Enhancement on effective piezoelectric coefficient d33 of Bi3.15Dy0.85Ti3O12 ferroelectric thin films

Effects of annealing temperature (600-800 °C) on microstructure, ferroelectric and piezoelectric properties of Bi_3.15Dy_0.85Ti₃O₁₂ (BDT) thin films prepared by metal-organic decomposition were studied. The remnant polarization 2P_r and spontaneous polarization 2P_s (16.2 µC/cm² and 23.3 µC/cm² under 690 kV/cm), effective piezoelectric coefficient d₃₃ (63 pm/V under the bipolar driving field of 310 kV/cm) of BDT thin film annealed at 700 °C are better than those of others. The higher 2P_s and relatively permittivity ε_r induced by moderate annealing temperature should be responsible for the enhancement of piezoelectric properties. The improved d₃₃ may make BDT a promising candidate for piezoelectric thin film devices.     

Annealing temperature dependence of effective piezoelectric coefficients for Bi3.15Eu0.85Ti3O12 thin films

The effects of annealing temperatures 600, 650, 700, and 750 °C on microstructure, chemical composition, leakage current, ferroelectric, dielectric, and piezoelectric properties of Bi_3.15Eu_0.85Ti₃O₁₂ (BET) thin films prepared by metal–organic decomposition were studied in detail. The largest spontaneous polarization 2P _s (98.7 μC/cm² under 300 kV/cm), remnant polarization 2P _r (81.7 μC/cm² under 300 kV/cm), dielectric constant ε_r (889.4 at 100 kHz), effective piezoelectric coefficient d ₃₃ (46.7 pm/V under 260 kV/cm), and lowest leakage current (1.3 × 10⁻⁶ A/cm² under 125 kV/cm) of BET thin film were obtained with annealing at 700 °C. The mechanisms concerning the dependence of the enhancement d ₃₃ are discussed according to the phenomenological equation, and the improved piezoelectric performance could make BET thin film a promising candidate for piezoelectric thin film devices.     

Properties of La-substituted Na0.5Bi4.5Ti4O15 ferroelectric thin films

Ferroelectric Na_0.5La_0.5Bi₄Ti₄O₁₅ (NaLaBTi) thin films were prepared by a chemical solution deposition method. The NaLaBTi thin films annealed at 750 °C under oxygen atmosphere were randomly oriented polycrystalline. Electrical properties of the NaLaBTi thin films were compared to Na_0.5Bi_4.5Ti₄O₁₅ thin films and better properties were observed in the NaLaBTi thin films. Remnant polarization (2P_r) and coercive electric field (2E_c) were 43 µC/cm² and 204 kV/cm at an applied electric field of 478 kV/cm, respectively. Leakage current density was 1.95 × 10^− 6 A/cm² at 100 kV/cm. Dielectric constant and dielectric loss were 805 and 0.05 at 1 kHz, respectively. Switchable polarization was suppressed by 15% after 1.44 × 10¹⁰ switching cycles.     

The influence of annealing temperatures on the properties of Bi2VO5.5/LaNiO3/Si thin films

Bi₂VO_5.5 ferroelectric thin films were fabricated on LaNiO₃/Si(100) substrate via chemical solution deposition. Ferroelectric and dielectric properties of the thin films annealed at 500-700 °C were studied. The thin film annealed at 700 °C exhibited more favorable ferroelectric and dielectric properties than those annealed at lower temperatures. The values of remnant polarization 2P_r and coercive field E_c for the film annealed at 700 °C are 10.62 µC/cm² and 106.3 kV/cm, respectively. The leakage current of the film is about 1.92 × 10^− 8 A/cm² at 6 V. The possible mechanism of the dependence of electrical properties of the films on the annealing temperature was discussed.     

