Jin Seong Kim

Optical analysis of doped ZnO thin films using nonparabolic conduction-band parameters

The optical properties of impurity doped ZnO thin films were analyzed by taking into account the nonparabolicity in the conduction-band and the optically determined carrier concentration and mobility were correlated with those measured by Hall measurement. The Drude parameters obtained by applying a simple Drude model combined with the Lorentz oscillator model for the optical transmittance and reflectance spectrum were analyzed by using the carrier density dependent bare band effective mass determined by the first-order nonparabolicity approximation. The squared plasma energy multiplied by the carrier density dependent effective mass yielded fairly linear relationship with respect to the carrier concentration in wide carrier density range of 1019 − 1021 cm−3, verifying the applicability of the nonparabolicity parameter for various types of impurity doped ZnO thin films. The correlation between the optical and Hall analyses was examined by taking the ratios of optical to Hall measurements for carrier densi...

Hydrogen in polycrystalline ZnO thin films

The influence and the states of hydrogen in polycrystalline ZnO thin films were investigated by preparing films with different amounts of oxygen vacancies at various hydrogen potentials. The most notable effect of hydrogen addition was passivation of grain boundaries. The majority of hydrogen incorporation in polycrystalline ZnO films was attributed to hydrogen interstitials, and a substantially smaller number of multicentre bonds at oxygen vacancies were formed even at high hydrogen potentials. The major source of free carriers in polycrystalline ZnO films deposited without intentional hydrogen addition was oxygen vacancies with 2+ charge state with large atomic relaxation.

Microstructure and Structural Analysis of the x(Na0.5K0.5)NbO3-(1-x)BaTiO3 Ceramics for MLCCs

하주연 ・김진성1 ・이희수1 ・최연규2 ・이연숙3,* 부산대학교 재료공학부 (주)삼성정밀화학 부산대학교 하이브리드 소재 솔루션 국가핵심연구센터 Microstructure and Structural Analysis of the x(Na0.5K0.5)NbO3-(1-x)BaTiO3 Ceramics for MLCCs Jooyeon Ha, Jinseong Kim, Heesoo Lee, Youn-Kyu Choi, and Yeonsook Lee* School of Materials Science & Engineering, Pusan National University, Busan 609-735, KOREA Samsung Fine Chemicals Co., Ltd., Daejeon 305-380, KOREA National Core Research Center for Hybrid Materials Solution, Pusan National University, Busan 609-735, KOREA

Structural variation of hydrothermally synthesized KNbO3 nanowires

KNbO3 (KN) nanowires were synthesized using various process conditions and their structures and morphologies were investigated. Homogeneous KN nanowires were formed in specimens synthesized at 130 °C for 24.0–48.0 h. These KN nanowires have a tetragonal structure that is known to be stable at high temperatures in the range of 225–435 °C. Tetragonal KN nanowires changed to orthorhombic KN nanoplates when the process time increased and homogeneous orthorhombic KN nanoplates existed for specimens synthesized for 144.0 h. In addition, tetragonal and orthorhombic structures coexisted in KN nanoplates synthesized at 130 °C for 72.0 h. For specimens synthesized at 100 °C, a long process time of 144.0 h was required to develop homogeneous KN nanowires that were also considered to have both tetragonal and orthorhombic structures. On the other hand, for specimens synthesized at 150 °C for 8.0 h, KN nanowires and a cube-shaped KN phase coexisted. Furthermore, a K4Nb6O17 second phase was formed in specimens synthesized for short periods of time (<8.0 h), indicating that the formation of homogeneous KN nanowires is difficult at 150 °C. Therefore, homogeneous KN nanowires with a tetragonal structure can be obtained at a low temperature of 130 °C with a short process time in the range of 24.0–48.0 h.KNbO3 (KN) nanowires were synthesized using various process conditions and their structures and morphologies were investigated. Homogeneous KN nanowires were formed in specimens synthesized at 130 °C for 24.0–48.0 h. These KN nanowires have a tetragonal structure that is known to be stable at high temperatures in the range of 225–435 °C. Tetragonal KN nanowires changed to orthorhombic KN nanoplates when the process time increased and homogeneous orthorhombic KN nanoplates existed for specimens synthesized for 144.0 h. In addition, tetragonal and orthorhombic structures coexisted in KN nanoplates synthesized at 130 °C for 72.0 h. For specimens synthesized at 100 °C, a long process time of 144.0 h was required to develop homogeneous KN nanowires that were also considered to have both tetragonal and orthorhombic structures. On the other hand, for specimens synthesized at 150 °C for 8.0 h, KN nanowires and a cube-shaped KN phase coexisted. Furthermore, a K4Nb6O17 second phase was formed in specimens synthesiz...

