Design, Simulation, and Microfabrication of 3D RF-MEMS Filters
Wireless products are popular with the public at present. In microwave circuits, filters play an important role. These products are required to be miniaturized. However, conventional designed filters cannot be limitless reduced due to the operation frequency. In this research, slow-wave lines and micromachined techniques are applied to fabricate 3D high frequency miniaturized lowpass filter. The characteristics of filters are simultaneously investigated with the increasing metal thickness.
Firstly, slow-wave lines are applied to design a high frequency miniaturized lowpass filter. The designed filter is 4.18 × 6.0 mm in area. From the simulation results of Sonnet, the cut-off frequency of designed filter is set on 4.1 GHz, good insertion loss and impedance match are observed. In our research, Ansoft HFSS is the first time to be applied for the simulation of our designed filter, especially for the 3D metal structures.
In fabrications, surface micromachining and micro-electroplating technologies are applied to fabricate 3D miniaturized filters with different metal thickness on quartz substrate. The selection of adhesion layer and seed layer is important that adhesion layers should provide good adhesive force and easily to be removed, and seed layers should have good conductivity. Per different metal test, it is found that composes of titanium and copper is a better choice. Therefore, our miniaturized lowpass filters are fabricated successfully.
In measurement results, good scattering response curves of lowpass filters have been investigated and fabricated. It is observed that both power loss and 3 dB frequency are decreased with the increasing metal thickness. This means the cut-off frequency can be adjusted by controlling the thickness of interdigital and meander lines in our proposed lowpass filter, which implies to gain benefit from the thickening of conductor.
In point of our fabrication and measured results, the variations of metal thickness play an important role to determine the characteristics of filters. Based on our electroplated samples and measured results, we have successfully investigated the miniaturized lowpass filters which are potential and popular at present. Our results show that this reduced-sized lowpass filter have good performance with low loss and compact size and is very promising for use in MIC/MMIC applications.
[1] D.-S. Hung, Y.-C. Lo, R.-Y. Yu, C. Wang, and W. Hsu (November 2003). 3D MEMS S-band Resonators in Chip Size, 奈米工程暨微系統技術研討會, Taipei, Taiwan.