Fabrication of comb-drive actuators for straining nanostructured suspended graphene

TL;DR

This paper presents the design and fabrication of a comb-drive actuator system for applying strain to suspended graphene, enabling detailed transport and mechanical property measurements of nanostructured graphene devices.

Contribution

It introduces an optimized fabrication process including a gold layer to reduce resistance and allows post-integration nanostructuring of graphene for advanced device functionalities.

Findings

Reduced device resistance from 51.6 kΩ to 236 Ω with gold layer

Achieved minimum feature size of 30 nm in graphene nanostructuring

Measured mechanical resonance frequency variations with strain

Abstract

We report on the fabrication and characterization of an optimized comb-drive actuator design for strain-dependent transport measurements on suspended graphene. We fabricate devices from highly p-doped silicon using deep reactive ion etching with a chromium mask. Crucially, we implement a gold layer to reduce the device resistance from $\approx51.6$ k$\mathrm{\Omega}$ to $\approx236$ $\mathrm{\Omega}$ at room temperature in order to allow for strain-dependent transport measurements. The graphene is integrated by mechanically transferring it directly onto the actuator using a polymethylmethacrylate membrane. Importantly, the integrated graphene can be nanostructured afterwards to optimize device functionality. The minimum feature size of the structured suspended graphene is 30 nm, which allows for interesting device concepts such as mechanically-tunable nanoconstrictions. Finally, we characterize the fabricated devices by measuring the Raman spectrum as well as the a mechanical resonance frequency of an integrated graphene sheet for different strain values.