Aspect Ratio Microstructures Research Articles

Fabrication technologies for microsystems utilizing photoetchable glass

Photoetchable glass is a very promising material for the production of components for a wide variety of microsystems. High aspect ratio microstructures can be realized by using slightly modified semiconductor equipment and relatively low fabrication costs are achievable already in small scale production. The application potential of photoetchable glass is mainly determined by the fact that this material can be applied in corrosive and high temperature environment which is of major importance for applications in chemistry and biology. Further advantages are transparency, high Young's modulus and good thermal and electrical insulation.Microstructures generated from photoetchable glass have been produced commercially for various applications mentioned in the text. The photostructuring of this glass is used as an example to show how these microsystems can be manufactured on a large production scale. The principle chemical and physical processes together with the fabrication technologies are explained.In order to promote the utilization of photoetchable glass in microsystems technology the Institute of Microtechnology in Mainz (IMM) and the Schott company have built up a production line for micro devices using FOTURAN produced by Schott. The joint venture covers the design and production of micro devices, the optimization of the fabrication process and the development of advanced equipment for processing FOTURAN in high volume quantities.

Planar very high aspect ratio microstructures for large loading forces

We report on a novel technology called Scream for High Aspect Ratio proportions (SHARP) which adds a new dimension to the Single Crystal Reactive Etching And Metallization (SCREAM) process. The fabrication technology increases the height and capacitive area of mechanical beams to improve the planarity and further extend the loading capabilities of very deep actuator structures. The process is based on a repeated sequence of thermal oxidations and reactive ion etches (RIE). Part of the technique consists of oxidizing through single crystal silicon (SCS) structural beams of a device by thermally growing a thick silicon dioxide (SiO2) layer (H2O2 precursors) after the first trench RIE etch, thus yielding an ultra-thick (>30 μm) SiO2 etch mask for further deep vertical etching (>100 μm) to form high aspect ratio structures.

The micromilling process for high aspect ratio microstructures

High aspect ratio microstructures are currently created by several processes which include lithography (X-ray, deep ultraviolet, etc.) and mechanical machining (diamond machining, microdrilling, etc.). The lithographic processes require more extensive processing equipment such as an energy source, mask/mask holder/mask aligner, photoresist and substrate, and chemical development capacity. In addition, these processes are serial in nature and each adds to the tolerances of the finished structure. The current mechanical processes provide for the direct removal of the substrate material in a single step but are more limited in the geometric patterns which can be created. In conventional machining, the process which provides the most versatility in geometric patterns is milling. The micromilling process has two basic components. The first is the fabrication of small milling cutters with very sharp cutting edges. The second is the actual removal of the workpiece material with a very precise and repeatable machine tool. Several basic cutter designs have been fabricated using focused ion beam micromachining and are undergoing testing. The cutter diameters are nominally 100 micrometers and 22 micrometers. Results have been obtained which show that this process can be very effective for the rapid fabrication of molds and mask structures.

Design of Dispersion Strengthened NiAl

Recent work on the development of mechanically alloyed, dispersion strengthened NiAl is reviewed. The alloy design approach used in our research group to address the shortcomings of monolithic, cast NiAl are outlined. Significant progress has been made in establishing the thermomechanical processing steps necessary to produce a large grain aspect ratio microstructure without substantial dispersoid coarsening. Some new results on the creep resistance of AIN dispersion strengthened NiAl are presented. Finally, possible directions for continued development of this material are discussed.

