Abstract
The two-dimensional and virtually massless character of graphene attracts great interest for radio frequency devices, such as surface and bulk acoustic wave resonators. Due to its good electric conductivity, graphene might be an alternative as a virtually massless electrode by improving resonator performance regarding mass-loading effects. We report on an optimization of the commonly used wet transfer technique for large-area graphene, grown via chemical vapor deposition, onto aluminum nitride (AlN), which is mainly used as an active, piezoelectric material for acoustic devices. Today, graphene wet transfer is well-engineered for silicon dioxide (SiO2). Investigations on AlN substrates reveal highly different surface properties compared to SiO2 regarding wettability, which strongly influences the quality of transferred graphene monolayers. Both physical and chemical effects of a plasma treatment of AlN surfaces change wettability and avoid large-scale cracks in the transferred graphene sheet during desiccation. Spatially-resolved Raman spectroscopy reveals a strong strain and doping dependence on AlN plasma pretreatments correlating with the electrical conductivity of graphene. In our work, we achieved transferred crack-free large-area (40 × 40 mm2) graphene monolayers with sheet resistances down to 350 Ω/sq. These achievements make graphene more powerful as an eco-friendly and cheaper replacement for conventional electrode materials used in radio frequency resonator devices.
Highlights
Graphene is a monolayer of hexagonal-oriented carbon atoms with outstanding electronic properties [1]
We report on an optimization of the commonly used wet transfer technique for large-area graphene, grown via chemical vapor deposition, onto aluminum nitride (AlN), which is mainly used as an active, piezoelectric material for acoustic devices
Investigations on AlN substrates reveal highly different surface properties compared to SiO2 regarding wettability, which strongly influences the quality of transferred graphene monolayers
Summary
Graphene is a monolayer of hexagonal-oriented carbon atoms with outstanding electronic properties [1]. For an unfailing use as an active electrode, graphene needs to exhibit low sheet resistances since the conductivity of the electrode material strongly affects the quality factor of a resonator [6,7]. These findings require high-quality large-area graphene on insulating substrates. In the field of RF microelectromechanical systems (RF MEMS), used e.g., in wireless communication, graphene is able to reveal both its conductive and two-dimensional character as an alternative electrode material in full strength In this case, the transfer substrates are of piezoelectric nature, such as aluminum nitride (AlN). This is essential in order to improve the structural as well as the electric quality of graphene on the transfer substrate
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