Reduced Thermal Resistance of Membrane Fabry-Perot Laser Bonded on Si Through Room-Temperature, Surface-Activated Bonding Assisted by a-Si Nano-Film

A membrane distributed-reflector (DR) laser bonded on a Si substrate is a promising light source for on-chip optical interconnection, as it features a low threshold current and enough output power. Benzocyclobutene (BCB) adhesive wafer-bonding or hydrophilic bonding technologies have been used to integrate the membrane laser with Si. However, the thermal conductivity of BCB is low, which results in a high thermal resistance of the membrane laser, and the process of both bonding technologies requires annealing. Thus, the bonded wafer accumulated thermal stress. In this study, we introduce a chemical mechanical polishing (CMP) process to flatten the wafer surface and investigate the surface activated bonding (SAB) based on an Ar fast atom beam (FAB) assisted by an a-Si layer to achieve a room temperature bonding. Based on this room temperature bonding technology, a membrane Fabry-Perot (FP) laser is demonstrated for the first time, and its thermal characteristics are measured. A higher optical saturation current (55 mA) was obtained compared to that of the conventional membrane FP laser (40 mA) with a 2- $\mu \text{m}$ -thick BCB bonding layer. From the lasing wavelength variation against the heat dissipation power and temperature, it was found that a reduction in thermal resistance of approximately 50% (240 K/W to 120 K/W) was achieved by eliminating the BCB layer; the simulation results also showed the same trend.