ngxia Li

Preparation and investigation of nano-thick FTO/Ag/FTO multilayer transparent electrodes with high figure of merit

In order to improve the conductivity of the single–layered nano-thick F doped SnO2 (FTO) thin films, an Ag mid–layer is embedded between the FTO layers. In our work, the effects of mid–layer Ag and top FTO layer on the structural, electrical and optical properties of FTO/Ag/FTO multilayered composite structures deposited on quartz glass substrates by magnetron sputtering at 100 °C have been investigated. As the thickness of Ag mid–layer increases, the resistivity decreases. As the top FTO layer thickness increases, the resistivity increases. The highest value of figure of merit φTC is 7.8 × 10−2 Ω−1 for the FTO (20 nm)/Ag (7 nm)/FTO (30 nm) multilayers, while the average optical transmittance is 95.5% in the visible range of wavelengths and the resistivity is 8.8 × 10−5 Ω·cm. In addition, we also describe the influence of Ag and top FTO layer thickness on structural, electrical and optical properties of the nano-thick FTO (20 nm)/Ag/FTO multilayers and the mechanism of the changes of electrical and optical properties at different Ag and top FTO layer thicknesses.

Multilayer thin films with compositional PbZr0.52Ti0.48O3/Bi1.5Zn1.0Nb1.5O7 layers for tunable applications.

The dielectric properties and tunability of multilayer thin films with compositional PbZr0.52Ti0.48O3/Bi1.5Zn1.0Nb1.5O7 (PZT/BZN) layers (PPBLs) fabricated by pulsed laser deposition on Pt/TiO2/SiO2/Si substrate have been investigated. Dielectric measurements indicate that the PZT/BZN bilayer thin films exhibit medium dielectric constant of about 490, low loss tangent of 0.017, and superior tunable dielectric properties (tunability = 49.7% at 500 kV/cm) at a PZT/BZN thickness ratio of 3, while the largest figure of merit is obtained as 51.8. The thickness effect is discussed with a series connection model of bilayer capacitors, and the calculated dielectric constant and loss tangent are obtained. Furthermore, five kinds of thin–film samples comprising single bilayers, two, three, four and five PPBLs were also elaborated with the final same thickness. The four PPBLs show the largest dielectric constant of ~538 and tunability of 53.3% at a maximum applied bias field of 500 kV/cm and the lowest loss tangent of ~0.015, while the largest figure of merit is 65.6. The results indicate that four PPBLs are excellent candidates for applications of tunable devices.

Investigation on preparation and electric field tunable dielectric properties of novel bismuth magnesium niobate transparent capacitors for opto-electronic devices

Transparent capacitors, based on bismuth magnesium niobate (Bi1.5MgNb1.5O7, BMN), have been fabricated on indium tin oxide glass substrates by rf magnetron sputtering. The effect of post-annealing conditions on structural, electrical, and optical properties of BMN thin films was investigated. X-ray diffraction patterns and scanning electron microscopy reveal that the BMN thin films post-annealed at an oxygen partial pressure of 0.1 MPa have the best crystalline quality compared to BMN films post-annealed under all other conditions. The BMN thin films exhibit an average transmittance of 85% in the visible light range (380–780 nm), while the value of optical absorption edge is 3.59 eV. Dielectric measurements indicate that the thin films exhibit a medium dielectric constant of about 99, a low loss tangent of 0.0037, and superior tunable dielectric properties at room temperature. Calculations of dielectric tunability and the figure of merit (FOM) display a maximum value of 28% at 1.3 MV cm−1 and ∼57, respectively. The results show that BMN thin films have great potential for use in electric field tunable transparent capacitors.

Fully transparent thin-film varactors: fabrication and performance

We report the fabrication of fully transparent thin-film varactors using a dielectric material, barium strontium titanate (Ba0.6Sr0.4TiO3, BST), as an electric field tunable layer, transparent conductive oxide (Sb doped SnO2, ATO) as a bottom electrode and ATO/Ag tri-layer film as a top electrode. This kind of varactor using ATO/Ag/BST/ATO capacitors shows a transmittance of about 80% (including the substrate) in the visible region, a medium capacitance of about 463 pF, a low loss tangent of about 0.015, and superior tunable dielectric properties at room temperature. Calculations of dielectric tunability and figure of merit (FOM) display a maximum value of ∼53% at 560 kV cm−1 and ∼66, respectively. We believe that the transparent thin-film varactors using ATO/Ag/BST/ATO capacitors presented in this paper could be a milestone for future see-through electronic devices.

The effect of segregation structure on the colossal permittivity properties of (La0.5Nb0.5)xTi1−xO2 ceramics

