Hyun Jai Kim

Microwave Dielectric Properties of LaZn0.5Ti0.5O3 Ceramics Prepared by Sol–Gel Process

Some dielectric properties of LaZn0.5Ti0.5O3 (LZT) ceramics prepared by means of the sol–gel method have been investigated. The calcination of powders derived from amorphous gel at 600° C results in the formation of a pure orthorhombic phase of LZT. The high sintering ability of the prepared powders enables the fabrication of dielectric ceramics at low sintering temperatures (1350–1400° C). At higher temperatures, the sintering process is followed by a decomposition reaction with the formation of La2TiO5 and ZnO vapor. A dielectric material having e r30 and Qf060000 GHz is obtained at 1350° C.

Effect of ZnO additive on microstructure and microwave dielectric properties of CaTi1-x(Fe0.5Nb0.5)xO3 ceramics

The microwave dielectric properties of the CaTi1-x (Fe0.5Nb0.5)x O3 (0.4≤x≤0.7) solid solutions and the influence of 1 wt% ZnO as a sintering additive are investigated. With the increase of x, dielectric constant (er) and product of quality factor and frequency (Qf) decrease. The temperature coefficient of resonant frequency (τf) value of nearly 0 ppm/°C can be realized for x=0.54. The properties of this material are: er=59.9, Qf=3870 GHz. ZnO forms a liquid phase on the grain boundaries and improves the sinterability and grain growth. The correlation between average grain size and Q-factor is observed for ZnO-doped ceramics.

Dielectric Properties of ( 1-x)CaTiO3–xLa(Zn1/2Ti1/2)O3 Ceramics at Microwave Frequencies

The microwave dielectric properties and sintering conditions of the (1- x)CaTiO3– xLa(Zn1/2Ti1/2)O3 system were investigated for the development of a microwave dielectric material having a high Qf0, moderate er and zero τf. A microwave dielectric material having er of 50, Qf0 of 38000, and τf of zero was obtained from the compound 0.5CaTiO3–0.5La(Zn1/2Ti1/2)O3. The sintering temperature of compounds decreased with increasing amount of La(Zn1/2Ti1/2)O3 and a cooling rate of less than 3° C/min was optimum for obtaining the best Qf0 for all compositions tested.

Low Temperature Sintering of ZnO-Doped 0.01Pb(Mg1/2W1/2)O3?0.41Pb(Ni1/3Nb2/3)O3?0.35PbTiO3?0.23PbZrO3 Ceramics

ZnO was added to 0.01Pb(Mg1/2W1/2)O3–0.41Pb(Ni1/3Nb2/3)O3–0.35PbTiO3–0.23PbZrO3 (0.01PMW–0.41PNN–0.35PT–0.23PZ) ceramics to reduce their sintering temperatures to below 900 °C. The effects of the ZnO additive on the densification and piezoelectric properties of the PMW–PNN–PT–PZ + 0.1 wt % Y2O3 + x wt % ZnO (0≤x≤2.5) ceramics were investigated. The structure of the PMW–PNN–PT–PZ ceramics was found to change from pseudocubic to tetragonal as their ZnO content was increased. The piezoelectric constant, the mechanical quality factor, and the electromechanical factor of the ceramics increased as their ZnO content increased. The optimum piezoelectric properties were found to be d33=594 pC/N, kp=57%, and Qm=64, for PMW–PNN–PT–PZ + 0.1 wt % Y2O3 + 1.5 wt % ZnO sintered at 900 °C for 2 h.

Microwave Dielectric Properties of the (1-x)La2/3TiO3–xLaAlO3 System

The microwave dielectric properties of the (1- x)La2/3TiO3– xLaAlO3 system in which LaAlO3 having e r=22, Qf0=46,000 (at 7 GHz), and τ f=-40–-50 ppm/° C was incorporated with La2/3TiO3 having e r≥90 and positive τ f was investigated. The (1- x)La2/3TiO3– xLaAlO3 crystal system was pseudo-cubic in the range 0.1≤x≤0.7. Its lattice constant increased with increasing x even though the amount of LaAlO3 containing Al(0.57 A) ions which are smaller than Ti(0.64 A) increased. As the amount of LaAlO3 increased from x=0.1 to 0.9, the relative dielectric constant (e r) decreased from 50 to 23 and the temperature coefficient of the resonant frequency (τ f) decreased from +84 to -50. On the other hand, the value of Qf0 reached a maximum (148000 at 9.7 GHz) at x=0.7, where a rapid increase in the peak intensity of XRD occurred, and further increased after prolonged sintering. The microwave dielectric properties of e r=37, Qf0=47000 GHz (f0=9 GHz), and τ f=-2 ppm/° C were obtained near 0.6La2/3TiO3–0.4LaAlO3 (x=0.4) composition.

