Effect of air-loading on the performance limits of graphene microphones
R. Pezone (TU Delft - Electronic Components, Technology and Materials)
G. Baglioni (TU Delft - QN/van der Zant Lab, Kavli institute of nanoscience Delft)
C. van Ruiten (Student TU Delft)
Sebastian Anzinger (Infineon Technologies AG)
H. S. Wasisto (Infineon Technologies AG)
Pasqualina M Sarro (TU Delft - Electronic Components, Technology and Materials)
P.G. Steeneken (TU Delft - Dynamics of Micro and Nano Systems, TU Delft - QN/Steeneken Lab, Kavli institute of nanoscience Delft)
S. Vollebregt (TU Delft - Electronic Components, Technology and Materials)
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Abstract
As a consequence of their high strength, small thickness, and high flexibility, ultrathin graphene membranes show great potential for pressure and sound sensing applications. This study investigates the performance of multi-layer graphene membranes for microphone applications in the presence of air-loading. Since microphones need a flatband response over the full audible bandwidth, they require a sufficiently high mechanical resonance frequency. Reducing membrane thickness facilitates meeting this bandwidth requirement, and therefore, also allows increasing compliance and sensitivity of the membranes. However, at atmospheric pressure, air-loading effects can increase the effective mass, and thus, reduce the bandwidth of graphene and other 2D material-based microphones. To assess the severity of this performance-limiting effect, we characterize the acoustic response of multi-layer graphene membranes with a thickness of 8 nm in the pressure range from 30 to 1000 mbar, in air and helium environments. A bandwidth reduction by a factor ∼ 2.8 × for membranes with a diameter of 500 μm is observed. These measurements show that air-loading effects, which are usually negligible in conventional microphones, can lead to a substantial bandwidth reduction in ultrathin graphene microphones. With analytical and finite element models, we further analyze the performance limits of graphene microphones in the presence of air-loading effects.
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