituted bismuth titanate thin films. The thin films were prepared on fused silica and Pt(111)/Ti/SiO2/Si substrates by chemical solution deposition. Two green emission bands and a red one were observed in the upconversion photoluminescence spectra for all the films pumped by a 980 nm laser diode, which correspond to 2H11/2, 4S3/2, and 4F9/2 to 4I15/2 transitions of Er3+ ions, respectively. A two-photon energy-transfer process was confirmed by the power dependence of emission intensity. Compared with that of Er3+–Yb3+-substituted bismuth titanate thin films, the improved photoluminescence is related to the reduced defects such as oxygen vacancies due to B-site (Ti4+) substitution by W6+ ions, while the large ferroelectric remnant polarization can be attributed to the increased structure distortion and the reduced oxygen vacancies due to cosubstitution of A-site (Bi3+) and B-site (Ti4+) by Er3+, Yb3+, and W6+ ions, respectively. The combination of the strong upconversion photoluminescence and the good ferroelectric properties in the thin films would open the possibility of realizing novel multifunctional optoelectronic integration device applications.

We report on growth of 25%Bi(Ni0.5Ti0.5)O3–75%PbTiO3 (25BNiT–PT) solid solution thin films and good electrical properties such as high remanent polarization, high dielectric constant, and low dissipation factor. The thin films prepared on Pt/TiO2/SiO2/Si substrates by pulsed laser deposition were well crystallized with a phase-pure perovskite structure. Well-saturated P–E hysteresis loops were observed with a much larger remanent polarization than that of corresponding ceramic counterparts reported before in literature. The remanent polarization Pr and coercive field Ec were 40.9 μC/cm2 and 117 kV/cm, respectively, for the thin films annealed at 650°C. The thin films had a high dielectric constant of about 400–500 and a low dissipation factor of 0.03 at a frequency of 1 kHz. The good polarization characteristics of the thin films are very significant for high-temperature ferroelectric device applications.

Pb0.5Sr0.5TiO3 (PST50) thin films with different Cr doping amounts were prepared on LaNiO3 coated silicon substrates by a chemical solution deposition method. Their dielectric and ferroelectric properties were studied at room temperature. The dielectric constant decreased from 417 to 207 (at 1 kHz), as the Cr content increased from 0 to 8%. When the content of Cr was 3%, the tunability and the figure of merit factor reached maximal values of 61.3% and 21.4, respectively. The remnant polarization of the Cr-doped PST thin films decreased from 7.4 μC/cm2 to 2.0 μC/cm2, as the Cr content increased from 0 to 5%.

(Bi3.6Eu0.4)Ti3O12 (BEuT) thin films with different Li+ doping contents were prepared on fused silica and Pt/Ti/SiO2/Si substrates by chemical solution deposition, and the effects of Li+ doping contents on the photoluminescence and ferroelectric properties of the thin films were investigated in detail. The results showed that an appropriate amount of Li+ doping could effectively improve emission intensities for two characteristic Eu3+ emission transitions of 5D0→7F1 (594 nm) and 5D0→7F2 (617 nm) compared with BEuT thin films without Li doping. This photoluminescence improvement can be attributed to the dual roles of Li+ ions, one of which is that Li ions can act as co-activators which are helpful to the energy transfer from the host to the Eu3+ ions, leading to a higher quantum yield; the other is that Li ion doping can induce local distortion of crystal field surrounding the Eu3+ activator because Bi3+ and Li+ ions have different ionic radii. In addition, the Li+-doped BEuT thin films had larger remanent polarization than BEuT thin films without Li doping prepared under the same experimental conditions. These results suggest that Li+ doping is an effective way to improve photoluminescence and ferroelectric properties of the (Bi,Eu)4Ti3O12 thin films.

Pr3+/La3+-codoped Bi4Ti3O12 (BPLT) ferroelectric thin films were prepared on fused silica and Pt/TiO2/SiO2/Si substrates by the chemical solution deposition method, and their photoluminescence and electrical properties were investigated. Different from Pr-doped ATiO3 (A=Sr, Ca) titanate thin films showing a red emission with the highest emission peak at 612 nm, BPLT thin films exhibited a strong blue–green emission at 493 nm. This can be ascribed to their difference of host lattice between Pr-doped titanate with a simple perovskite structure and BPLT with a bismuth-layered perovskite structure and/or the difference of site symmetry of Pr ions. It was also found that the luminescent intensity was enhanced by the incorporation of La3+ ions into Pr3+-doped Bi4Ti3O12 (BPT) thin films. Meanwhile, the introduction of La3+ also greatly enhanced the ferroelectric properties of the BPT thin films. The dual enhancement of photoluminescence and ferroelectric polarization can be attributed to crystallization improvement of the BPLT thin films. It is expected that BPLT thin films can find potential applications in new multifunctional photoluminescence ferroelectric thin-film devices.

