High-yield fabrication of suspended graphene membranes

Researchers from the Chair for Electronic Devices at RWTH and at AMO GmbH have demonstrated a method for fabricating large-scale arrays of micro cavities sealed by graphene membranes with high yield.

High mechanical strength, extreme thinness and exceptional hermeticity make graphene an ideal material for the realisation of micro- and nanoelectromechanical systems based on suspended membranes. Highly sensitive pressure sensors, microphones, accelerometers, mass and gas sensors based on suspended graphene membranes have already been demonstrated, but the path of these innovations towards industrial applications is still hampered by the lack of reliable scalable fabrication methods.

Sebastian Lukas and colleagues at the Chair for Electronic Devices at RWTH and at AMO GmbH have now demonstrated a method for fabricating large-scale arrays of micro cavities sealed by a graphene membranes with high-yield (up to 99% yield for membranes with a diameter of few µm). The method is based on a “hot and dry” transfer process of large area graphene on top of prefabricated cavities, where “hot” refers to the use of high temperature during transfer to promote the adhesion of graphene to the substrate with the cavities, and “dry” refers to the absence of liquids when graphene and target substrate are brought into contact. Graphene was grown by chemical vapor deposition (CVD) and either transferred as monolayer or as artificially-stacked bi-layers.

To systematically investigate the yield of their fabrication method, Lukas and co-workers have used an automated object-detection routine that allowed them to analyze more than 2,000,000 membranes via scanning electron spectroscopy (SEM).  This large number makes the work highly statistically relevant. The membrane where additionally investigated with Raman spectroscopy and atomic force microscopy (AFM) to confirm that the membranes are freely suspended. The same type of investigation has been performed also on membranes fabricated by transferring graphene with the proprietary dry-transfer method developed by Applied Nanolayers (Netherlands) and on membranes fabricated on a 150mm cavity wafer manufactured by Fraunhofer IZM.

The fabrication method developed by Lukas and co-workers leads to higher yields of intact membranes than previously reported in literature. Membranes formed by double-layer graphene showed higher mechanical stability than those based on single-layer. The scalability of the approach to large-area fabrication has been furthermore demonstrated within the 2D-EPL multi-project wafer. The graphene membranes where then used to fabricate piezoresistive pressure sensors, which showed a sensitivity of 0.5 to 3.0 × 10^–6 mbar^–1, in line with the previously reported values for piezoresistive graphene membrane pressure sensors realized with large-scale processes.

These results indicate the potential of the proposed fabrication method for large-scale manufacturing of graphene membranes for sensors applications.  The technique is further transferable to other 2D materials with minor process modifications to exploit the superior piezoresistive properties of those materials, e.g., the transition-metal dichalcogenides MoS₂ and PtSe₂.

The results have been reported in ACS Nano.

The works is the result of a collaboration between the Chair for Electronic Devices (ELD), AMO GmbH, research partners at Fraunhofer IZM and University of Applied Sciences Berlin and  a commercial collaboration with Applied Nanolayers, B.V. (Netherlands).

 

Bibliographic information

High-Yield Large-Scale Suspended Graphene Membranes over Closed Cavities for Sensor Applications

Sebastian Lukas, Ardeshir Esteki, Nico Rademacher, Vikas Jangra, Michael Gross, Zhenxing Wang, Ha-Duong Ngo, Manuel Bäuscher, Piotr Mackowiak, Katrin Höppner, Dominique J. Wehenkel, Richard van Rijn, and Max C. Lemme

ACS Nano 2024 18 (37), 25614-25624
DOI: 10.1021/acsnano.4c06827