Shinichi Izuo

Electrophoresis of DNA in micro-pillars fabricated in polydimethylsiloxane

We describe the fabrication of a device containing micro-pillars and separation of DNA. It was made of polydimethylsiloxane (PDMS) and made by a replica molding method using a patterned silicon wafer as a mold. The device has a micro-channel in which 15 µm pillars are arranged in a hexagonal lattice with 1 µm spacing. Electrophoresis of DNA in the pillars showed the average speed of DNA migration was dependent on its lengths. The PDMS device not only demonstrates the possibility of rapid DNA separation, but also has an advantage in mass production cost by using the replication method.

Silicon micro optical switching device with an electromagnetically operated cantilever

Abstract We report on a new concept 2×2 fiber-optical switching device with an electromagnetically operated cantilever. The device is composed of a switching mirror module and a fiber array module. The switching mirror module consists of a fixed mirror, a moving mirror, a cantilever, support glasses and magnets. The mirrors and the cantilever are micromachined from one silicon wafer by deep silicon etching. As the cantilever has a magnetic film on its surface, it is driven by an electromagnet and latched by permanent magnets. The fiber array module consists of four optical fibers with graded index fibers, which are aligned parallel and fixed in a glass holder. The required current to operate the cantilever is 34 mA (0.3 V) and 20 ms for the pulse width, and the required magnetomotive force is 9.5 A·turns. The shortest switching time is 20 ms. The surface roughness of the mirrors are about 30 nm, the reflection loss of one mirror is −0.05 dB, crosstalk is smaller than −60 dB, and the insertion loss is −1.5 dB. Owing to the optical fibers preassembled as a module, the proposed device facilitates the optical path adjustment and the assembly.

Application of a microfluidic device for counting of bacteria.

Aims:  To develop a miniaturized analytical system for counting of bacteria.

Initial pits for electrochemical etching in hydrofluoric acid

This paper reports on a characterization of structures fabricated by electrochemical etching in hydrofluoric acid (HF) using different types of initial pits. An initial pit has been thought to require a sharp tip in order to collect electronic holes generated by illumination. Therefore, the initial pits have been formed by etching in a KOH solution, which suffers from crystal orientation dependence. We successfully demonstrate the structures fabricated by the electrochemical etching with the initial pits, which have flat or round base. These pits are formed by isotropic wet etching or reactive ion etching (RIE), which are free from crystal orientation of silicon substrate. Furthermore, regular hole patterns can be achieved without initial pits. This makes the electrochemical etching process more simple. The electric field in the silicon is calculated and the calculated results support the experimental results.

A novel electrochemical etching technique for n-type silicon

A novel electrochemical etching (ECE) technique using a dimethylformamide (DMF) and hydrofluoric acid (HF)-based etchant has been developed for n-type silicon. The DMF-based HF etchant allows SiO 2 and TEOS, as well as SiN, to be used as a masking layer and enables straight pores over a 50 aspect ratio with smooth sidewalls to be successfully fabricated. The concentration of H 2 O in the DMF-based HF etchant affects the SiO 2 etch rate. In addition, the conductivity of the DMF-HF-based etchant and the applied voltage on the silicon affect the pore morphology. The light intensity illuminated on the silicon affects the Si etch rate, while the pore diameter remains constant. The above novel ECE technique is more compatible with other processes such as circuit fabrication.

An Rfmems Switched Capacitor Array for a Tunable Band Pass Filter

In this paper, we present an RFMEMS switched capacitor array, which is proposed as a RF component to achieve various kinds of tunable RF filters. Our RFMEMS switched capacitor array consists of RFMEMS direct contact switches and metal-insulator-metal capacitors. In order to obtain reliable capacitors, the metal sacrificial layer for the RFMEMS switch fabrication is also applied to the capacitor implementation. We have achieved a C- to Ku-band tunable band pass filter by using the RFMEMS switched capacitor array. The capacitance of capacitor is designed corresponding to each tuning state of the band pass filter, which is selected by the RFMEMS switch operation. The insertion losses of the band pass filter were 7.1dB, 4.9 dB and 6.2 dB at 8 GHz, 12 GHz and 16 GHz, respectively.

Silane-free atmospheric-plasma silicon deposition for MEMS devices

We have developed a silane-free atmospheric-pressure plasma Si deposition process and investigated the properties of the deposited films by fabricating strain gauge type pressure sensors for the first time. The Si deposition process, which is known as plasma-enhanced chemical transport, utilizes the temperature difference between the solid Si source and the substrate in atmospheric hydrogen plasma. The Si films were deposited at a low temperature of 300 °C at 700 Torr. The Si films were composed of poly-crystals. The gauge factor became approximately 10. The bridge voltage of the pressure sensor was found to be proportional to the pressure. The Si films were deemed appropriate for use as MEMS devices.

High power handling capability of movable-waveguide direct contact MEMS switches

The authors presented the characteristics of high power handling capability with direct contact MEMS switches. The switch has a movable-waveguide, fabricated on a silicon cavity. Two types of MEMS switches with different number of contact points were fabricated. In high power handling experiments with hot switching mode, a multiple-contact type switch failed at 1.6 W in 7 GHz RF signal, while a single-contact type switch was succeeded up to 2.4 W. These results were considered from the viewpoint of contact force and surface asperities according to the relation between input power and insertion loss.

Pillar Structures with the Space of Sub-Microns Fabricated by the Macroporous Based Micromachining

This paper reports on a new macroporous based micromachining technique. The macroporous silicon is formed by electrochemical etching in hydrofluoric acid. Using this etching technique, SiO2 pillar structures with the space of 200nm have been successfully fabricated in a channel formed on a silicon substrate. The space between the SiO2 pillars is less than lithographic resolution. These structures will be used for DNA separation.

Electrochemical Etching for n-type Silicon using a Novel Etchant

In this paper, electrochemical etching using a novel etchant for n-type silicon is presented. Using a novel etchant that is Dimethylformamide (DMF) and hydrofluoric acid (HF) based, macropores have been successfully fabricated and selectivity over the masking layer, such as silicon dioxide and silicon nitride, have been improved. Concentration of H2O in DMF-HF based etchant influences on etch rate of silicon dioxide. Conductivity of DMF-HF based etchant effects on pore morphology. These results make electrochemical etching process more compatible with other processes such as circuit.