Flexible graphene FETs fabricated by laser induced forward transfer

In this study, we utilize Laser-Induced Forward Transfer (LIFT) technology to digitally integrate single-layer graphene pixels, as well as source and drain (S/D) metal electrodes, onto PDMS and Kapton PI substrates. This is done for the purpose of developing a flexible Graphene Field Effect Transistor (GFET). We showcase the direct integration of intact graphene pixels with lateral dimensions ranging from 40 to 200 μm in between the S/D electrodes. The transferred pixels exhibit high structural quality and a low defect density due to the solvent-free, single-step transfer process. To attain this level of transfer quality, we conducted a thorough investigation and optimization of the laser transfer process parameters (e.g. laser fluence, beam shape and size, alignment), tailored to the flexible substrates we're interested in. The structural integrity of the transferred pixels was confirmed through characterization techniques involving optical microscopy, Raman spectroscopy, and electrical measurements. Furthermore, we fabricated the Source, Drain, and Gate electrodes using a combination of LIFT and laser sintering of metal nanoparticle inks. Initially, we achieved the fabrication of micro-patterns with the desired geometry and a minimum feature size of < 50 μm, through LIFT. Subsequently, laser sintering, a method fully compatible with metal nanoparticle inks or pastes and thermally sensitive substrates, was selectively applied to the printed patterns, resulting in high electrical conductivity (with reported resistivity as low as 3 times the bulk value). The electrical performance of the laser-printed and sintered patterns was assessed using a 4-point probe IV station. The results we demonstrated underscore the adaptability and versatility of LIFT for transferring low-dimensional materials, particularly single-layer graphene and metal nanoparticles with an average diameter of 50 nm. This technology provides a digital solution for addressing complex use-cases and applications in the field of electronics, particularly for the next generation of flexible GFETs.