Olga V. Makarova

Fabrication of high density, high aspect-ratio polyimide nanofilters.

A novel fabrication process produces high porosity polymer nanofilters with smooth, uniform, and straight pores with high aspect ratios. The process utilizes electron beam lithography and energetic neutral atom beam lithography and epitaxy techniques. The method has the potential to produce a new generation of high-precision, very-high-porosity, biocompatible filters with pore sizes down to 100nm.

Microfabrication of freestanding metal structures using graphite substrate.

Abstract A novel method of fabricating freestanding electroformed metal structures using a rigid porous graphite substrate is reported. Polymethylmethacrylate’s adhesion to graphite is much stronger compared with metal-coated silicon or graphite, because of graphite’s high porosity and microroughness. Another advantage of graphite is its easy sacrificial removal by abrasion. Results are presented on the fabrication of high-aspect-ratio freestanding copper grids used as collimators in mammography and medical imaging. The method can be used in the production of micromolds for hot embossing and injection mold fabrication of microelectromechanical systems (MEMSs) and for fabrication of arrays of microparts on pick-and-place carriers for assembly into MEMS.

Development and Monte Carlo Analysis of Antiscatter Grids for Mammography

Mammography arguably demands the highest fidelity of all x-ray imaging applications, with simultaneous requirements of exceedingly high spatial and contrast resolution. Continuing technical improvements of screen-film and digital mammography systems have led to substantial improvements in image quality, and therefore improvements in the performance of anti-scatter grids are required to keep pace with the improvements in other components of the imaging chain. The development of an air-core honeycomb (cellular) grid using x-ray lithography and electroforming techniques is described, and the production of a 60 mm × 60 mm section of grid is reported. A crossed grid was constructed with 25 μm copper septa, and a period of 550 μm. Monte Carlo and numerical simulation methods were used to analyze the theoretical performance of the fabricated grid, and comparisons with other grid systems (Lorad HTC and carbon fiber interspaced grids) were made over a range of grid ratios. The results demonstrate essentially equivalent performance in terms of contrast improvement factor (CIF) and Bucky factor (BF) between Cu and Au honeycomb grids and the Lorad HTC (itself a copper honeycomb grid). Gold septa improved both CIF and BF performance in higher kVp, higher scatter geometries. The selectivity of honeycomb grids was far better than for linear grids, with a factor of ∼3.9 improvement at a grid ratio of 5.0. It is concluded that using the fabrication methods described, that practical honeycomb grid structures could be produced for use in mammographic imaging, and that a substantial improvement in scatter rejection would be achieved using these devices.

220 GHz folded waveguide circuits for high power amplifiers

Folded waveguide interaction circuits for a vacuum electronic amplifier have been designed. Microfabrication efforts to produce the FWGs are underway and preliminary analysis of the properties of these slow wave circuits has been completed.

9.3: Fabrication of solid copper 220 GHz folded waveguide circuits by UV lithography

We report the fabrication results for an all-copper 220 GHz folded waveguide circuit. The fabrication method is based on UV lithography using SU-8 negative photoresist followed by copper electroforming. The method achieved the necessary dimensional accuracy, smooth vertical side walls, low cost of fabrication, and all-copper structure suitable for high power applications.

Nanoporous ultrananocrystalline diamond membranes

Micro- and nanoporous membranes have a wide range of applications in many fields, including medical diagnostics, drug delivery, and hemodialysis. Ultrananocrystalline diamond coatings are becoming more and more significant in medical applications because of the highest degree of biocompatibility, unmatched by other materials. The pores ranging in diameter from 100 to 2000 nm have been fabricated in a 1-μm-thick ultrananocrystalline diamond film on silicon wafers using e-beam and optical lithography, reactive ion etching, and laser writing.

Microfabrication of freestanding metal structures released from graphite substrates

A sacrificial layer is usually used to release electroformed microstructures. Because of the chemistry applied to the sacrificial layer, only a limited number of metals can be used for electroforming. A novel method to fabricate freestanding electroformed copper structures is presented. A graphite substrate allows the release of the metal part, by abrasive removal of the graphite after electroforming. Results on fabrication of high-aspect-ratio freestanding copper grids are presented; these can be used as x-ray collimator in medical imaging to reduce scattered radiation. This process has potential application to the fabrication of injection molds and microparts on pick-and-place carriers for microelectromechanical systems (MEMS).

Fabrication of solid copper two-level waveguide circuits for a THz radar system by UV lithography

The availability of reliable, compact source operating at 0.67 THz will have a significant impact on a variety of defense applications such as high data-rate communication, high resolution imaging in inclement conditions, and radar. As frequency increases, waveguide feature structure dimensions and tolerances decrease. Submicron precision and surface finish are needed in order to achieve the required power performance of the circuits. Thermal management of high radiation power is needed for stabile continuous operation, which can only be achieved with an all-copper structure for the waveguide. We report the fabrication of solid copper two-level folded waveguide circuits. The fabrication method is based on UV-lithography using copper plate as a substrate for SU-8 resist, followed by copper electroforming.