The newly discovered colossal permittivity (CP) TiO2 ceramics continue to arouse considerable interest owing to their applications in the field of high-performance capacitors. Here this work broadens the CP TiO2 systems to report the (La0.5Nb0.5)xTi1−xO2 (x = 0.01, x = 0.02, x = 0.03, x = 0.05, and x = 0.10) ceramics. The microstructure of the grain-boundary segregation has been found and the relationship between the segregation structure and dielectric properties has been established. The impedance spectroscopy analysis suggests that the segregation structure can increase the grain-boundary activation energies, which can be responsible for the effective suppression of long electron transfer to maintain a low loss and improve the temperature stability. However, the excessive segregation second phase can cause the deterioration of the dielectric properties. The analyses of the variable dielectric response with polarizable activation energies clearly indicate that the CP mechanism can be a combination of electron-pinned defect-dipoles, hopping polarization and interfacial polarization. More importantly, the comparisons of the polarizable activation energies under different amounts not only reveal that the deterioration of dielectric properties can be caused by the accessorial interfacial polarization by the excessive segregation second phase, but also can be an exact evaluation of the contribution of the segregation structure on the dielectric properties. The co-doping amount x = 0.03 provides the maximum beneficial effect of the segregation structure, embodied by the optimal performance with the highest permittivity (er = 49 692), effective control of loss to maintain it at a low level (tan δ = 0.02896) and the best temperature stability (ΔC/C−50 to 150°C ≤ ±5.84). We believe this work enriches the theory on the co-doping TiO2 system and provides comprehensive guidance for methods to maintain the low loss of CP materials.

Low loss, high tunable BaZr0.2Ti0.8O3/BaSn0.85Ti0.15O3 heterostructure thin films

Ferroelectric BaZr0.2Ti0.8O3/BaSn0.85Ti0.15O3 (BZT/BTS) heterostructure thin films (∼200-nm-thick) have been prepared on Pt/TiOx/SiO2/Si substrates by pulsed laser deposition. The heterostructure thin films are crack free, compact, and crystallized in a perovskite structure. Dielectric measurements indicate that the BZT/BTS heterostructure thin films exhibit a low dielectric loss of below 0.007, a medium dielectric constant of ∼441, and the superior tunable dielectric properties at room temperature. Calculations of tunability and figure of merit (FOM) display a maximum value of 68.5% at 500 kV/cm and ∼101, respectively. The FOM value is higher than that of the single-layer BTS and BZT thin films. A brief discussion is given on the lower loss compared to the single-layer thin films. The results indicate that BZT/BTS heterostructure thin films are excellent candidates for electrically steerable applications.

Coexistence of superconductivity and charge-density-wave domain in 1T-FexTa1−xSSe

A series of 1T-FexTa1−xSSe (0 ≤ x ≤ 0.1) single crystals were fabricated via the chemical-vapor-transport method and investigated by structure, transport, and magnetic measurements along with the density-functional-theory (DFT) calculations. The superconductivity (SC) in parent 1T-TaSSe can be gradually suppressed by Fe-substitution (x ≤ 0.03), accompanied by the disappearance of charge-density-wave (CDW). DFT calculations show that the Fe-substitution effectively inhibits the CDW superstructure and thereby the CDW domains are destroyed. With further increasing x (x > 0.03), the disorder-induced scattering increases, and the system enters into the possible Anderson localization state. Our results prove the SC develops in the CDW phase and coexists with the CDW domain in 1T-TaSSe system.

Oxygen vacancy regulation and its high frequency response mechanism in microwave ceramics

Li2ZnTi3−xMxO8 {M = Al3+, Nb5+, (Al0.5Nb0.5)4+, (Zn1/3Nb2/3)4+, and (Li1/4Nb3/4)4+} systems were fabricated by a facile solid-state reaction method. According to the substitution rule of radius and valence, all of the doping ions {Al3+, Nb5+, (Al0.5Nb0.5)4+, (Zn1/3Nb2/3)4+, and (Li1/4Nb3/4)4+} should occupy Ti4+ sites. EPR spectra showed that paramagnetic Ti3+ centers and oxygen vacancies co-existed in the pure Li2ZnTi3O8 ceramics. The oxygen vacancies in Li2ZnTi3O8 were attributed to the deoxidation process during high temperature sintering. The inhibitory effects of acceptor ion, donor ion and co-doped ions on oxygen vacancies were related to the lattice energy (U) of O(1). An appropriate amount of (Al0.5Nb0.5)4+, (Zn1/3Nb2/3)4+ and (Li1/4Nb3/4)4+ greatly reduced the microwave dielectric loss of the Li2ZnTi3O8 systems. And, the microwave dielectric loss deteriorated seriously in Al3+-doped systems. For the first time, a systematic exposition on the response process of dielectric loss in Li2ZnTi3O8 ceramics was discussed based on the ac impedance analysis and terahertz time-domain spectroscopy (THz-TDS) analysis in detail. Deeper analysis revealed that the absorption of structural phonon oscillation and long-range movement of weakly bound defects () were two major contributors to the microwave dielectric loss.

Improved performance of transparent-conducting AZO/Cu/AZO multilayer thin films by inserting a metal Ti layer for flexible electronics

In order to improve the performance of transparent conductive Al-doped ZnO (AZO)/Cu/Al-doped ZnO multilayer thin films, multilayer thin films of titanium-embedded AZO/Cu/AZO structures have been designed and deposited onto flexible polycarbonate substrates to develop an indium-free transparent flexible electrode. The effect of Ti layer on the structural, optical, and electrical properties of multilayer thin films was investigated. The experiments reveal that the AZO/Ti/Cu/AZO fabricated in argon-oxygen mixtures has the best performance (commutation quality factor of 422.0): resistivity of 3.85×10-5  Ω·cm, sheet resistance of 4.31  Ω/sq, carrier concentration of 1.65×1022  cm-3, mobility of 9.87  cm2/Vs, and acceptable luminous transmittance of above 82% in the visible range.