Fabrication Tolerant Heterogeneously Integrated Lithium Niobate Modulator on Bi-Layer Silicon Nitride using Micro Transfer Printing

Paper in proceeding, 2025

The integration of Lithium Niobate (LN) on low-loss, CMOS-compatible SiN platforms combines the high Pockels effect of LN with SiN's low loss and CMOS compatibility, enabling efficient modulation and processing. Micro transfer printing (µTP) facilitates the integration of functional materials such as LN, III-V, and BTO, enabling the creation of compact, multifunctional chips. LN-SiN Mach-Zehnder Modulators (MZMs) require long interaction lengths (in the cm range) for low-voltage operation, necessitating µTP of cm-long LN coupons. These coupons should ideally cover the MZM arms, including signal and ground electrodes (~100 µm wide). However, µTP of long coupons faces challenges such as limited rotational alignment accuracy, especially if the electrode incorporated on the LN coupon. Additionally, hybrid SiN-LN modulators encounter mode transition loss and reflections at the SiN-LN interface, which are typically mitigated with long tapers. However, tapering LN coupons for µTP often causes cracks and fabrication complexities [1]. This work presents design (Fig. 1(a)) and fabrication of LN-SiN modulator with simulated VπL=3.6 V·cm (Fig. 1(b)) and 3-dB bandwidth of over 100 GHz (Fig. 1(d)). The design features bi-layer SiN waveguides (750 nm and 200 nm thick) for adiabatic optical mode coupling [2], achieving ultra-low transition loss, and minimal reflection without LN tapers thereby alleviating the alignment accuracy requirement for µTP [3]. We also present the fabrication of the device, including the high-yield fabrication and µTP of LN coupons up to 1 cm long, 100 µm wide.