Recent research development of ferroelectric thin films has been introduced from the viewpoint of various electronic device application such as nonvolatile memory, infrared sensor, piezoelectric transducers and electrooptic devices. Explained materials of the ferroelectric thin films are PZT, Bi-layer-structured ferroelectrics, BiFeO₃, YMnO₃ and P (VDF-TrFE).

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The piezoelectric MEMS deformable mirrors for adaptive optics have been developed to realize low voltage and large stroke deformable mirrors. The PZT film was deposited on a Pt-coated silicon-on-insulator (SOI) substrate and the 19 segmented electrodes were prepared on it. The circular diaphragm structure was fabricated by etching the Si substrate from the back side and the unimorph actuator array composed of a PZT film and a Si layer was accomplished. Finally a Al reflective layer was coated over the backside of the membrane as a mirror surface. The displacement profiles measurements by a laser Doppler vibrometer showed that the each actuator generated large displacement of approximately 5μm at 10V. Furthermore we could successfully reproduce the Zernike modes up to 4^th order by applying the voltage calculated by control function matrix.

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According to the previous psychophysical experimental results, since human beings feel different sensations for pressure and shearing vibration applied to their finger surface, a new tactile display array consisting of multi-axial micro actuators is required to enhance degree of tactile virtual reality. In the present paper, we experimentally design serial and parallel typed two-axial micro actuators, which are utilized for the key part of the tactile display. The serial typed two-axial actuator comprises bimorph actuators connected in series. The parallel typed two-axial actuator is composed of two bimorph piezoelectric actuators and two small links connected by three joints. We formulate kinematics for the parallel typed two-axial actuator because the endpoint is controlled in the two-dimensional coordinate. We perform a series of experiments to evaluate these two-dimensional actuators. Although the serial typed actuator has different characteristics on x- and y-directional coordinates, it has an advantage on compactness. On the other hand, the parallel typed two-axial actuator has almost same characteristics on both x- and y- coordinates, and has wide strokes of about 1mm. Considering these characteristics depended upon actuator type, we will design the tactile display combined the serial and parallel typed two-axial actuator.

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In the previous paper, we experimentally designed serial and parallel typed two-axial micro actuators, which were utilized for key parts of advanced tactile displays. The serial typed two-axial actuator comprises bimorph piezoelectric actuators connected in series. The parallel typed two-axial actuator was composed of two bimorph piezoelectric actuators and two small links connected by three joints. We formulated kinematics for the parallel typed two-axial actuator because the endpoint is controlled in the two-dimensional coordinate. Since relationship between applied voltage and displacement caused by the voltage shows a hysteresis loop in the bimorph piezoelectric actuator used as components of the two-axis actuators, we produce a control system for these two-axial actuators based on a multi-layered artificial neural network to compensate the hysteresis. The neural network is comprised of 4 neurons in the input layer, 10 neurons in the hidden layer and one neuron in the output layer. The output neuron emitts time derivative of voltage; two bits signal expressing loading or unloading condition is generated by two input neurons; one of the other two input neurons and the other calculate current values of voltage and displacement, respectively. The neural network is featured with a feedback loop including an integral unit to reduce number of neurons. In the learning process, the network learns the hysteresis including a minor loop. In the verification test, the endpoint of the two-axial actuator traces the desired circular trajectory in the two-dimensional coordinate system.

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130 nm-thick lead zirconate titanate(PZT)/45 nm-thick HfO₂ stack and single 45 nm-thick HfO₂ dielectric film were utilized as insulator layer in π-type radio frequency (RF) capacitive shunt switches for achieving high isolation performance in broadband application. Thin PZT film in perovskite structure mainly with (1 1 1) orientation was successfully prepared at low temperature (500°C) using sol-gel method. The thin PZT film exhibited excellent ferroelectric properties and high dielectric constant (k ≈ 1185). Thin HfO₂ film was prepared by sputtering method in a gas mixture of O₂ and Ar. The thin HfO₂ film had the dielectric constant of about 17 and the dielectric strength of about 24 MV/cm. The switch of PZT/HfO₂ stack dielectric showed isolation performance better than -20 dB in the frequency range of 1 ∼ 35 GHz. The switch of HfO₂ had isolation performance better than -40 dB in the frequency of 5 ∼ 35 GHz, suggesting its attractive prospective in practical broadband application.

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This study describes the development of Remote-Type Haptic Catheter Sensor System which enables the mechanical property evaluation of a blood vessel. This system consists of a feedback circuit and a piezoelectric ultrasound transducer, and is operated based on a phase shift method so that the entire system oscillates at its inherent resonance frequency. Ultrasound reflected by the blood vessel makes a phase shift of the resonance system depending on the acoustic impedance of the reflector. The phase shift is then measured as a change in resonance frequency of the system; therefore, the detection resolution is highly improved. The correlation between the acoustic impedance and the resonance frequency change of the sensor system was demonstrated using silicone rubbers, metals and actual blood vessels from a pig. The performance of the sensor was also examined using vessel shaped phantom model. Finally, the discussion surveys a possibility of the novel sensor system in an application for intra vascular diagnosis.

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Preparation of <001>oriented Pb(ZrTi)O₃(PZT) thin films and their applications to the micro-piezoelectric devices were investigated. The <001>oriented PZT thin films, which have a composition near the morphotropic phase boundary, were deposited on Pt/MgO and Pt/Ti/Si substrates by rf-magnetron sputtering. Both of these thin films show the excellent piezoelectric properties without a poling treatment. The piezoelectric properties of the PZT thin films were examined on the micro fabricated cantilever structure. The PZT thin films on Pt/MgO have high piezoelectric coefficient d₃₁=100×10^-12m/V, extremely low ε_r=240, and remarkably high electromechanical coupling coefficient k₃₁. The PZT thin films on Pt/Ti/Si have very high d₃₁of 150×10^-12m/V and ε_r=700. The PZT thin films on Pt/Ti/Si were applied to the angular rate sensors with a tuning fork type and the actuators of the ink-jet printer heads with 400 pressure chambers. These PZT thin films are suitable for the use in micro piezoelectric sensors and actuators.

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We have investigated the degradation of ferroelectric property of Pb(Zr,Ti)O₃(PZT) thin films derived from wet etching of PZT thin films. We have also investigated the reduction of the degradation with LaNiO₃ (LNO) thin films as a buffer layer between Pt and PZT thin films. The polarization and dielectric constant of the PZT thin films were reduced to about 70% through wet etching. It has found that the degradation can be avoided with LNO thin films.

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