Recent applications of polyimide to micromachining technology

In this paper, applications of polyimide materials to micromachining technology are reviewed. First, the use of polyimide-based materials as sensor materials are discussed. In this case, the polyimide material is used as an integral part of the micromachined devices. Emphasis is given to the development and characterization of a piezoresistive composite of polyimide and graphite particles. The composite material is characterized for the mechanical properties (Young's modulus, residual stress) and the electromechanical property (piezoresistive coefficient). Second, the use of both photosensitive and nonphotosensitive polyimides as electroplating molds for the fabrication of thick and high aspect ratio metallic microstructures is presented. Extensions of the basic micromolding process, which enable the fabrication of controlled gaps between metallic microstructural components and higher aspect ratio microstructures, are presented. Electroplated metallic microstructures realized using these technologies are shown. In addition, various applications of the polyimide micromolding technologies are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Development of micromachined devices using polyimide-based processes

Abstract Currently there are several techniques under investigation for the fabrication of metallic microstructures, including photoresist-based technologies, stencil-based technologies and photoelectroforming-based technologies. In this paper, high aspect ratio and thick metallic microstructures are investigated using polyimide-based technologies. The use of polyimide processes offers several advantages, including compatibility with conventional integrated circuit fabrication techniques, chemical and thermal stability for electroplating in a wide variety of acidic, basic and solvent-based solutions, the ability to fabricate devices using conventional cleanroom equipment and materials, and the flexibility to integrate the polyimide into the final micromachined system as a dielectric or structural material. After a review of the polyimide-based processes, selected applications utilizing this technology will be discussed.

Development of microstructures of high grain aspect ratio during zone annealing of oxide dispersion strengthened superalloys

Two extruded bars of the nickel base mechanically alloyed materials MA 6000 and MA 760 have been zone recrystallised in a calibrated gradient furnace. Selected area channelling patterns in the scanning electron microscope have been employed to study the crystallographic texture of the grains of large aspect ratio produced by zone annealing, and microbeam electron diffraction has enabled the orientations of the submicrometre sized equiaxed grains in the material behind the (secondary) recrystallisation front to be studied. In both alloys a curved secondary recrystallisation interface is observed, with the surface recrystallising at a lower temperature than the interior. This is considered to result indirectly from the strain gradients occurring during extrusion. A <110> texture is present, and reasons for this are discussed. In MA 6000 progressive grain rotation towards <110> has been measured behind the recrystallisation interface, although this is not observed in MA 760 as it transforms at a lower temperature. Quenching experiments have shown that nucleation of secondary recrystallisation occurs at temperatures higher than that at which the recrystallisation interface grows at the zoning speed employed. It is suggested that the microstructure develops via the thermally activated unpinning of interfaces which have mobility advantages.MST/1948

Development of microstructures of high grain aspect ratio during zone annealing of oxide dispersion strengthened superalloys

AbstractTwo extruded bars of the nickel base mechanically alloyed materials MA 6000 and MA 760 have been zone recrystallised in a calibrated gradient furnace. Selected area channelling patterns in the scanning electron microscope have been employed to study the crystallographic texture of the grains of large aspect ratio produced by zone annealing, and microbeam electron diffraction has enabled the orientations of the submicrometre sized equiaxed grains in the material behind the (secondary) recrystallisation front to be studied. In both alloys a curved secondary recrystallisation interface is observed, with the surface recrystallising at a lower temperature than the interior. This is considered to result indirectly from the strain gradients occurring during extrusion. A texture is present, and reasons for this are discussed. In MA 6000 progressive grain rotation towards has been measured behind the recrystallisation interface, although this is not observed in MA 760 as it transforms at a lowe...

New hybrid (e-beam/x-ray) exposure technique for high aspect ratio microstructure fabrication

A new lithographic technique will be described in this paper which makes it possible to increase the height-to-width (aspect) ratio of electron-beam-exposed patterns in the resist layer, without significantly increasing proximity effects. The technique consists of applying two resist layers on the substrate, separated by a thin metal film. The pattern is electron-beam exposed on the top resist layer, and after development, a thin (2000–3000 Å) gold or other x-ray absorbing material is used to form an in situ x-ray mask to expose a much thicker bottom resist layer in an x-ray exposure system. It is shown that with this technique, lines of 0.25-μm wide with vertical walls, can be obtained in 2-μm-thick PMMA resist or an aspect ratio of eight can be easily achieved. It is also shown that the in situ mask can be registered to a previous level on the workpiece with accuracy better than 0.1 μm.