Kazuyuki Minami

Fabrication of distributed electrostatic micro actuator (DEMA)

A distributed electrostatic micro actuator (DEMA) has been proposed. The actuator has many small driving units which consist of two wave-like insulated electrodes. Both ends of insulated electrodes are connected to each other, and the driving unit has narrow gap for deformation caused by electrostatic forces. The driving units have large area of electrodes and are distributed in series and in parallel. So, a strong electrostatic force can be obtained, and the deformation and the generated force of the actuator would be large. Macro model of the DEMA was fabricated with polyimide films, and the deformation of the actuator was measured. When the applied voltage was 200 V, the deformation ratio was 36%. A micro actuator was fabricated by use of photolithography and electroplating. The displacement of 28 mu m was observed when applied voltage was 160 V. Experimental results of the micro actuator were compared with the results simulated by finite element method (FEM) analysis. >

Future of active catheters

Abstract A prototype of a catheter that can move like a snake, incorporating distributed shape memory alloy (SMA) actuators, a related device (built-in circuit and techniques (laser CVD) are described. The outer diameter of the active catheter is 2.8 mm and it has many links fabricated using three-dimensional silicon micromachining. A silicon batch process is used for the fabrication of a link to minimize the assembly work. Problems that may occur in the fabrication of active catheters in the future are discussed and possible solutions are suggested. To minimize the number of lead wires in an active catheter that has many distributed SMA actuators, a packaged signal-processing IC for communication and control purposes has been developed. A new heating method (indirect heating), which is necessary for mounting IC chips on a link, has been developed. A micro assembly process that uses polymer as adhesive, deposited by laser CVD, has been studied to develop the future generation of smaller active catheters.

Silicon resonant angular rate sensor using electromagnetic excitation and capacitive detection

A new silicon resonant angular rate sensor is presented. The sensor consists of a packaged glass-silicon-glass structure and is made by a batch-fabrication process. The sensor is a tuning fork with both sides suspended by torsion bars. Electromagnetic excitation and capacitive detection are used. The applied angular rate generates the Coriolis force and the resonator starts torsional vibration around the torsion bars. The test device shows a sensitivity of 0.7 fF sec/deg. In this paper, the working principles, fabrication process, and simulated and measured outputs of the sensor are described. The scaling rule of the angular rate sensor are also considered.

Distributed electrostatic micro actuator

A micro actuator that is called a distributed electrostatic actuator, because it consists of many driving units, and that is driven by electrostatic force is described. Each driving unit has wavelike electrodes, which are insulated and pull each other by the electrostatic force. The deformation of this actuator depends on the electrostatic force, the elasticity of the structure, and the external force. The motion of the actuator was analyzed with the finite-element method (FEM), and a macro model of the actuator was fabricated to verify its motion. It was confirmed that the actuators apparent compliance can be controlled by a feedback control system using capacitive displacement sensing and electrostatic driving.<<ETX>>

Fabrication and packaging of a resonant infrared sensor integrated in silicon

Abstract A novel integrated infrared (IR) sensor is described that incorporates a resonant silicon/silicon dioxide microbridge. The resonance frequency of the microbridge is sensitive to the incident IR power as a result of the thermally induced stress variation resulting from the absorption of the IR radiation. A merged process including on-wafer stress-free packaging, NMOS circuitry and bulk silicon micromachining is illustrated. One-port electrostatic excitation and capacitive detection was used, the resonator being electrically floating. Relative responsitivities of 450 ppm/μW of absorbed power were obtained.

Cryogenic dry etching for high aspect ratio microstructures

Cryogenic reactive ion etching (RIE) has been used to fabricate microstructures. The cryogenic system has a cathode stage that is temperature controlled from 0 to -140 degrees C. A magnetic field and a narrow gap between electrodes are introduced to increase plasma density. The etching behavior of silicon and polyimide film has been investigated. Directional etching was achieved at low temperature. The etch rate was increased by using Sm-Co permanent magnets and also a high flow rate of the etching gas under constant pressure. In the case of silicon wafer etching, a maximum etch rate of 1.6 mu m/min was achieved with normalized side etch of less than 0.02 at cathode temperature of -120 degrees C. Etching selectivity was over 900 at a power density of less than 4.0 W/cm/sup 2/. In the case of the polyimide film etching, normalized side etch of less than 0.01 with an etch rate of 0.8 mu m/min was achieved at -100 degrees C. The cryogenic RIE system can be used to fabricate 3-D silicon and polyimide structures with high aspect ratio.<<ETX>>

Thin beam bulk micromachining based on RIE and xenon difluoride silicon etching

A new process for fabricating thin mechanical beam structures from single crystal silicon is developed. Lateral and vertical dimensions of the beam can be precisely defined. The beam is positioned in the middle of a silicon wafer at exactly equal distances from both sides. The beam design is not limited by crystal orientations of silicon. The silicon beam structure is essentially stress-free because the whole structure is made of uniformly doped single crystal silicon. This thin beam process offers significantly expanded design freedom to bulk silicon micromachining. Additionally, a very high aspect ratio silicon dioxide structure can be fabricated with a similar technique.

Active catheter with multi-link structure based on silicon micromachining

Wc dcvclopcd a new prototype active catheter with multi-link structure based on silicon micromachining. Many links are connected with joints made of Shape Memory Alloy (SMA) actuators. The active catheter can be used for medical purposes as an interventional therapy. As this has multi-link structure, it can bend actively on demand and conform to the shape of narrow blood vessels. The outer diameter of the fabricated active cathctcr is 2.8. Micro coil of SMA is used as the actuator for the joint. Two heating methods, direct heating and indirect heating of SMA was examined. Indirect heating by surrounding nickel thin film heater is compatible with built-in circuit for driving the SMA actuator. We used silicon batch process for the fabrication of the link to minimize assembly work. UV (Ultra Violet) curing resin was used to fix the actuator and to make electrical contact. Bending motions, bending angle, force, and frequency response of the active catheter were measured.

High-rate directional deep dry etching for bulk silicon micromachining

Cryogenic reactive ion etching (RIE) of silicon using SF6 gas and a multilayer Ni/Al mask has been studied and high-rate, directional deep etching was demonstrated. The temperature of the cathode wafer stage was controlled at a low temperature (-60 degrees C) and a magnetic field was applied to enhance the plasma density. A high flow rate (1 sccm) of the etching gas and low pressure (0.5 Pa) produced by high-speed exhausting were effective for high-rate etching and directional etching. A trade-off of the RF power density was necessary between the etching rate and the etching selectivity to the mask with selectivity improving at higher etch rates. The system could be used to etch through a silicon wafer of 200 mu m in thickness. An etching rate of 0.8 mu m min-1 and vertical walls as thin as 20 mu m were obtained in the through wafer etching. On the other hand, the etching rate was reduced in narrow deep grooves. This etching method is effective in fabricating three-dimensional silicon microstructures with high aspect ratio.

Fine frequency tuning in resonant sensors

To realize highly sensitive resonant IR sensors the control of mechanical properties of the p+ silicon film is essential. Microfocus Raman spectroscopy and secondary ion mass spectrometry were used to measure the stress and boron concentration profile in the p+ silicon film respectively. Measurements of bending in cantilevers, of transversal stress gradient and boron profile in the films were found as being consistent with each other. Prediction of mechanical properties of micromechanical structure can be realized by using these techniques. Fine tuning of the resonance frequency in the final, packaged device, was realized by using an electrostatically activated axial force.