Ryoichi Takayama

Preparation of c-axis oriented PbTiO3 thin films and their crystallographic, dielectric, and pyroelectric properties

Highly c‐axis oriented and epitaxial PbTiO3 thin films were grown on MgO single crystals and epitaxial Pt film substrates by the rf‐magnetron sputtering method. The films with a 98% c‐axis orientation rate were obtained under low deposition rate (<20 A/min) and low gas pressure (∼1 Pa) using a PbO‐rich target. Phase transition of the PbTiO3 thin film was studied by high‐temperature x‐ray diffraction. It was found that the c‐axis of the tetragonal phase was parallel to the substrate just below Tc and the c‐axis becomes perpendicular to the substrate with lowering of temperature. These films show high resistivity (∼1010/Ω cm). It was found that significant pyroelectric currents are detected on all specimens without poling treatment. The polarization directions of the films are the same in all specimens. One of these films had a low relative dielectric constant of 97 and a high pyroelectric coefficient of 2.5×10−8 C/cm2 K without poling treatment. These films will be suitable for applications such as pyroele...

Preparation of epitaxial Pb(ZrxTi1−x)O3 thin films and their crystallographic, pyroelectric, and ferroelectric properties

Lead zirconate‐titanate (PZT) thin films with tetragonal and rhombohedral structures have been successfully grown with good epitaxy on MgO single crystals and on [100]‐oriented platinum thin films by rf‐magnetron sputtering. The PZT films were obtained by using sputtering targets with compositions of Pb(ZrxTi1−x)O3, where x=0.2–0.8. The tetragonal PZT thin films have a strong [001] orientation, and the rhombohedral ones are (100) oriented. Asymmetric D‐E hysteresis loops were observed on the tetragonal films. Nearly symmetric loops were observed on the rhombohedral films and the rhombohedral loops around the morphotropic phase boundary had slim loops. The tetragonal thin films of x=0.45 have a spontaneous polarization of 45 μC/cm2, a remanent polarization of 40 μC/cm2, and a coercive field of 150 kV/cm. It was found that significant pyroelectric currents are detected on both [001]‐oriented tetragonal and (100)‐oriented rhombohedral PZT films even without a poling treatment, and the direction is the same i...

Epitaxial growth and the crystallographic, dielectric, and pyroelectric properties of lanthanum‐modified lead titanate thin films

Using an rf‐magnetron sputtering method, highly c‐axis‐oriented La‐modified PbTiO3 (PLT) thin films with compositions of Pb1−xLaxTi1−x/4O3, where x=0.05, 0.10, and 0.15, have been obtained on MgO single‐crystal and epitaxial Pt thin‐film substrates under conditions of low gas pressure and low deposition rate. The degree of c‐axis orientation of the PLT films decreases, and the tetragonality of PLT becomes smaller with increasing La content. The Curie point of the films decreases at a rate of 18 °C/at. % of La with an increase of La content. D‐E hysteresis loops were observed, and these became slim and symmetric with increasing La. It was found that significant pyroelectric currents are detected on all as‐grown specimens even without a poling treatment, and the directions are the same in all specimens. Relative dielectric constant er decreases, and pyroelectric coefficient γ increases with increasing degree of c‐axis orientation. er and γ became large with increase of La content in the films. Considering t...

Preparation and characteristics of pyroelectric infrared sensors made of c‐axis oriented La‐modified PbTi03 thin films

Highly c‐axis oriented La‐modified PbTiO3 (PLT) thin films were deposited on (100) oriented Pt thin film or (100) cleaved MgO single crystals by rf‐magnetron sputtering. Figures of merit for infrared detector were studied on the PLT thin films. It was found that a composition Pb1−xLaxTi1−x/4O3 where x=0.10 (PL10) was the most suitable for the infrared detector. The films have the advantage of having pyroelectric effect and polarization with the same direction even without a poling treatment. The films have high figures of merit Fv(=γ/cver) of 0.83×10−10 (C cm/J) and Fm(=γ/cv(er tan δ)1/2) of 1.2×10−8 (C cm/J) because of relative low‐dielectric constant er of 200 and high‐pyroelectric coefficient γ of 5.3×10−8 C/cm2 K. Both the Fv and the Fm of the films are 3 times as large as those of PbTiO3 ceramics. High sensitive pyroelectric infrared sensors were fabricated by using the PL10 films. The thickness of the films is 2 μm, and the electrodes were vacuum evaporated Ni‐Cr of approximate area 7×10−4 cm2. The ...

Preferred Orientations of NiO Films Prepared by Plasma-Enhanced Metalorganic Chemical Vapor Deposition

Thin films of nickel oxide (NiO) with NaCl-type structure were prepared on glass substrates at 400°C by plasma-enhanced metalorganic chemical vapor deposition using nickel acetylacetonate as a source material. The relationship between O2 flow rate, and preferred orientation and microstructure of the NiO films was investigated. Highly crystalline NiO film with (111) orientation was obtained at O2 flow rates as low as 3 cm3/min. As the O2 flow rate increased from 3 to 70 cm3/min, the orientation of NiO films changed from (111) to (100) and deposition rate decreased from 17 to 11 nm/min. Films with both (111) and (100) orientation had columnar structure. The origin of the preferred orientation of the NiO films was discussed.

