Kyung Hyun Ko

Photocatalysis and hydrophilicity of doped TiO2 thin films

TiO(2) thin films were prepared using the dip-coating method with a polymeric sol including additives such as Al, W, and Al+W to examine two major properties: photocatalysis and hydrophilicity. W-doped films showed the best photocatalytic efficiency, while Al-doped film was poorer than undoped samples. However, good hydrophilicity in terms of saturation contact angle and surface conversion rate was found in Al- and (Al+W)-mixed-doped films. It was found that deep electron-hole traps and high surface acidity of W-doped TiO(2) thin film were the major factors in high photocatalytic efficiency. In addition, low surface acidities of Al- and (Al+W)-doped films provided better hydrophilicity than W-doped ones. However, the amount of [Ti(3+)] point defects on the surface was another major factor, probably the most important, in getting the best hydrophilicity. Conclusively, it seemed that many parts of the photocatalysis mechanism depend more on bulk-related properties than do those of hydrophilicity, which can be defined as an interfacial (surface) or near-surface-restricted process.

Voltage tunable dielectric properties of rf sputtered Bi2O3-ZnO-Nb2O5 pyrochlore thin films

Abstract The Bi2O3-ZnO-Nb2O5 (BZN) pyrochlore thin films were prepared on platinized Si substrates using a reactive rf magnetron sputtering. The structures, surface morphologies, dielectric properties and voltage tunable dielectric properties of films with deposition parameters were investigated. The sputter deposited BZN pyrochlore thin films have a cubic pyrochlore phase and secondary phases of zinc niobate and bismuth niobate when crystallized at 600∼800 °C. The dielectric constant and tunability of thin films changed with an O2/Ar ratio and post-annealing temperature. The BZN pyrochlore thin films sputtered in 15% O2 and annealed at 700 °C had a dielectric constant of 153, tan δ of ∼0.003 and maximum tunability of 14% at 1000 kV/cm of dc bias field under 1 MHz.

Cold spray of SiC and Al2O3 with soft metal incorporation: A technical contribution

Al + SiC, Al + Al2O3 composites as well as pure Al, SiC, and Al2O3 coatings were prepared on Si substrates by the cold gas dynamic spray process (CGDS or cold spray). The powder composition of metal (Al) and ceramic (SiC, Al2O3) was varied into 1:1 and 10:1 wt.%, respectively. The propellant gas was air heated up to 330 °C and the gas pressure was fixed at 0.7 MPa. SiC and Al2O3 have been successfully sprayed producing coatings with more than 50 µm in thickness with the incorporation of Al as a binder. Also, hard ceramic particles showed peening effects on the coating surfaces. In the case of pure Al metal coating, there was no crater formation on hard Si substrates. However, when Al mixed with SiC and Al2O3, craters were observed and their quantities and sizes depended on the composition, aggregation and size of raw materials.

Thin film coatings of WO3 by cold gas dynamic spray: A technical note

Dense and adhesive WO3 films were prepared on a silicon substrate by the cold gas dynamic spray process (or cold spray). In contrast to standard metallic coatings, there was no sizable crater formation and plastic deformation. However, the aggregation of raw powder particles of a relatively large size was found to be destroyed upon impact on the substrate, forming a highly irregular surface with very fine secondary particles and providing good interlocking powder and void reduction among the particles in the coating. High-resolution images of the substrate interface showed that particles at the interface were more densely packed and that good adhesion was obtained. There fore, the particle bombardment onto the first layer of the coating could provide enhanced adhesion to the substrate mechanically and/or chemically.

Low-voltage and high-tunability interdigital capacitors employing lead zinc niobate thin films

Employing high-tunability PbO–ZnO–Nb2O5 thin film dielectrics, low-voltage and high-tunability interdigital capacitors (IDCs) were implemented on a silicon substrate. In order to reduce the bias voltage of the IDC and increase its tunability, its electrodes were fully embedded into the thin film dielectrics to confine fringing electric fields within them. At 4V, the tunability of the IDCs was analyzed in terms of the electrode width and spacing by measuring reflection coefficients at 1GHz. The fabricated IDC with width and spacing of 1.5 and 1.8μm, respectively, achieved tunability of 26% and a Q factor of 10 at 5.5V.

