Sensitive Transfer-Free Wafer-Scale Graphene Microphones.

Area of Science:

• Materials Science
• Nanotechnology
• Acoustics

Background:

• Micro-electromechanical microphones dominate portable devices, but face physical limits for further miniaturization and performance enhancement.
• Graphene's unique properties (flexibility, strength, thinness, conductivity) offer potential for next-generation microphone breakthroughs.
• Current fabrication methods for graphene devices often involve transfers, leading to defects and yield issues.

Purpose of the Study:

• To demonstrate a novel, transfer-free fabrication process for multilayer graphene (MLGr) membranes for acoustic sensing.
• To evaluate the performance of these graphene membranes compared to existing micro-electromechanical systems (MEMS) microphones.
• To establish a scalable and high-yield manufacturing method for graphene-based microphones.

Main Methods:

• Developed a process for locally growing graphene on silicon wafers.
• Created suspended MLGr membranes (7 nm thick, 85-300 μm diameter) using bulk micromachining and sacrificial layer etching.
• Utilized a transfer-free approach to avoid contamination and defects associated with membrane transfer.

Main Results:

• Demonstrated MLGr membranes with mechanical compliance up to 92 nm Pa^-1, significantly exceeding commercial MEMS microphones (around 3 nm Pa^-1).
• Achieved 100% yield for membranes up to 155 μm diameter using the transfer-free method.
• Observed significantly smaller device-to-device variations in mechanical compliance compared to transferred graphene membranes.

Conclusions:

• The transfer-free fabrication method enables high-volume production of high-performance graphene microphones.
• This approach circumvents limitations of transfer-based methods, paving the way for advanced acoustic devices.
• The demonstrated technology represents a significant advancement toward commercializing graphene microphones for mobile applications.