High-yield fabrication of bubble-free magic-angle twisted bilayer graphene devices with high twist-angle homogeneity

TL;DR

This paper introduces an optimized fabrication protocol for magic-angle twisted bilayer graphene that achieves high twist-angle homogeneity and reproducibility, facilitating advanced studies of its exotic phases.

Contribution

The authors develop a deterministic anchoring and bubble removal process that significantly improves the uniformity and consistency of MATBG devices compared to traditional manual methods.

Findings

Up to 38% of devices show regions with twist-angle within 0.1 degrees.

Achieved twist-angle variation as low as 0.02 degrees.

Regions up to 36 micrometers square with uniform twist-angle.

Abstract

Magic-angle twisted bilayer graphene (MATBG) stands as one of the most versatile materials in condensed-matter physics due to its hosting of a wide variety of exotic phases while also offering convenient tunability. However, the fabrication of MATBG is still manual, and remains to be a challenging and inefficient process, with devices being highly dependent on specific fabrication methods, that often result in inconsistency and variability. In this work, we present an optimized protocol for the fabrication of MATBG samples, for which we use deterministic graphene anchoring to stabilize the twist-angle, and a careful bubble removal techniques to ensure a high twist-angle homogeneity. We use low-temperature transport experiments to extract the average twist-angle between pairs of leads. We find that up to 38 percent of the so fabricated devices show micrometer square sized regions with a twist-angle in the range 1.1 plus/minus 0.1 degrees, and a twist-angle variation of only 0.02 degrees, where in some instances such regions were up to 36 micrometer square large. We are certain that the discussed protocols can be directly transferred to non-graphene materials, and will be useful for the growing field of moire materials.