Green Removal of DUV-Polarity-Modified PMMA for Wet Transfer of CVD Graphene

Abstract

To fabricate graphene-based high-frequency electronic and optoelectronic devices, there is a high demand for scalable low-contaminated graphene with high mobility. Graphene synthesized via chemical vapor deposition (CVD) on copper foil appears promising for this purpose, but residues from the polymethyl methacrylate (PMMA) layer, used for the wet transfer of CVD graphene, drastically affect the electrical properties of graphene. Here, we demonstrate a scalable and green PMMA removal technique that yields high-mobility graphene on the most common technologically relevant silicon (Si) substrate. As the first step, the polarity of the PMMA was modified under deep-UV irradiation at λ = 254 nm, due to the formation of ketones and aldehydes of higher polarity, which simplifies hydrogen bonding in the step of its dissolution. Modification of PMMA polarity was confirmed by UV and FTIR spectrometry and contact angle measurements. Consecutive dissolution of DUV-exposed PMMA in an environmentally friendly, binary, high-polarity mixture of isopropyl alcohol/water (more commonly alcohol/water) resulted in the rapid and complete removal of DUV-exposed polymers without the degradation of graphene properties, as low-energy exposure does not form free radicals, and thus the released graphene remained intact. The high quality of graphene after PMMA removal was confirmed by SEM, AFM, Raman spectrometry, and by contact and non-contact electrical conductivity measurements. The removal of PMMA from graphene was also performed via other common methods for comparison. The charge carrier mobility in graphene films was found to be up to 6900 cm2/(V·s), demonstrating a high potential of the proposed PMMA removal method in the scalable fabrication of high-performance electronic devices based on CVD graphene.

Voltage controlled Fabry–Perot modulator

“…6). According to the position of the Dirac's point of the bottom sheet (R 13 ), which is shifted towards negative voltages, the p-type conductivity of graphene can be determined [14,21]. When voltage is applied, the electrostatic potential changes the charge carrier density, which causes a shift in the Fermi level [20], thus changing the conductivity of both graphene sheets.…”

“…Annealing of graphene is carried out by placing samples on a 120°C hotplate for 2 h. Subsequently, a combination of deep UV radiation (λ = 254 nm) and immersion in an isopropyl alcohol solution is used to remove PMMA, following the procedure described in Ref. [14].…”

“…determines the depth of transmission dips. These spectral properties can be used for practical applications, for example, in the enhancement of antenna radiation properties [14,15].…”

Nanoelectromechanical Temperature Sensor Based on Piezoresistive Properties of Suspended Graphene Film

“…(c) Au electrodes are sputtered on both sides of the cavity using Magnetron Sputtering equipment. (d) CVD graphene, with PMMA, is transferred onto the substrate by wetting transfer technology [ 8 , 37 ]. The contact of the suspended graphene with air can ensure the stability of pressure outside the cavity.…”

“…The conventional wet transfer will remove PMMA after transferring the graphene with PMMA to the target substrate. This increases the probability of graphene breakage [ 37 ]. However, the devices in this article do not require PMMA removal, and PMMA plays a positive effect on the device’s performance in the subsequent experiments.…”