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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 positivetone 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.

We fabricated microlenses and the logo of the National Institute of Advanced Industrial Science and Technology (AIST) on Pyrex glass by employing thermal nanoimprint technology. The mold material used for imprinting on Pyrex glass was an amorphous Ni-P alloy that was deposited on Inconel-600 by electroless plating technology. The complete fabrication technique consisted of highly accurate processing by focused-ion-beam (FIB) on material that involved a high-temperature thermal treatment that has the advantage of improving the hardness of the mold. An amorphous Ni-P alloy layer on an Inconel-600 substrate was characterized by measuring its X-ray diffraction spectrum. Using this technique we successfully developed a low-cost mold for imprinting on Pyrex glass instead of using a more expensive glass-like carbon mold that is commonly used for this purpose. Microlenses with concave curvatures having radii of 12 and 20 mm were created on the mold by a FIB system equipped with three-dimensional computer-aided-design (CAD) software. This mold was used for thermal imprinting on Pyrex glass substrates to fabricate microlenses and the AIST logo. When polished Inconel-600 was used as a substrate for molds, the accuracy of the Ni-P mold proved to be of higher quality than a mold made of unpolished Inconel-600. The microlenses made using Ni-P/ polished-Inconel-600 molds showed lubricious surfaces that were not possible to achieve using Ni-P/unpolished-Inconel-600 molds. Moreover, some of the parameters in Ni-P electroless plating were changed in order to make three kinds of molds with P content ratios of 4, 8, and 16 wt %. The micro-vickers hardness caused by thermal treatment and the differences among the transcript values on Pyrex glass were also evaluated experimentally.

The authors are developing an on-fiber device that uses a quartz fiber as a substrate material and a large-area display and a wearable health monitor by woven fibers with embedded electrical circuit. The electrical circuit will be formed by inserting some electroconductive material into the concave pattern by inkjet and electroless-plating after thermally imprinting on the surface of the quartz fiber. To imprint the quartz fiber, a mold should be able to withstand the high temperature of 1400°C. Therefore, a mold for quartz imprinting on quartz fiber was fabricated with a glasslike carbon substrate polished by chemical-mechanical-polishing. Mold patterns with high accuracies were processed by applying microelectromechanical system fabrication techniques such as photolithography and reactive ion etching. Precise patterns with 5μm minimum linewidths were transferred on the front surface of a 200μm square quartz fiber by thermal nanoimprint technology. The width of the imprinted quartz fibers grew from 200to296μm by the loading force, but part of the loading force was also used up in deforming the quartz fibers. Filling rates, defined as the ratio of the height of imprinted patterns to the depth of mold patterns, were calculated and then the relationship between the filling rate and the aspect ratio of mold patterns was investigated. The molding accuracy was found to be independent of the size of the mold patterns, but it did exhibit its dependency on the aspect ratio of the mold patterns. The expected overlay accuracy, which is important for making circuitry in the future, was approximately 5μm judging from the imprinted patterns on the quartz fiber.

A new surface smoothing method using thermal nanoimprinting technology with a 0.2-nm-high atomically stepped sapphire mold has been investigated for quartz glass with a glass transition temperature (T g ) above 1000 °C. Atomic-scale patterning of approximately 0.1-nm-high step arrays has been achieved on the quartz glass. Imprinting was performed at 1.3 MPa and 1000 °C with loading for 10 min, and postannealing at 1000 °C for 180 min in vacuum was found to partially smooth the atomically stepped morphology of the glass surface.