Yuzo Katayama

Electrical properties of (Zr,Sn)TiO4 dielectric thin film prepared by pulsed laser deposition

We have been successful in obtaining temperature‐stable crystallized thin film of (Zr,Sn)TiO4. Preferential (111)‐oriented (Zr,Sn)TiO4 thin film was prepared by pulsed laser deposition. Effects of crystallization were elucidated based on a comparison of electric properties of crystallized and amorphous (Zr,Sn)TiO4 film. For crystallized film, the temperature coefficient of capacitance (TCC) was 20 ppm/°C at 3 MHz and the dielectric constant er=38 in the microwave range of 1–10 GHz. These values are superior to those for amorphous film (TCC=220 ppm/°C, er=27). The crystallization of this material was found quite effective for improving dielectrical properties. Atomic force microscope images showed the surface morphologies of crystallized and amorphous film of (Zr,Sn)TiO4 to differ.

Optimization of zinc oxide thin film for surface acoustic wave filters by radio frequency sputtering

Abstract Electrical characteristics of zinc oxide (ZnO)/glass surface acoustic wave (SAW) filters, the structure of which is ZnO thin film on a glass substrate with aluminum inter digital transducers, are greatly influenced by deposition parameters of a radio frequency sputtering for making ZnO thin films. The deposition conditions for making the ZnO thin film are also considered to obtain good piezoelectricity for SAW devices. Oxygen concentration in the radio frequency sputtering greatly affects the properties of ZnO thin films. The interface microstructure of ZnO thin films is investigated by cross-section transmission electron spectroscopy. The growth figures of ZnO on glass and ZnO on Al are similar. The average crystal size of ZnO on glass is larger than that of ZnO on Al.

Fabrication and Characterization of (Sr, Ba)Nb2O6 Thin Films by Pulsed Laser Deposition

Thin films of (Sr, Ba)Nb2O6 (SBN) have been fabricated using a pulsed laser deposition technique. The c-axis oriented films were obtained on SrTiO3 (100) substrates at temperatures higher than 650° C in an oxygen atmosphere (containing 8% O3) of 3 mTorr. Phi scans on the (221) plane showed that the films have two antiphase domains. The a-axis of SBN is aligned at ±18.4° with respect to the a-axis of SrTiO3. The epitaxial relationship between SBN and SrTiO3 is SBN // SrTiO3 . The lattice mismatch between SBN films and SrTiO3 substrates is less than 1%, which contributes to the exellent crystallinity of SBN thin films. The rocking curves of the (002) peak of SBN films grown at 700° C showed the FWHM of 0.31°.

Influence of H2O partial pressure in the sputtering chamber on the crystallinity and relative dielectric constant of SrTiO3 thin film prepared at low substrate temperature

Abstract It has been investigated here how the crystallinity and relative dielectric constant of low-temperature sputtered SrTiO 3 film is influenced by H 2 O partial pressure the in deposition chamber. With increasing H 2 O partial pressure, the relative dielectric constant of SrTiO 3 film prepared at a substrate temperature of 280°C tends to degrade, and the amorphous layer in the interface between bottom electrode and dielectric film increases in thickness observed in TEM images. H 2 O partial pressure and relative dielectric constant can be estimated from in situ spectrum analysis of hydrogen in plasma emission. The monitoring and control of H 2 O partial pressure are necessary for the SrTiO 3 deposition process to achieve stable dielectric properties.

Crystallinity and Surface Morphology of Epitaxial (Sr,Ba)Nb 2 O 6 Thin Film Prepared by Pulsed Laser Deposition with Two-Step Growth Sequence

We have prepared epitaxially grown SBN thin film with c-axis orientation by an ArF pulsed laser deposition on SrTiO 3 (100). Pole figures show that the SBN film has a twin structure aligned at ±18.4: with the a-axis of SrTiO 3 . The epitaxial relationship of SBN //SrTiO 3 is determined. The lattice mismatch between SBN and SrTiO 3 is approximately 0.9%, which contributes to the desirable crystallinity of the SBN thin film. Furthermore, we have tried to form the SBN film with a two-step growth sequence in order to improve surface morphology. The amorphous initial growth region of 5 monolayers (2 nm thickness) is prepared with no substrate heating followed by post-annealing treatment at 720°C and additional growth on the initially crystallized layer. RHEED patterns of the SBN film with the two-step growth sequence have remained streaky throughout the film formation, compared with spotty patterns observed from films prepared by a conventional sequence. Atomic force microscope (AFM) images show that both the initial stage and final stage have extremely flat surfaces of rms≦ lnm which is a remarkably improved figure compared with the roughness rms ≧3nm for the film deposited at 720°C from the initial stage. These results suggest that the two-step growth sequence makes it possible to improve surface morphology to a nanometer level.

Ba0.3Sr0.7TiO3 Thin Film Production on Atomically Flat SrTiO3 (100) Substrates by a Pulsed Laser Deposition and Dielectric Properties

Atomically flat SrTiO3 (100) substrates have been obtained using annealing treatments at 1000° C in O2 flow. Ba0.3Sr0.7TiO3 (BSTO) films have been produced on these substrates using a pulsed laser deposition. Film thickness dependence on the dielectric constants of the BSTO films are examined in this study. The BSTO films produced on these atomically flat SrTiO3 substrates showed higher dielectric constants than those formed on the commercially supplied SrTiO3 substrates. It is considered that this phenomenon is caused by the stresses of the mismatch between the films and substrates. The interface flatness between the films and substrates is measured by transmission electron microscopy (TEM) which is desirable for the production of dielectric films.

Preparation and electrical properties of (Zr,Sn)TiO{sub 4} dielectric thin films by laser ablation

(Zr,Sn)TiO{sub 4} is considered as a promising dielectric material for microwave devices owing to the temperature stability of capacitance and excellent microwave properties. Preferential (111)-oriented (Zr,Sn)TiO{sub 4} thin film was obtained by an ArF laser ablation. Properties of the crystallized film were as follows; the temperature coefficient of capacitance TCC was 17.6 ppm/C at 3 MHz and the dielectric constant {var_epsilon}{sub r}, 38 in the microwave range of 1GHZ--10GHz. It has turned out that the crystallization of this material is quite effective for improving dielectrical properties. Surface morphologies were observed by atomic force microscope (AFM). Grains grew on the crystallized film at 1 {micro}m x 1 {micro}m size.