Masaaki Ichiki

Structural and optical properties of poly lactic acids

Fibrous and crystal structures of a helical polymer, poly‐L‐lactic acid (PLLA), were analyzed by using x‐ray diffraction experiments. It was confirmed that the molecular residues were arranged on a nonintegral 10/3 helix as De Santis and Kovacs [Biopolymers 6, 299 (1968)] reported. The atomic positions in a monomeric unit, which were proposed by Hoogsteen, Postema, Pennings, ten Brinke, and Zugenmaier [Macromolecules 23, 634 (1990)], were validated. However, the previous reports on the positions of the two helical chains were found to be in error. The correct positions were determined. The second helical chain shifts from the base center by 0.45, 0.25, and 0.61 A along a, b, and c axes. Besides, the second chain rotates by 2.46° with respect to the first. Distribution function of the crystallites in various drawn fibers were determined as a function of spiral angle. Optical gyrations of PLLA and poly‐D‐lactic acid fibers were successfully measured by using high accuracy universal polarimeter, as functions of temperature and drawing ratio. By using x‐ray data of the change of the fibrous structure by drawing treatments, the gyration tensor components of PLLA could be calculated. It is of great interest that gyration tensor component g33 along the helical axis is extremely large, ∼(3.85±0.69)×10−2, which corresponds to a rotatory power of (9.2±1.7)×103°/mm, about two orders of magnitude larger than those of ordinary crystals. This is the first experimental evidence that helical polymers will produce enormous optical activity in the solid state. Helical polymers will be important for the elucidation of gyro‐optical properties of solids and promising for new optical applications utilizing their large optical activity.

Photovoltaic effect of lead lanthanum zirconate titanate in a layered film structure design

This letter reports on the formation of a layered film structure and the highly improved photovoltaic output of the lead lanthanum zirconate titanate (PLZT) employed. The photovoltaic current of the PLZT film per unit width was more than 102 times larger than that of bulk PLZT, while the photovoltaic voltage per unit thickness in the layered film structure was almost the same as that in bulk ceramics. These differences are due to the characteristics of the film structure and configuration of the electrode. A simple model is used for the phenomenological explanation of the improved photovoltaic effect of the PLZT film.

Electrical properties of piezoelectric sodium-potassium niobate

Piezoelectric material is one of the most important components of the micro-electro mechanical system (MEMS). Most piezoelectrics have useful multi-functions for MEMS, e.g. sensor, actuator and transducer. An AFM cantilever, scanning mirror device and pumping system for a micro-chamber, are the typical applications of piezoelectric material on MEMS. Lead-based materials, e.g. lead zirconate titanate and lead lanthanum zirconate titanate, have been most popular among many piezoelectric materials. Recently alkali oxide materials, including potassium sodium niobate, have been given attention in view of their ultrasonic application and also as promising candidates for a piezoelectric non lead-based system. But this material system has been reported difficult to sinter only in the conventional method and it is possible to sinter by use of the hot isostatic press (HIP) method. In this report the synthesis process is, however, limited to the conventional solid state reaction method for the wide use of this material system. Several kinds of impurity doping into the base material is carried out in the sample preparation procedure. The physical, electrical properties and crystal structure of the several kinds of sodium-potassium niobate materials will be shown.

Low-temperature growth of high-quality lead zirconate titanate thin films by 28 GHz microwave irradiation

Pb(ZrxTi1−x)O3 (PZT) thin films were coated on Pt/Ti/SiO2/Si substrates by a sol-gel method and then crystallized by 28 GHz microwave irradiation. The elevated temperature generated by microwave irradiation to obtain the perovskite phase is only 480 °C, which is significantly lower than that of conventional thermal processing. X-ray diffraction analysis indicated that the PZT films crystallized well in the perovskite phase. A scanning electron microscopy image showed that the film has a spherulite grain structure and most of the grains are approximately 2 μm in size. The average values of the remanent polarization, coercive field, dielectric constant, and loss of the PZT films are 40μC∕cm2, 50 kV/cm, 1100, and 004, respectively. It is clear that microwave irradiation is effective for obtaining well-crystallized PZT films with good properties at low temperatures.

Preparation and Application of Lead Zirconate Titanate (PZT) Films Deposited by Hybrid Process: Sol-Gel Method and Laser Ablation

Among the many ferroelectric film fabrication techniques, the sol-gel process provides high purity, large deposition area and easy composition control. However, the thickness limit of a crack-free single-layer film is about 0.2 µm and about 10 times of coating and thermal treatment processing are needed to deposit 1.5 µm-thick films. In laser ablation, the deposition rate is expected to be 1–2 µm/h, but the film quality is lower than that deposited by the sol-gel method. In this work, the hybrid process, involving the sol-gel method and laser ablation, was used to make 1.65 µm-thick lead zirconate titanate (PZT) films with well-crystallized perovskite phase at the (111) orientation. We deposited (111)-oriented 0.15 µm-thick PZT film on Pt/Ti/SiO2/Si substrates using the sol-gel method and then deposited 1.5 µm-thick PZT films by laser ablation. The remanent polarization of 28.6 µC/cm2 and the coercive field of 58.0 kV/cm were obtained while the dielectric constant and loss values measured at 1 kHz were approximately 1050 and 0.045, respectively. The piezoelectric coefficient d31 was also investigated and found to be 16.65±4 pC/N. In the application, a micromirror actuated by the hybrid PZT films was designed and fabricated successfully by a three-mask lithography process. The scanning angle of 6±2 degrees was demonstrated, while resonating with 5 Vp-p at the resonance frequency (1975 Hz).