Pyroelectric linear array infrared sensors made of c-axis-oriented La-modified PbTiO3 thin films

High sensitive pyroelectric linear array infrared sensors have been fabricated by using highly c‐axis‐oriented and spontaneous polarized La‐modified PbTiO3 (PLT) thin films. The PLT thin films were deposited on (100)‐oriented Pt thin film on (100)‐cleaved MgO single crystals by rf magnetron sputtering. The PLT thin films have high figures of merit for voltage responsivity (Rv) and specific detectivity (D*) without a poling treatment. Two types of linear array sensors, reticulated and nonreticulated ones, were fabricated. The reticulated and nonreticulated sensors have 64 elements with 200‐μm pitch and 128 elements with 100‐μm pitch, respectively. Ni‐Cr electrodes of approximate area 1.9×10−4 or 3.0×10−4 cm2 were deposited by vacuum evaporation on the PLT thin films with a thickness of 3–4 μm. Pyroelectric coefficients and their uniformity increased upon decreasing the deposition area of an element. Therefore, the elements of reticulated sensors have considerably larger Rv and D* compared with the nonretic...

Pyroelectric properties and application to infrared sensors of PbTiO3, PbLaTiO3 and PbZrTiO3 ferroelectric thin films

Abstract Highly c-axis oriented PbTiO3 and Pb1−xLaxTi1−x/4O3(PLT), and PbZrxTi1−xO3(PZT) thin films were successfully grown with good epitaxy on MgO single crystal and (100)-oriented Pt thin films by rfmagnetron sputtering method. It was found that the thin films have remarkably large pyroelectric effect and high figures of merit for infrared sensors without a poling treatment. The PLT thin films with x = 0.1 have high pyroelectric coefficient γ of 6.5 × 10−8 C/cm2 K and relatively low dielectric constant e r of 200. High performance pyroelectric infrared sensors (single element and linear array) were fabricated by using the PLT thin films, the new structures and device processes. The single element sensors have remarkably high D* (500, 25, 1) of 5 × 108 cmHz1/2/W and very fast response. Another type of single element sensors with high sensitivity at low frequency can be also offered. The linear array sensors with reticulated PLT films (64 elements, 5 elements/mm) have a small cross talk of 3% at 100 Hz. ...

Preparation of (001)-oriented Pb(Zr,Ti)O/sub 3/ thin films and their piezoelectric applications

Preparation of (001) oriented Pb(Zr,Ti)O3 (PZT) thin films and their applications to a sensor and actuators were investigated. The (001) oriented PZT thin films were epitaxicially grown on (100)Pt/(100)MgO single crystal substrates by rf-magnetron sputtering. The PZT thin films on (100)Pt/(100)MgO buffer layer/glass substrates and (11 l)Pt/Ti/Si substrates also had high (001) orientation. All of these thin films showed the excellent piezoelectric properties without a poling treatment. These PZT thin films were applied to the angular rate sensor with a toning fork for a car navigation system, the dual-stage actuator for positioning a magnetic head of high-density hard disk drive (HDD) and the actuator for a inkjet printer head.

NaCl-Type Oxide Films Prepared by Plasma-Enhanced Metalorganic Chemical Vapor Deposition

Thin films of MgO, NiO and CoO with NaCl-type structure were prepared by plasma-enhanced metalorganic chemical vapor deposition using metal acetylacetonato complexes as source materials. Soda-lime glass, Si(111), stainless steel and fused silica were used as the substrates. X-ray diffraction patterns indicated that (100) preferred-orientation NaCl-type oxide films were obtained at substrate temperatures of 150°C or above, independent of the kind of substrate. Scanning electron microscopy images showed that each film had a smooth surface and a columnar structure with growth perpendicular to the film surface.

Pyroelectric infrared array sensors made of c-axis-oriented La-modified PbTiO3 thin films

Highly sensitive pyroelectric infrared sensors (linear array and two-dimensional array) have been fabricated by using highly c-axis-oriented La-modified PbTiO3 (PLT) thin films, together with a new process and new sensor structures. The PLT thin films were deposited by RF magnetron sputtering. The films have a high pyroelectric coefficient γ of 6.5 × 10−8 C/cm2 K and a high figure of merit for specific detectivity D* without a poling treatment. Two types of linear array sensors, reticulated and non-reticulated ones, have been fabricated. The reticulated and non-reticulated sensors have 64 elements with 0.2 mm pitch and 128 elements with 0.1 mm pitch, respectively. A remarkably high D* value of 5 × 108 cm Hz 12/W and a very low crosstalk of < 3% at 100 Hz have been attained. The linear array and discrete JFET chips are incorporated within a pin-grid package. A high performance two-dimensional sensor with 32 × 32 elements based on a new method of reading-out signals can be formed. An array sensor with a new device structure has been designed by using an optical scanning slit. On the infrared system with F = 1 optics and Δf = 20 Hz filter, a noise equivalent temperature of 0.2 K has been obtained.