High density 3-dimensional optical and electrical I/O structures for chip-scale-packaged Si photonic optical transceivers have been developed.
The optical I/O is a vertical polymer waveguide structure made of UV curable resins. The waveguide structure includes 125-μm-pitch 8°-tilted cores, which is called “optical pin.” The tilted optical pins were formed by oblique illuminated photolithography. The optical pins for transmitters confine emitted light from grating couplers in a temperature range from -40°C to 85°C. The optical pins for receivers have inverted-cone shape which acts as a spot size converter connecting a multimode fiber and a smaller integrated surface-illuminated photodiode. Combination of multimode transmission and the optical pins alleviates coupling tolerance as compared with conventional single-mode transmission.
The electrical I/O structure for flip-chip bonding comprises 250-μm-pitch regularly arranged through-glass-vias (TGVs). The TGV is a hermetically-sealed W wire and has connecting pads at both ends. The TGVs are connected to a Si photonic chip by Au-to-Au ultrasonic bonding. The outer I/O pads are covered with electroless-plated Ni/Au, so that conventional lead-free soldering can be available.
The optical and electrical interfaces for the optical I/O cores with TGVs are placed on the same side of the module. This configuration enables simultaneous optical and electrical bonding to polymer-waveguide-embedded printed circuit boards. Because the developed I/O structures minimize area penalty and support 25 Gbps/ch transmission, Si photonic optical transceivers with the developed I/O structures are suitable for use in photonics electronics converged systems.
This research was partly supported by the New Energy and Industrial Technology Development Organization (NEDO).