Ryouichi Takayama

PIEZOELECTRIC PROPERTIES OF C-AXIS ORIENTED PB(ZR,TI)O3 THIN FILMS

Piezoelectric properties of the c-axis oriented Pb(Zr,Ti)O3 (PZT) thin films were investigated. The PZT films with a composition near the morphotropic phase boundary were epitaxially grown on (100)Pt-coated MgO substrates by rf-magnetron sputtering. The PZT films exhibited excellent ferroelectricity with a remanent polarization more than 50 μC/cm2. In order to examine intrinsic piezoelectric properties, cantilever structures were microfabricated with the PZT films. The piezoelectric coefficient d31 of PZT films, which were not subjected to poling treatments, was measured directly from the transverse expansion of the cantilever beams. The measurements revealed that the PZT films were naturally polarized and had a relatively large piezoelectric coefficient d31 of 100×10−12 m/V without poling.

Superlattices of PbZrO3 and PbTiO3 prepared by multi‐ion‐beam sputtering

Artificial superlattices consisting of antiferroelectric PbZrO3 (PZO) and ferroelectric PbTiO3 (PTO) have been fabricated by a multi‐ion‐beam sputtering technique. The epitaxial PZO and PTO layers were sequentially grown on (100)Pt/MgO substrates at a low substrate temperature of 415 °C with a periodicity from 5 to 100 perovskite unit cells. X‐ray diffraction studies revealed the superlattice structures with a‐axis oriented PTO layers on a‐axis oriented PZO layers. The dielectric and ferroelectric properties of the superlattice films were enhanced with increasing periodicity.

Crystallographic characterization of epitaxial Pb(Zr,Ti)O3 films with different Zr/Ti ratio grown by radio-frequency-magnetron sputtering

Crystallographic structure of as-grown epitaxial Pb(Zr,Ti)O3 (PZT) films was investigated with regard to the Zr/Ti ratio and crystalline orientation. PZT films with (001) and (111) orientation were epitaxially grown on (100) and (111)SrTiO3 substrates respectively using radio-frequency (rf) sputtering. Four circle x-ray diffraction measurements revealed that the crystallographic dependence on Zr/Ti composition in PZT films was much different from bulk PZT. In particular, (001)-oriented PZT films showed tetragonal structure even in the Zr/Ti composition of 70/30 where the bulk PZT ceramics are rhombohedral phase. In addition, although (001)-oriented PZT films with Zr/Ti ratio of 53/47 and 70/30 showed tetragonal structure, (111)-oriented PZT films with the same Zr/Ti ratio were identified as the rhombohedral structure. The cell volume of the PZT films with both orientations increased, suggesting the excess Pb atoms in the films due to the impinging energetic sputtered particles induces the anomalous crysta...

Antiferroelectric PbZrO3 thin films prepared by multi‐ion‐beam sputtering

Antiferroelectric PbZrO3 thin films have been fabricated by a multi‐ion‐beam sputtering technique at a substrate temperature as low as 415 °C. Single crystal perovskite PbZrO3 films oriented along the a axis could be epitaxially grown on (100)MgO, (100)Pt/MgO substrates using a PbTiO3 buffer layer. The PbZrO3 films achieved high dielectric constants of about 400, which are almost 2.4 times larger than that of bulk PbZrO3. The measurements of D–E hysteresis loops and Curie temperature demonstrated the antiferroelectric to ferroelectric phase transition of PbZrO3 films with a thickness of 1770 A, while for PbZrO3 films of 875 A the phase transition could not be clearly observed.

Pyroelectric infrared sensors made of La-modified PbTiO3 thin films and their applications

Abstract High sensitive pyroelectric infrared (IR) sensors have been fabricated by using c-axis oriented La-modified PbTiO3 (Pb1–xLaxTi1−x/4O3, PLT) thin films. The PLT thin films were deposited on (100)-cleaved MgO single crystal substrates by intermittent rf-magnetron sputtering method. The PLT thin films have high figures of merit for IR sensor without a poling treatment. High performance pyroelectric IR sensors (single element type and linear array type) were fabricated by using PLT (x=0·1, γ=5·5x10−8 C/cm2K, ϵr=200) thin films. The sensors have remarkably high D* of 3–6x108 cmHz1/2/W and very fast response. A new compact IR sensing system using the linear array sensor (8 elements) has been developed for a new type of room air-conditioner. This system can measure thermal distribution (8x64) by horizontal scanning of the vertical linear array. Image processing with neural network concept makes possible high-accuracy using a few data from the sensor elements. This sensing system provides ‘‘smart aircond...

Processing and characterization of ferroelectric thin films by multi-ion-beam sputtering

Abstract Ferroelectric thin films of PbTiO3, (Pb,La)TiO3 (PLT) and Pb(Zr,Ti)O3 (PZT) were successfully fabricated using a multi-ion-beam sputtering technique. X-ray diffraction (XRD) measurements demonstrated that the films with perovskite structure were grown on (100)Pt MgO and (111)Pt/Ti/SiO2/Si substrates at a low substrate temperature of 415°C. The PZT films about 630 A in thickness exhibited a high dielectric constant of 675 and an excellent ferroelectric P-E hysteresis loop. In order to promote the surface reactions, the substrates were irradiated with XeCl excimer laser beam during the deposition at a room temperature. The results of XRD revealed the formation of perovskite PZT thin films.