Nanoscale Metrology of Gate Dielectrics for Graphene Nanoribbon Transistors

Atomically precise graphene nanoribbons (GNRs) present a promising alternative to silicon as channels for field-effect transistors (FETs) due to their high carrier mobility and tunable bandgaps. While the fabrication of GNRFETs has been successfully demonstrated, their experimental performance still falls short of their theoretical potential. This performance gap is often attributed to factors such as GNR quality, metal-GNR contact resistivity, and the properties of the dielectric materials. Given the extreme dimensions of these components, nanoscale metrology poses a significant challenge, as traditional semiconductor metrology techniques cannot adequately resolve these nanofeatures. In this work, we studied the dielectric properties and homogeneity of various materials, including HfOx, SiNx, and novel 2D layered dielectrics, as well as their interface quality with GNRs. Advanced scanning probe microscopy techniques, including conductive atomic force microscopy (CAFM) and kelvin probe force microscopy (KPFM), were employed to achieve nanoscale characterization. Nine-atom-wide armchair GNRs (9-GNRs) were synthesized on Au(111)/mica substrates using an on-surface synthesis method and transferred onto dielectrics via a wet-transfer process. The dielectrics were synthesized using atomic layer deposition, plasma-enhanced chemical vapor deposition, and/or vapor-transport methods. High-resolution electrical mapping via CAFM provided critical insights into the quality and uniformity of the dielectrics, while KPFM measurements revealed surface potential variations, offering a deeper understanding of the electrostatic properties of the gate dielectrics. Our findings contribute to the identification and optimization of dielectric materials for GNR devices, providing a better understanding of their interaction with GNRs and paving the way for improved device performance.