  An unresolved challenge facing electronics at a few-nm scale is that
resistive channels start leaking due to quantum tunneling. This affects the
performance of nanoscale transistors, with single-molecule devices displaying
particularly low switching ratios and operating frequencies, combined with
large subthreshold swings.1 The usual strategy to mitigate quantum effects has
been to increase device complexity, but theory shows that if quantum effects
are exploited correctly, they can simultaneously lower energy consumption and
boost device performance.2-6 Here, we demonstrate experimentally how the
performance of molecular transistors can be improved when the resistive channel
contains two destructively-interfering waves. We use a zinc-porphyrin coupled
to graphene electrodes in a three-terminal transistor device to demonstrate a
>104 conductance-switching ratio, a subthreshold swing at the thermionic limit,
a > 7 kHz operating frequency, and stability over >105 cycles. This performance
is competitive with the best nanoelectronic transistors. We fully map the
antiresonance interference features in conductance, reproduce the behaviour by
density functional theory calculations, and trace back this high performance to
the coupling between molecular orbitals and graphene edge states. These 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.
