Fig. 1. Si₃N₄ waveguide model and effective mode field area under frequency domain field variations

Fig. 2. Waveguide dispersion curves：（a） waveguide dispersion curves for different waveguide widths with the waveguide height set to 0.76 μm； （b） waveguide dispersion curves for different waveguide heights with the waveguide width set to 2 μm

Fig. 3. Dispersion characteristic curve of a silicon nitride microcavity with a radius of 224 μm at a central pumping frequency of 150 THz

Fig. 4. Take the steady-state solution curve at X=12，the black curve corresponds to the lower branch and the red curve corresponds to the upper branch，dashed lines represent unstable solutions

Fig. 5. Thermal response curve of a silicon nitride microcavity with a radius of 224 μm at a central pumping frequency of 150 THz

Fig. 6. （a） The second-order dispersion and the evolution of the cavity spectrum considering the effects of the second- and third-order dispersions； （b） the transition process of respiratory oscillation boundary to stable soliton under different dispersions

Fig. 7. Detuned-period oscillations of breathing solitons in silicon nitride in the 2 μm band and the formation of final soliton optical combs

Fig. 8. SEM images and transmission spectrum：（a） SEM image of 100 GHz silicon nitride microcavity； （b） SEM image of waveguide cross section； （c） 2 μm transmission spectrum of silicon nitride microcavity