Nanogap electrodes are defined as two metals lying on the same plane and separated by an ultra-short channel of about 10 nm in length. Filling the nanogap with a functional material gives rise to electronic nanodevices and circuit elements with lower power consumption, faster speed, and higher level of integration than devices in vertical (sandwich-like) geometry.
Examples of devices benefiting from this architecture are high speed Schottky diodes implemented in radio frequency identification (RFID) tags and near-field communication (NFC) applications, enabling long-distance wireless communication among electronic devices, forming thus the cornerstone of what is nowadays called the Internet of Things. The large aspect ratio (width vs length) of these nanochannels may also be advantageous to nanoscale photodetectors, where the short nanochannel favours high sensitivity and fast response speed, characteristics well-sought after in light-sensing optoelectronic devices. Ability to fabricate these devices on plastic (flexible) substrates opens up further the application landscape to new opportunities, for example in the field of light-weight wearable electronics and low-cost smart labels.
The commonly employed fabrication techniques of nanogap electrodes are electron beam lithography or scanning probe lithography techniques, both of which are time-consuming and require expensive infrastructure. Therefore, the lack of a facile, inexpensive, high-throughput technique for the manufacturing of -especially dissimilar- nanogap electrodes, also on flexible substrates, has hindered their commercial and scientific exploitation.
The objectives of this project were, first, to optimise and further advance the process steps of an innovative, simple, low-cost and reliable technique, named adhesion lithography (a-Lith), which has been developed at Imperial College London, for the fabrication of symmetric or asymmetric metal nanogap structures on rigid and plastic substrates. Then, the aim was to fabricate various electronic and optoelectronic devices with these nanogap electrodes and characterise their performance. Finally, the possibility for industrial uptake of the technology would be also explored.
In the duration of the project, major steps towards upscaling the a-Lith process were performed and a range of electronic (radiofrequency diodes, resistive switching memories, molecular junctions) and optoelectronic (light-emitting diodes, photodetectors) devices were fabricated using the a-Lith fabricated nanogap electrodes on rigid as well as flexible substrates. The obtained results attracted significant industrial interest and further upscaling of the manufacturing process is now being undertaken in collaboration with an industrial partner, active in low-cost flexible electronics.
