Tiny VCSEL chip self-assembly for advanced chip-to-wafer 3D and hetero integration

A 12-channel vertical cavity surface emitting laser (VCSEL) chip was heterogeneously self-assembled to a glass interposer wafer by liquid surface tension as a driving force. The size of the VCSEL chip was 0.35 mm wide and 3 mm long. From the square dummy chips having structurally similar periphery to the VCSEL, the step structure at the chip edge was found to be significantly dependent on the alignment accuracies. From the rectangular dummy chips having the same sizes to the long VCSEL, the tiny chips were precisely self-assembled with alignment accuracies within 2 μm even when they were manually placed on water droplets provided on host Si wafers. After self-assembly of the VCSEL chip and the subsequent thermal compression, the VCSEL was accurately positioned, successfully emitted 850-nm light, and exhibited no degradation of the I-V characteristics. This paper also presents our recent progress on the hybrid integration of chip-scale photonic devices with 3D/TSV technologies for optical interconnections.