Quantum interference enhances the performance of single-molecule transistors
A collaboration between this department and the Department of Chemistry in Oxford, the University of Lancaster, the Institute for Quantum Computing (Ontario) and Queen Mary University of London looked at the quantum effects in nanoscale electronic devices which promise to lead to new types of functionality not achievable using classical electronic components.
In the paper 'Quantum interference enhances the performance of single-molecule transistors' published in Nature Nanotechnology, the authors explain how quantum behaviour also presents an unresolved challenge facing electronics at the few-nanometre scale; resistive channels start leaking owing to quantum tunnelling. This affects the performance of nanoscale transistors, with direct source-drain tunnelling degrading switching ratios and subthreshold swings, and ultimately limiting operating frequency due to increased static power dissipation.
The usual strategy to mitigate quantum effects has been to increase device complexity, but theory shows that if quantum effects can be exploited in molecular-scale electronics, this could provide a route to lower energy consumption and boost device performance. In this paper the authors demonstrate these effects experimentally, showing how the performance of molecular transistors is improved when the resistive channel contains two destructively interfering waves. A zinc-porphyrin was used, coupled to graphene electrodes in a three-terminal transistor to demonstrate a >104 conductance-switching ratio, a subthreshold swing at the thermionic limit, a >7KHz operating frequency and stability over >105 cycles. The authors fully mapped the anti-resonance interference features in conductance, and reproduce the behaviour by density functional theory calculations, and traced back the high performance to the coupling between molecular orbitals and graphene edge states.
The results demonstrate how the quantum nature of electron transmission at the nanoscale can enhance (rather than degrade) device performance, and highlight directions for future development of miniaturised electronics.
