Papers by Author: Ryutaro Maeda

Abstract: Flexible micropumps are important components for advanced microfluidic systems. Here, polyimide (PI) for flexible micropumps was focused on. This is because PI has many advantageous properties such as good biocompatibility, high thermal stability, and superior mechanical strength. However, the difficulty in realizing an all-PI micropump lies in fabricating microstructures on PI film surfaces. In this paper, we present improved performances of a flexible all-PI micropump fabricated using high-temperature hot embossing above 320 oC that is considerably higher than its glass transition temperature of 275 oC. The fabricated micropump had diffuser/nozzle valves and a chamber with 5 mm diameter, and it was functioned by vibrating a 2-µm-thick PI diaphragm with alternating air pressures outside of the diaphragm. The flow rate of deionized water in the micropump reached to 110 μl/min at 3 Hz.

Abstract: Small condenser microphones with high performances are strongly demanded. This paper describes a silicon condenser microphone fabricated on silicon on insulator (SOI) substrate using only one photo mask with improved sensitivity performance. The improvements were due to reduction of the floating capacitance, thinning of the silicon diaphragm, and increasing the electrode area at the back plate of the microphone. This microphone consists of a diaphragm with the thickness of 10 μm and the diameter of 2 mm, a SiO2 insulative spacer (4-μm-thick buried oxide), and a 300-μm thick silicon back plate with the meshed structures having small (60 μm) hexagonal shaped acoustic holes. The gap between the 10-μm-thick silicon diaphragm and the back plate was 4 μm. This microphone was confirmed to function in the auditory frequency region with a sensitivity of –85 ~ -70 dB.

Abstract: High dielectric capacitors , that has around 1000 in dielectric constant, can be successfully formed by nanotransfer on non-heat-resisting substrates. PZT film could be released from the Si substrate and bonded onto the polymer one. The releasing characteristics have the relationships with the thickness of Pt layer. The formed PZT has perovskite structure and clear columnar texture.

Abstract: This study explores the dynamic mechanical properties (e.g., storage shear modulus, loss tangent and shear viscosity) and formability of a polyimide film by visco-elasticity measurement and hot-embossing tests. The variations of storage shear modulus, tangent delta and the shear viscosity were measured as a function of the temperature for two frequencies. As a polyimide goes through its glass transition, it exhibits dramatic decreases in shear modulus and viscosity as well as the peak of tangent delta, and continues to show strong dependence on frequency and temperature. Moreover, the filling characteristics (e.g., surface appearance, replicated depth and surface roughness) of polyimide were investigated by hot-embossing tests at different temperatures using a mold with an aspect ratio of 2.5:1.

Abstract: This study investigated a thermal imprint technique to pattern parylene microstructures over an area of 25
25 mm2. A nickel mold having arrays of 25 m-high, 10 m-wide and 1 mm-long lines with 10 m spacing was fabricated using the deep RIE silicon etching followed by the electroplating process. Imprint tests were then carried out under different conditions of temperature, imprint-hold time and applied pressure to investigate a thermal imprint condition for the complete filling of parylene. Good release results without damage or deformation in parylene microstructures were achieved by the help of a release agent in the imprint temperature range of 160 oC to 250oC. With increasing temperature, the depths of imprinted structures increased and their distribution came to be homogeneous. Complete filling was obtained under the imprint temperature of 250oC, applied load of 195 kgf (3 MPa) and imprint hold time of 1800 s.

Abstract: Photovoltaic lead lanthanum zirconate titanate 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 micro-electro-mechanical systems.

Abstract: This paper reports on the formation of film structures and the highly improved photovoltaic output current of the lead lanthanum zirconate titanate (PLZT) employed. The photovoltaic effect of ferroelectrics has the advantage of its simple mechanisms of non-bias applications which are indispensable for semiconductor p-n junctions. But the output current of PLZT bulk is too low for use as a device current source. The PLZT film structure exhibited μA output current upon light illumination. The photovoltaic current of the PLZT film was more than 102 times than that of bulk PLZT. These differences are due to the characteristics of the design of the film including the configuration of the electrode. The PLZT film also has the advantage of easy output control and suitability for use on Si. Results show that the photovoltaic effect of the ferroelectric film is useful as the current source for micro-electro-mechanical systems (MEMS).

Abstract: Flat PZT cantilevers have been successfully fabricated from the Pt/Ti/PZT/Pt/Ti/SiO2/SOI multi-layered structure through MEMS technologies. A displacement of the tip of the cantilever driven at 6 V is measured to be 7.6 μm and the transverse piezoelectric constant calculated from the displacement is –103 pm/V. 1D optical scanners have been designed, simulated, fabricated and tested. The rotation angles of the mirror of the scanners were 60-70% of the simulated values.