Sahn Nahm

A generalized rule for large piezoelectric response in perovskite oxide ceramics and its application for design of lead-free compositions

We present a general rule for the perovskite oxide ceramics: “A large piezoelectric constant in ABO3 perovskite ceramics can be obtained by tuning the weight ratio of A and B sites, WA/WB or WB/WA, to 3. Piezoelectric constant decreases significantly when WA/WB or WB/WA is in the range of 0.5–2.0, termed as forbidden zone.” A comparative analysis was conducted for broad range of materials demonstrating the applicability of proposed rule. Further based on this rule optimized compositions in BaTiO3 and alkali niobate based systems were developed. Polycrystalline ceramics in modified BaTiO3 system were found to exhibit longitudinal piezoelectric coefficient (d33) of 330 pC/N, while alkali niobate ceramics showed d33 of 294 pC/N.

Effects of oxygen pressure and Mn-doping on the electrical and dielectric properties of Bi5Nb3O15 thin film grown by pulsed laser deposition

Bi5Nb3O15 (B5N3) thin films grown at temperatures above 500 °C developed a crystalline B5N3 phase that decomposed into a BiNbO4 phase in the film grown at 700 °C, probably due to Bi2O3 evaporation. The leakage current density of the B5N3 film grown at 200 °C under an oxygen pressure (OP) of 100 mTorr was high at approximately 6.3 × 10−7 A cm−2 at 0.2 MV cm−1, with a small breakdown field of 0.24 MV cm−1 due to the presence of intrinsic oxygen vacancies. The electrical properties of the B5N3 films improved with increasing OP during the growth but the dielectric constant (er) decreased. The Mn-doping also improved the electrical properties of the B5N3 films grown under low OP by producing doubly ionized oxygen vacancies, which decreased the number of the intrinsic oxygen vacancies. Furthermore, the Mn-doping increased the er value of the B5N3 film, confirming the effectiveness of such doping in improving both the electrical and the dielectric properties of the B5N3 film. In particular, the 5.0 mol% Mn-doped B5N3 film grown at 200 °C under an OP of 100 mTorr exhibited a low leakage current density of 7.9 × 10−8 A cm−2 at 0.2 MV cm−1 and a large breakdown field of 0.4 MV cm−1 with a high er of 64.

Electrical properties of Bi5Nb3O15 thin film grown on TiN/SiO2/Si at room temperature for metal - Insulator - Metal capacitors

Buckling was observed in Bi₅Nb₃O₁₅ (BiNbO) films grown on TiN/SiO₂/Si at 300°C but not in films grown at room temperature and annealed at 350 °C. The 45-nm-thick films showed a high capacitance density and a low dissipation factor of 8.81 fF/¿m² and 0.97% at 100 kHz, respectively, with a low leakage current density of 3.46 nA/cm² at 2 V. The quadratic and linear voltage coefficients of capacitance of this film were 846 ppm/V² and 137 ppm/V, respectively, with a low temperature coefficient of capacitance of 226 ppm/°C at 100 kHz. This suggests that a BiNbO film grown on a TiN/SiO₂/Si substrate is a good candidate material for high-performance metal-insulator-metal capacitors.

A Flexible Amorphous Bi5Nb3O15 Film for the Gate Insulator of the Low-Voltage Operating Pentacene Thin-Film Transistor Fabricated at Room Temperature

The amorphous Bi(5)Nb(3)O(15) film grown at room temperature under an oxygen-plasma sputtering ambient (BNRT-O(2) film) has a hydrophobic surface with a surface energy of 35.6 mJ m(-2), which is close to that of the orthorhombic pentacene (38 mJ m(-2)), resulting in the formation of a good pentacene layer without the introduction of an additional polymer layer. This film was very flexible, maintaining a high capacitance of 145 nF cm(-2) during and after 10(5) bending cycles with a small curvature radius of 7.5 mm. This film was optically transparent. Furthermore, the flexible, pentacene-based, organic thin-film transistors (OTFTs) fabricated on the poly(ether sulfone) substrate at room temperature using a BNRT-O(2) film as a gate insulator exhibited a promising device performance with a high field effect mobility of 0.5 cm(2) V(-1) s(-1), an on/off current modulation of 10(5), and a small subthreshold slope of 0.2 V decade(-1) under a low operating voltage of -5 V. This device also maintained a high carrier mobility of 0.45 cm(2) V(-1 )s(-1) during the bending with a small curvature radius of 9 mm. Therefore, the BNRT-O(2) film is considered a promising material for the gate insulator of the flexible, pentacene-based OTFT.

Characterization of Liquid Phase in (Na0.5K0.5)NbO3 Ceramics with V2O5 Additions

The characterizations of the microstructure and the chemical compositions on (Na0.5K0.5)(Nb0.93V0.07)O3 ceramics system sintered at 900 °C for 8 h were carried out using high resolution transmission electron microscopy (HRTEM), energy filtered (EF) TEM, and energy dispersive spectroscopy (EDS). The liquid phase was found at the triple junction of the grains and abnormal grain growth occurred in the presence of liquid phase. The liquid phase has formed by the melting of V2O5 at the sintering temperature. The presence of V element in liquid phase was confirmed by EDS analyses. The interface between the matrix phase and the liquid phase was atomically flat and consists of a stepped ledge structure of one or two atomic height. The KVO3 phase which may be formed during the cooling of the specimens was observed at these interfaces and have a good orientation relation with the matrix.