Shigeyoshi Umemiya

Rotating Symmetrical Piezoelectric Microactuators for Magnetic Head Drives

A unique piezoelectric microactuator for the head-slider drive dual-stage actuator systems in magnetic disk drives has been developed. This microactuator is based on a rotating symmetrical structure and a symmetrical operation. The piezoelectric actuator elements used in the system have a simple rectangular multilayered structure. A prototype model with pico slider and head suspension has been tested to demonstrate 0.86 µm displacement at a dc applied voltage of 30 V and observed main resonant frequency of over 20 kHz. No fluctuation in flying height was observed.

Piezoelectric Properties of PZT Film Prepared by Chemical Solution Deposition Method

The influence of the stress and orientation of a lead zirconate titanate (PZT) film on its piezoelectric properties was investigated. Preferentially (111) oriented PZT films were prepared on various substrates with different thermal expansion coefficient, such as stainless steel, alumina, magnesia, and silicon by the CSD method. Preferentially (100) oriented PZT films were also prepared on stainless steel. The displacements of cantilevers of the PZT films with the substrates were measured by the laser Doppler vibration method, and the d31 piezoelectric coefficient was calculated from the displacement. Compressive stress degraded the d31 piezoelectric coefficient of (111) oriented PZT film. In the PZT film with compressive stress, the change of orientation to the (100) direction effectively improved the d31 coefficient. An excellent piezoelectric coefficient (d31 = 55 pm/V) of PZT film was obtained on the stainless steel substrate.

Piezoelectric Microactuators for Use in Magnetic Disk Drives

A head-slider drive dual-stage microactuator system for use in magnetic disk drives was developed. This microactuator system has a symmetrical structure and operation, and utilizes simple rectangular multilayered piezoelectric actuator devices. A prototype model with a pico slider and head suspension was tested and demonstrated. It exhibited a 0.8 µm displacement at a dc applied voltage of 30 V and a fundamental resonant frequency of over 20 kHz.

Influence of SRO Top Electrode on Fatigue Characteristics of FRAM

Fatigue characteristics were investigated in PZT capacitors using both Pt/SRO top electrodes and IrO2 top electrodes. Fatigue of PZT capacitors with IrO2 top electrode showed degradation with a 600 oC annealing processes. We assumed that this degradation was caused by the difference in location within the capacitors where defects were located. It is proposed that the capacitors with Pt/SRO top electrode, the defects existed at the interface between Pt and SRO from SIMS analysis. In the capacitor with IrO2 top electrode, on the other hand, the defects existed at the interface between IrO2 and PZT. Fatigue characteristics of PZT capacitors with SRO top electrode showed superiority to those with IrO2 top electrode, because it wasn’t attributed to defects located at the within the top electrode. INTRODUCTION Ferroelectric Random Access Memory (FRAM) are promising nonvolatile RAM (NVRAM) devices for personal electronic equipments, in particular, for mobile applications. Consequently, these devices are required for high density and low power consumption. Thinner ferroelectric films or 3D structures are needed for these purposes, because they are suitable to operate at lower voltage with higher stored charge. In this study, we chose Metal Organic Chemical vapor deposition (MOCVD) method to deposit Pb(Zr,Ti)O3 (PZT) thin film, because this method has numerous advantages like low film porosity, thinner film and good step coverage. Among the requirements for FRAM capacitors, important properties concerned for reliability are high remanent polarization, low leakage current density, high endurance to thermal imprint and fatigue free behavior. In particular, fatigue is explained as the characteristic of ferroelectrics whose remanent polarization decreases with increasing cycling of bipolar applied voltage pulses. It is proposed that this phenomenon is caused by the decrease of switchable domains owing to the pinning phenomenon. This pinning is assumed to occur in the vicinity of grain boundaries, and at the interface between ferroelectrics and electrodes. [1] In the work of Colla et al. [2], fatigue was clarified to be dominated by inhibition of domain nucleation at the electrode surface. In general, the processes of FRAM includes thermal annealing processes to recover its electric characteristics after top electrode sputtering. In ferroelectric film including Pb, for example, PbTiO3, Pb(Zr,Ti)O3 and (Pb,La)(ZrTi)O3, Pb diffuses into electrode and hereby the defects are produced at the interface between PZT and electrodes. The defects at the interface induces the fatigue. In this study, we chose Pt/SRO and IrO2 top electrodes because SRO and IrO2 are good oxide top electrodes in fatigue characteristics. Pt on SRO was used for contact with probe. fatigue characteristics for capacitors with various top electrodes were investigated after annealing at various temperatures in order to better understand the fatigue mechanism. Key Engineering Materials Online: 2004-08-15 ISSN: 1662-9795, Vol. 269, pp 69-74 doi:10.4028/www.scientific.net/KEM.269.69

Measurement of d15 Shear-Mode Piezoelectric Response in PZT Thin Film

Piezoelectric films using d15 shear-mode can be applied to many useful MEMS devices. The small displacement derived from the d15 shear-mode was directly observed by a SPM measurement. An isolated PZT(52/48) active part having a pair of driving Cu electrodes was processed in a 5 m-thick sputtering film. The displacement measurement of the active part and its FEM analysis suggested that the estimated d15 piezoelectric constant of the film was 590 pm/V. And, the d31 value of the film was -120 pm/V measured by a conventional cantilever method. The obtained piezoelectric constants of the PZT film are near those of bulk.

Measurement of d 15 shear-mode displacement in ferroelectric PZT film

d15 shear-mode displacements in a ferroelectric PZT(52/48) film could be observed by using a FIB processing and SPM probe measurement for the first time ever. The PZT sample with a beam shape was fabricated by a combination of a sputtering deposition, a FIB machining, and a Cu damascene process. In order to compensate for the effect of constraints arisen from the beam sample structure, FEM simulation analyses were employed. The obtained d15 piezoelectric constant of the sputter PZT film was 590 pm/V. The d31 piezoelectric constant of the same PZT film was also measured by a conventional tip displacement of cantilever method. The obtained d31 value was −120 pm/V. Though the d15 value is as large as that of bulk shape, the d31 value was slightly smaller than that of bulk. The difference may be explained that an intrinsic stress existed in the lower portion of the PZT film.