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Highly-sensitive wafer-scale transfer-free graphene MEMS condenser microphones
Roberto Pezone1, Sebastian Anzinger2, Gabriele Baglioni3
1Laboratory of Electronic Components, Technology and Materials (ECTM), Department of Microelectronics, Delft University of Technology, Delft, The Netherlands.
Microsystems & Nanoengineering
|February 22, 2024
Summary
This study introduces wafer-scale integrated graphene MEMS microphones, achieving higher sensitivity and smaller size than traditional devices. These advancements overcome limitations in current microphone technology for improved performance.
Area of Science:
- Materials Science
- Electrical Engineering
- Acoustics
Background:
- Micro-electro-mechanical system (MEMS)-based microphones face performance limitations due to physical, design, and material constraints.
- Graphene shows promise as a microphone diaphragm material, but its full potential for smaller, more sensitive, and scalable on-chip MEMS microphones remains unexplored.
- Previous attempts using graphene-polymer heterostructures compromised performance due to added mass and stiffness.
Purpose of the Study:
- To demonstrate the first wafer-scale integrated MEMS condenser microphones utilizing multi-layer graphene.
- To investigate the performance of graphene diaphragms in MEMS microphones without transfer steps or polymer layers.
- To study the effect of back-plate integration for capacitive read-out in graphene-based MEMS microphones.
Main Methods:
- Fabrication of wafer-scale integrated MEMS condenser microphones with 7 nm multi-layer graphene diaphragms (2R = 220-320 μm) suspended over a back-plate with a 5 μm residual gap.
- Utilized MEMS-compatible wafer-scale technologies, avoiding transfer steps and polymer layers.
- Characterized device designs for electrical integration and studied the impact of back-plate introduction for capacitive read-out.
Main Results:
- Achieved high mechanical compliances (C_m = 0.081-1.07 μmPa⁻¹) – 10-100x higher than silicon diaphragms.
- Pull-in voltages ranged from 2-9.5 V.
- Demonstrated an estimated sensitivity (S₁) of 24.3-321 mV Pa⁻¹ at 1.5 V bias, which is 1.9-25.5x higher than state-of-the-art microphones, with approximately 9x smaller area.
Conclusions:
- Successfully demonstrated wafer-scale integrated MEMS condenser microphones using multi-layer graphene.
- The developed graphene microphones offer significantly improved sensitivity and reduced area compared to existing technologies.
- This work paves the way for next-generation, high-performance, and compact acoustic sensors.