Improved dielectric and ferroelectric properties in Ti-doped BiFeO3-PbTiO3 thin films prepared by pulsed laser deposition

Ti-modified thin films of multiferroic 0.72Bi(Fe_1 − xTi_x)O₃-0.28PbTiO₃ (BFPT, x = 0 and 0.02) solid solution were prepared by pulsed laser deposition. The BFPT (x = 0 and 0.02) films possess a tetragonal structure with highly preferential (001) orientation. The effects of the ionic substitution on the properties of BFPT (x = 0 and 0.02) films have been investigated. The leakage current of the BFPT (x = 0.02) thin film is significantly reduced, and the dielectric and ferroelectric properties greatly improved by the aliovalent ionic substitution of Ti⁴⁺ for Fe³⁺. The BFPT (x = 0.02) thin film exhibits a reasonably high remnant polarization P_r with 2P_r up to 90 μC/cm² at 312 kV/cm and a switchable polarization up to 92 μC/cm² at 417 kV/cm.     

Effect of Na/K excess on the electrical properties of Na0.5Bi0.5TiO3-K0.5Bi0.5TiO3 thin films prepared by sol-gel processing

(Na_0.85K_0.15)_0.5Bi_0.5TiO₃ (NKBT) thin films derived from different amounts of Na/K excess content were fabricated via an aqueous sol-gel method on a Pt(111)/Ti/SiO₂/Si substrate, and the effect of Na/K excess content on the microstructure and electrical properties of the NKBT thin films was investigated. A second phase appears when Na/K excess content is below 20 mol%. Appropriated Na/K excess can enhance the polarization and dielectric properties due to compensation of Na/K loss that occurred during heat treatment. The 20 mol% excess derived NKBT thin film exhibits the best ferroelectric and dielectric properties with a remnant polarization (Pr) of 13.6 μC/cm², and a coercive field (Ec) of 104.8 KV/cm, together with a dielectric constant of 406 and a dissipation factor of 0.064. Similar to the dielectric response change with Na/K excess content, the decreasing concentration of charged defects is the main reason resulting in the increase of the piezoelectric property. The film with a 20 mol% excess content exhibited an effective d₃₃^? of about 56 pm/V. Also, the NKBT with a 20 mol% excess content exhibits the lowest current density of 5.6 × 10^− 5 A/cm² at 10 V.     

Deflection of wafers and cantilevers with Pt/LNO/PZT/LNO/Pt/Ti/SiO2 multilayered structure

The present paper describes a Pt/LNO/PZT/LNO/Pt/Ti/SiO₂ multilayers deposited on 4-inch Si wafers. We have evaluated the variation of the deflection of the Si wafers with deposition of each of the thin films. The deposition of the multilayers has resulted in downward deflection (center is higher than edge) of the Si wafers. The multilayers have been also deposited onto SOI wafers and fabricated into piezoelectric micro cantilevers through MEMS bulk micromachining. The micro cantilevers have shown the upward deflection. We have characterized the ferroelectric and piezoelectric properties of the PZT thin films through electrical tests of the micro cantilevers. The dielectric constant, saturation polarization, remanent polarization and coercive field were measured to be 1050, 31.3 μC/cm², 9.1 μC/cm² and 21 kV/cm, respectively. The transverse piezoelectric constant, d₃₁, was measured to be − 110 pm/V from the DC response of the micro cantilevers.     

Structural and electrical properties of BiFeO3 thin films by solution deposition and microwave annealing

Lead-free polycrystalline BiFeO₃ (BFO) thin films were developed using a chemical solution deposition method to deposit the films and the multi-mode 2.45 GHz microwave furnace to optimize the annealing condition of the films. Phase-pure BFO films were obtained at 500 °C-600 °C for 1-5 min with a heating rate of 10 °C/min. The film by microwave annealing (MW) at 550 °C for 5 min exhibited a (012)-preferred orientation with a dense morphology of grain size ~ 294 nm. Its dielectric constant of 96.2, low leakage current density of 2.466 × 10^− 6 A/cm², polarization (2P_r) and coercive field (2E_c) of 0.931 μC/cm² and 57.37 kV/cm, respectively, were improved compared to those by conventional annealing (CA) at the same annealing conditions.     

