Frederic Perennes

Sharp beveled tip hollow microneedle arrays fabricated by LIGA and 3D soft lithography with polyvinyl alcohol

This paper describes a fabrication process of hollow microneedle arrays with a sharp beveled tip for transdermal drug delivery. A master is fabricated through a double deep x-ray lithography process. First, a polymethylmethacrylate (PMMA) sheet is exposed to produce single PMMA parts with a sawtooth profile. The tip angle of each tooth determines the final tip angle of the microneedles. The PMMA parts are assembled and glued on a conductive substrate and then exposed through a second x-ray mask containing an array of hollow triangles as absorbing structures. A metal layer is then electrodeposited around the needles in order to form the future base of the array. A polyvinyl alcohol (PVA) solution is cast on top of the master to form a negative mold of the microneedle array after a low temperature curing and peel-off steps. A liquid PMMA solution is cast on top of the PVA negative mold and after the full PMMA polymerization the PVA is dissolved in water. This fabrication method can be performed in a non-clean room environment and requires little instrumentation. It is therefore compatible with a low-cost mass-fabrication scheme.

Focusing X-rays with simple arrays of prism-like structures.

This report discusses the optimization strategy, the theoretical background and first experimental data of a new refractive lens for focusing X-rays. In order to reduce the absorption of X-rays in this transmission lens, optically passive material was removed from the necessarily concave lens shape in a highly regular pattern. The feature dimensions require lens production and replication by deep X-ray lithography, which allows shaping in only one dimension. Consequently such a lens can focus in one direction only, so a crossed lens pair is needed for two-dimensional focusing. The single lens is composed of two large prisms of millimetre size, which touch each other at one of the tips, like an old sand clock. Each large prism contains a highly regular structure of essentially identical prism-like smaller segments. The first lens prototypes focused an X-ray beam with a vertical size of 500 microm and a photon energy of 8 keV to a line with a width of only 2.8 microm. This is only slightly worse than the line width of 1.73 microm expected for its focal length of f = 2.18 m. The photon density enhancement in the focus was 25, but could have been larger as the lens can intercept a beam height of 2.6 mm.

X-ray lithography for micro- and nano-fabrication at ELETTRA for interdisciplinary applications

ELETTRA (http://www.elettra.trieste.it/index.html) is a third generation synchrotron radiation source facility operating at Trieste, Italy, and hosts a wide range of research activities in advanced materials analysis and processing, biology and nano-science at several various beam lines. The energy spectrum of ELETTRA allows x-ray nano-lithography using soft (1.5 keV) and hard x-ray (10 keV) wavelengths. The Laboratory for Interdisciplinary Lithography (LIILIT) was established in 1998 as part of an Italian national initiative on micro- and nano-technology project of INFM and is funded and supported by the Italian National Research Council (CNR), INFM and ELETTRA. LILIT had developed two dedicated lithographic beam lines for soft (1.5 keV) and hard x-ray (10 keV) for micro- and nano-fabrication activities for their applications in engineering, science and bio-medical applications. In this paper, we present a summary of our research activities in micro- and nano-fabrication involving x-ray nanolithography at LILITs soft and hard x-ray beam lines.

On the feasibility of large-aperture Fresnel lenses for the microfocusing of hard X-rays

Like visible light, X-rays can also be focused by refraction in transmission lenses. For visible light this requires convex lenses while for X-rays one needs to use concave lenses instead. Both lens types can be lightened by the material removal strategy introduced by Fresnel, which results in a lens subdivided into zones. Until now, for the focusing of X-rays, stacks of standard lenses and of Fresnel lenses have mostly been produced. The first are dubbed compound refractive lenses, abbreviated as CRL. State-of-the-art systems of this kind now achieve almost theoretical performance for the focus size and the transmission. On the other hand, the latter Fresnel systems, which promise to provide larger apertures, are still in their infancy. This report discusses systematically the properties of two possible schemes for their realisation. It then compares the optimized apertures of these two schemes with those for CRLs. The best Fresnel lenses in this study are found to provide experimentally more than 50% of the expected refraction efficiency at 8.5 keV photon energy. The photon flux in their focus is then almost identical to that of perfect Be CRLs with the same focal length. This report will also interpret experimental data reported previously for other Fresnel lenses.

Fabrication of 3D micro and nanostructures for MEMS and MOEMS: an approach based on combined lithographies.

X-ray lithography is an established technique for the micro fabrication of MEMS and MOEMS well known for low sidewall surface roughness, submicron critical dimension, and high aspect ratio. Recently the typical characteristics of this technique has been developed approaching new opportunities deriving by the possibility to perform tilted exposure and by the combined use with electron beam lithography that allow to shape with direct patterning already the final material in 3D micro and nanostructures. The general approach is to concentrate the complexity of the multi layer fabrication process required to obtain 3D nanostructures mostly on the lithographic process. This capability represent a micro- and nanofabrication tool enabling new technologies. In this paper will be shown a multiple-tilted X-ray lithography procedure combined with e-beam lithography to create sub-micrometric patterns of arbitrary shape buried in 3D structure. The use of deep x-ray lithography in multi exposure configuration has been also exploited for the production of biodegradable 3D scaffold structures and of micro needles based transdermal delivery tools fabrication.

