Potassium Niobate Thin Films Research Articles

Erratum: “Resistance degradation in sputtered sodium potassium niobate thin films and its relationship to point defects” [Appl. Phys. Lett. 121, 162902 (2022)

Erratum: “Resistance degradation in sputtered sodium potassium niobate thin films and its relationship to point defects” [Appl. Phys. Lett. <b>121</b>, 162902 (2022)

Resistance degradation in sputtered sodium potassium niobate thin films and its relationship to point defects

The reliability of piezoelectric thin films is crucial for piezoelectric micro-electromechanical system applications. The understanding of resistance degradation in piezoelectric thin films requires knowledge about point defects. Here, we show the resistance degradation mechanism in the lead-free alternative sodium potassium niobate (KNN) thin films and the relationship to point defects in both field-up and field-down polarities. The conduction mechanism of KNN thin films is found to be Schottky-limited. Furthermore, a reduction in Schottky barrier height accompanies the resistance degradation resulting from interfacial accumulation of additional charged defects. We use thermally stimulated depolarization current measurements and charge-based deep level transient spectroscopy to characterize the defects in KNN thin films. Our results show that oxygen vacancies accumulate at the interface in field-up polarity, and multiple defects accumulate in field-down polarity, potentially oxygen vacancies and holes trapped by potassium vacancies. We use wafer deposition variation to create samples with different film properties. Measurement results from these samples correlate resistance degradation with the defect concentration. We find the natural logarithm of leakage current to be linearly proportional to the defect concentration to the power of 0.25. The demonstrated analysis provides a precise and meaningful process assessment for optimizing KNN thin films.

Synthesis, structural and optical properties of $$\hbox {K}_{0.5}\hbox {Na}_{0.5}\hbox {NbO}_{3}$$K0.5Na0.5NbO3 thin films prepared by spin coating route

In this paper, lead-free sodium potassium niobate thin films have been prepared by using a chemical solution deposition-based spin coating route. The effect of different anealing temperatures on structural and optical properties has been studied. The phase analysis of thin films was investigated by using X-ray diffraction analysis. The microstructure and surface roughnes of thin films were studied by using atomic force microscopy. Raman spectroscopy analysis revealed that increase in annealing temperature gives rise to better crystallinity and perovskite phase. Optical parameter of thin films has been studied by using reflectance spectroscopy at room temperature. Photoluminescence analysis has been conducted by using an exciting wavelength of 300 nm at room temperature.

Optimization of Sodium Potassium Niobate Thin Films with Different Deposition Layers

Sodium Potassium Niobate, KNN with different deposition layers on Si substrate was successfully prepared by sol-gel spin coating and subsequently annealed at 650°C for 10 min. Several deposition layers of KNN were systematically studied with different characterizations. The KNN thin films with five deposition layers showed a good result in terms of its homogeneity and uniformity of thickness that was measured to be around 280 nm. Further study on the surface roughness was obtained by AFM and its value of around 1.698 nm was recorded from the scanned area of 1 µm × 1 µm of thin films. It was also reported that the NbO6 octahedral vibrational modes of υ6, υ5, υ4, υ2, υ1, υ3, υ1+υ5 was detected in a wide range of 200 cm−1 to 900 cm−1, shown by Raman analysis. The elemental composition was also studied and the results were confirmed with deconvolution of XRF spectrum.

Optimizing the processing conditions of sodium potassium niobate thin films prepared by sol-gel spin coating technique

In the present study, potassium sodium niobate (KNN) thin films were synthesized by means of sol-gel spin coating method. Along with the synthesis, the effects of annealing temperature and various number of coating layers on both the structural and electrical properties were looked into. The results of the study revealed that the annealing temperature had a great impact on the properties of KNN. In addition, the XRD diffractograms and texture coefficient of the synthesized films confirmed that a highly oriented orthorhombic perovskite structure was obtained at 650°C, whereas at a relatively higher temperature (700°C), a spurious phase of K4Nb6O17 was evolved. In addition, the growth of KNN at 650°C exhibited a reasonable resistivity value for piezoelectric applications. Looking into the results, it was discovered that the KNN thin films also found to be dependent on a number of coating layers. Field emission scanning electron microscopy (FESEM) showed that KNN with five coating layers was highly crystalline, cracks-free, and had significantly more homogenous surface morphology and the size of grains being uniform, the resistivity of KNN thin films improved with the increasing number of coating layers i.e., up to five.

