SBT Thin Films Research Articles

Improved piezoelectric performance via orientation regulation in novel BNT-BT-SBT thin film

Lead-free piezoelectric thin films are urgently needed in microelectronic and microelectromechanical systems. In this work, (1-x)(0.94Bi0.5Na0.5TiO3-0.06BaTiO3)-x(Sr0.7Bi0.2□0.1)TiO3 (abbreviated as BNT-BT-xSBT) piezoelectric thin films were prepared successfully. The optimal piezoelectric performance can be achieved when x = 0.02 at morphotropic phase boundary (MPB). Further, to explore the impacts of orientation control on the properties of thin films, (100), (110), and (111)-oriented BNT-BT-0.02SBT thin films were prepared on Nb-SrTiO3 single crystal. The (110) preferred orientation thin film can achieve a high inverse piezoelectric coefficient (d33*) of 170 pm/V, which has a great improvement contrasted with non-oriented films. From the perspective of engineering domain configuration, the high d33* of (110)-oriented thin film can be characterized that the ferroelectric domain can get a complete flip in the direction of non-easily polarized axes. In short, orientation regulation is of great importance in improving the piezoelectric properties of thin films and has important applications in microelectronic sensing.

Macrodomain structure formed in (Sr0.7Bi0.2□0.1)TiO3-modified Bi0.5Na0.4 K0.1TiO3 thin film

The performance of piezoelectric materials can often be improved near the morphotropic phase boundary (MPB), in this work, we introduced (Sr0.7Bi0.2□0.1)TiO3 into Bi0.5Na0.4 K0·1TiO3 thin films to regulate their properties. (1-x)BNKT–xSBT (x = 0.05, 0.10, 0.20, 0.30) lead free piezoelectric thin films were deposited on Pt(111)/Ti/SiO2/Si substrates by the sol–gel method, which was designed by the principle of optimal tolerance factor. The XRD and Raman spectra were investigated in detail to prove the formation of MPB in BNKT–0.10SBT thin films, and the most direct evidence is the movement of TF-R near room temperature. The rarest is the formation of macrodomain structure at MPB, which is especially beneficial to the improvement of piezoelectric property. There is no doubt that the most excellent ferroelectric (Pm = 59 μC cm−2, Pr = 13 μC cm−2 @700 kV/cm) and piezoelectric properties (72% higher than the initial component) can be obtained from the BNKT–0.10SBT thin film. The MPB formed when tolerance factor was adjusted to 0.9816, meanwhile macrodomain structure was observed under electric field, so that the ferroelectric and piezoelectric properties have been significantly improved at this point. This study provides a useful guide to research MPB in BNT-based thin films in order to improve ferroelectric and piezoelectric performances.

Enhanced energy storage capability of (1-x)Na0.5Bi0.5TiO3-xSr0.7Bi0.2TiO3 free-lead relaxor ferroelectric thin films

In today's global traditional energy shortage environment, developing renewable and environmental-friendly energy has become a trend. In this work, the (1-x)Na0.5Bi0.5TiO3-xSr0.7Bi0.2TiO3 ((1-x)NBT-xSBT, x=0.2, 0.3, 0.4, and 0.5) relaxor ferroelectric thin films are grown on Pt/Si/SiO2 substrate via the sol-gel method. The structure, dielectric properties, energy density, thermal stability, frequency stability, and fatigue endurance for long-term stability of the (1-x)NBT-xSBT thin films are studied systematically. The experimental results demonstrate that the NBT-0.5SBT thin film exhibits an excellent discharge energy density (Wrec ~35.014 J/cm3) and efficiency (η ~73.8%) under 3200 kV/cm at room temperature (RT). More importantly, the corresponding thin film display superior the thermal stability (20–140 °C), frequency stability (102–104 Hz), and fatigue endurance for long-term stability (104 st). Therefore, this contribution will provide a convenient and efficient way for preparing high-performance dielectric capacitors for application in power pulse systems.

Effects of vanadium substitution on the electrical performance of amorphous SrBi2Ta2O9 thin-film capacitors

The effects of vanadium substitution on the dielectric properties of amorphous SrBi 2 Ta 2 O 9 (SBT) thin films have been investigated. Vanadium substitution at the Ta site exists in the V 3+ valence state and acts as an acceptor, reducing the number of intrinsic oxygen vacancies and the leakage current of the amorphous SBT thin films. Furthermore, the dielectric properties are also improved. The leakage current values of the 92 and 31 nm thick SBTV thin-film capacitors were 8.8 nA cm −2 and 0.62 μA cm −2 at 1 V, respectively.

