Although graphene is a promising material for transparent electrodes in flexible displays, solar cells, and medical devices, conventional fabrication methods often damage it.

Chungnam National University researchers, however, have developed a photoresist-free patterning technique known as OFP-G that creates sub-5-micrometer graphene electrodes with low electrical resistance, thereby solving a major fabrication bottleneck. By preserving graphene’s structure and conductivity, the method could lead to advanced, flexible, high-performance electronic and bioelectronic devices.

Transparent electrodes transmit light while conducting electricity and are increasingly important in bioelectronic and optoelectronic devices. Their combination of high optical transparency, low electrical resistance, and mechanical flexibility makes them well-suited for applications such as displays, solar cells, and wearable or implantable technologies.

In a significant advancement, researchers led by Professor Wonsuk Jung at Chungnam National University in the Republic of Korea have introduced a new fabrication technique—one-step free patterning of graphene, or OFP-G—which enables high-resolution patterning of large-area monolayer graphene with feature sizes smaller than 5 micrometers, without the use of photoresists or chemical etching.

Available online in Microsystems & Nanoengineering, the method addresses a key limitation of conventional microelectrode fabrication, where lithographic processes often damage graphene and degrade its electrical performance.

“Conventional photolithography inevitably induces graphene damage and delamination at the microscale. Our approach achieves exceptionally low electrical resistance and high pattern fidelity, even for fine patterns at the 5 μm scale, without etching-induced defects or chemical contamination,” Prof. Jung said. “Notably, OFP-G allows high-resolution features to be precisely and individually patterned across large-area CVD-grown monolayer graphene electrodes in a single step.” 

Graphene is a one-atom-thick sheet of carbon atoms arranged in a hexagonal lattice that features exceptional transparency, electrical conductivity, and mechanical flexibility. Preserving these properties during patterning is critical for device performance. Rather than removing graphene material, the OFP-G method works by selectively modifying its chemical bonds. In this process, monolayer graphene transferred onto a silicon dioxide substrate is brought into contact with a pre-etched glass substrate that defines the desired pattern.

The process is carried out under vacuum at 380 °C, where the glass enters a conductive solid-electrolyte state. When 1,000 V voltage is applied, mobile alkali ions migrate within the glass, creating oxygen-rich regions at the graphene interface. These regions locally convert carbon–carbon bonds into carbon–oxygen bonds only in the contact areas, producing a precise stencil-like pattern while leaving the surrounding graphene intact.

Using this approach, the researchers fabricated graphene channels as narrow as 5 micrometers. Because the method avoids photoresists and transfer polymers, the graphene surface remains clean and free of contamination. The high processing temperature also helps remove residues from earlier fabrication steps, resulting in high-quality graphene patterns. Raman spectroscopy, X-ray photoelectron spectroscopy, and molecular dynamics simulations confirmed the patterned regions maintain structural integrity and experience reduced interfacial strain, without etching-induced defects.

Electrical measurements showed that graphene patterns with widths of 5 and 20 micrometers exhibited low resistances of 11.5 ohms and 9.4 ohms, respectively. In contrast, graphene patterned using conventional photolithography showed negligible conductivity, indicating disrupted electrical pathways caused by damage and contamination.

Because the process avoids photoresists entirely, it is particularly suitable for applications where surface cleanliness is critical, such as biosensors, neural interfaces, and nanoscale electronic devices. In the long term, this technique could help accelerate the integration of graphene into flexible and transparent electronic devices for healthcare, energy, and smart technology applications.

“Our approach offers a scalable, reproducible, and contamination-free pathway for patterning high-resolution graphene, and opens new possibilities for the integration of graphene in flexible and transparent electronics,” Prof. Jung stated.

Located in Daejeon, South Korea, Chungnam National University (CNU) is a national institution established in 1952. It offers diverse programs in engineering, medicine, sciences, and the arts, fostering innovation and global collaboration. CNU excels in biotechnology, materials science, and information technology.

Reference
Title of original paper: “Direct and residue-free patterning of sub-5 µm CVD monolayer graphene with highly enhanced conductivity and pattern fidelity.” Journal: Microsystems & Nanoengineering