Lead potassium niobate thin films grown by Pulsed Laser Deposition

By pulsed laser deposition, lead potassium niobate Pb2KNb5O15 was grown on (001) oriented Gd3Ga5O12 substrate using a platinum buffer layer. The PKN thin films were characterized by X-Ray diffraction and Scanning Electron Microscopy (SEM). The dependence of their structural properties as a function of the deposition parameters was studied. It has been found that the out of plane orientation of PKN film depends on the oxygen pressure used during the growth. Indeed, PKN thin film is oriented [001] for low pressure and is oriented [530] for high pressure. For these two orientations, the crystalline quality of PKN film was determined using omega scans.

Precursor Homogeneity and Crystallization Effects in Chemical Solution Deposition‐Derived Alkaline Niobate Thin Films

Chemical solution deposition‐derived potassium niobate and sodium niobate thin films have been prepared under protective atmosphere using an alkoxide approach. A profound dependency of the quality and homogeneity of the resulting thin films on the preparation of the alkaline precursor has been found. In addition to this, an additional increase in microstructure homogeneity for the significantly more sensitive potassium niobate system is obtainable if the precursor solution is further stabilized by acetylacetone although ambient humidity is already strongly suppressed. The observed behavior is attributed to the stabilization of the heterometallic complex in the precursor solution until film deposition commenced. Further on, the crystallization pathway of the respective alkaline niobate thin films has been evaluated and indication of crystallization through a metastable phase has been provided which seems to play a key role in orientation control. Finally, the temperature dependency of the lattice parameter spacing for potassium niobate and sodium niobate thin films has been presented and evidence of a strong substrate‐induced lattice deformation has been given.

Preparation and Properties of (110) Oriented Lead-Free Sodium Potassium Niobate Thin Films by MOD Method

Ferroelectric (K 0.5 Na 0.5 ) NbO3 (KNN) thin films have been successfully prepared by a metallorganic compound decomposition (MOD) method. The stable KNN precursor solutions were prepared from commercial sodium acetate and potassium acetate and niobium ethoxide synthesized in our laboratory. Uniform and dense KNN thin films were obtained using spin-coating and rapid thermal treatment at 500 ∼ 650°C. KNN thin films possess pure perovskite phase and exhibit (110) preferential orientation. The dielectric constant and dielectric loss of KNN thin films annealed at 600°C are about 219 and 0.07 at 1 kHz, respectively.

Fabrication and Evaluation of Highly (110)-Oriented Potassium Niobate Thin Films Prepared by RF-Magnetron Sputtering

Epitaxial (110)-oriented KNbO3 thin films were deposited on a (100) MgO substrate by RF-magnetron sputtering. To clarify the sputtering conditions necessary for obtaining a highly oriented KNbO3 thin film, the relationships among the degree of orientation, the composition ratio of K/Nb, and the lattice plane spacing were evaluated for KNbO3 thin films deposited using several types of target. In the deposition method using dual targets of KNbO3 and K2CO3, a higher orientation and a larger K/Nb ratio were incompatible. In single-target sputtering with a mixture target of KNbO3:K2CO3, as the substrate temperature decreased, although the K/Nb ratio increased and the (220)-plane spacing approached that of orthorhombic bulk KNbO3, the orientation deteriorated. Using a single K-rich target, K5NbOx, containing no CO2, a highly (110)-oriented KNbO3 thin film with a K/Nb ratio of 0.40 and a (220)-plane spacing near that of orthorhombic bulk KNbO3 was obtained by increasing the RF power applied to the O2-radical source. Moreover, the displacement current in the oriented KNbO3 thin film with a K/Nb ratio of 0.40 was observed when an electric field was applied to the interdigital transducer formed on the thin film. This indicates the existence of spontaneous polarization in the oriented KNbO3 thin film.

