Recently discovered two-dimensional (2D) materials with superlative properties have the potential to advance semiconductors but creating 2D devices with both good electrical contacts and stable performance has proved challenging.

An enhanced optical microscope image of a Hall-bar structure used to characterize transistor properties for devices made with ultraclean transferred contacts. The long radial lines, made from deposited gold, connect the small contacts at the center of the device to large probe pads for easy measurements.

A nearly ideal transistor made from a two-dimensional material stack — with only a two-atom-thick semiconducting layer — was fabricated using a completely clean and damage-free fabrication process. The method shows vastly improved performance compared to 2D semiconductors fabricated with a conventional process and could provide a scalable platform for creating ultra-clean devices in the future.

The two-step, ultra-clean nanofabrication process separates the “messy” steps of fabrication — those that involve “dirty” metallization, chemicals, and polymers used to form electrical connections to the device — from the active semiconductor layer. Once the messy fabrication is complete, the contacts can be picked up and transferred onto the clean active device layer, preserving the integrity of both layers. While the thinness allows them to be transparent and to be picked up and placed anywhere, the thinness also means there is nearly zero volume — the device is almost entirely surface. Because of this, any surface dirt or contamination will degrade a device.

Currently, most devices are not encapsulated with a layer that protects the surface and contacts from contamination during fabrication. The new method can not only protect the semiconductor layer so that they don’t see performance degradation over time but can also yield high-performance devices.

The transferred contacts were made from metal embedded in insulating hexagonal boron nitride (h-BN) outside a glovebox and then the contact layer was dry-transferred onto the 2D semiconductor, which was kept pristine inside a nitrogen glovebox. This process prevents direct-metallization-induced damage while simultaneously providing encapsulation to protect the device.

For more information, contact Holly Evarts at This email address is being protected from spambots. You need JavaScript enabled to view it.; 212-854-3206.

Tech Briefs Magazine

This article first appeared in the September, 2019 issue of Tech Briefs Magazine.

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