W-Band 4th Order Waveguide Filter Based on Double Layer SU8 Microfabrication

Area of Science:

• Microwave Engineering
• Materials Science
• Nanofabrication

Background:

• SU-8 photoresist is a versatile material for microelectromechanical systems (MEMS) fabrication.
• Waveguide bandpass filters are critical components in high-frequency communication systems.
• Micromachining offers potential for miniaturized and high-performance RF components.

Purpose of the Study:

• To investigate the fabrication accuracy of W-band SU-8 micromachined waveguide bandpass filters.
• To assess the suitability of SU-8 for creating high-precision, layered RF structures.
• To analyze the challenges and propose solutions for SU-8 micromachining of filters.

Main Methods:

• Design of a 4th order waveguide bandpass filter using cylindrical resonators excited in TM010 mode.
• Fabrication using a layered SU-8 micromachining process with silver coating.
• Characterization of manufacturing tolerances including thickness, stacking, and angle deviation.
• Electromagnetic simulation and experimental measurement of filter performance.
• Stress and deformation analysis for structural integrity.

Main Results:

• Excellent manufacturing tolerances achieved: ±4 μm in thickness, ±10 μm in stacking accuracy, and ±1° in vertical angle deviation.
• Measured return loss of 12.4 dB and minimum insertion loss of 0.8 dB, consistent with simulations.
• Identified challenges in SU-8 processing with proposed general solutions for high-precision devices.
• Stress analysis confirmed the filter's ability to withstand pressure while maintaining performance.

Conclusions:

• The SU-8 micromachining process enables high-accuracy fabrication of W-band waveguide bandpass filters.
• The proposed fabrication method and solutions address key challenges in SU-8 processing for RF applications.
• The demonstrated performance validates SU-8 as a suitable material for advanced microwave component manufacturing.