V-doping effects on ferroelectric properties of K0.5Bi4.5Ti4O15 thin films

V-doped K_0.5Bi_4.5Ti₄O₁₅ (K_0.5Bi_{4.5 − x/3}Ti_4 − xV_xO₁₅, KBTiV-x, x = 0.00, 0.01, 0.03, and 0.05) thin films were prepared on a Pt(111)/Ti/SiO₂/Si(100) substrate by a chemical solution deposition method. The thin films were annealed by using a rapid thermal annealing process at 750 °C for 3 min in an oxygen atmosphere. Among them, KBTiV-0.03 thin film exhibited the most outstanding electrical properties. The value of remnant polarization (2P_r) was 75 μC/cm² at an applied electric field of 366 kV/cm. The leakage current density of the thin film capacitor was 5.01 × 10⁻⁸ at 100 kV/cm, which is approximately one order of magnitude lower than that of pure K_0.5Bi_4.5Ti₄O₁₅ thin film capacitor. We found that V doping is an effective method for improving the ferroelectric properties of K_0.5Bi_4.5Ti₄O₁₅ thin film.     

Lead-free piezoelectric thin films of Mn-doped NaNbO3-BaTiO3 fabricated by chemical solution deposition

Lead-free piezoelectric thin films of NaNbO₃-BaTiO₃ were fabricated on Pt/TiO_x/SiO₂/Si substrates by chemical solution deposition. Perovskite NaNbO₃-BaTiO₃ single-phase thin films with improved leakage-current and ferroelectric properties were prepared at 650 °C by doping with a small amount of Mn. The 1.0 and 3.0 mol% Mn-doped 0.95NaNbO₃-0.05BaTiO₃ thin films showed slim ferroelectric P-E hysteresis and field-induced strain loops at room temperature. The 1.0 and 3.0 mol% Mn-doped 0.95NaNbO₃-0.05BaTiO₃ films showed remanent polarization values of 6.3 and 6.2 μC/cm², and coercive field of 41 and 55 kV/cm, respectively. From the slope of the field-induced strain loop, the effective piezoelectric coefficient (d₃₃) was found to be 40-60 pm/V.     

Nd-substituted SrBi2Ta2O9 ferroelectric thin films prepared by radio frequency magnetron sputtering

Nd-substituted SrBi₂Ta₂O₉ (SNBT) thin films are sputtered on Pt/Ta/SiO₂/Si substrates. X-ray diffraction and x-ray photoelectron spectroscopy studies indicate that Nd³⁺ is substituted into the bismuth layered perovskite structure, preferentially at the Sr²⁺ site. The annealed thin film is polycrystalline with plate/needle-like grain microstructure. Secondary ion mass spectrometry results show that elements in SNBT thin film homogeneously distribute along film depth and interfacial diffusion takes place during post annealing. The Nd substitution leads to enhanced remnant polarization (2P_r = 18 μC/cm²) and reduced coercivity (2E_c = 64 kV/cm) at 180 kV/cm measured at 25 °C. After 10¹⁰ switching cycles, around 9% remnant polarization is decreased.     

A study on the electrical properties of Pb(Zr, Ti)O3 thin films crystallized by the electrical resistive heating of Pt thin film

The electrical properties of Pb(Zr, Ti)O₃ thin films annealed by Pt thin film heater were investigated. By the thin film heater, we successfully crystallized Pb(Zr, Ti)O₃ thin films at a high temperature above 750 °C in a few seconds. The thin film heater has some advantages, such as a low thermal budget, little Pb-loss and enhanced surface morphology compared with the conventional furnace because it has a fast heating rate. The electrical properties of the Pb(Zr, Ti)O₃ thin film crystallized by thin film heater improved considerably comparing to those crystallized in conventional furnace. The remanent polarization, breakdown field, and leakage current density measured to be 22.7 μC/cm², 853 kV/cm, and 6.93 × 10⁻⁷ A/cm², respectively.     

