Fig. 5: Wafer-scale fabrication process for developing nanoscale gaps for STR sensors and other various applications with ALD defining nanogap size. | npj Biosensing

Fig. 5: Wafer-scale fabrication process for developing nanoscale gaps for STR sensors and other various applications with ALD defining nanogap size.

From: Surface Transmon Resonance (STR): a handheld nanogap biosensor for real-time, label-free molecular binding kinetics

Fig. 5

A The substrate has been coated with Ti and Au, where Ti acts as an adhesion layer. B PMMA and photoresist have been deposited on top of the metal, and the photoresist was exposed with the desired pattern. The sample is exposed to oxygen plasma to etch away the PMMA and photoresist. C The exposed metal is ion milled. D Atomic layer deposition is used to define the gap width and, in this case, alumina is deposited. After ALD, Ti and Au are deposited, and liftoff is performed. It was found during fabrication that most of the alumina within the gap was removed after liftoff, resulting in a functional sensor. E The resulting structure can be exposed to an etchant to remove the alumina in the gap region if desired. F The resulting structure and nanogap is formed. G Resulting SEM of 200 μm sensor region. H SEM image of nanogap region. I Measurement of S11 Magnitude of 50 nm gap sensor immersed in air, IPA, and water.

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