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.

Synthesis of highly tetragonal BaTiO3 nanopowders using acetone as a solvent by alkoxide-hydroxide route

BaTiO3 (BT) nanopowders were synthesized in acetone to remove the TiO2 second phase, which was formed in the specimens synthesized in the 2-methoxyethanol solvent at above 100 °C due to H2O evaporation. No TiO2 second phase was formed in the specimens synthesized in acetone, even at 260 °C, due to the low boiling temperature of acetone which evaporated at above 55 °C and suppressed the H2O evaporation by increasing the vapor pressure in the vessel. However, for the BT nanopowders synthesized at 250 °C for 60 h, TiO2 second phase was formed at a Ba/Ti ratio of ≤1.5 and the BT nanopowders were agglomerated at a ratio of ≥3.0. Homogeneous BT nanopowders were obtained at a ratio of 2.0 and they exhibited a high c/a ratio of 1.0082 with a small size of 95.2 nm. Therefore, these nanopowders can be a good candidate for future multi-layer ceramic capacitor.

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.

Microstructure and Electrical Properties of Amorphous Bi 5 Nb 3 O 15 Films Grown on Cu/Ti/SiO 2 /Si Substrates Using RF Magnetron Sputtering

Amorphous Bi5Nb3O15 (BNO) films were grown at room temperature (RT) on a Cu/Ti/SiO2 /Si substrate using radio frequency magnetron sputtering. All the films were well formed on the Cu electrode with a sharp interface between the film and the electrode. The dielectric constant of the amorphous BNO film grown under 25 W was 46, with a low dissipation factor of 2.7% at 100 kHz. This film exhibited a low leakage current density of 5.5 × 10-8 A/cm2 at 4.5 V and a large breakdown voltage of 7.2 V. However, the electrical properties deteriorated as the sputtering power and the growth temperature increased due to the increased surface roughness; this was because a film with a rough surface generally has a larger surface area, and there can be electric field intensification at surface asperity, which degrade the electrical properties of the film. In addition, the electrical properties were not influenced by the oxygen partial pressure (OPP) because the variation of OPP during the growth of the films did not affect their surface roughness. The amorphous BNO film grown on the Cu/Ti/SiO2/Si substrate at RT under 25 W may be a good candidate material for an embedded capacitor.

Effects of Ambient Gas Pressure on the Resistance Switching Properties of the NiO Thin Films Grown by Radio Frequency Magnetron Sputtering

NiO films were grown on a Pt substrate by radio frequency (RF) magnetron sputtering using a NiO ceramic target. A crystalline NiO phase with the [111] preferred orientation was formed for the films grown above 100 °C. Resistance switching behavior was not observed in the NiO films annealed in the air or in ambient O2 after film deposition. However, the NiO films annealed in ambient N2 exhibited resistance switching properties. The stability of the switching voltage was considerably influenced by the oxygen to argon ratio during film growth. In particular, the NiO film grown under an 8.0 mTorr oxygen partial pressure exhibited stabilized switching voltages (Vset~1.45±0.20 V and Vreset~0.62±0.09 V). Therefore, the control of the ambient gas pressure during the growth and annealing of the NiO films was important for obtaining good resistance switching properties.

Effect of laser beam energy density on the structural and electrical properties of TiO2-doped Bi5Nb3O15 thin film grown by pulsed laser deposition

With the addition of TiO2, the dielectric constant (?r) of a Bi5Nb3O15(B5N3) film was slightly increased and the leakage current decreased, probably due to the increased dipole moment and the decreased number of free electrons in the film, respectively. The energy density of the laser beam considerably influenced the structure and electrical properties of the 1.0?mol% TiO2-doped B5N3 (TBN) films. At low beam energy densities (?2.0?J?cm?2), Bi3NbO7 and Bi8Nb18O57 phases with a porous microstructure were formed and a poor interface was also formed between the film and the electrode. However, for the TBN film grown at 200??C at a high beam energy density of 4.0?J?cm?2, a dense Bi3NbO7 phase was formed with a sharp interface. The ?r value of this TBN film was very high, approximately 115, with a low leakage current density of 1.4 ? 10?8?A?cm?2 at 0.5?MV?cm?1 and a high breakdown field of 0.55?MV?cm?1. This improvement in the ?r value and the electrical properties was explained by the formation of a dense Bi3NbO7 phase with a (1?1?1) preferred orientation, Ti doping and a sharp interface, indicating that the TBN film is a good candidate material for embedded capacitors.