Effect of air-loading on the performance limits of graphene microphones
Roberto Pezone (TU Delft - Electronic Components, Technology and Materials)
Gabriele Baglioni (TU Delft - QN/van der Zant Lab, Kavli institute of nanoscience Delft)
C. van Ruiten (Student TU Delft)
Sebastian Anzinger (Infineon Technologies AG)
Hutomo Suryo Wasisto (Infineon Technologies AG)
Pasqualina Maria Sarro (TU Delft - Electronic Components, Technology and Materials)
Peter 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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