Bi-propellant Micro-Rocket Engine

Micro-satellites (from 10 kg up to 100 kg) have mass, volume, and electrical power constraints due to their low dimensions. These limitations lead to the lack in currently available active orbit control systems in micro-satellites. Therefore, a micro-propulsion system with a high thrust to mass ratio is required to increase the potential functionality of small satellites. Mechatronic is presently working on a liquid bipropellant micro-rocket engine under contract with ESA (Contract No.16914/NL/Sfe - Microturbomachinery Based Bipropellant System Using MNT). The advances in Mechatronics project are to realise a micro-rocket engine with propellants pressurised by micro-pumps. The energy for driving the pumps would be extracted from a micro-turbine. Cooling channels around the nozzle would be also used in order to maintain the wall material below its maximum operating temperature. A mass budget comparison with more traditional pressure-fed micro-rockets shows a real benefit from this system in terms of mass reduction. In the paper, an overview of the project status in Mechatronic is presented.

Replication of deep x-ray lithography fabricated microstructures through casting of soft material

We introduce simple double-casting replication methods for high-aspect-ratio microstructures fabricated by deep x-ray lithography using intermediate molds of soft materials. Two types of soft material are investigated. The ability to fabricate polymethylsiloxane (PDMS) molds with well-type structures with aspect ratios up to 35:1 is demonstrated for structure densities below 50%, and the reproduction from this mold of pillar-type polymethyl methacrylate (PMMA) structures with aspect ratios of 20:1 is achieved. Polyvinyl alcohol (PVA), a water soluble polymer, is also tested as a sacrificial intermediate mold and successfully used for the replication of structures with aspect ratios up to 5:1. Double-casting replication methods are described and discussed for their potential improvement.

Design and prototyping of a micropropulsion system for microsatellites attitude control and orbit correction

Silicon micromachining is an attractive technique for batch production of a wide class of miniaturized components and systems. In particular, micromachined components can be combined with semiconductor lasers, microlenses, and micromechanics to develop a new class of instruments. A worldwide impulse in micromachining is originated by the space industry. Space exploration in the new millennium will mostly rely on drastically miniaturized spacecraft by today’s standards. It is worth to note that the space community is used to speak about nanosatellites when satellite mass ranges between 1 and 10 kg, while microsatellites range between 10 and 100 kg (ESA/IPC 81 Information Note, Paris, October 2000). A key point for precise micronanosatellites orbit and attitude control is the development of a suitable propulsion system, weighting a few grams and capable of few μN of thrust. A microthruster complying these requirements is under development jointly by our laboratory and Mechatronic, using MEMS technology. The...

Design and Fabrication of Microturbine Rotors for Small Power Generation

TASC/INFM, Sincrotrone Trieste (ELETTRA), and Mechatronic GmbH have started the design of a microturbine powered with compressed gas to be used as an electrical generator in a micro/nanosatellite. The research is funded by ESA for the realization of a liquid bipropellant micro-rocket engine that uses a micro-turbine and micro-pumps in order to pressurize the propellants. The turbine rotors have been fabricated with LIGA technology and die sinking Electro Discharge Machining. LIGA is well adapted to the production of high aspect ratio microstructures with very steep and well polished side walls and it does not limit the choice of material to silicon and derivative but offers the possibility to fabricate the turbine in metallic compounds. Moreover it has been found that LIGA, when coupled with EDM, is an optimum technique to obtain enbloc rotors with small diameter and high aspect ratio blades. The first step of the process is the fabrication of an X-ray mask containing a set of turbine rotors. The mask has been used on the ELETTRA deep X-ray lithography beamline to expose millimeter thick PMMA sheets glued on metallic substrates. After development the substrate is selectively electroplated with copper. The negative tone structures are then used as microelectrodes in a following EDM process. This further step allows obtaining turbines made of every conductive material. In particular we machined

Characterisation of adaptive optic pyramid wavefront sensors fabricated by deep X-ray lithography

A novel type of wavefront sensor for adaptive optics, utilizing a pyramidal prism in the focus of a telescope, has recently been reported. The key part, the pyramid wavefront sensor, requires accurate control of the quality of the turned edges, the surfaces and the size of the pyramid tip. The classical figuring and polishing techniques used so far to fabricate the pyramid are time consuming and do not guarantee uniform repeatability of the optical characteristics required for the implementation of a large number of these devices for multiconjugated adaptive optics. We propose a new manufacturing method for the pyramid sensors using the deep X-ray lithography process, allowing very precise contral of the surfaces of the components produced. The fabrication method and characterisation of the first pyramids are presented.