Enhanced thermal dissipation for BCB-bonded 3D integrated membrane photonic circuits

Abstract Indium–phosphide membrane on silicon is a nanophotonics platform which allows for monolithic integration of sub-micron nanophotonic waveguide circuits with native and efficient amplifiers and lasers. Active devices such as amplifiers have a high topography that requires a thick dielectric layer for planarization and wafer bonding, which poses challenges in thermal dissipation. Herein, we comprehensively analyzed the performance of distributed feedback lasers (DFBs) bonded on Si using a 2 µ m-thick benzocyclobutene (BCB) layer, and with and without a 5 µ m-thick gold thermal shunt to the substrate for efficient thermal dissipation. The thermal resistance of shunted devices is 176 and 115 K W −1 for 0.5 mm and 0.75 mm lengths, respectively, which is a 2× improvement compared to reference membrane devices with no thermal shunt. This thermal resistance is maintained across various BCB thicknesses up to 30 µ m, ensuring the possibility of using such devices for scalable 3D integration on other platforms or with electronics. Moreover, we showed that the thermal resistance value is around 110–120 K W −1 for 0.75 mm-long shunted DFBs having array density values in the range of 40–200 µ m, and that the temperature rise at the end of the DFB contact is as low as 1.3 °C at 8 kA cm −2 driving current. Both of these characteristics demonstrate the density scaling potential of these nanophotonic devices.