Enhancement of Memory Retention Time of Metal/Ferroelectric/Insulator/Semiconductor Structure by Using Fast Annealing and Nitrogen Radical Irradiation

Fast annealing was used to improve the electronic properties of ferroelectric and buffer layers in Pt/SrBi2Ta2O9(SBT)/SiO2/n-Si metal-ferroelectric-insulator-semiconductor (MFIS) structures. Damage of the SiO2 layer due to SBT constituent diffusion was reduced significantly as annealing time at high temperature of the ferroelectric SBT can be reduced from 1 − 2 hours to few minutes. Leakage currents through both the SiO2 buffer and the SBT ferroelectric layers were decreased in the sample prepared by using fast annealing. The C-V and the I-V characteristics also show electronic improvement at the interface and reduced of thermal diffusion of constituent elements. It is shown by SEM and atomic force microscopy(AFM) images revealed that the SBT thin film with fast annealing had a gets better surface morphology. The retention time of a capacitor with a MFIS structure in the ON and the OFF states was improved, and the maximum is retention time was longer than 23 days.

Characteristics of SrTiO3 Insulated Layer in SBT Ferroelectric Thin Films

Low temperature processing of SBT thin films with SrTiO 3 (STO) seeded layer deposited onto Ir/SiO 2 /Si (MIM structure) and CeO 2 /Si (MFIS structure) substrate using MOD method was investigated. The Sr 0.8 Bi 2.6 Ta 2 O 9 + x (SBT) thin films with a STO seeded layer on MIM structure showed prefer (115) orientation, well crystalline and lower crystal temperature than those without STO seeded layer. The SBT thin films with STO seeded layer on MFIS structure also showed prefer (115), (006) orientation and well crystalline SBT phase annealed at 700°C. The seeded layer, STO, effectively protected the evaporation of Bi through the Pt top electrode and diffusion of Bi into the Ir bottom electrode on MIM structure. It also can improve the crystallization of SBT phase, grain growth and lower crystallized temperature of SBT thin film. The memory window and leakage current densities of SBT thin films with STO seeded layers are improved significantly in comparison with those films without the STO seeded layer. In the MIM structure, the SBT thin film with STO seeded layer can decrease the leakage current density to 10−9 A/cm 2 at 100 kV/cm. In the MFIS structure, the SBT thin film with STO seeded layer also can improve the memory window and lead to lower leakage current at low voltage.

Highly a-oriented SrBi 2Ta 2O 9 thin film on (111) Pt/TiO 2/SiO 2/Si substrate by eclipse pulsed laser deposition

A highly a-oriented SrBi 2Ta 2O 9 thin film with a polycrystalline structure was deposited on a preferentially oriented (111) Pt/TiO 2/SiO 2/Si substrate by eclipse pulsed laser deposition (PLD) method. The SrBi 2Ta 2O 9 thin film exhibited flat and smooth surface with the surface roughness of about 0.5 nm resulting from reducing particulates generated by on-axis PLD. The SrBi 2Ta 2O 9 thin film showed a good ferroelectric property with the high remanent polarization of 12 μC/cm 2 and the low coercive electric field of 140 kV/cm. For the highly a-oriented SBT thin film, domain switching and reading were performed by Kelvin probe force microscope (KFM). The KFM data indicate a good ferroelectric property of the highly a-oriented SrBi 2Ta 2O 9 thin film with high KFM signals that reflect ferroelectric polarizations.

ENHANCEMENT OF MEMORY RETENTION TIME OF MFIS STRUCTURE WITH SBT FERROELECTRIC AND SiO2 BUFFER LAYERS TREATED BY NITROGEN RADICAL IRRADIATION

ABSTRACT Nitrogen radical irradiation has been used to improve the retention memory characteristic of Pt/SrBi2Ta2O9(SBT)/SiO2/n-Si metal–ferroelectric–insulator–semiconductor (MFIS) structures. It is demonstrated leakage currents through buffer and ferroelectric layers have decreased due to improvements of electronic property by the irradiation treatment. Furthermore, C-V characteristics also show wide memory window and steep slope in depletion region corresponding to good interface layers and minimized diffusion between layers. Nitrogen incorporated in surface layers of SiO2 and SBT has been confirmed by X-ray Photoelectron Spectroscopy(XPS). Ultraviolet Photoyield Spectroscopy(UV-PYS) measurements show Fermi level energy and band gap of SBT surface layer are modified and depend on radiation time. Surface morphology of SBT thin films with various treatment periods were investigated by SEM and AFM images. The retention time of capacitor in ON and OFF states of MFIS structures is longer than 2 weeks.