Pulsed laser deposited KNbO3 thin films for applications in high frequency range

Potassium niobate thin films were grown by pulsed laser deposition on various substrates. Influence of deposition conditions on film characteristics was studied. Structural investigation evidenced that single phase polycrystalline randomly oriented films were grown on sintered alumina whereas epitaxial films were grown on (100)SrTiO3 and (100)MgO substrates. The microstructure was highly controlled by the structural characteristics. Interdigited capacitors built from KNbO3 films on two different substrates (alumina and MgO) showed the strong influence of the structural characteristics on the dielectric behavior. The variation of the equivalent capacitance measured on the interdigital capacitor on MgO was 6.4% at 2.5 GHz while it was 1.5% on alumina, in both cases for a moderate applied field of ∼15 kV cm−1. The results show the potentiality of these ferroelectric materials for use in frequency agile microwave electronics.

Preparation of KNbO3 Thin Film by Self-Assembly of Perovskite Nanosheet

Potassium niobate thin films with a perovskite structure were prepared by a new nanosheet self-assembly technique on a SiO2 glass substrate. A homogeneous nanosheet precursor solution was obtained by dissolving layered perovskite K2NbO3F in water at room temperature without any modifier. It was confirmed by X-ray diffraction that the films have a pseudocubic perovskite structure and show continuous transformation from layered perovskite K2NbO3F to perovskite KNbO3. The ultraviolet-visible absorption spectra of the films showed an increase in absorbance with the thickness of thin films, suggesting the growth of a self-assembled multilayer consisting of perovskite nanosheets and K+ ions.

Optical properties of potassium niobate thin films prepared by the polymeric precursor method

Thin films of potassium niobate were deposited on MgO (100) substrates by the polymeric precursor method and annealing in static air at 600 °C for 20 h. The obtained films were characterized by X-ray diffraction, atomic force microscopy (AFM) and the prism coupling method. The phi-scan diffraction evidenced the growth of the films with fourfold symmetry. AFM study shows that the films are homogeneous, dense and present a smooth surface. The refractive index and optical losses were strongly influenced by the degree of crystallinity.

Potassium niobate thin films prepared through polymeric precursor method

Thin films of potassium niobate were deposited on (100) Si substrates by the polymeric precursor method (Pechini method). Annealing in static air was performed at 600° C for 20 h. The obtained films were characterized by X-ray diffraction and atomic force microscopy (AFM). Electrical characterization of the films pointed to ferroelectricity via hysteresis loop. The dielectric constant, dissipation factor and resistance were measured in frequency region from 10 Hz to 10 MHz. At 1 MHz, the dielectric constant was 158 and the dissipation factor was 0.11.

Potassium niobate thin films prepared through polymeric precursor method

Thin films of potassium niobate were deposited on (100) Si substrates by the polymeric precursor method (Pechini method). Annealing in static air was performed at 600° C for 20 h. The obtained films were characterized by X-ray diffraction and atomic force microscopy (AFM). Electrical characterization of the films pointed to ferroelectricity via hysteresis loop. The dielectric constant, dissipation factor and resistance were measured in frequency region from 10 Hz to 10 MHz. At 1 MHz, the dielectric constant was 158 and the dissipation factor was 0.11.

