Efficient heat sink by ultrathin BCB bonding for InP membrane lasers

Wafer bonding is a key process in heterogeneous photonic integration and benzocyclobutene (BCB) is widely used for adhesive wafer-to-wafer bonding when it comes to handling complex topography on both wafers. However, until now a major drawback of bonding with BCB was the high thermal impedance of lasers due to the low thermal conductivity of BCB. We demonstrate, that by optimizing the membrane device topography and introducing the BCB reflow step into the process flow it is possible to achieve full planarization of 1 μm topography at the wafer scale while ensuring only 135 nm of BCB between the laser p-contact and the substrate. We show experimentally, that the thermal impedance of 500 μm long distributed feedback (DFB) laser was reduced from 585 to 271 K W ⁻¹ when bonded to Si substrate, and to 174 K W ⁻¹ when bonded to SiC substrate using the new method.