Cheng-Shing Hsu

Effect of CuO additive on sintering and microwave dielectric behavior of LaAlO3 ceramics

Abstract The dielectric properties and the microstructures of LaAlO 3 ceramics with CuO additions (0.25–1 wt%) have been investigated. The sintered LaAlO 3 ceramics are characterized by X-ray diffraction spectra and scanning electron microscopy (SEM). The ceramic samples show that a dielectric constant (ϵ r ) of 19–22 and a Q × f value of 5000–48,000(at 9.7 GHz) can be obtained at low sintering temperatures of 1370–1460°C. The temperature coefficient of resonant frequency varies from −50 to −80 ppm/°C. At the level of 0.5 wt% and 1 wt% CuO additions, low Q × f value of the LaAlO 3 ceramics is owing to the formation of the second phase LaAl 11 O 18 . With CuO addition, an 100–200°C reduction in sintering temperature can be achieved for the LaAlO 3 ceramics.

Improved high-Q microwave dielectric resonator using ZnO and WO3-doped Zr0.8Sn0.2TiO4 ceramics

Abstract The effect of WO 3 addition on the microstructures and the microwave dielectric properties of Zr 0.8 Sn 0.2 TiO 4 ceramics have been investigated. It is found that low-level doping of ZnO (1 wt%) and WO 3 (up to 1 wt%) can significantly improve the density and dielectric properties of Zr 0.8 Sn 0.2 TiO 4 ceramics. Zr 0.8 Sn 0.2 TiO 4 ceramics with additives could be sintered to a theoretical density higher than 98% at 1340°C. Second phases were not observed at the level of 0.25–1 wt% WO 3 addition. The dielectric constant (ϵ r ) and the temperature coefficient of resonant frequency (τ f ) were not significantly affected, while the unloaded quality factors Q were effectively promoted by WO 3 addition. An ϵ r value of 37.8, Q· f value of 61,000 (at 7 GHz), and τ f value of −3.9 ppm/°C were obtained for 1 wt% ZnO-doped Zr 0.8 Sn 0.2 TiO 4 ceramics with 0.25 wt% WO 3 addition sintered at 1340°C.

Improved high Q value of 0.5LaAlO3-0.5SrTiO3 microwave dielectric ceramics at low sintering temperature

The dielectric properties and the microstructures of 0.5LaAlO3-0.5SrTiO3 ceramics with B2O3 additions (0.25 − 1 wt%) prepared with conventional solid-state route have been investigated. Doping with B2O3 (up to 0.5 wt%) can effectively promote the densification and the dielectric properties of 0.5LaAlO3-0.5SrTiO3 ceramics. It is found that LaAlO3-SrTiO3 ceramics can be sintered at 1400°C due to the liquid phase effect of B2O3 addition observed by Scanning Electronic Microscopy. The dielectric constant as well as the Q × f value decreases with increasing B2O3 content. At 1430°C, 0.5LaAlO3-0.5SrTiO3 ceramics with 0.25 wt% B2O3 addition possesses a dielectric constant (e r) of 34.5, a Q × f value of 43,200 (at 7 GHz) and a temperature coefficient of resonant frequency (τf) of −10.7 ppm/°C.

Dielectric properties of 0.95Ba(Zn1/3Nb2/3)O3-0.05BaZrO3 ceramics at microwave frequency

Abstract The microwave dielectric properties of conventional solid-state route prepared 0.95Ba(Zn 1/3 Nb 2/3 )O 3 –0.05BaZrO 3 ceramics have been investigated. Ordering structure was not observed at sintering temperatures 1350–1500 °C. The dielectric constant values ( e r ) saturated at 40–41. BaZrO 3 was found to effectively promote the Q × f value of Ba(Zn 1/3 Nb 2/3 )O 3 ceramics. The Q × f values of 15,000–96,000 (at 7 GHz) can be obtained when the sintering temperatures are in the range of 1350–1450 °C. The temperature coefficient of resonant frequency τ f was a function of sintering temperature. The e r value of 42, Q × f value of 96,000 (at 7 GHz) and τ f value of 27 ppm/°C were obtained for 0.95Ba(Zn 1/3 Nb 2/3 )O 3 –0.05BaZrO 3 ceramics sintered at 1450 °C for 2 h. For applications of high selective microwave ceramic resonator and filter, 0.95Ba(Zn 1/3 Nb 2/3 )O 3 –0.05BaZrO 3 is proposed as a suitable material candidate.

Effect of RF power and substrate temperature on physical properties of Zr0.8Sn0.2TiO4 films by RF magnetron sputtering

Physical properties of rf-sputtered crystalline (Zr0.8Sn0.2)TiO4 (ZST) thin films deposited on n-type Si(100) substrates at different rf powers and substrate temperatures have been investigated. The structural and morphological characteristics analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) were found to be sensitive to deposition conditions, such as rf power from 300 W to 400 W and substrate temperature (400°C, 450°C). Highly oriented ZST (111) and (002) perpendicular to the substrate surface were identified at a rf power of 400 W and a substrate temperature of 450°C. The selected-area diffraction pattern showed that the deposited films exhibited a polycrystalline microstructure. The grain size as well as the deposition rate of the film increased with the increase in both the rf power and the substrate temperature. The leakage current decreased with increasing rf power and substrate temperature. As rf power=400 W and substrate temperature=450°C, a leakage current of 7.2×10-11 A was obtained at 1 V.