A Technology For Optical Interconnections Based On Multichip Integration

Concepts for optical interconnects between electronic circuits and systems based on multichip integration, a new form of hybrid integration, are presented. In this integration scheme, chips of different substrate types, such as Si and GaAs, are imbedded in a potting material and connected with photolithographically defined metallizations to form a multichip. Within a multichip, the interconnection scheme would retain the high packing density and minimal numbers of packaging operations achievable with monolithic integration and still permit the individual optimization of material types and device designs to perform electronic and optical functions. Also, the elimination of large bonding pads on the component chips within a multichip will alleviate the pinout problem of complex integrated circuits at the chip level by allowing the pitch between input/output lines to be decreased. Multiplex-ing many slow lines with fast GaAs multiplexers can alleviate the same problem at the multichip level. Off-chip connections between multichips can be made either electrically or optically. Optical interconnections would have low crosstalk. Preliminary results with an epoxy potting material show that continuous lines can be photolithographically patterned from the chip to the epoxy. Tests with a discrete breadboard demonstrate that fast edge transitions can be retained with a diode laser driven directly by a commercial GaAs digital circuit at rates of 1.4 GHz.