The Effects of Various Substrate Temperature of Bi2O3 Buffer Layer on SBT (SrBi2Ta2O9) Thin Films Deposited by R.F. Magnetron Sputtering

The SBT(SrBi2Ta2O9) thin films with Bi2O3 buffer layer were deposited on Pt/Ti/SiO2/Si substrate by R.F. magnetron sputtering method in order to improve the ferroelectric characteristics. In SBT thin films, the deficiency of bismuth due to its volatility during the process results in an obvious non stoichiometry of the films and the presence of secondary phases. Bi2O3 buffer layer was found to be effective to achieve lower temperature crystallization and improve ferroelectric properties of SBT thin films. Ferroelectric properties and crystallinities of SBT thin films with various substrate temperature of Bi2O3 buffer layer were observed, using X-Ray Diffraction (XRD), Precision LC (Radient Technologies. Inc.) and GDS (glow discharge spectrometer).

IMPROVED FERROELECTRIC PROPERTIES OF SrBi4−0.1Pr0.1Ti4O15 THIN FILMS

ABSTRACT Thin films with the composition of SrBi4Ti4O15(SBTi) and SrBi4−0.1Pr0.1Ti4O15 (SBPTi) have been prepared on Pt/TiO2/SiO2/Si substrates by sol-gel method structure characterization of the SBT and SBPT thin films was revealed by x-ray diffraction (XRD). Using Pt/SBPT/Pt/TiO2/SiO2/Si configuration, ferroelectric properties of the film were well established with the hysteresis loop. A notable enlargement of remnant polarization (2Pr) and a decrease of the coercive field (Ec) are observed. The 2Pr of SBPTi reaches a value as large as34.76 μC/cm2, nearly twice greater than that of SrBi4Ti4O15 without Pr-doping. The SBPTi film shows little change of Pns and −Pns up to 1010 switching cycles, suggesting an excellent fatigue-endurance characteristic.

Study on the Electrical Properties of Direct-Patternable SBT Films Formed by Photochemical Metal-Organic Deposition

The ferroelectric properties of UV irradiated and non-irradiated SBT thin films using photosensitive starting precursors were investigated. The observation of surface microstructure showed that UV irradiation and increase in anneal temperature induced the grain growth of SBT. The measured remnant polarization values of UV irradiated and non-irradiated SBT films after anneal at 700oC were 5.8 and 4.7 )C/cm2 and after anneal at 750oC, the values were 10.8 and 9.3 )C/cm2, respectively.

Ferroelectric characteristic of group IV elements added SrBi 2Ta 2O 9 thin films

The SrBi 2Ta 2O 9 (SBT) thin film added IV group elements was fabricated on the Pt/Ti/SiO 2/Si substrate by the metal–organic decomposition (MOD) method, the Pt electrode was deposited on the SBT thin film by the DC spattering method. The electric properties of the ferroelectric capacitor were measured. The remanent polarization and the relative dielectric constant of the SBT thin film have decreased, according to the amount of IV group elements addition. The IV group elements added SBT thin film with low relative dielectric constant and low remanent polarization is suitable for the application of the ferroelectric gate FET type memory.

Electrical and ferroelectric properties of SBT thin films formed by photochemical metal-organic deposition

The electrical and ferroelectric properties of SBT thin films prepared by photochemical metal-organic deposition using photosensitive starting precursors were characterized. Fourier transform infra-red spectroscopic observation showed that a complete removal of organic groups was possible by UV exposure of spin-coated SBT precursor film at room temperature. The values of measured remnant polarization and leakage current density at 400 kV/cm were 5.8 μC/cm 2 and 3.48 × 10 −8 A/cm 2 after anneal treatment at 700 °C of the UV-exposed SBT precursor film and 10.8 μC/cm 2 and 6.94 × 10 −8 A/cm 2 after anneal treatment at 750 °C. The SBT films annealed at 700 and 750 °C remained fatigue-free up to 10 10 switching cycles.

Characteristics of Fatigue Induced by Distribution of Defect Charges in SrBi2Ta2O9 Capacitors

Pt/SrBi2Ta2O9 (SBT)/Pt capacitors have been successfully fabricated using a metalorganic decomposition (MOD) technique. The switchable polarization of SBT capacitors showed a tendency to increase with the number of switching cycles at first and then decrease after 2×109 switching cycles. During the switching process, a competition existed between the depinning behavior of domains and the aggregation of defect charges at the interfaces between SBT thin films and electrodes. It was this competition that determined the fatigue characterization for SBT capacitors. Higher external voltages facilitated the recovery of polarization suppression, which suggests that more domains in the SBT thin films were easily depinned by a higher external field and the pinning depth due to defect charges was different.

