Transfer-Free Wafer-Scale Graphene Electronics on Sapphire

The realisation of commercial graphene solid-state electronics devices has been held back by challenges of processing high-quality monolayer graphene at scale. In this work, we used wafer-scale graphene as the electrode in selected electronic devices, notably OLEDs and memristors. The graphene was grown by Paragraf Ltd using their proprietary growth process to produce high quality, monolayer graphene grown directly onto 50 mm sapphire wafers in batches of up to 37 wafers in metal-organic chemical vapour deposition (MOCVD) reactors. All processes in device production are compatible with semiconductor production lines, and we find graphene to be remarkably robust to these processes.<br/><br/>Graphene memristors in non-volatile memory or neuromorphic computing applications could offer high integration density as well as robustness against common memristor degradation mechanisms. The latter includes oxygen vacancy diffusion into the electrode and unwanted metal ion diffusion from the electrodes, both of which are prevented by the in-plane covalent bonding of graphene. Wafers containing 2520 memristors of different sizes with graphene electrodes were fabricated. The as-fabricated graphene memristors showed a high <i>ON/OFF</i> ratio of 10⁷ ~ 10⁸ when under a bias pulsing rate of 0.5Hz – 1Hz, robust endurance (switching remained stable after &gt;2700 cycles), stability (no device degradation after 1.8 hrs of switching at 26Hz – 46Hz) and low voltage operation (low <i>V_set</i> ~1.6V and <i>V_reset</i> ~-1.55V).<br/><br/>Graphene is considered as a promising material for replacing ITO, which has long term supply issues due to its limited elemental abundance, but for this to become possible. The as-grown graphene was patterned using photolithography and its conductivity was enhanced by doping with nitric acid prior to deposition of the OLED stack. The electrical and optical performances of the as-fabricated graphene-based OLEDs were identical to control devices with conventional ITO anodes [1].<br/><br/>[1] Weng Z, et al. <b>Wafer-Scale Graphene Anodes Replace Indium Tin Oxide in Organic Light-Emitting Diodes.</b> <i>Advanced Optical Materials,</i> 2101675 (2021). DOI: 10.1002/adom.202101675