Hybrid-integrated smart pixels for dense optical interconnects

The recent progress of the performance of a CMOS-LSI is rapid and continuous, and the required bandwidth for communication between chips will be enormous. Dense optical interconnects by smart pixels may be used to such an application because it would have enough bandwidth and short delay of signaling. On-chip and chip-to-chip optical interconnects and electrical interconnects were compared and the advantages of the use of optics were indicated. For on-chip communication, high-speed (70% of the velocity of the light) propagation of signals by optical interconnects are useful and it enables whole chip synchronization. The considerable reduction of power dissipation using optics was estimated for chip-to-chip interconnects. The effect of hybrid integration with small parasitic capacitance was simulated and the sensitivity improvement of more than 13 dB was expected. How to fabricate a smart pixel is the most difficult subject. We had successfully fabricated smart pixels with VCSELs and PDs using polyimide bonding technique. CW lasing of the VCSEL was observed and it proved that the polyimide bonding technique was useful to making smart pixels. The integrated receiver was also fabricated in the same manner. It showed a high sensitivity of -9.2 dBm for a bit-rate of 622 Mbit/s. High-performance characteristics of the receiver resulted from the low parasitic integration with polyimide bonding technique.