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Dispersion-based graphene materials are promising candidates for various sensing applications. They offer the advantage of relatively simple and fast deposition via spin-coating, Langmuir-Blodgett deposition, or inkjet printing. Film uniformity and reproducibility remain challenging in all of these deposition methods. Here, we demonstrate, characterize, and successfully apply a scalable structuring method for graphene dispersions. The method is based on a standard lift-off process, is simple to implement, and increases the film uniformity of graphene devices. It is also compatible with standard semiconductor manufacturing methods. We investigate two different graphene dispersions via Raman spectroscopy and Atomic Force Microscopy and observe no degradation of the material properties by the structuring process. Furthermore, we achieve high uniformity of the structured patterns and homogeneous graphene flake distribution. Electrical characterizations show reproducible sheet resistance values correlating with material quantity and uniformity. Finally, repeatable humidity sensing is demonstrated with van der Pauw devices, with sensing limits of less than 1% relative humidity., Comment: 35 pages

Graphene is a promising candidate for future electronic applications. Manufacturing graphene-based electronic devices typically requires graphene transfer from its growth substrate to another desired substrate. This key step for device integration must be applicable at the wafer level and meet the stringent requirements of semiconductor fabrication lines. In this work, wet and semidry transfer (i.e. wafer bonding) are evaluated regarding wafer scalability, handling, potential for automation, yield, contamination and electrical performance. A wafer scale tool was developed to transfer graphene from 150 mm copper foils to 200 mm silicon wafers with-out adhesive intermediate polymers. The transferred graphene coverage ranged from 97.9% to 99.2% for wet transfer and from 17.2% to 90.8% for semidry transfer, with average cop-per contaminations of 4.7x10$^{13}$ (wet) and 8.2x10$^{12}$ atoms/cm$^2$ (semidry). The corresponding electrical sheet resistance extracted from terahertz time-domain spectroscopy varied from 450 to 550 ${\Omega}/sq$ for wet transfer and from 1000 to 1650 ${\Omega}/sq$ for semidry transfer. Although wet transfer is superior in terms of yield, carbon contamination level and electrical quality, wafer bonding yields lower copper contamination levels and provides scalability due to existing in-dustrial tools and processes. Our conclusions can be generalized to all two-dimensional (2D) materials.

Two-dimensional (2D) materials, such as graphene, are seen as potential candidates for fabricating electronic devices and circuits on flexible substrates. Inks or dispersions of 2D materials can be deposited on flexible substrates by large-scale coating techniques, such as inkjet printing and spray coating. One of the main issues in coating processes is nonuniform deposition of inks, which may lead to large variations of properties across the substrates. Here, we investigate the role of surface morphology on the performance of graphene ink deposited on different paper substrates with specific top coatings. Substrates with good wetting properties result in reproducible thin films and electrical properties with low sheet resistance. The correct choice of surface morphology enables high-performance films without postdeposition annealing or treatment. Scanning terahertz time-domain spectroscopy (THz-TDS) is introduced to evaluate both the uniformity and the local conductivity of graphene inks on paper. A paper-based strain gauge is demonstrated and a variable resistor acts as an on-off switch for operating an LED. Customized surfaces can thus help in unleashing the full potential of ink-based 2D materials.

We report on the fabrication and characterization of field effect transistors (FETs) based on chemical vapor deposited (CVD) graphene encapsulated between few layer CVD boron nitride (BN) sheets with complementary metal oxide semiconductor (CMOS) compatible nickel edge contacts. Non-contact Tera-hertz time domain spectroscopy (THz-TDS) of large-area BN/graphene/BN (BN/G/BN) stacks reveals average sheet conductivity >1 mS/sq and average mobility of 2500 cm$^{2}$/Vs. Improved output conductance is observed in direct current (DC) measurements under ambient conditions, indicating potential for radio-frequency (RF) applications. Moreover, we report a maximum voltage gain of 6 dB from a low frequency signal amplifier circuit. RF characterization of the GFETs yields an f$_{T}$ x L$_{g}$ product of 2.64 GHz$\mu$m and an f$_{Max}$ x L$_{g}$ product of 5.88 GHz$\mu$m. This study presents for the first time THz-TDS usage in combination with other characterization methods for device performance assessment on BN/G/BN stacks. The results serve as a step towards scalable, all CVD 2D material-based FETs for CMOS compatible future nanoelectronic circuit architectures., Comment: 6 pages