Effect of polymer residues on the electrical properties of large-area graphene-hexagonal boron nitride planar heterostructures

Damage-Free Atomic Layer Etch of WSe2: A Platform for Fabricating Clean Two-Dimensional Devices

The development of a controllable, selective, and repeatable etch process is crucial for controlling the layer thickness and patterning of two-dimensional (2D) materials. However, the atomically thin dimensions and high structural similarity of different 2D materials make it difficult to adapt conventional thin-film etch processes. In this work, we propose a selective, damage-free atomic layer etch (ALE) that enables layer-by-layer removal of monolayer WSe₂ without altering the physical, optical, and electronic properties of the underlying layers. The etch uses a top-down approach where the topmost layer is oxidized in a self-limited manner and then removed using a selective etch. Using a comprehensive set of material, optical, and electrical characterization, we show that the quality of our ALE processed layers is comparable to that of pristine layers of similar thickness. The ALE processed WSe₂ layers preserve their bright photoluminescence characteristics and possess high room-temperature hole mobilities of 515 cm²/V·s, essential for fabricating high-performance 2D devices. Further, using graphene as a testbed, we demonstrate the fabrication of ultra-clean 2D devices using a sacrificial monolayer WSe₂ layer to protect the channel during processing, which is etched in the final process step in a technique we call sacrificial WSe₂ with ALE processing (SWAP). The graphene transistors made using the SWAP technique demonstrate high room-temperature field-effect mobilities, up to 200,000 cm²/V·s, better than previously reported unencapsulated graphene devices.

All-2D Material Inkjet-Printed Capacitors: Toward Fully Printed Integrated Circuits

A well-defined insulating layer is of primary importance in the fabrication of passive ( e.g., capacitors) and active ( e.g., transistors) components in integrated circuits. One of the most widely known two-dimensional (2D) dielectric materials is hexagonal boron nitride (hBN). Solution-based techniques are cost-effective and allow simple methods to be used for device fabrication. In particular, inkjet printing is a low-cost, noncontact approach, which also allows for device design flexibility, produces no material wastage, and offers compatibility with almost any surface of interest, including flexible substrates. In this work, we use water-based and biocompatible graphene and hBN inks to fabricate all-2D material and inkjet-printed capacitors. We demonstrate an areal capacitance of 2.0 ± 0.3 nF cm^-2 for a dielectric thickness of ∼3 μm and negligible leakage currents, averaged across more than 100 devices. This gives rise to a derived dielectric constant of 6.1 ± 1.7. The inkjet printed hBN dielectric has a breakdown field of 1.9 ± 0.3 MV cm^-1. Fully printed capacitors with sub-micrometer hBN layer thicknesses have also been demonstrated. The capacitors are then exploited in two fully printed demonstrators: a resistor-capacitor (RC) low-pass filter and a graphene-based field effect transistor.