Deposition and Patterning Technique for Realization of Pb(Zr0.52, Ti0.48)O3 Thick Film Micro Actuator

The deposition technology for thin PZT (Pb(Zr0.52,Ti0.48)O3) layers has reached an advanced state in the application area of memory fabrication. On the other hand, the application of PZT layers for actuation of micro electromechanical system (MEMS) is not well established. A relatively thicker film is necessary for this application. Conventional preparation techniques provide poor deposition rates and the accumulated residual stress during deposition results in the deposited layer peeling off. Another difficulty lies in the low etching rate of the multilayered structure of SiO2/Ti/Pt/PZT. These are the reasons why we have studied thick PZT film preparation technology and efficient pattering processes. Thick film deposition processes include repeated multilayer coating by the sol-gel method, the excimer laser ablation deposition (ELAD), and the jet molding system (JMS). Pattering processes include RIE, ECR and deposition methods on a non-planar surface. The electrical properties of PZT layers were determined for microfabricated actuators.

Photovoltaic properties of (Pb,La)(Zr,Ti)O3 films with different crystallographic orientations

Photovoltaic (Pb,La)(Zr,Ti)O3 films in a layered structure of different crystallographic orientations are fabricated by an optimized metalorganic deposition method. Such films of (001) orientation exhibit a photovoltaic electrical power of approximately 20 times higher than that of random films. The anisotropic optical properties of the oriented films, including dark conductivity, photoconductivity, and photovoltaic tensor surfaces, are obtained quantitatively. These results show that the photovoltaic output current and power of the oriented films are highly improved to be equal to those of semiconductors and suitable for application in the optical sensor of microelectromechanical systems.

Fabrication of piezoelectric microcantilevers using LaNiO3 buffered Pb(Zr,Ti)O3 thin film

We have fabricated piezoelectric microcantilevers using LaNiO3 (LNO) buffered Pb(Zr0.52,Ti0.48)O3 (PZT) thin films through the microelectromechanical system (MEMS) microfabrication process. It has been found that the LNO thin films reduce the degradation caused by wet and dry etching for the MEMS microfabrication process. The displacement of the microcantilevers with LNO thin films draws a symmetric butterfly curve against dc actuation, while that without LNO thin film draws an asymmetric butterfly curve. The transverse piezoelectric constant d31 for the LNO buffered PZT thin films is ?100 to ?120 pm V?1 at a voltage of 10 to 30 V, which is more than twice that for non-buffered PZT thin films.

X-Ray Diffraction and Scanning Electron Microscopy Observation of Lead Zirconate Titanate Thick Film Formed by Gas Deposition Method

A lead zirconate titanate ( Pb(Zr, Ti)O3, PZT) thick film was produced using the Jet Molding System which was developed from a gas deposition method. Some of the characteristics of the deposited lead zirconate titanate were determined by X-ray diffraction, scanning electron microscopy and atomic force microscopy. The dielectric constant was determined to be 760 after 500° C and 10 min of heat treatment for nonpolarized sample. Through scanning electron microscope observation, some properties of the deposition of ultrafine particles of PZT were determined. A joining of the deposited particles could be observed, which means a kind of sintering was caused by the deposition process. Crystal structure analysis was carried out using X-ray diffraction for structural comparison before and after deposition. The perovskite structure of PZT was proved to be retained during the deposition process.

Application of Gas Jet Deposition Method to Piezoelectric Thick Film Miniature Actuator

Currently the development of piezoelectiric miniature actuators is a subject of interest in the industrial field of mobile electronic devices. Although the deposition of PZT(Pb(Zr.52, Ti.48)O3) in the thickness range of 10 to 100 µm is a key technology for the realization of miniature actuators, thick films of PZT have rarely been prepared by other deposition methods for glued PZT structures. It is also difficult to obtain a thickness of less than 50 µm. This is the reason why we have designed and fabricated a two-dimensional miniature scanner actuated with a relatively thick piezoelectric layer by a recently introduced gas deposition method of ultra fine particles with a subsonic gas jet stream. A piezoelectric PZT layer, of thickness 30 microns is deposited onto a stainless steel substrate and patterned by the simple lift off method, to fabricate a bimorph type actuator beam. Mirror scanning is performed by four independent actuator beams. The device can be scanned along two axes by two independent resonant frequencies. Deflection of the fabricated scanning mirror is measured by laser interferometer and compared with the simulation results obtained by FEM (finite element method). Scanning of the laser light is also demonstrated by the fabricated device.