SU-8 Ka-band filter and its microfabrication

Abstract

This paper presents the design and microfabrication of a coaxial dual model filter for applications in LMDS systems. The coaxial structure is formed by five conductive layers, each of which is of 700 µm thickness. The filter uses an air filled coaxial transmission line. It is compact with low dispersion and low loss. The design has been extensively tested using a prototype filter micromachined using laser drilling on a copper sheet and the results show a good agreement with the theoretical calculations. The laser fabrication has exposed weakness in suitability to volume production, uneven edges and oxide residuals on the edges, which affects the filter performance. A process for fabrication of such a filter in SU-8 has been developed which is based on a UV lithographical process. In order to fabricate such thick SU-8 layers, the SU-8 process has been optimized in terms of UV radiation and post exposure baking. During the test fabrication, the optimized SU-8 process has produced microstructures with an aspect ratio of 40:1 and a sidewall of 90 ± 0.1 • . The high quality SU-8 structures can be then either coated with a conductive metal or used as moulds for producing copper structures using an electroforming process. The microfabrication process presented in this paper suits the proposed filter well. It also reveals a good potential for volume production of high quality RF devices.

Static Zero-Power-Consumption Coplanar Waveguide Embedded DC-to-RF Metal-Contact MEMS Switches in Two-Port and Three-Port Configuration

“…Examples include etching away parts of the lossy substrate close to the line [15]- [17]; creating hollow waveguides by bonding substrates with etched grooves [18], [19]; suspending elements of the transmission line above the lossy substrate by etching away sacrificial layers below them [20]- [23]; and using 3-D polymer or metal-printing techniques to achieve air-filled transmission lines [24]- [26] or coaxial waveguides filled with low-loss polymers [27]. Reduction of ohmic losses by increasing the metal thickness of coplanar waveguides has been shown using synchrotron radiation lithography [28].…”

Pressure Free Fabrication of 3D Microcomponents Using Al Powder

“…[19,20,21] The PDMS slurry was prepared by mixing the PDMS precursor with curing agent (Dow Corning Corp. Sylgard 184) in a weight ratio of 10:1 and left for 30 min to allow the trapped air to escape. The mixture was then poured on the SU-8 master mould templates and placed in a vacuum condition until all residual bubbles had been removed.…”

“…The ultra-thick SU-8 process (UTSP) developed by Jin et al has been used to produce 40:1 aspect ratio features in 1000 lm thick SU-8. [19,20,21] The UTSP process is also adopted in the experiments for producing the master moulds. Figure 1 shows a picture of an SU-8 microgear fabricated using the UV lithography following the UTSP process.…”

Design of Quick-Dry Surface Using Structured Surface

“…SU-8 is used extensively because it allows us to produce microstructures with a high aspect ratio (>7) and excellent mechanical properties (11) . The structures were arrays of pillars of different sizes and pitches.…”