Multiferroic properties of BiFeO3/Bi4Ti3O12 double-layered thin films fabricated by chemical solution deposition

Multiferroic BiFeO₃/Bi₄Ti₃O₁₂ (BFO/BTO) double-layered film was fabricated on a Pt(111)/Ti/SiO₂/Si(100) substrate by a chemical solution deposition method. The effect of an interfacial BTO layer on electrical and magnetic properties of BFO was investigated by comparing those of pure BFO and BTO films prepared by the same condition. The X-ray diffraction result showed that no additional phase was formed in the double-layered film, except BFO and BTO phases. The remnant polarization (2P_r) of the double-layered film capacitor was 100 μC/cm² at 250 kV/cm, which is much larger than that of the pure BFO film capacitor. The magnetization-magnetic field hysteresis loop revealed weak ferromagnetic response with remnant magnetization (2M_r) of 0.4 kA/m. The values of dielectric constant and dielectric loss of the double-layered film capacitor were 240 and 0.03 at 100 kHz, respectively. Leakage current density measured from the double-layered film capacitor was 6.1 × 10^− 7 A/cm² at 50 kV/cm, which is lower than the pure BFO and BTO film capacitors.     

Dielectric and ferroelectric properties of Ba(Sn0.15Ti0.85)O3 thin films grown by a sol-gel process

Ferroelectric Ba(Sn_0.15Ti_0.85)O₃ (BTS) thin films were deposited on LaNiO₃-coated silicon substrates via a sol-gel process. Films showed a strong (1 0 0) preferred orientation depending upon annealing temperature and concentration of the precursor solution. The dependence of dielectric and ferroelectric properties on film orientation has been studied. The leakage current density of thin films at 100 kV/cm was 7 × 10⁻⁷ A/cm² and 5 × 10⁻⁵ A/cm² and their capacitor tunability was 54 and 25% at an applied field of 200 kV/cm (measurement frequency of 1 MHz) for the thin films deposited with 0.1 and 0.4 M spin-on solution, respectively. This work clearly reveals the highly promising potential of BTS compared with BST films for application in tunable microwave devices.     

Preparation and characterization of highly (1 1 1)-oriented (Pb,La)(Zr,Ti)O3 thin films by sol-gel processing

Lanthanum modified lead zirconate titanate (Pb_0.91La_0.09)(Zr_0.65Ti_0.35)O₃ (PLZT) ferroelectric thin films were grown on Pt/Ti/SiO₂/Si(1 0 0) and fused quartz substrates using a sol-gel method with rapid thermal annealing processing. The results showed that the highly (1 1 1)-oriented pervoskite PLZT thin film growth on Pt/Ti/SiO₂/Si(1 0 0) substrates. The electrical measurements were conducted on PLZT films in metal-ferroelectric-metal capacitor configuration. The PLZT thin films annealed at 600 °C showed well-saturated hysteresis loops with remanent polarization and coercive electric field values were 10.3 μC/cm² and 36 kV/cm, respectively, at an applied field of 300 kV/cm. At 100 kHz, the dielectric constant and dielectric loss of the film are 682 and 0.021, respectively. The PLZT thin film on fused quartz substrate, annealed at 600 °C, exhibited good optical transmittance, the band gap of optical direct transitions is 3.89 eV.     

Microstructure and electric properties of (104)/(014)-oriented Bi3.15Nd0.85Ti3O12 films on Pt (111)/Ti/SiO2/Si by sol-gel method

Bi_3.15Nd_0.85Ti₃O₁₂ (BNdT) thin films with predominant (104)/(014) orientation were fabricated directly on (111)Pt/Ti/SiO₂/Si substrates through a sol-gel process. The volume fraction of (104)/(014)-oriented grains in the film was estimated to be about 65% according to X-ray pole figure. The BNdT film is dense and uniform and consists of columnar grains penetrating the whole film thickness. The (104)/(014)-oriented BNdT film capacitors showed excellent ferroelectric properties with 2P_r = 46.4 μC/cm² and E_c ≈ 140 kV/cm. The films also exhibit excellent piezoelectric property, with high piezoelectric coefficient d₃₃ ≈ 17 pm/V.     