電子ビーム蒸着法によるニオブ酸カリウム薄膜の作製

電子ビーム蒸着法によるニオブ酸カリウム薄膜の作製

RF-Magnetron Sputtered Au/(Na,K)NbO3/SiO2/Si MFIS-diode Structures

AbstractRecently we proposed ferroelectric sodium potassium niobate (Na0.5K0.5NbO3, NKN) thin films to be a candidate for applications in nonvolatile memories and electrically tunable devices [1-5]. In this paper we report on processing and characterization of metal-ferroelectric-insulatorsemiconductor (MFIS) diode structures based on RF-magnetron sputtered NKN films. 0.7 μm thick NKN films have been deposited at 650 °C on the thermally grown 47 nm thick SiO2 layer on Si(001) wafers. Stoichiometric Na0.5K0.5NbO3 ceramic target was sputtered in an O2-Ar atmosphere with a total pressure of 5 mTorr. Grown films were analyzed as deposited as well as after an oxygen annealing at 600 °C for 30 minutes. The NKN films exhibit a strong (001) preferential orientation, which was appreciably improved after the oxygen annealing. A leakage current density of 2.3 nA/cm2 at an electric field of 400 kV/cm, and a memory window of 7.2 V was measured for Au/NKN/SiO2(47nm)/Si(001) diode structures at the programmable voltage of 40 V. I-V measurements were performed in the time domain to distinguish between the relaxation of polarization, “true” leakage current, and the degradation of the resistance in ferroelectric NKN film.

Electro-optic effect in a nano-crystals doped glass

Nano-composites, including amorphous inorganic matrixes and organically modified glass matrixes doped with nano-crystallites of ferroelectrics, were studied. Several interesting phenomena were experimentally observed. Nano-domains having a dimension of 10 nm were observed in epitaxially grown potassium niobate thin films. Some ferroelectric-like properties were measured in amorphous lead zirconate titanate and barium titanate thin films containing 3 to 5 nm-size particles those have an ordered structure. A large electro-optical (Pockels') effect, which exists only in those materials with an anisotropy structure, was detected in an organically modified titanium dioxide glass doped with nano-crystallites of antimony sulphoiodide.

スパッタ法によるニオブ酸カリウム薄膜の配向性制御

Potassium niobate thin films were prepared on amorphous (SrO-SiO2) layer/Si wafer by means of RF magnetron sputtering using a (KNbO3+ K2CO3) mixed powder target. Amorphous (SrO-SiO2) layers under the potassium niobate thin films were prepared by means of RF magnetron sputtering using a (SrCO3 + SiO2) mixed powder target. Crystallization and orientation of the potassium niobate thin films depended on (KNbO3 + K2CO3) target compositions and amorphous (SrO-SiO2) layer target compositions under the potassium niobate thin films. The orientation of potassium niobate thin films could be controlled by a favorable choice of (KNbO3 + K2CO3) target compositions and amorphous (SrO-SiO2) layer target compositions, and produced highly [110] oriented perovskite type potassium niobate thin films.

Electric field induced domain rearrangement in potassium niobate thin films studied by in situ second harmonic generation measurements

We report a sensitive technique to study domain rearrangement in ferroelectric thin films using in situ second harmonic generation (SHG) measurements. The following film system on a MgO substrate was studied: KNbO3(110)‖120 Å SrTiO3(100)‖MgO(100). From x-ray diffraction, four possible domain variants in the film growth plane were determined to be KNbO3[11̄0]‖SrTiO3 and MgO[001], [001̄], [010], or [01̄0] denoted as variants X+, X−, Y+ and Y−, with area fractions AX+, AX−, AY+ and AY−, respectively, in the film growth plane. The SHG signal (532 nm) from the films generated by a transmitted fundamental beam of 1064 nm was measured and theoretically correlated to the area fractions of different domain variants in the film. The magnitude and signs of net area fractions (AX+−AX−) and (AY+−AY−) were determined as a function of external field applied along the MgO〈001〉 direction in the film growth plane. No remnant poling was observed in KNbO3 films after application and removal of external fields up to 10 kV/cm at room temperature. We propose mechanisms to correlate this behavior to the pinning of domain wall motion by low angle grain boundaries in KNbO3.

Heteroepitaxial growth of KNbO3 single-crystal films on SrTiO3 by metalorganic chemical vapor deposition

Potassium niobate (KNbO3) thin films have been deposited on silicon (Si) and strontium titanate (SrTiO3) substrates by metalorganic chemical vapor deposition. Stoichiometric KNbO3 films were obtained by adjusting the partial pressure of precursors. The crystallinity was examined by x-ray diffraction and reflection high-energy electron diffraction. Single-crystal (010) KNbO3 films with smooth surface were heteroepitaxially grown on (110)SrTiO3 substrate at 850 °C.