Direct Patterning of p-Type-Doped Few-layer WSe₂ Nanoelectronic Devices by Oxidation Scanning Probe Lithography

Abstract

Direct, robust and high resolution patterning methods are needed to downscale the lateral size of 2D materials to observe new properties and to optimize the overall processing of these materials. In this work we report a fabrication process where the initial micro-channel of a few-layer WSe 2 field-effect transistor is treated by oxygen plasma to form a self-limited oxide layer on top of the flake. This thin oxide layer has a double role here. First, it induces the so called p-doping effect in the device. Second, it enables the fabrication of oxide nanoribbons with controlled width and depth by oxidation scanning probe lithography (o-SPL). After the removal of the oxides by deionized H 2 O etching, a nanoribbon-based field effect transistor is produced. Oxidation SPL is a direct writing technique that minimizes the use of resists and lithographic steps. We have applied this process to fabricate a 5 nm thick WSe 2 field-effect transistor where the channel consists in an array of 5 parallel 350 nm halfpitch nanoribbons. The electrical measurements show that the device presents an improved conduction level compared to the starting thin layer transistor and a positive threshold voltage shift associated to the p-doping treatment. The method enables to pattern devices with sub-50 nm feature sizes. We have patterned an array of 10 oxide nanowires with 36 nm half-pitch by oxidation SPL.

Scalably Nanomanufactured Atomically Thin Materials‐Based Wearable Health Sensors

“…Reproduced with permission. [ 497 ] Copyright 2018, American Chemical Society. d) Schematics of the facile wet transfer and soft lithography patterning of graphene films.…”

“…Scanning probe lithography (SPL) is a versatile nano‐lithographic technique that can fabricate high‐resolution (e.g., sub‐10 nm) patterns with arbitrary geometries and good overlay accuracy under ambient conditions. [ 495–498 ] SPL uses a sharp scanning probe to apply a voltage between a probe tip and the substrate without using a sacrificial resist. SPL also allows non‐destructive, in situ inspection after the fabrication with the same tool.…”

“…SPL has also been adopted to pattern 2D materials for device fabrication. [ 496,497,502 ] For example, Dago et al [ 497 ] developed an oxidation SPL (o‐SPL) to fabricate p‐doped few‐layer WSe 2 nanoribbon‐based FETs (Figure 5c), combing an oxygen plasma treatment with the SPL. During the SPL process, a thin self‐limited oxide layer was formed to act as the hole‐dopant layer underneath the WSe 2 flake.…”

“…[ 503 ] This feature appeals to processing 2D materials such as graphene and WSe 2 , which are sensitive to resist residues. [ 497,504–506 ] Furthermore, SPL exhibits unique capabilities to pattern the material surface, to fabricate complex patterns in situ with sub‐10‐nm precision and single‐nanometre accuracy in positioning, and to allow post‐patterning in situ metrology. [ 507 ] Finally, SPL can pattern various materials, including polymers and biological matter.…”

New Concepts for Production of Scalable Single Layer Oxidized Regions by Local Anodic Oxidation of Graphene

“…A decade ago, LAO of graphene began to be developed through scanning probe techniques in conditions similar to those practiced on Si (operating voltage usually < 15 V), and, more recently, on 2D transition metal dichalcogenides . Features such as dots and stripes produced by LAO have been manufactured previously with scanning nanoprobes (AFM), and the behavior with variable voltage, probe speed or humidity has been described qualitatively in just a few works .…”