We report on reversible bipolar resistance switching effects in multiferroic BiFeO3 thin films without electroforming. The BiFeO3 thin films with (110) preferential orientation were prepared on LaNiO3-electrodized Si substrates with a Pt/BiFeO3/LaNiO3 device configuration. The resistance ratio of high resistance state (HRS) to low resistance state (LRS) of the devices was as high as three orders of magnitude. The dominant conduction mechanisms of LRS and HRS were dominated by ohmic behavior and trap-controlled space charge limited current, respectively. The resistance switching mechanism of the devices was discussed using a modified Schottky-like barrier model taking into account the movement of oxygen vacancies.

The coexistence of unipolar and bipolar resistive switching (RS) behaviors of Ag-nanoparticles (Ag-NPs) doped NiFe2O4 (NFO) based memory devices was investigated. The switching voltages of required operations in the unipolar mode were smaller than those in the bipolar mode, while ON/OFF resistance levels of both modes were identical. Ag-NPs doped NFO based devices could switch between the unipolar and bipolar modes just by preferring the polarity of RESET voltage. Besides, the necessity of identical compliance current during the SET process of unipolar and bipolar modes provided an additional advantage of simplicity in device operation. Performance characteristics and cycle-to-cycle uniformity (>103 cycles) in unipolar operation were considerably better than those in bipolar mode (>102 cycles) at 25 °C. Moreover, good endurance (>600 cycles) at 200 °C was observed in unipolar mode and excellent nondestructive retention characteristics were obtained on memory cells at 125 °C and 200 °C. On the basis of tem...

xBiAlO 3 -(1-x)PbTiO 3 (xBA-PT, x = 0-0.1) solid solution thin films were prepared on indium tin oxide-coated glass substrates using a chemical solution deposition method at an annealing temperature of 600"C, and the effects of bismuth aluminate (BA) content on the structural, dielectric, and ferroelectric properties of the thin films were investigated. Formation of the solid solution thin films has been confirmed by XRD and Raman analysis. The thin films crystallize in the perovskite structure without the formation of any detectable secondary phase. With increasing BA content, the thin films transform the tetragonal phase into a pseudocubic phase. When x is 0.08, the thin film exhibits high dielectric constant and large remanent polarization (2P r ) values, which are 384 and 58 μC/cm 2 , respectively. In addition, the dielectric loss and the leakage current density were considerably reduced by adding BA to the thin films.

Au-doped Bi3.6Eu0.4Ti3O12 (BET) thin films were prepared on fused silica and Pt/Ti/SiO2/Si substrates by a chemical solution deposition method. The existence of Au nanoparticles (NPs) has been confirmed by X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscope analysis. Enhanced photoluminescence (PL) of Eu3+ ions was obtained in a wide range of Au doping level. Role of the Au NPs in the PL enhancement was investigated by means of optical absorption, excitation, and emission spectra, as well as decay lifetime measurements. The results indicated that the intra-4f transition of Eu3+ ions can be intensively activated by the coupling of the charge transfer band of BET with the 5D0 state of Eu3+ ions. The influence of Au NPs on the PL properties of Eu3+ ions in the present thin films was attributed to the band bending at Au/BET interface and the localized surface plasma resonance absorption of Au NPs in the visible light region. The dielectric and ferroelectric properties of Au-doped BET thin films were investigated as well.

We report reproducible resistive switching performance and relevant physical mechanism of sandwiched Pt/CoFe2O4/Pt structures in which the CoFe2O4 thin films were fabricated by a chemical solution deposition method. Uniform switching voltages, good endurance, and long retention have been demonstrated in the Pt/CoFe2O4/Pt memory cells. On the basis of the analysis of current-voltage characteristic and its temperature dependence, we suggest that the carriers transport through the conducting filaments in low resistance state with Ohmic conduction behavior, and the Schottky emission and Poole-Frenkel emission dominate the conduction mechanism in high resistance state. From resistance-temperature dependence of resistance states, we believe that the physical origin of the resistive switching refers to the formation and rupture of the oxygen vacancies related filaments. The nanostructured CoFe2O4 thin films can find applications in resistive random access memory.

