Cascaded on-chip phonon shield for membrane microresonators.

Area of Science:

• Solid-state physics
• Materials science
• Mechanical engineering
• Nanotechnology

Background:

• Acoustic wave coupling between membrane resonators and support structures degrades performance.
• High-quality factor (Q) resonators are crucial for sensitive measurements and advanced devices.
• Existing methods for vibration isolation can be complex or external to the resonator system.

Purpose of the Study:

• To suppress acoustic wave coupling in silicon nitride (Si₃N₄) membrane resonators.
• To enhance the mechanical quality factor of Si₃N₄ resonators through on-chip vibration isolation.
• To achieve reliable fabrication of high-Q Si₃N₄ membrane resonators at room temperature.

Main Methods:

• Design and fabrication of cascaded low-frequency silicon resonators on the substrate of Si₃N₄ membrane resonators.
• Ensuring separation between the resonant frequencies of the silicon resonators and the membrane resonator's mechanical modes.
• Characterization of membrane frame displacement response using optical interferometry to quantify vibration isolation.

Main Results:

• Successful suppression of acoustic wave coupling between the Si₃N₄ membrane and its support.
• Achieved mechanical isolation exceeding 30 dB from the mounting surface.
• Fabricated Si₃N₄ membrane resonators with a mechanical quality factor of approximately 2×10⁶ at room temperature.

Conclusions:

• Cascaded on-chip silicon resonators effectively isolate Si₃N₄ membrane resonators from substrate vibrations.
• The developed method enables reliable fabrication of high-Q Si₃N₄ resonators.
• This advancement is critical for applications requiring high mechanical sensitivity and stability.