Laser-micromachined silicon-platelet feedhorns for large-scale submillimeter and millimeter-wave focal planes

Large-scale focal planes for cosmic microwave background (CMB) and submillimeter astronomy require arrays of feedhorns, typically fabricated from silicon platelets using deep reactive-ion etching (DRIE). This work presents the first silicon-platelet feedhorn arrays produced by laser micromachining, a potentially faster and cheaper alternative.

The technology was first demonstrated for the 80–170 GHz band, covering the 90/150 GHz bands common to CMB experiments, then expanded to large-scale production on 150 mm wafers and to submillimeter wavelengths. The resulting feedhorn array is optimized for 330–370 GHz (centered at 350 GHz) and is destined for the CCAT 350 GHz module of Prime-Cam. The paper details the design and fabrication processes.

Optical performance was compared directly to simulation and to identical-design feedhorns made with traditional DRIE, validating the laser-micromachined approach.

Future developments discussed include improved sidewall control and using thicker wafers (thus fewer wafers per array), which could significantly reduce production costs and labor.