Martin Börner

High Aspect Ratio Vertical Cantilever RF-MEMS Variable Capacitor

An electrostatically actuated, microwave microelectromechanical system variable capacitor fabricated using deep X-ray lithography is presented. A single exposure has been used to produce the novel high aspect ratio microstructure, which includes a thin, vertically oriented, movable nickel cantilever beam and a 40:1 vertical aspect ratio capacitance gap. The 0.8-pF capacitor operates in the 1-5GHz region and has Q-factors of 36 at 4GHz and 133 at 2 GHz. The variable capacitance ratio is 1.24:1 over a 20-V tuning range at 4GHz

Reducing pull-in voltage by adjusting gap shape in electrostatically actuated cantilever and fixed-fixed beams

A gap with variable geometry is presented for both cantilever beam and fixed-fixed beam actuators as a method to reduce the pull-in voltage while maintaining a required displacement. The method is applicable to beams oriented either in a plane parallel to or perpendicular to a substrate, but is most suitable for vertically oriented (lateral) beams fabricated with a high aspect ratio process where variable gap geometry can be implemented directly in the layout. Finite element simulations are used to determine the pull-in voltages of these modified structures. The simulator is verified against theoretical pull-in voltage equations as well as previously published finite element simulations. By simply varying the gap in a linear fashion the pull-in voltage can be reduced by 37.2% in the cantilever beam case and 29.6% in the fixed-fixed beam case over a structure with a constant gap. This can be reduced a further 4.8% by using a polynomial gap shape (n = 4/3) for the cantilever beam and 1.2% for the fixed-fixed beam by flattening the bottom of the linearly varying gap.

High Aspect-Ratio Coplanar Waveguide Wideband Bandpass Filter With Compact Unit Cells

This paper introduces a micromachined thick single-metal-layer high aspect-ratio coplanar waveguide (CPW) wideband bandpass filter with compact unit cells based on the electromagnetic bandgap (EBG) concept. The filter is miniaturized as a result of using the EBG concept in design, and also by realizing high aspect-ratio structures with polymer-based deep X-ray lithography fabrication. Cascaded unit cells in the EBG model consist of capacitive and inductive parallel periodically loaded transmission lines, which determine the filter bandwidth. Compact unit cells are realized by using high aspect-ratio CPW stepped-impedance resonators. The main advantage of this approach is that the high aspect-ratio CPW structures make short unit cells practically realizable, resulting in a compact filter structure. A bandpass filter with 47% bandwidth is designed and fabricated using deep X-ray lithography, and the performance and physical size is compared to a conventional quarter-wavelength-based admittance inverter filter.

X-ray grating interferometer for biomedical imaging applications at Shanghai Synchrotron Radiation Facility

An X-ray grating interferometer was installed at the BL13W beamline of Shanghai Synchrotron Radiation Facility (SSRF) for biomedical imaging applications. Compared with imaging results from conventional absorption-based micro-computed tomography, this set-up has shown much better soft tissue imaging capability. In particular, using the set-up, the carotid artery and the carotid vein in a formalin-fixed mouse can be visualized in situ without contrast agents, paving the way for future applications in cancer angiography studies. The overall results have demonstrated the broad prospects of the existing set-up for biomedical imaging applications at SSRF.

Closer to nature – bio-inspired patterns by transforming latent lithographic images

Inspired by nature, a new strategy to create three-dimensional organic structures spanning orders of magnitude by using a combination of deep UV or X-ray direct lithography with a solid-state forming process. The stored latent lithographic image is transferred to three-dimensional curvilinear surfaces by forming the irradiated film under conditions of permanent material coherence.

An Ultra-Deep High-Q Microwave Cavity Resonator Fabricated Using Deep X-Ray Lithography

An ultra-deep polymer cavity structure exposed using deep X-ray lithography is used as a template for metal electroforming to produce a 24-GHz cavity resonator. The metal cavity is 1.8 mm deep and has impressive structure, including extremely vertical and smooth sidewalls, resulting in low conductor loss. The measured resonator has an unloaded quality factor of above 1800 at a resonant frequency of 23.89 GHz.

Template-Based Dielectric Resonator Antenna Arrays for Millimeter-Wave Applications

An approach suitable for millimeter-wave dielectric resonator antenna (DRA) arrays is presented. The methodology involves fabricating precise cavities in acrylic templates and filling them with composite dielectric materials to create a monolithic polymer-based DRA (PRA) array layer. The excitation feed lines are fabricated on a separate substrate layer and the two layers are aligned and bonded together to form the PRA antenna array module. The impact of the acrylic frame on the PRA performance is analyzed through simulations. A four-element array operating at 60 GHz is realized to demonstrate the approach. The performance is characterized through simulation and also experimentally verified. The array offers a wide 12% impedance bandwidth at 60 GHz and broadside radiation with 10.5-dBi realized gain and stable radiation patterns. The use of polymer-based materials provides opportunities for cost-effective volume fabrication using molding techniques.

Highly precise micro-retroreflector array fabricated by the LIGA process and its application as tapped delay line filter

We report on the fabrication of a one-dimensional micro-retroreflector array with a pitch of 100 μm. The array was fabricated by x-ray lithography and the lithographie, galvanik und abformung (LIGA) process in a 1 mm thick poly(methyl methacrylate) (PMMA) layer and subsequently covered with Au. The area of the array is 1 mm×10 mm. The high precision of the LIGA-based fabrication process allows one to use the element in spectrometers. Here, it is suggested to apply it to the implementation of a transversal filter for femtosecond pulses. We present a theoretical description of the performance of the retroreflector array as a filtering device and show experimental results.

COMPACT THICK METAL DIPLEXER WITH MULTI- COUPLED FOLDED HALF WAVELENGTH RESONATORS

A thick metal microstrip diplexer is presented. The circuit is based on compact folded half wavelength resonators and uses a source/load-multi-resonator coupling method providing improved performance and greater design ∞exibility. Source/load coupling with multiple resonators introduces additional transmission zeros, and this coupling is enhanced by using high-aspect-ratio metal structures. Tall, narrow metal arms connected to the ports and extended to the non-adjacent resonators provide efiective multi-resonator bypass coupling. The high-aspect-ratio diplexer fabricated using polymer- based deep X-ray lithography and 0.22mm thick metal electroplating demonstrates the advantages of thick metal structures for coupled resonator applications.

The recent development of an X-ray grating interferometer at Shanghai Synchrotron Radiation Facility

An X-ray grating interferometer has been installed at Shanghai Synchrotron Radiation Facility (SSRF). Three sets of phase gratings were designed to cover the wide X-ray energy range needed for biological and soft material imaging capabilities. The performance of the grating interferometer has been evaluated by a tomography study of a PMMA particle packing and a new born mouse chest. In the mouse chest study, the carotid artery and carotid vein inside the mouse can be identified in situ without contrast agents.