Smaller, more powerful devices are possible with new technology

The shrinkage of semiconductors will further enable a new silicon revolution. But because it is impossible, the next best hope is the integration of semiconductors with 2-D atom-thin materials, such as graphene, on which circuits can be created on an incredibly small scale. A research team reports a new method to make this infamous difficult combination work on an industrial scale.

The technique is in today Nature communication by researchers from KTH Royal Institute of Technology in Stockholm, in collaboration with the RWTH Aachen University, Universität der Bundeswehr München, AMO GmbH and Protemics GmbH, in Germany.

A reliable, industrially scalable method of integrating 2-D materials such as graphene with silicon semiconductors will help electronic scaling and introduce new features for sensor technology and photonics.

However, the integration of 2-D materials into the semiconductor or a substrate with integrated electronics poses a number of challenges. “There is always this critical step of transferring from a special growth substrate to the final substrate on which you build sensors or components,” says Arne Quellmalz, a researcher in photonic microsystems at KTH.

“You may want to combine a graphene photodetector for on-disk optical communication with silicon readout electronics,” says Quellmalz. “But the growth temperatures of those materials are too high, so you can not do this directly on the substrate of the device.”

Experimental methods for the transfer of cultured 2-D material to desired electronics have been experienced by a number of shortcomings, such as the deterioration of the material and its electronic transport properties, or by contamination of the material.

Quellmalz says that the solution lies in the existing semiconductor manufacturing toolkits: the use of a standard dielectric material called bisbenzocyclobutene (BCB), in conjunction with conventional wafer bonding equipment.

“We basically glue the two waffles together with a BCB resin,” he says. “We heat the resin until it becomes sticky like honey, and press the 2-D material against it.”

At room temperature, the resin becomes solid and forms a stable connection between the 2-D material and the wafer, he says. “To stack material, we repeat the steps of heating and pressing. The resin becomes viscous again and behaves like a pillow, or a waterbed, which supports the layer stack and adapts to the surface of the new 2-D material. ”

The researchers found the transfer of graphene and molybdenum disulfide (MoS₂), as a representative of transition metal dicalcogenides, and stacked graphene with hexagonal boron nitride (hBN) and MoS₂ and heterostructures. It is understood that all transferable layers and heterostructures were of high quality, that is, they had uniform coverage of more than 100 millimeters of silicone wafers and showed little stress in the transferred 2-D material, the newspaper reads.