On-chip higher-order topological micromechanical metamaterials

Area of Science:

• Condensed Matter Physics
• Materials Science
• Acoustics and Wave Phenomena

Background:

• Higher-order topological band gaps offer unique applications by integrating multi-dimensional topological boundary states on-chip.
• Micromechanical metamaterials are rapidly advancing for micro-systems, but require topological manipulation of elastic waves at high frequencies (MHz).
• Current higher-order topological mechanical systems are limited to large scales (cm) and low frequencies (kHz).

Purpose of the Study:

• To experimentally realize an on-chip micromechanical metamaterial exhibiting higher-order topological insulator properties for elastic waves at MHz frequencies.
• To demonstrate the feasibility of integrating topological boundary states at multiple dimensions within a single micro-scale device.
• To bridge the gap between theoretical topological concepts and practical applications in advanced micromechanical systems.

Main Methods:

• Fabrication of an on-chip micromechanical metamaterial using silicon chip etching.
• Induction of a higher-order topological phononic band gap via band inversion at the Brillouin zone corner.
• Configuration of elliptic pillar orientations to control topological properties.
• Experimental validation, theoretical analysis, and numerical simulations to confirm topological states.

Main Results:

• Successful experimental realization of the first on-chip micromechanical metamaterial functioning as a higher-order topological insulator at MHz frequencies.
• Demonstration of coexisting topological edge and corner states within a single silicon chip, driven by higher-order band topology.
• Validation of results through consistent experimental, theoretical, and simulation data.

Conclusions:

• The study presents the first on-chip micromechanical metamaterial with higher-order topological properties for elastic waves.
• This work opens new avenues for materials and applications leveraging topological elastic waves in micro-scale devices.
• The developed system enables multi-dimensional topological boundary states on a single chip, advancing intelligent micro-systems and sensing.