Flip-chip bonding of VCSELS with CMOS circuits achieves gigabit-per-second performance
To further the integration of optoelectronic devices and complementary metal-oxide semiconductor (CMOS) circuits, researchers at Bell Labs?Lucent Technologies (Holmdel and Murray Hill, NJ) have demonstrated what they say is the first flip-chip-bonded CMOS/vertical-cavity surface-emitting-laser (VCSEL) array capable of gigabit-per-second performance per laser. The researchers built on their previous flip-chip bonding of gallium arsenide multiple-quantum-well modulator arrays to CMOS circuits. The experimental devices consisted of 2 10 arrays of bottom-emitting VCSELs operating at 970 nm, which enabled transmission through the III-V substrate. Testing confirmed laser threshold voltages of 1.4?1.5 V and threshold currents of 0.9?1.0 mA at room temperature?both of which are within the drive capability of commercial CMOS devices. Continuous-wave output powers of 4.3 mW were obtained. The simple two-transistor VCSEL driver was based on a current-shunting principle that provides a low-area tunable-power circuit with a measured small-signal bandwidth of approximately
2 GH¥in a 0.5-?m CMOS device. Integrating efficient, low-threshold VCSELs and low-area, low-power CMOS circuits capable of high bit rates could lead to advanced optical transceivers and local-area-network switches. Contact John Cunningham at [email protected].