Enhanced ferroelectric properties in Bi-doped K0.5Na0.5NbO3 thin films prepared by pulsed laser deposition

Lead-free ferroelectric Bi-doped K_0.5Na_0.5NbO₃ (KNN) and undoped KNN films were prepared by pulsed laser deposition. Bi-doped film exhibited good crystallization and improved ferroelectric properties. The dielectric constant and loss tangent were 1038 and 0.138 at 1 kHz, respectively. The remanent polarization (P_r = 28 μC/cm²) of Bi-doped film was about four times larger than that of the undoped film, which attributed to the decrease of oxygen vacancies concentration. The coercive field (E_c = 24 kV/cm) of Bi-doped films was half of the undoped film. The conduction mechanisms of Bi-doped film determined to be Space-Charge-Limited-Current and Poole–Frenkle emission at low and high electric field, respectively.     

Ferroelectric and fatigue-free properties of Au/(Bi,La)4Ti3O12/ITO thin film capacitors by pulsed laser deposition

Ferroelectric Bi_3.25La_0.75Ti₃O₁₂ (BLT) thin films were deposited on indium-tin-oxide (ITO) coated glass substrates by pulsed-laser-ablation method. Films deposited at 400 °C and annealed at 650 °C resulted in remnant polarization and coercive field values of 14-16 μC/cm² and 90-100 kV/cm, respectively. The fatigue measurements were conducted until 1 × 10¹¹ cycles but the individual switched and unswitched polarizations showed unequal magnitudes. Such an unequal switching polarization proves that an extrinsic effect mainly associated with the electrode exists in this thin film capacitor. The overall switching polarizations showed no polarization degradation, suggesting that BLT films are fatigue resistive even on hybrid-metal-oxide electrodes.     

Growth and electrical performance of Pb(Mg1/3Nb2/3)O3-PbTiO3-Pb(Fe1/2Nb1/2)O3 single crystals

For the first time, we have grown ferroelectric single crystals Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃-Pb(Fe_1/2Nb_1/2)O₃ (PMN-PT-PFN) from the melt by the simple slow cooling process. The chemical composition of the single crystals PMN-PT-PFN (0.59/0.31/0.10) is near the morphotropic phase boundary (MPB). X-ray diffraction (XRD) was used to study phase structure of the as-grown crystals, energy dispersive X-ray spectrometer (EDS) and electron probe micro-analyzer (EPMA) were employed to confirm the chemical composition and element distribution of the as-grown crystals, respectively. The ferroelectric, dielectric and piezoelectric properties of the as-grown PMN-PT-PFN (0.59/0.31/0.10) single crystal oriented along the (0 0 1) axis were measured, which showed that the remnant polarization (P_r), coercive electric fields (E_c), the Curie temperature (T_c) and the piezoelectric coefficient (d₃₃) were 50.2 μC/cm², 13.9 kV/cm, 158 °C and about 1800 pC/N, respectively. All the results indicated that the PMN-PT-PFN (0.59/0.31/0.10) single crystals are promising for applying to field of high frequency.     

Variations of microstructures and electrical properties of Bi4Ti3O12/SrTiO3/(La0.5, Sr0.5)CoO3/MgO epitaxial thin films by annealing

Epitaxial thin films of a heterostructure with Bi₄Ti₃O₁₂(BIT)/SrTiO₃(ST) were successfully grown with a bottom electrode consisting of La_0.5Sr_0.5CoO₃(LSCO) on MgO(001) substrates using pulsed laser deposition. The grown BIT and ST (001) planes were parallel to the growth surface with the orientation relationship of BIT <110>//ST <010>. In the as-deposited film, the BIT (001) plane appeared to expand to relieve a lattice mismatch with the ST (001) plane. However, annealing for 20-40 min induced the BIT (001) plane to contract horizontally with its c-axis expanding, which was associated with a local perturbation in the layer stacking of the BIT structure. This structural distortion was reduced in the film annealed for 1 h, with restoration of the periodicity of the layer stacking. Correspondingly, the dielectric constant of the as-deposited film was increased from 292 to 411 by annealing for 1 h. In parallel, the film was paraelectric but became more ferroelectric, with the remanent polarization and the coercive field changing from 0.1 μC/cm² and 14 kV/cm to 1.7 μC/cm² and 69 kV/cm, respectively.