Improvement of shearing tool life by bevelled punches with high slenderness ratio

In the present investigation the cutting edge of a slender punch was bevelled in an attempt to prevent bending or breakage in use. Tests with Kovar sheet showed that use of a bevelled punch significantly reduces the risk of bending or breakage, a particular problem when clearance on both sides of the punch is unbalanced. This is because the punch guides itself in the later stage of the stroke. Tool life tests shearing Kovar sheet with the bevelled punch produced a smaller burr on the product than with the conventional punch. The application of such punches is found to be most suitable for thin materials such as are used in the manufacture of IC and LSI parts.     

Quasi-3D microstructure fabrication technique utilizing hard X-ray lithography of synchrotron radiation

 Quasi-three-dimensional (3D) microstructure fabrication technique utilizing hard X-ray lithography (HXL) has been developed. In this technique, as the intensity distribution of the X-rays is controlled by a newly developed bending mirror, the exposure residual depth of polymethyl methacrylate (PMMA) resist is controlled over the exposed area. The maximum difference of depths was approximately 50 μm over the large area more than 60 mm (horizontal) × 5 mm (vertical). We also investigated the effects of controlling the beam intensity distribution for exposure changing X-ray mask absorber shapes and angle on the obtained quasi-3D resist pattern shapes. As the results, Quasi-3D PMMA patterns with inclined shape sidewall and graded depths were successfully fabricated. We believe this technique greatly expands applications of LIGA process. Received: 10 August 2001/Accepted: 24 September 2001 This paper was presented at the Fourth International Workshop on High Aspect Ratio Microstructure Technology HARMST 2001 in June 2001.     

Fabrication of a spiral microcoil using a 3D-LIGA process

LIGA processes have been developed generally in the 2.5D world. We introduced techniques of 3D X-ray lithography and worm injection molding with a unscrewing release mechanism, and succeeded in the development to three dimensions of LIGA process. We called this technology 3D-LIGA process, and came to be able to fabricate the plastic molded product with a spiral microstructure. Furthermore, we succeeded in the trial production of a spiral microcoil using 3D-LIGA process and metallization technique combining flat and smooth electroplating with a leveling agent and an isotropic chemical etching. The diameter of this microcoil was 0.5 mm and the length was 1 mm. The width of the Cu coil line was 10 μm, and the pitch was 20 μm. Moreover, we measured characteristics of this microcoil as an inductor. The inductance and the quality factor at the frequency of 1 GHz were 91 nH and 5.8, respectively. This is the first time successful fabrication of an electric device with a 3D form like a spiral microcoil using the 3D-LIGA process has been achieved.     

Development of precision transfer technology of atmospheric hot embossing by ultrasonic vibration

We succeeded to transfer a precise micro-pattern combining with an ultrasonic vibration in an atmospheric hot embossing on the almost same condition as a vacuum hot embossing. This paper reports the effect of the ultrasonic vibration that was verified experimentally. In the conventional method, a metallic mold and a plastic sheet are heated more than the glass transition temperature of the plastic, and the softened plastic is flowed into the pattern only by applying a load. On the other hand, a longitudinal ultrasonic vibration is added in the molding process of an ultrasonic-vibration hot embossing. The synergy effect of the load and the ultrasonic vibration enables flowing of the plastic into a more precise pattern of the metallic mold. The longitudinal wave generated by an ultrasonic vibration system of the frequency 15 kHz and output 900 W. A pattern of the Ni mold used in the experiment was a pyramid hole in which a peak was cut and sidewalls were rounded. Entrance lengths of pyramids were from 100 to 530 μm and its all of the depth were 260 μm. A polycarbonate was chosen with a replication material. Compared with the condition that the ultrasonic vibration was not used, a contact force and a contact time could be reduced to about 1/3 and 1/12, respectively.     

Preliminary comparison of respiratory signals using acceleration on neck and humidity in exhaled air

Microsystem Technologies - A microelectromechanical system is recently used for measurements of vital signs. Although the neck is regarded as an alternate observatory location of heartbeats, there...     