We report uniform bipolar resistive switching characteristic with self-compliance effect of Pt/TiO2/p-Si devices in which TiO2 thin films were prepared directly on p-Si substrates by chemical solution deposition method. The resistive switching parameters of the Pt/TiO2/p-Si cell obtained, such as distribution of threshold voltages, retention time, as well as resistance variation of high resistance state (HRS) and low resistance state (LRS), were investigated, and the conduction mechanisms of HRS and LRS were analyzed. The conductive mechanism at LRS and low voltage region of HRS was dominated by Ohmic law. At the high voltage region of HRS, the conductive mechanism followed the space charge limited current theory. The resistive switching phenomenon can be explained by electron trapping and de-trapping process, in which the defects (most probably oxygen vacancies) act as electron traps. Our study suggests that using p-type silicon as bottom electrode can provide a simple method for fabricating a resistive random access memory with self-compliance function. In addition, the Pt/TiO2/p-Si configuration is compatible with complementary metal oxide semiconductor process.

We report on a new route to greatly enhance the photoluminescence of Eu3+ doped ferroelectric polycrystalline oxide thin films: surface modification of grains with silver nanoclusters (NCs). The Ag doped Bi3.6Eu0.4Ti3O12 (BET) thin films were prepared by a chemical solution deposition method. According to the XRD, TEM and XPS analysis, partially oxidated Ag NCs have been formed on the surfaces of the BET grains. A greatly enhanced photoluminescence was obtained in a wide range of Ag doping level. Role of the Ag NCs in the photoluminescence enhancement was investigated by means of absorption, emission and excitation spectra, as well as decay lifetime measurement. The results indicate that the intra-4f transition of Eu3+ can be intensively activated by the coupling of the charge transfer band of BET with the 5D0 state of Eu3+ ions, and the enhancement of Eu3+ ions emission in the present thin films was attributed to the surface modification of BET crystalline grains by Ag NCs. In addition, the influences of Ag NCs on the dielectric and ferroelectric properties of these materials were discussed as well.

We reported on W-doping induced antiferroelectric to ferroelectric phase transition in PbZrO3 (PZO) thin films prepared on Pt/Ti/SiO2/Si substrates by a chemical solution deposition method. The phase transition has been studied through polarization-electric field hysteresis loop, capacitance-voltage characteristic, and Raman scattering measurements. Suitable amount W-doping increased the saturated polarization of antiferroelectric W-doped PZO thin films, whereas the ferroelectric W-doped PZO thin films exhibited higher dielectric constant with a high dielectric-bias voltage tunability of about 70%. With increasing W-doping content, the orientation of the thin films changed from preferred (111)Cubic to complete (100)Cubic, due to W-doping-induced lattice distortion, meanwhile the Curie temperature dropped, and dielectric maximum broadened. Our study demonstrates that W-doping is an effective way to tailor the electrical properties of PZO thin films through the induced antiferroelectric-ferroelectric phase transition.

The up-conversion (UC) photoluminescence and ferroelectric properties of Bi4−xErxTi3O12 (BErT) thin films were studied in terms of annealing temperature and Er3+ doping concentration. The thin films were prepared by chemical solution deposition method. There are two green emission bands centered at 527 and 548 nm, and a red emission band centered at 663 nm in UC luminescence spectra measured under a 980 nm laser excitation at room temperature, which correspond to the radiative transitions from 2H11/2, 4S3/2, and 4F9/2 to 4I15/2, respectively. The quenching concentration of Er3+ ions for green emission was as high as 20 mol % for Bi3.2Er0.8Ti3O12 thin films. The large Er3+ quenching concentration and efficient energy transfer between two neighboring Er3+ ions result in the improved UC emission. The dependence of UC emission intensity on pumping power indicated a two-photon UC emission process in the thin films. The combination of UC emission and ferroelectricity was realized in the capacitors of Pt/Bi3.25E...

A strong blue up-conversion photoluminescence and a greatly enhanced ferroelectric polarization were observed in Tm 3+ -Yb 3+ -W 6+ -triply-doped bismuth titanate thin films. The thin films were prepared on fused silica and Pt/Ti/SiO 2 /Si (111) substrates by chemical solution deposition and annealed at 700°C. The strong blue up-conversion emission centered at 478 nm, corresponding to 1 G 4 → 3H6 transitions of Tm 3+ ions, was confirmed to be a three-photon energy-transfer process by pumping laser power dependence of emission intensity. The enhanced ferroelectricity with a high remnant polarization (Pr) value of about 32 μC/cm 2 is attributed to the weakened domain pinning due to the reduced oxygen vacancies by W 6+ substitution for Ti 4+ ions. The thin films combining the strong blue up-conversion photoluminescence with the good ferroelectric properties would provide possibility of realizing novel multifunctional optoelectronic integration device applications.