Martin Boerner

Deep x-ray lithography processing for batch fabrication of thick polymer-based antenna structures

Deep x-ray lithography is applied for the first time to fabricate polymer-based antenna structures with different portions of ceramic contents. To produce successful and viable antenna structures, three different methods are proposed using positive and negative tone resists. In the first method the structures are lithographically fabricated avoiding an intermediate molding step using SU-8 as a photosensitive resist filled with fine ceramic powder with particles in the submicron range. In the second and third methods a polymethylmethacrylate (PMMA) mold is first fabricated by x-ray lithography, and then SU-8/MMA mixed with the high ceramic powder content is injected into the mold. In these methods a final step of crosslinking for SU-8 and polymerization for MMA is also required. Optimized fabrication parameters allow the production of high quality antenna structures as thick as 2.3 mm. X-ray lithography capabilities in fabrication of antennas and other passive microwave components with special features reinforce the idea of fabricating integrated passive microwave circuits along with active circuits using this emerging technology.

Development of Polymer-Based Dielectric Resonator Antennas for Millimeter-Wave Applications

The goal of this paper is to use polymer-based materials (instead of hard ceramics) in fabrication of dielectric resonator antennas at millimeter-wave frequencies. The soft nature of polymers facilitates machining of antennas, while the low permittivity of polymers naturally enhances the bandwidth. More importantly, advantageous properties (e.g., ∞exibility and photosensitivity) of some polymers introduce special capabilities which can not be achieved by ceramics. A photosensitive polymer is utilized in this paper to fabricate polymer-based resonator antennas. As a result, deep X-ray lithography is enabled to produce high quality antenna structures. The proposed dielectric resonator antennas which inherently have very low relative permittivity (usually in a range from 3 to 5) are excited efiectively using a slot-coupled feeding method and analyzed in both the frequency and time domains. Impedance and radiation properties are compared with higher permittivity ceramic antennas. Impedance bandwidths up

Photoresist-Based Polymer Resonator Antennas: Lithography Fabrication, Strip-Fed Excitation, and Multimode Operation

Artificially modified materials are becoming increasingly important in antenna design. Attractive features make polymer composites very promising materials for improving the fabrication process and antenna performance. In this study, a photosensitive polymer composite is utilized to fabricate precise dielectric-resonator antenna structures using deep-X-ray lithography. The multimode operation and miniaturization aspects of strip-fed composite antennas with very low permittivity (εr <; 5 ) are investigated for the first time. The prototype antenna offers a -10 dB impedance bandwidth of 48%, from 18.8 GHz to 30.7 GHz, and gain in the range of 5 dBi. The nonradiating modes are removed by the special boundary conditions enforced by the vertical strip. Stable radiation patterns and low cross-polarization levels over the entire impedance bandwidth are therefore preserved. Further improvements in impedance bandwidth are presented, and the antenna performance and fabrication processes are discussed.

Microwave performance of photoresist-alumina microcomposites for batch fabrication of thick polymer-based dielectric structures

The goal of this paper is to investigate the electrical properties of photoresist-alumina microcomposites with different portions of ceramic content. Substrates of photoresist-alumina microcomposites are fabricated and a comprehensive analysis is performed to characterize their dielectric constant and dielectric loss tangent at microwave frequencies up to 40 GHz. To evaluate the performance of these materials for microwave applications, the properties of various lithographically fabricated antenna elements are examined and analysed based on the measured electrical properties. The experimental results show that the electrical properties of the photoresist composite are nonlinearly affected by ceramic content and also a minimum percentage of ceramic portion is required to improve the electrical properties of the photoresist composite. For instance, comparison of 0 wt% with 23 wt% SU8-alumina shows that no reduction is achieved for the dielectric loss tangent. Comparison of 38 wt% with 48 wt% SU8-alumina microcomposite shows that the dielectric loss tangent is improved from 0.03 to 0.01 and the dielectric constant is increased from 3.8 to 5.0 at 25 GHz. These improvements can result in superior performance for the photoresist-based microwave components.

SU-8 resonator antenna

Originally developed and patented by IBM in 1989 and commercially introduced by MicroChem Corporation in 1996, SU-8 rapidly found wide use in UV and X-ray lithography as a negative tone photoresist for microsystem technology applications [1]. Its very low optical absorption in UV and X-ray ranges leads to uniform exposure conditions for thicknesses up to a few millimetres resulting in high structural quality and excellent sidewall verticality. Cured SU-8 is highly resistant to solvents, acids and bases and has excellent thermal stability, making it attractive for applications in which the SU-8 is considered as a permanent part of the device. For instance, it is used in fabrication of X-ray lenses [2], metamaterials [3], single-mode and multi-mode optical waveguides [4], [5], and micro channels for bio applications [6].

Photodefinable microcomposites for antenna applications

If properly mixed, polymer-ceramic composites offer a unique combination of appealing thermal, mechanical and electrical properties [1], [2]. Some of these advantages are attributed to the polymer or to the ceramic and some to the polymer and ceramic interaction. For instance, the improved thermal stability is due to this composition [2]. Flexibility in design by different distribution of ceramic micropowder, wide range of obtainable dielectric constant, and relatively low cost are among other features of polymer composites. Compared to pure ceramics, they have lower processing temperature and density, they are softer and easier for fabrication, and they are more biocompatible. Due to these fascinating characteristics, polymer-ceramic composites have received increasing attention for a wide variety of applications in recent years.

Photoresist-based dielectric resonator antenna fabrication and performance: A review

Some of the techniques that we have used to facilitate the fabrication and enhance the performance of photoresist-based dielectric resonator antennas are presented. These techniques are discussed under three different categories of material development, fabrication process, and antenna performance.

Fabrication of photoresist-based polymer resonator antennas using ultra-thick SU-8 based dry films

The purpose of this paper is to demonstrate fabrication of various photoresist-based polymer resonator antenna structures using ultra-thick SU-8 based dry films. First, a set of dielectric resonator antenna geometries with modified shapes was designed and included in an X-ray mask. Then the ultra-thick dry films were exposed through this mask to construct antennas. 2 mm tall structures with fine features down to 50 μm are achieved. The preliminary results show the existence of new modes in modified shapes which can be utilized for future antenna applications. Over 90% optically transparency makes these SU-8 based structures highly attractive for transparent antenna applications.

Polyester-styrene/ceramic nanocomposites for antenna applications

Polyester-styrene polymer composites of high permittivity ceramic nano powders (barium titanate) are fabricated and electrically measured for antenna applications. It is shown that the usage of high permittivity ceramic contents can increase the relative permittivity of the composites to around 10 at microwave frequencies. The Polyester-styrene composite material preparation technique is described. The materials are used to fabricate various dielectric resonator antenna elements. Details of the antenna fabrication techniques are discussed. Results show fabricated antenna elements and arrays with large impedance bandwidth. The presented techniques provide a precise method for fabrication of complicated or multi-segment dielectric resonator antennas.

Front and Backside Structured Gratings for X-Ray Phase Contrast Imaging

We report on fabricating x-ray gratings with extreme aspect ratios for phase contrast imaging. We modified the LIGA process by splitting the fabrication sequence on both sides of a thin membrane. Image quality is compared with existing gratings.