Abstract
Graphene-based point-of-care (PoC) and chemical sensors can be fabricated using photolithographic processes at wafer-scale. However, these approaches are known to leave polymer residues on the graphene surface, which are difficult to remove completely. In addition, graphene growth and transfer processes can introduce defects into the graphene layer. Both defects and resist contamination can affect the homogeneity of graphene-based PoC sensors, leading to inconsistent device performance and unreliable sensing. Sensor reliability is also affected by the harsh chemical environments used for chemical functionalisation of graphene PoC sensors, which can degrade parts of the sensor device. Therefore, a reliable, wafer-scale method of passivation, which isolates the graphene from the rest of the device, protecting the less robust device features from any aggressive chemicals, must be devised. This work covers the application of molecular vapour deposition technology to create a dielectric passivation film that protects graphene-based biosensing devices from harsh chemicals. We utilise a previously reported “healing effect” of Al2O3 on graphene to reduce photoresist residue from the graphene surface and reduce the prevalence of graphene defects to improve graphene device homogeneity. The improvement in device consistency allows for more reliable, homogeneous graphene devices, that can be fabricated at wafer-scale for sensing and biosensing applications.
Highlights
The demand for point-of-care (PoC) devices is increasing, with the identification of new pathogens and increased testing for infectious diseases, such as COVID-19 [1,2].Standard diagnostic laboratory tests require expensive equipment and trained professionals which takes time for processing, whereas PoC tests are rapid and cheaper, providing results in a matter of minutes in a clinical or remote setting
We report the development of an Al2 O3 passivation layer, deposited using molecular vapour deposition, for use in graphene sensors and biosensors
Chemical vapour deposited (CVD) monolayer graphene grown on Cu substrate and transferred on 300 nm thermal SiO2 /525 μm Si wafers using PMMA-based wet transfer were supplied by Graphenea Inc (San Sebastián, Spain) [50]
Summary
The demand for point-of-care (PoC) devices is increasing, with the identification of new pathogens and increased testing for infectious diseases, such as COVID-19 [1,2]. It is desirable to confine exposure to chemical interactions to the active graphene component of the device only, during solution-based functionalisation processes or biosensing measurements that occur in the solution This confinement can be achieved using a passivation layer to provide a protective barrier between any liquid media and the metal electrodes, whilst allowing full contact with the graphene [31]. ALD is a less destructive deposition technique that uses precursor materials, that are sequentially injected into a deposition chamber, to promote the growth of uniform and conformal materials It creates much higher quality high-k dielectrics than either PVD or CVD, with better thickness control and less damage to the graphene, but is much slower than sputtering or evaporation [43,44]. Al2 O3 passivation using MVD is shown to produce reproducible graphene biosensors for fast and reliable point-of-care diagnostics in liquid media
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