Inclination of mold pattern’s sidewalls by combined technique with photolithography at defocus-positions and electroforming

We succeeded in achieving inclined sidewalls in a positive-tone photoresist structure by adjusting the focus offsets in a projection ultraviolet (UV) lithography system. In our experiments, highly precise patterns on Ni-electroformed mold were replicated from a photoresist master. The practicality of the mold was then evaluated by thermal nanoimprint experiments on polycarbonate (PC). When the focus offsets became small by moving the UV image plane (defined by wafer surface) closer to the lens the inclined angles of the photoresist walls increased. In this work, the release force was measured using a desktop nanoimprint system equipped with a load cell that measured not only the compression power but also the tensile force in the de-molding process. Starting from the glass transition temperature T _g (144°C) of PC, the heating temperature in the molding process was changed by increments of 10°C resulting in T _g + 10, T _g + 20, and T _g + 30°C. The result showed that the release force decreased with increasing incline angles. It was observed that the more inclined the sidewalls of the mold pattern were, further small the release forces became, and the mold pattern became to be defended from deformation.     

Fabrication of glass-like carbon molds to imprint on glass materials by MEMS processing technologies

We processed a precise relief structure on the surface of a glass-like carbon (GC) substrate by applying micro-electro-mechanical-systems (MEMS) technologies, and made a high temperature resistant mold for thermal imprinting on glass materials. An attractive feature of GC is its chemical stability at high temperatures (above 1,000 °C). The down side is its brittleness that makes microfabrication with GC a difficult task. We investigated to find if photolithography combined with reactive-ion-etching (RIE), which are generally used in MEMS fabrication, could be applied for the fabrication of GC molds. In our work with the RIE process, we made masking layers using Au and a positive-tone photoresist. By taking advantage of the difference between the etching rates of the masking materials and GC, we fabricated convex mold patterns with vertical and curved sidewalls. From the experimental results imprinted on Pyrex glass and on quartz, the practicability of using both kinds of GC molds appeared to be quite promising. We believe that in the near future these techniques will be successfully applied in the fabrication of large-size GC molds.     

Effect of applying ultrasonic vibration in thermal nanoimprint lithography

In our previous works we had shown that the use of ultrasonic vibration in micro hot embossing processes proved to be effective in improving the molding accuracy. We then decided to extend this technology of ultrasonic vibration to nanoimprint lithography also, and investigate its effect on nanoimprints experimentally. This task also required the use of a heater capable of sustaining three kinds of stresses, namely loading force, thermal stress, and ultrasonic vibration in the molding process. This work led to the development of an ultrasonic nanoimprint system with a built-in pyrolytic graphite/pyrolytic boron nitride all-in-one heater. The material chosen for nanoimprinting was polycarbonate with its glass transition temperature being 150°C. The research in the area showed that the timing point at which an impression of ultrasonic vibration begins is an important factor. When an ultrasonic vibration was impressed at an early stage in a molding process the height of the imprinted pattern seemed to increase where high amplitudes of the acoustical vibration were involved. Moreover, when the molding accuracies of line/space pattern with line widths of 500, 750 nm, and 1 μm were compared among themselves, the effect of assistance from ultrasonic vibration became quite noticeable in the case of small lines patterns; this was the case even where the amplitudes of the ultrasonic vibration were small. As for the application of ultrasonic vibration on nanoimprinting is concerned, it was found to greatly improve the molding accuracy of the process.     

Guide structure with pole arrays imprinted on nylon fiber

For the next generation of micro–electro-mechanical-systems (MEMS) with flexibility and large size, we are developing new kinds of MEMS that will be woven fabric of “on-fiber-devices”. An on-fiber-device is realized by thin-film-coating, patterning, and etching on the surface of a thin fiber that is then transformed into fiber-shaped device to make MEMS such as sensors and actuators. These on-fiber-devices that themselves are in shape of fibers are woven and criss-crossed resulting in new devices with novel functions. The contact points, interconnecting the woven fibers are designed to be fixed with respect to each other where they can make electrical contacts as necessary. We have developed a thermal nanoimprint technology to fabricate weaving guide structures supporting electric contact points on the surface of a thin fiber. The cross-sectional shape of the weaving guide structure was made to be rectangular, and arrays of cylinder poles of 5, 10 and 20 μm in diameters were arranged as supporting structures for making electrical contacts with the bottom of the weaving guide structure. A mold for this purpose required a two-step structure capable of imprinting weaving guide structure, and the contact points on the surface of a fiber in one stamping operation. Such a mold was fabricated by combining MEMS processing with Ni-electroforming technology. Four kinds of guide structures with depths of 20, 30, 40 and 50 μm were processed by adjusting the dry-etching during the making of a Si master. Using these electroformed-Ni molds, these different weaving guide structures, each with a set of 5-, 10- and 20-μm diameter cylinder poles were transferred onto a 90-μm diameter nylon fiber by thermal imprinting.