Impact of Lithium Diffusion on SiN Waveguide Loss in imec Silicon Nitride Photonics Platform (iSiNPP)

Integrated photonics based on silicon nitride (SiN) has matured significantly, offering ultra‑low‑loss waveguides and broad spectral transparency. However, the current SiN platform lacks native active functionalities such as photodetectors and light sources. To achieve fully integrated photonic systems, heterogeneous integration of additional materials such as III‑V semiconductors and lithium niobate (LNO) is essential.

LNO is particularly promising due to its strong Pockels effect, enabling highly efficient electro‑optic phase shifting and high‑speed modulation. After LNO is integrated onto SiN through micro‑transfer printing or wafer bonding, subsequent processing steps, including metallization, typically require elevated temperatures and mechanical stresses. These conditions can cause lithium diffusion into other layers.

Since SiN waveguides lie adjacent to the bonded LNO, lithium diffusion may alter the refractive index or absorption behaviour of the waveguide stack, potentially increasing propagation loss in otherwise ultra‑low‑loss photonic circuits.

This internship aims to systematically investigate the impact of lithium diffusion under various post‑processing conditions on SiN waveguide performance. The work will involve:

• Thermal and mechanical post‑processing of LNO under controlled conditions
• Waveguide loss measurements and correlation with process parameters

The outcome will help establish optimized integration and processing schemes for next‑generation electro‑optic LNO modulators integrated in SiN photonic platforms.