IMPROVEMENT OF MEMORY RETENTION IN METAL-FERROELECTRIC-INSULATOR-SEMICONDUCTOR STRUCTURE BY SrBi2Ta2O9 SURFACE MODIFICATION INDUCED BY NITROGEN AND OXYGEN RADICAL IRRADIATION

ABSTRACT A Pt/SrBi2Ta2O9(SBT)/SiO2/n-Si metal–ferroelectric–insulator–semiconductor (MFIS) structure has been prepared with SrBi2Ta2O9 thin film whose surface was modified by irradiation of nitrogen or oxygen radical. The leakage current is reduced by irradiation treatment and C-V characteristic shows clear memory window and sharp slopes corresponding to good interface layer. It is estimated from X-ray Photoelectron Spectroscopy and Ultraviolet Photoyield Spectroscopy that the SBT thin films with nitrogen treatment have exhibited the higher threshold energy than that without the irradiation. Memory window of the MFIS structures are in the range of 1–2 V when the gate voltage is varied from 3–6 V. Retention time of ON and OFF states is 1 week in the structure irradiated with oxygen radical and 12 days in that with nitrogen radical although that without the irradiation is only 3 hours.

Effects of the Chelating Agent on the Fabrication of SBT Thin Films: Part II. Microstructural Properties

The effects of the chelating agent on the micro structural properties of SBT thin films annealed at different temperatures are investigated. The films were prepared on Pt/Ti/SiO2/Si substrates by a chemical solution deposition technique. Strontium acetate, bismuth nitrate and tantalum ethoxide were used as precursor materials, with methanol and glacial acetic as solvents. We make a comparative investigation of the surface microstructure, grain size distribution, crystallinity, and degree of crystal orientation for films prepared using acetoin and alkanolamines as chelating agent.

Effects of the Chelating Agent on the Fabrication of SBT Thin Films: Part I. Stoichiometry and Crystallization Behavior

The effects of the chelating agent on the thermal evolution of SrBi 2 Ta 2 O 9 precursor powders were investigated. The precursor solutions were prepared from non-hydrolyzing precursors of bismuth and strontium and a tantalum alkoxide. The utilization of alkanolamines as chelating agent was found to produce the segregation of metallic bismuth in the as-prepared powders, which led to the formation of a multiphase system. On the other hand, acetoin, one of the Hydroxyketones, showed outstanding characteristics for the low-temperature synthesis of SrBi 2 Ta 2 O 9 : elimination of residual organics at low temperature, an earlier onset of crystallization, and no segregation of secondary phases during the whole crystallization process.

Enhanced ferroelectric properties of multilayer SrBi 2Ta 2O 9/SrBi 2Nb 2O 9 thin films for NVRAM applications

Ferroelectric SrBi 2Ta 2O 9/SrBi 2Nb 2O 9 (SBT/SBN) multilayer thin films with various stacking periodicity were deposited on Pt/TiO 2/SiO 2/Si substrate by pulsed laser deposition technique. The X-ray diffraction patterns indicated that the perovskite phase was fully formed with polycrystalline structure in all the films. The Raman spectra showed the frequency of the O–Ta–O stretching mode for multilayer and single layer SrBi 2(Ta 0.5Nb 0.5) 2O 9 (SBNT) samples was ∼827–829 cm −1, which was in between the stretching mode frequency in SBT (∼813 cm −1) and SBN (∼834 cm −1) thin films. The dielectric constant was increased from 300 (SBT) to ∼373 at 100 kHz in the double layer SBT/SBN sample with thickness of each layer being ∼200 nm. The remanent polarization (2 P r) for this film was obtained ∼41.7 μC/cm 2, which is much higher, compared to pure SBT film (∼19.2 μC/cm 2). The coercive field of this double layer film (67 kV/cm) was found to be lower than SBN film (98 kV/cm).

Diffusion processes in seeded and unseeded SBT thin films with varied stoichiometry

SrBi 2Ta 2O 9 (SBT) is a bismuth layered perovskite (BLP) with interesting ferroelectric properties for memories applications. The previous study on the synthesis of seeded and unseeded SBT thin films by the authors [G. González Aguilar, M.E.V. Costa, I.M. Miranda Salvado, J. Eur. Ceram. Soc. 25 (2005) 2331] has shown an increase of the crystallinity of the films and an improvement of the thin film ferroelectric properties when using SBT seeds. However, the detailed role of the seeds as an improver of the thin film properties has not been investigated so far. In the present work we study the role of the seeds, particularly with respect to the reactions between film and (bottom) underlying platinum electrode. The comparison of the results obtained by characterizing the seeded and unseeded thin films via Rutherford backscattering (RBS) and particle induced X-ray emission (PIXE) techniques reveals an effective modification of the substrate–thin film interface by the presence of the seeds. Moreover, the evaluation of the thin film ferroelectric properties by atomic force microscopy (AFM) shows an improvement of the local piezoelectric hysteresis loops by the seeds. These seeding effects as well as those observed in non-stoichiometric SBT thin films with different bismuth contents are used to discuss the barrier-like role of the SBT seeds against reactions between film and the platinum electrode and its contribution to the improvement of the thin film properties.

Effect of Ta Content on The Ferroelectric Characteristics of SBT Thin Films

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