Taku Hirasawa

Preparation of (001) oriented Pb(Zr,Ti)O 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. These thin films, which have a composition close to the morphotropic phase boundary, were epitaxially grown on (100)MgO single-crystal substrates by RF magnetron sputtering. These (001)-oriented PZT thin films could be obtained on various kinds of substrates, such as glass and Si, by introducing (100)-oriented MgO buffer layers. In addition, the (001)-oriented PZT thin films could be obtained on Si substrates without buffer layers by optimizing the sputtering conditions. All of these thin films showed excellent piezoelectric properties without the need for poling treatment. The PZT thin films on the MgO substrates had a high piezoelectric coefficient, d31, of -100 pm/V, and an extremely low relative dielectric constant, epsivr, of 240. The PZT thin films on Si substrate had a very high d31 of -150 pm/V and an epsivr = 700. These PZT thin films were applied to an angular rate sensor with a tuning fork in a car navigation system, to a dual-stage actuator for positioning the magnetic head of a high-density hard disk drive, and to an actuator for an inkjet printer head for industrial on-demand printers.

Piezoelectric power generating mechanism with spring material

Oscillators (101 a and 101 b) are attached to a spring material (100) whose both ends (105 a and 105 b) are held, and piezoelectric elements (103 a, 103 b, and 106) are attached to the spring material or the oscillators. Assuming that an axis parallel to an axis connecting the both ends of the spring material is a Y-axis, an axis parallel to a plane including the Y-axis and the oscillators and orthogonal to the Y-axis is an X-axis, and an axis orthogonal to the Y-axis and the X-axis is a Z-axis, the oscillators are asymmetric with respect to a plane including the Y-axis and the Z-axis. Consequently, when acceleration is applied, torsional vibrations act on the spring material. When the torsional rigidity of the spring material is set to be low, the resonant frequency of the torsional vibrations can be reduced. Since the both ends of the spring material are held, the spring material is bent in a small amount. Therefore, it is possible to realize a downsized piezoelectric power generating mechanism with a low resonant frequency.

New camera module with thin structure, high resolution and distance-detection capability

Our new type of camera module has a four-lens-array and an imaging sensor. The imaging sensor is divided to four regions, and these four regions are aligned in one-to-one correspondence with the four lenses. Four color filters are placed over the four imaging regions. First region has a blue filter, second has a red, and the other two have green filters, and two regions with green filters are aligned diagonally. Diffraction gratings are formed on aspheric surfaces of the four lenses, and MTF characteristics of these lenses are improved. The four images taken through the different lenses have parallax, but these parallaxes can be calculated by comparison of the two green images. Pixel shifts of blue, red and green images are realized by rotating the four-lens-array slightly with respect to the imaging sensor. After correcting the parallaxes, the green image, the parallax-corrected blue image and the parallax-corrected red image are composed to generate the resultant color image with high resolution. Distances between objects and the four-lens-array are detected by use of the above parallaxes, and measurement error is less than 2.5% for near objects. With above configuration and functions, our camera module has realized smaller height, higher image resolution and distance-detection capability, and will be applied for cellular phones and automobile vehicles.

Resonantly Enhanced Emission from a Luminescent Nanostructured Waveguide.

Controlling the characteristics of photon emission represents a significant challenge for both fundamental science and device technologies. Research on microcavities, photonic crystals, and plasmonic nanocavities has focused on controlling spontaneous emission by way of designing a resonant structure around the emitter to modify the local density of photonic states. In this work, we demonstrate resonantly enhanced emission using luminescent nanostructured waveguide resonance (LUNAR). Our concept is based on coupling between emitters in the luminescent waveguide and a resonant waveguide mode that interacts with a periodic nanostructure and hence outcouples via diffraction. We show that the enhancement of resonance emission can be controlled by tuning the design parameters. We also demonstrate that the enhanced emission is attributable to the accelerated spontaneous emission rate that increases the probability of photon emission in the resonant mode, accompanied by enhanced the local density of photonic states. This study demonstrates that nanostructured luminescent materials can be designed to exhibit functional and enhanced emission. We anticipate that our concept will be used to improve the performance of a variety of photonic and optical applications ranging from bio/chemical sensors to lighting, displays and projectors.

Improved light extraction from white organic light-emitting devices using a binary random phase array

We have developed a binary random phase array (BRPA) to improve the light extraction performance of white organic light-emitting devices (WOLEDs). We demonstrated that the scattering of incoming light can be controlled by employing diffraction optics to modify the structural parameters of the BRPA. Applying a BRPA to the substrate of the WOLED leads to enhanced extraction efficiency and suppression of angle-dependent color changes. Our systematic study clarifies the effect of scattering on the light extraction of WOLEDs.