  Development of memory devices with ultimate performance has played a key role
in innovation of modern electronics. As a mainstream technology nonvolatile
memory devices have manifested high capacity and mechanical reliability,
however current major bottlenecks include low extinction ratio and slow
operational speed. Although substantial effort has been employed to improve
their performance, a typical hundreds of micro- or even milli- second write
time remains a few orders of magnitude longer than their volatile counterparts.
We have demonstrated nonvolatile, floating-gate memory devices based on van der
Waals heterostructures with atomically sharp interfaces between different
functional elements, and achieved ultrahigh-speed programming/erasing
operations verging on an ultimate theoretical limit of nanoseconds with
extinction ratio up to 10^10. This extraordinary performance has allowed new
device capabilities such as multi-bit storage, thus opening up unforeseen
applications in the realm of modern nanoelectronics and offering future
fabrication guidelines for device scale-up.
