Ulf Lindberg

A Hybrid Cold Gas Microthruster System for Spacecraft

A hybrid cold gas microthruster system suitable for low Δv applications on spacecraft have been developed. Microelectromechanical system (MEMS) components together with fine-mechanics form the micr ...

Anisotropic etching of Z-cut quartz

The etch rate in monocrystalline quartz depends on the crystalline orientation. Etch-rate diagrams for micromachining of monocrystalline quartz in, for instance, hydrofluoride-based etchants, are a necessity if one requires the best manufacturing conditions for an etched structure. In this paper we use the development of side-wall profiles in etched grooves, on a Z-cut quartz wafer, to produce two-dimensional etch diagrams. The etch conditions are eight combinations of temperature, from 22 degrees C to 80 degrees C, and etchant mixtures of HF and NH4F diluted in water.

Micro vials on a silicon wafer for sample introduction in capillary electrophoresis

Abstract A multi-sample holder produced by photolithographic and anisotropic etching techniques on a monocrystalline silicon wafer is described. Well defined volumes are created by utilizing the crystal orientations of the silicon material. By using step and repeated lithography, a large number of identical cavities can be obtained on a single chip. The surface is covered with a thin film of gold, which serves as a cathode during electrokinetic injections. Evaluation was carried out by injecting a mixture of pd(A) oligonucleotides (40–60) bases from a 118-nl sample well on to a 50 ωm I.D. polyacrylamide-filled gel column. When compared with injections from classical vials, no additional zone broadening was observed.

Wetting properties of silicon surfaces

The wetting properties of silicon surfaces are believed to be important for the process of silicon-silicon direct bonding, and for the broader issue of biocompatibility. The authors have investigated 14 different surface treatments, including several etching and surface modifying agents, and the contact angles to water were measured for each surface treatment. It was shown that the contact angle could be controlled almost continuously between 5 degrees and 96 degrees by varying the surface treatment. Removing the native oxide layer in hydrofluoric acid results in a hydrophobic surface, whereas hydrophilic surfaces are obtained by inserting the wafer in, e.g. boiling NH/sub 3/:H/sub 2/O/sub 2/:H/sub 2/O. Protein compatibility was investigated by measuring the degree of interaction with insulin. The hydrophobic surfaces showed a relatively strong interaction, whereas hydrophilic surfaces are almost completely inert towards insulin.<<ETX>>

Quasi-buckling of micromachined beams

Buckling of structures with imperfections, quasi-buckling (QB), is studied. At the bifurcation load, these structures show a smooth transition into one of the stable postbuckling equilibrium states, instead of the traditional sudden change in deflection characteristics. QB structures can show the classical snap-through buckling behaviour, i.e., a sudden change of postbuckling equilibrium state. The QB is described with a generalized temperature, Tg, representing the compression of the structure. Imperfections and distributed deflection loads are represented by a generalized pressure, pg. Experiments on micromachined beams, exposed to heating (Tg) and to a Lorentz force (pg), verify that the QB phenomena can efficiently transfer a longitudinal stress into a transversal deflection, with a scale-factor depending on both Tg and pg.

Wet chemical etching mechanism of silicon

We review what can be said on wet chemical etching of single crystals from the viewpoint of the science of crystal growth. Starting point is that there are smooth and rough crystal surfaces. The kinetics of smooth faces is controlled by a nucleation barrier that is absent on rough faces. The latter therefore etch faster by orders of magnitude. The analysis of the diamond crystal structure reveals that the {111} face is the only smooth face in this lattice-other faces might be smooth only because of surface reconstruction. In this way we explain the minimum of the etch rate in KOH:H/sub 2/O in the <001> direction. Two critical predictions concerning the shape of the minimum of the etch rate close to <001> and the transition from isotropic to anisotropic etching in HF:HNO/sub 3/ based solutions are tested experimentally. The results are in-agreement with the theory.

A planar polymer microfluidic electrocapture device for bead immobilization

A planar microfluidic electrocapture device that captures and concentrates beads by a local electrical field has been assembled and tested. The device presented also enables on-line observations o ...

Polishing of Quartz by Rapid Etching in Ammonium Bifluoride

The etch rate and surface roughness of polished and lapped AT-cut quartz subjected to hot (90, 110, and 130degC), concentrated (50, 65, 80 wt%) ammonium bifluoride have been investigated. Having used principal component analysis to verify experimental solidity and analyze data, we claim with confidence that this parameter space does not, as elsewhere stated, allow for a polishing effect or even a preserving setting. Etch rates were found to correlate well, and possibly logarithmically, with temperature except for the hottest etching applied to lapped material. Roughness as a function of temperature and concentration behaved well for the lapped material, but lacked systematic variation in the case of the polished material. At the lowest temperature, concentration had no effect on etch rate or roughness. Future efforts are targeted at temperatures and concentrations closer to the solubility limit.

Batch processing of laterally mobile structures in single-crystalline silicon

Abstract The introduction of elements free to move in the lateral wafer directions may have a great impact on the evolution of silicon micromechanics. Such laterally mobile structures allowing rotation and sliding motion can be used in sensor and actuator applications that have been inaccessible so far due to performance or cost limitations of present technology. This paper deals with the possibility of making these structures in single-crystalline silicon and outlines some fabrication processes using lamination of two oxidized wafers to form a sacrificial layer that will attach the mobile structure to the substrate, and a lamination of silicon surfaces to attach the overlay to the substrate. Both the mobile structure and the overlay will then have anisotropic properties, which gives new possibilities when designing three-dimensional mobile structures.