Hironobu Sato

An all SU-8 microfluidic chip with built-in 3D fine microstructures

This paper describes the fabrication method of an all SU-8 microfluidic device with built-in 3D fine micromesh structures. 3D micromesh structures were seamlessly integrated into the SU-8 sealed microchannel. To eliminate gap formation and filling of the microchannel, the built-in micromeshes in the microchannel were formed by photolithography after bonding the SU-8 top-cover layer and the SU-8 bottom substrate. The lift-off method, using lift-off resist as a sacrificial layer, was utilized to release the all SU-8 microfluidic chips. Monolithic SU-8 structures realize uniform physical and chemical surface properties required in microfluidic devices for practical use. As an application, fragmentation of a water droplet in an organic carrier formed by a two-phase flow was demonstrated.

A novel fabrication of in-channel 3-D micromesh structure using maskless multi-angle exposure and its microfilter application

This paper presents a novel fabrication method of in-channel three-dimensional micromesh structures using the conventional photolithography. The micromesh was realized by exposing UV light from the backside of the SU-8 coated metal-patterned glass substrate for different angles. Numbers of exposure and irradiation angle decided the shape and the size of micromesh. Based on this technique, three different micromesh-inserted microchannel structures were fabricated. For hydrodynamic characterization, their flow resistances were measured. Finally, for the application of micro total analysis system (/spl mu/TAS), the microfilter was fabricated and its filtering property was demonstrated.

3D sheath flow using hydrodynamic position control of the sample flow

3D sheath flow was realized using hydrodynamic position control of the sample flow. The symmetric microgrooves formed on the channel walls were utilized to generate local directional streams. The sample introduced into the grooved area was shifted to the center region of the microchannel, and 3D sheath flow was formed passively. Using CFD (computational fluid dynamics) simulation, the flow shift area was designed to achieve 3D sheath flow no longer than 500 µm in channel length. Sample flow shift behavior was observed by using a confocal microscope. Since the structure of the inlets was very simple, it was possible to fabricate an in-plane multi-sample 3D sheath flow device. As a demonstration, a two-sample 3D sheath flow device was fabricated. The separated two-sample 3D sheath flow configuration was clearly observed.

A disposable, dead volume-free and leak-free monolithic PDMS microvalve

A new fabrication method of a membrane-inserted pneumatically-driven microvalve is presented. The device is entirely made from PDMS. To ensure dead volume-free and leak-free, the valve chamber is formed with smooth surface using molding of UV-curable bond. Also, to place a PDMS membrane on the molded PDMS substrate, bonding with spin-coated PDMS membrane is performed, indicating to align-less assembly. As a reference of bonding characterization, the curing ratio, defined as the ratio of soft bake time and hard cure time of PDMS at the same soft cure temperature, is introduced. The best bonding feature is obtained at the curing ratio of 0.06. The maximum tensile bonding strength is examined. Finally, the performance of the membrane-inserted monolithic PDMS valve is tested.

Pyrolyzed polymer mesh electrode integrated into fluidic channel for gate type sensor

This paper presents a novel means of introducing conductive pyrolyzed polymer structures into a muTAS platform. Insulation structures of polymer materials can be transformed into conductive structures through pyrolysis, and MEMS structures consisting of pyrolyzed polymer can be formed by a dual process of micromachining and pyrolysis. This work focuses on gate type sensing by a three-dimensional pyrolyzed polymer electrode. The three-dimensional SU-8 original structure was micromachined by multi-angle inclined lithography. Three-dimensional structures of pyrolyzed SU-8, which have meshes of 10 mum times 20 mum in dimension, could be obtained by pyrolysis in N2 atmosphere. Furthermore, the structures were integrated into the SU-8 fluidic channel with the 100 mum in height and 200 mum in width by a post-pyrolysis process. We will demonstrate the cross sectional sensing in electrochemical detection by making the best use of the three-dimensional mesh structure to overcome the restriction of planar electrode.

Properties and Surface Morphology of Indium Tin Oxide Films Prepared by Electron Shower Method

Indium tin oxide (ITO) thin films were prepared by electron beam evaporation (EB) with an electron shower. Lawnlike and VLS (vapor-liquid-solid) whiskers of ITO were grown at 300°C on the surface of the film with and without the electron shower, respectively. The electron resistivity of the ITO film fabricated with the electron shower was 4×10-4 Ωcm, which was one order of magnitude smaller than that prepared by the EB at the same substrate temperature (300°C). The electron shower activated the oxidation of In and Sn, but the film was oxygen deficient. The increasing crystallization of the oxygen deficient ITO film was the cause of the decreasing resistivity.

Design and Simulation of Particles and Biomolecules Handling Micro Flow Cells with Three-Dimensional Sheath Flow

In order to realize high performance particles and biomolecules handling systems, micro flow cell realizing three-dimensional (3-D) sheath flow was designed and the first prototype was fabricated. A finite element fluidic analysis is applied to realize optimal design of the flow cell. Especially, the structure of the sample injection part was considered to realize 3-D sheath flow. The high resolution flow monitoring method was studied and was applied to evaluate the flow behavior in the first prototype. The results indicated that the two steps introduction of the carrier flow is quite effective to put the sample flow away from the channel wall. This is very useful to avoid adsorption of the particles and the biomolecules on the wall due to the small flow rate near the wall. A simple micro flow switch for biomolecular separation is also proposed.

EHD Micro Pump using Pyrolyzed Polymer 3-D Carbon Mesh Electrodes

This paper presents the EHD (electro-hydrodynamic) micro pump using 3-D carbon mesh electrodes. The carbon electrodes were fabricated by pyrolysis of SU-8 micro mesh structures [1]. Low temperature SU-8 bonding method under 90°C was developed to realize wafer level carbon structure packaging. The pumping behaviors were evaluated using fluorinert as a sample solution. The maximum pressure and volume flow rate are about 23Pa and 400nL/min under applied voltage of 500V.

Interdigitated array 3D micromesh electrodes for electrochemical sensors

This paper describes the fabrication method of an interdigitated array 3D micromesh metal structure for electrochemical sensing electrodes. The inverse-micromesh structure formed by double backside exposure of the thick positive photoresist was utilized as a mold for electroplating. Ring-shaped Au patterns laid open by overexposure of the positive photoresist were employed as a seed layer for electroplating. An electrochemical sensor with interdigitated array 3D micromesh electrodes was realized by using the combination of the double-sided Cr pattern and protecting the resist layer to achieve selective electroplating. The diameter of the inclined micropillars was about 5 µm. The height and length of the micromeshes were 20 µm and 480 µm, respectively. The gap between the micromesh electrodes was 28 µm. The number of micromesh electrodes was 68 (34 anode and 34 cathode electrodes). The performance of the interdigitated array 3D micromesh electrochemical sensor was demonstrated using the redox reaction. The current signal measured by the 3D micromesh electrodes was 7.9 times higher than that of conventional planar electrodes.

Optimal Design of the Micromixer using Nonhomogeneous Multilayer Laminar Flow

An efficient micromixer using nonhomogeneous multilayer in the laminar flow regime is described. In order to increase the mixing efficiency, the CFD simulation was used to optimize the width of the multilayers. It is estimated that the reagents mixing is proceeded more than 10 times faster compared to previous multilayer micromixers. The optimized micromixer was fabricated, and its mixing efficiency was evaluated.