Sustainable Fabrication of Nanoscale Memories Based on Molecular Materials and Nanogap Electrodes

Nanotechnology is widely used in electronics to further miniaturise electronic components. Nanomaterials have played a major role in this, as they possess many attractive inherent properties derived from their low dimensionality. However, nanoparticles and self-assembled monolayers are usually processed from solution and they are difficult to be implemented with high yield in large area electronics. On the other hand, two-terminal electronic devices commonly comprise a generic metal/semiconductor/metal structure in a vertical (sandwich) configuration. This poses restrictions in the device fabrication when nanomaterials are involved, as the quality of the film is often compromised due to the small scale of the nanomaterials that do not guarantee uniform, continuous and pinhole-free film formation. A solution to this is offered by lateral devices, where the two metals are placed on the same plane and separated by a gap, which is filled by the semiconductor. If this gap is small enough, comparable to the dimensions of the materials used, the nanomaterials can effectively bridge this gap and connect the two electrodes electrically without causing a short-circuit.<br/><br/>Adhesion lithography (a-lith) is a nanopatterning technique with reduced manufacturing energy as compared, for example, with e-beam lithography, that allows the fabrication of asymmetric nanogap metal electrodes at a low cost and with high throughput on a variety of rigid and flexible substrates of arbitrary size. We have so far demonstrated ultra-high speed (GHz) Schottky diodes (1) and fast photodetectors (2) as well as multi-bit and ferroelectric memories (3) based on different solution-processed semiconductors and a-lith patterned electrodes separated by a &lt;10 nm gap.<br/><br/>Herein we present different classes of molecular materials, based on the polyoxometalate and Pb-free perovskite families, which are successfully implemented in nanoscale memory applications. Our results indicate that multi-state memory behaviour is within reach with polyoxometalate materials, while we also present molecular self-assembly approaches to better control the resistive switching at the nanoscale. Since only a few electrons are required to function, these devices hold promise for low power consumption and high-speed operation. Furthermore, we show that the combination of coplanar nanogap electrodes with Bi-based perovskites holds great promise for achieving low power consumption and fast switching speeds, while their planar geometry facilitates a light-controlled operation, enabling both analogue tuning of resistance states and elimination of sneak currents in the array configuration.<br/><br/>This work paves the way to the development of a new form of greener devices and systems that merge photonic, electronic and ionic effects, bringing new prospects for in-memory computing and artificial visual memory applications.<br/><br/>1. Georgiadou, D.G., J. Semple, A.A. Sagade, H. Forstén, P. Rantakari, Y.-H. Lin, F. Alkhalil, A. Seitkhan, K. Loganathan, H. Faber, and T.D. Anthopoulos, <i>100 GHz zinc oxide Schottky diodes processed from solution on a wafer scale.</i> Nature Electronics, <b>2020</b>. 3(11): p. 718<br/><br/>2. Georgiadou, D.G., Y.-H. Lin, J. Lim, S. Ratnasingham, M.A. McLachlan, H.J. Snaith, and T.D. Anthopoulos, <i>High Responsivity and Response Speed Single-Layer Mixed-Cation Lead Mixed-Halide Perovskite Photodetectors Based on Nanogap Electrodes Manufactured on Large-Area Rigid and Flexible Substrates.</i> Advanced Functional Materials, <b>2019</b>. 0(0): p. 1901371<br/><br/>3. Kumar, M., D.G. Georgiadou, A. Seitkhan, K. Loganathan, E. Yengel, H. Faber, D. Naphade, A. Basu, T.D. Anthopoulos, and K. Asadi, <i>Colossal Tunneling Electroresistance in Co-Planar Polymer Ferroelectric Tunnel Junctions.</i> Advanced Electronic Materials, <b>2020</b>. 6(2): p. 1901091