Jae-Hwan Park

Electric-field induced strains and pyroelectric coefficients in lead magnesium niobate-lead titanate solid solutions

Abstract In order to understand the electrostrictive behavior of Pb(Mg 1 3 Nb 2 3 )O 3 -PbTiO 3 (PMN-PT ) solid solutions, the dielectric constants, the electric field induced strains, the electric-field induced polarization, and the pyroelectric coefficients of (1 − x)PMN-xPT (x = 0.1 ~ 0.4) were investigated in the temperature range −50 °C ~ 200 °C. For x = 0.1 ~ 0.35, where the phase transition is diffuse, the strain has a maxima at the temperature of maximum pyroelectric coefficient (depolarizing temperature) rather than the temperature of maximum dielectric constant (Curie temperature). For x = 0.4, where the phase transition is relatively sharp, the strain decreases monotonically as the temperature increases. Relationships among the above experimental results are discussed.

Piezoelectric properties of Nb2O5 doped and MnO2—Nb2O5 co-doped Pb(Zr0.53Ti0.47)O3 ceramics

The effects of Nb2O5 addition and MnO2‐Nb2O5 co-addition on the piezoelectric properties of Pb(Zr0.53Ti0.47)O3 (PZT) ceramics are investigated. When Nb2O5 is added to PZT, the planar coupling factor (Kp) significantly increases but the mechanical quality factor (QM) as well as the electrical quality factor (QE) decreases. When MnO2 and Nb2O5 are co-doped, QM increases remarkably while Kp rarely changes. This increase in QM is ascribed to the domain pinning by Mn as is the case of previously reported MnO2-doped PZT, and the negligible change in Kp is ascribed to the barely changed tetragonality. Even though MnO2-Nb2O5 co-doped PZT shows a smaller induced strain than that of Nb2O5- doped PZT, excellent temperature stability is obtained. It is shown that MnO2‐Nb2O5 co-doped PZT may be a very suitable material for high-power piezoelectric actuators because of its high Kp, QM and QE, its low dielectric constant and its excellent temperature stability.

SnO2 반도체 나노선 네트웍 구조를 이용한 NO2 가스센서 소자 구현

Recently, one-dimensional semiconducting nanomaterials have attracted considerable interest for their potential as building blocks for fabricating various nanodevices. Among these semiconducting nanomaterials,, SnO2 nanostructures including nanowires, nanorods, nanobelts, and nanotubes were successfully synthesized and their electrochemical properties were evaluated. Although SnO2 nanowires and nanobelts exhibit fascinating gas sensing characteristics, there are still significant difficulties in using them for device applications. The crucial problem is the alignment of the nanowires. Each nanowire should be attached on each die using arduous e-beam or photolithography, which is quite an undesirable process in terms of mass production in the current semiconductor industry. In this study, a simple process for making sensitive SnO2 nanowire-based gas sensors by using a standard semiconducting fabrication process was studied. The nanowires were aligned in-situ during nanowire synthesis by thermal CVD process and a nanowire network structure between the electrodes was obtained. The SnO2 nanowire network was floated upon the Si substrate by separating an Au catalyst between the electrodes. As the electric current is transported along the networks of the nanowires, not along the surface layer on the substrate, the gas sensitivities could be maximized in this networked and floated structure. By varying the nanowire density and the distance between the electrodes, several types of nanowire network were fabricated. The NO2 gas sensitivity was 30~200 when the NO2 concentration was 5~20ppm. The response time was ca. 30~110 sec.

Effect of V2O5 on the electrical properties of TiO2-V2O5 humidity sensors

TiO2-V2O5 ceramic humidity sensors were prepared and measured to obtain the relationships between the added amount of V2O5 and the properties of the sensor elements, such as total pore volume, bulk impedance and the humidity-sensitive property in the low relative humidity region. It was observed that both the microstructure and the bulk impedance of the sensor element were strongly dependent on the added amount of V2O5. The equivalent circuit of the specimen was postulated for analysis and the sensor characteristics in low and high humidity regions are discussed. The samples which contained higher amounts of V2O5 seemed to be more strongly hygroscopic in low humidities, whereas the samples that had higher pore volumes contained water much more at high humidities.

산소플라즈마 전처리된 Polyethylene Naphthalate 기판 위에 증착된 ZnO:Ga 투명전도막의 특성

Transparent conducting oxide (TCO) films are widely used for optoelectronic applications. Among TCO materials,zinc oxide (ZnO) has been studied extensively for its high optical transmission and electrical conduction. In this study, the effectsof O2 plasma pretreatment on the properties of Ga-doped ZnO films (GZO) on polyethylene naphthalate (PEN) substrate werestudied. The O2 plasma pretreatment process was used instead of conventional oxide buffer layers. The O2 plasma treatmentprocess has several merits compared with the oxide buffer layer treatment, especially on a mass production scale. In this process,an additional sputtering system for oxide composition is not needed and the plasma treatment process is easily adopted as anin-line process. GZO films were fabricated by RF magnetron sputtering process. To improve surface energy and adhesionbetween the PEN substrate and the GZO film, the O2 plasma pre-treatment process was used prior to GZO sputtering. As theRF power and the treatment time increased, the contact angle decreased and the RMS surface roughness increased significantly.It is believed that the surface energy and adhesive force of the polymer surfaces increased with the O2 plasma treatment andthat the crystallinity and grain size of the GZO films increased. When the RF power was 100W and the treatment time was120 sec in the O2 plasma pretreatment process, the resistivity of the GZO films on the PEN substrate was 1.05×10-3Ω-cm,which is an appropriate range for most optoelectronic applications.

Properties of ZnO:Ga Thin Film Fabricated on Polyimide Substrate by RF Magnetron Sputtering

The effects of O2 plasma pretreatment on the properties of Ga-doped ZnO films on polyimide substrate were studied. GZO films were fabricated by RF magnetron sputtering process. To improve surface energy and adhesion between the polyimide substrate and the GZO film, O2 plasma pretreatment process was used prior to GZO sputtering. As the RF power and the treatment time increased, the crystallinity increased and the contact angle decreased significantly. When the RF power was 100 W and the treatment time was 120 sec, the resistivity of GZO films on the polyimide substrate was 1.90×10 Ω-cm.