Tunable Coplanar Waveguide ( CPW ) Line Integrating Bismuth Zinc Niobate ( Bzn ) Thin Films

In this paper, a tunable coplanar waveguide (CPW) line using the bismuth zinc niobate (BZN) thin fllm has been proposed and demonstrated for low-voltage phase shifter applications. In order to reduce the operation bias voltage the air gaps between the signal strip and ground plane are fllled with the tunable thin fllms. At low E-flelds of 1.3kV/cm, the fabricated CPW line shows the phase difierence of 10 degree at 10GHz.

Very High Tunable Inter-Digital Capacitor Embedded Fully into BZN Thin Film Dielectrics for Microwave Applications

In this paper, a tunable inter-digital capacitor (IDC) using the bismuth zinc niobate (BZN) pyrochlore thin film dielectrics is presented for microwave applications. In order to reduce the DC bias voltage and to increase the tunability of the IDC, its electrodes are fully embedded into the tunable BZN dielectrics. At 20 V DC applied, the IDC yields 75 % tunability at 5.8 GHz. This tunability is the highest at microwave frequencies, as far as authors know

Tunability of Bi-rich BZN Cubic Pyrochlore Thin Films by Reactive Sputtering

(Bi 3x Zn 2−3x )(Zn x Nb 2−x )O 7 thin films (x=1/2 and 2/3) have potential great for tunable RF and microwave devices due to medium dielectric constant and low dielectric loss. The tunable dielectric properties of Bi-rich, (Bi 1.5 Zn 0.5 )(Zn 0.5 Nb 1.5 )O 7 thin films were investigated. To make Bi-rich cubic pyrochlore thin films, Bi 2 O 3 –ZnO–Nb 2 O 5 monoclinic pyrochlore ceramic targets were used in reactive RF magnetron sputtering process. Substrate heating was employed to improve surface morphology and tunability. As-deposited films were crystallized or amorphous state depending on substrate temperature. All films were annealed at 600°C ∼ 800°C for 3 hours in the air. There were no zinc niobate secondary phases in the films before and after post-annealing, while quite significant amount BZN thin films were found in sputtered using cubic pyrochlore ceramic targets, especially after post-annealing. It was found that Bi-rich BZN films have much larger tunability when as-deposited phase are amorphous. The maximum tunability 38% was obtained when substrate is heated to 350°C and composition of films is close to exact stoichiometric cubic BZN.

Low-voltage and high-tunability inter-digital capacitors using lead zinc niobate (PbO-ZnO-Nb 2 O 5 ) thin films

In this work, we present tunable inter-digital capacitors (IDCs) employing high tunable PbO-ZnO-Nb2O5 (PZN) cubic pyrochlore thin film dielectrics for low-voltage and high-tunability microwave applications. In order to reduce the bias voltage of the IDC and increase its tunability, its electrodes were fully embedded into the thin film dielectrics to confine fringing electric fields within them. In 4 V, the tunability of the IDCs was analyzed in terms of the electrode width and spacing by measuring reflection coefficients at 1 GHz. The fabricated IDC with width and spacing of 1.5 and 1.8 mum, respectively, achieved tunability of 26 % and Q-factor of 10 at the applied DC voltage of 5.5 V.

RF Sputtered BZN Pyrochlore Thin Films for Voltage Tunable Dielectric Device Applications

The BZN pyrochlore thin films were prepared on platinized Si substrates using a reactive RF magnetron sputtering. The structures, surface morphologies, dielectric properties and voltage tunable properties of films with deposition parameters were investigated. The BZN thin films have a cubic pyrochlore phase and secondary phases of zinc niobate, bismuth niobate when crystallized at 6001C - 8001C. The dielectric constant and tunability of thin films are O2/Ar ratio and post-annealing temperature dependent. The BZN thin films sputtered in 15% 02 and annealed at 700°C had a dielectric constant of 153, tan 8 of -0.003 and maximum tunability of 14% at 1,000kV/cm.