Optoelectronic-VLSI Technology: Terabit/s I/O to a VLSI Chip

The concept of a manufacturable technology that can provide parallel optical interconnects directly to a VLSI circuit, proposed over 15 years ago in [1], now appears to be a reality. One such optoelectronic-VLSI (OE-VLSI) technology is based on the hybrid flip-chip area-bonding of GaAs/AlGaAs Multiple-Quantum Well (MQW) electro-absorption modulator devices directly onto active silicon CMOS circuits. The technology has reached the point where batch-fabricated foundry shuttle incorporating multiple OE-VLSI chip designs are now being run [2]. These foundry shuttles represent the first delivery of custom-designed CMOS VLSI chips with surface-normal optical I/O technology. From a systems point of view, this represents an important step towards the entry of optical interconnects in that: the silicon integrated circuit is state-of-the-art; the circuit is unaffected by the integration process; and the architecture, design, and optimization of the chip can proceed independently of the placement and bonding to the optical I/O. To date, over 5760 MQW modulator devices have been integrated onto a single CMOS IC with a device yield exceeding 99.95%. Each bonded device has a load capacitance of approximately 50fF (65fF including a 15µmx15µm bond pad) and can be driven by a CMOS inverter to accomplish the electrical-to-optical interface. Compact CMOS transimpedance receiver circuits have been developed to execute the photocurrent-to-logic-level voltage conversion. Operation of single-ended receivers [3] (one diode per optical input) fabricated in a 0.35µm linewidth CMOS technology, has been demonstrated over 1Gigabit/s with a measured bit-error-rate less than 10-10. Differential two-beam receiver, have similarly been operated to over 1Gbit/s. The