Pick & place integration of diamond nanophotonic structures for modular, on chip diamond quantum systems

Abstract

Diamond color centers have been increasingly gaining attention in research due to their desirable optical properties that make them suitable for applications such as quantum computing, quantum sensing and quantum communication. However, the main challenge has been on-chip integration of diamond color centers with high scalability and high yield. Many diamond integration methods have been researched, such as heterogeneous wafer bonding of diamond-on-insulator photonics. While this method offers high scalability and wafer level fabrication, optical performance is not guaranteed due to the non-ideal processing which results in lower yield. Another integration method is pick and place, which demonstrated high yield as the diamond color centers can be pre-selected before integration, and thus resulting in higher yield. Here, pick and place integration of diamond nano-photonic structures is presented. For that purpose, an adiabatic coupler is designed, with simulation results showing 0.36 dB insertion loss and 3dB misalignment tolerance of 180 nm and 5 um in x and z directions respectively. A mechanical support structure is designed such that optical losses at that interface are minimized. The simulated loss is reduced from 33 % to only 4 % and the cross-talk is -11 dB. Further optical measurement is needed to determine the achieved transmission of the integrated diamond chiplets. Finally, pick and place is performed with 6 different supporting structure designs. The yield is 25 % with minimum misalignment of 50 nm which is mainly dominated by random motion of the diamond chiplet as it gets closer to the receptor chip. This random motion is attributed to the surface roughness of the receptor chip and and lower surface of the diamond chiplet. In addition, residual charges in both chips results in Coulomb forces acting on the diamond chiplet and thus contributing to the misalignment. It is expected that the magnitude of the random motion, and consequently, the misalignment, will be improved by treating the receptor chip surface with HMDS and de-ionizing both the diamond chiplet and the receptor chip.