Design and Fabrication of a Narrow-bandwidth Micromechanical Ring Filter using a Novel Process in UV-LIGA Technology

This paper presents the design and a new low-cost process for fabrication of a second-order micromechanical filter using UV-LIGA technology. The micromechanical filter consists of two identical bulk-mode ring resonators, mechanically coupled by a flexural-mode beam. A new lumped modeling approach is presented for the bulk-mode ring resonators and filter. The validity of the analytical derivation is investigated using the finite element method by ANSYS software. The new low-cost fabrication process is used to achieve a high aspect ratio of 16 with 3 μm gap spacing. The rigid graphite serves as a low-cost primary substrate and plating base of nickel as structural material. The fabrication process needs only three UV-lithography steps with Mylar masks to fabricate the main structure and pattern the printed circuit board as a secondary substrate. The frequency response of the fabricated filter is characterized as a function of the DC-bias voltage using a fully differential drive and sense interface circuit. The experimental results demonstrates micromechanical filter with center frequency in the vicinity of 10.31 MHz and percent bandwidth less than 0.3% using a DC-bias voltage of 60 V. The detailed fabrication process can be applied as an appropriate low-cost alternative to X-ray LIGA and silicon-based micromechanical filters.