Low threshold vertical cavity surface emitting lasers integrated onto Si-CMOS ICs using novel hybrid assembly techniques

Abstract

A new heterogeneous integration technique has been developed and demonstrated to integrate vertical cavity surface emitting lasers (VCSELs) on silicon CMOS integrated circuits for optical interconnect applications. Individual oxide-apertured 850 nm AlGaAs VCSEL micro-devices discs, 8 Ctm tall and 55 ptm in diameter (pills), have been both bonded and electrically contacted within the dielectric stack of a commercially-fabricated silicon integrated circuit. To accomplish this, fully processed VCSEL device pills are assembled within dielectric recesses using a vacuum pick up tool, and solder bonded in place using a method developed at M.I.T.. VCSELs device characteristic show threshold currents of 1 to 2.5 mA and thermal impedances as low as 1.6 OC/mW, similar to native substrate device impedances. This technique intimately connects devices within the dielectric stack, allowing for size independent, wafer scale monolithic processing of heterogeneous circuits. The size and placement of these devices prevent the stress build up that occurs in growth on non-native substrates due to thermal expansion mismatches. These same devices can be used in more parallel assembly techniques such as fluidic self-assembly and magnetically-assisted statistical assembly. Thermal modeling of these devices has also been preformed, investigating the impact of integration on VCSEL device operation. The results show potential thermal impedance improvements for both single and arrayed devices due to integration on silicon. This model also investigates the impact of integration on a dielectric stack, as well as the impact of the current aperture of the VCSEL device. This work also investigated the forces associated with magnetically-assisted statistical assembly.

(cont.) A cantilever measurement tool was fabricated and utilized to measure the stiction force on patterned samarium cobalt thin films. The measurements revealed a force range that agreed with modeling results from previous work, while also showing the variation in force due to non-ideal films.