High-yield flip-chip bonding and packaging of low-threshold VCSEL arrays on sapphire substrates

Oxide-confined top-emitting 850 nm and bottom-emitting 980 nm vertical-cavity surface-emitting laser (VCSEL) 8×8 arrays were designed and fabricated for applications of optical interconnects. The arrays were flip-chip bonded onto sapphire substrates that contain complimentary metal-oxide-semiconductor (CMOS) driver and fan-out circuitries. The off-sited bonding contacts and minimized bonding force produced very high yield of the hybridization process without causing damage to the VCSEL mesas. The hybridized devices were further mounted either on printed circuit board (PCB) or in 68-pin pin-grid-array (PGA) packages. The transparent sapphire substrate allowed optical outputs from the top-emitting VCSEL arrays to transmit directly through without additional substrate removal procedure. Lasing thresholds below 250 μA for 850 nm VCSELs and 800 μA for 980 nm VCSEL were found at room temperature. The oxide confinement apertures of VCSELs were measured to be around 6 μm in diameter. High-speed data transmission demonstrated a bandwidth of up to 1 Gbits/s per channel for these hybridized VCSEL transmitters.