Microwave Dielectric Properties of (Pb, Ca)(Mg, Nb, Sn)O3 Ceramics

The microwave dielectric properties of (Pb0.4Ca0.6){(Mg1/3Nb2/3)1-xSnx}O3 (0≤x≤0.1) ceramics have been investigated. The (Pb0.4Ca0.6)(Mg1/3Nb2/3)O3 ceramic was tetragonal complex perovskite single phase material and single phase specimens having tetragonal complex perovskite could also be obtained in case of substituting by tin(Sn). The partial substitution of [Mg1/3Nb2/3]4+ by Sn4+ at B-site of the perovskite structure significantly improves the loss quality factor (Q) and slightly decreases dielectric constant (er) and temperature coefficient of resonant frequency (τf). The temperature coefficient of resonant frequency of 0 ppm/°C was realized at x=0.01. The Qfo value and er for this composition were found to be 7130 GHz and 64.7 respectively.

Effect of yttrium dopping on the ferroelectric fatigue and switching characteristics of Pb(Zr0.65Ti0.35)O3 thin films prepared by sol-gel processing

Abstract Variations of remanent polarization and coercive field of undoped and yttrium doped Pb(Zr0.65Ti0.35)O3 thin films prepared by Sol-Gel processing were observed using hysteresis measurement according to the cumulative switching cycles. Remanent polarization and coercive field of undoped Pb(Zr0.65Ti0.35)O3 thin films after 1010 polarization reversals were decreased and increased, respectively. But the variations of remanent polarization and coercive field of yttrium doped specimens with the polarization switching cycles were different from those of undoped specimens. In the case of yttrium doped specimens, remanent polarizations were not decreased and coercive fields were increased more than those of undoped specimens after fatigue. It was well known that doped yttrium reduced holes and increased vacancies in PZT thin films. This strongly suggests that the variations of holes and vacancies influence on the remanent polarizations and the coercive fields of Pb(Zr0.65Ti0.35)O3 thin films after fatigue....

Frequency tuning of unimorph cantilever for piezoelectric energy harvesting

Thin Film Materials Research Center, Korea Institute of Science & Technology, Cheongryang, Seoul 130-650, Korea*School of Electrical Engineering, College of Engineering, Korea Univ. Korea(2007 9 21 :2007 12 6 )Abstract Piezoelectric energy harvesting from our surrounding vibration has been studied for driving thewireless sensor node. To change the vibration energy into the electric-energy efficiently, the natural frequency ofcantilever needs to be adjusted to that of a vibration source. When adding 6.80g mass on the end of the fabricatedcantilever, a natural frequency shifts from 136 Hz into 49.5 Hz. In addition, electro-mechanical coupling factorincreased from 10.20% to 11.90% and resulted in the 1.18 times increase of maximum output power.Key wordsEnergy harvesting, Piezoelectric, Frequency tuning.

Analysis of Inhomogeneous Stress Distribution in the Piezoelectric Ceramics of Unimorph Cantilever for Energy Harvesting

Energy harvesting from the vibration through the piezoelectric effect has been studied for powering the wireless sensor node. As piezoelectric unimorph transducer structure can transfer low vibration to large displacement, this structure was commonly deployed to harvest electric energy from vibrations. Piezoelectric unimorph structure was composed of small stiff piezoelectric ceramic on the large flexible substrate. As there is the large Youngs modulus difference between the flexible substrate and stiff piezoelectric ceramic, flexible substrate could not homogeneously transfer the vibration to the stiff piezoelectric ceramic. As a result, most piezoelectric ceramics had been broken at the certain point. Even though the same stress was applied to unimorph cantilever at the end of the unimorph cantilever, there was the difference in output voltages depending on the potion of ceramics. The ratio of the lowest and highest voltage was around 2.4, which reveals the inhomogeneous stress distribution in ceramics.

A High Throughput Search of Dielectric Thin Films for Tunable Devices

The dielectric properties of (Ba,Sr)TiO3 (BSTO) and Zr doped BSTO thin films have been investigated to identify candidate thin film dielectric materials having low dielectric loss without degradation of the tunability by continuous composition spread (CCS) technique using off-axis rf magnetron sputtering. The optimized properties of BSTO thin films deposited on Pt/SiO2/Si substrate by CCS were dielectric loss 0.031, tunability 31.5, respectively. The optimized properties of Zr doped BSTO thin films deposited on Pt/SiO2/Si substrate by CCS were improved by dielectric loss 42%, FOM 68% at the same BSTO composition, respectively. To confirm the dielectric properties and compositions by CCS technique, Zr doped BSTO bulk ceramics were evaluated.