Flexible polymer pillars for optical chip assembly: materials, structures, and characterization

Abstract

In an effort to address the need for robust optical chip I/O interconnects, we describe the fabrication and testing of microscopic polymer pillars for use as a flexible optical bridge between the chip and the substrate. The polymer pillars are photoimaged using the polymer Avatrel to a height of up to 350 mm. The photodefinable polymer Avatrel was used for the fabrication of the optical pillars due to its ease of processing and its unique material properties that include high Tg and low modulus. To evaluate the performance of the polymer pillars, the optical coupling efficiency from a light source to an optical aperture with and without an optical pillar is measured. For a light source with 12o beam divergence, a 30x150 mm polymer pillar improves the coupling efficiency by 3 to 4.5 dB compared to pillar-free (free-space) optical coupling. Due to the high mechanical compliance of the optical pillars, we also demonstrate that polymer pillars enhance the optical coupling efficiency between the chip and the substrate when they are misaligned in the lateral direction and that the displacement tolerance can be doubled from 15 to 30 mm for a 1dB power loss budget.