A Sliding Ferroelectric Tunnel Junction With a 19-Million-Fold Readout

Sliding ferroelectrics can retain their switching ability through repeated use, but their weak polarization has made the two electrical states difficult to distinguish in a two-terminal device. Researchers at the Chinese Academy of Sciences’ Institute of Semiconductors and the University of Hong Kong addressed that readout problem by engineering the interfaces of a Cr/h-BN/3R-MoS₂/monolayer-graphene tunnel junction. They also extended the design to a 1T′-ReS₂ system. 810

How the layered junction amplifies the signal

Each part of the stack has a distinct job. Hexagonal boron nitride (h-BN) provides a relatively uniform tunneling barrier that limits leakage. In 3R-MoS₂, tiny relative movements between layers reverse the sliding-ferroelectric polarization, changing the potential experienced by electrons crossing the junction. Monolayer graphene serves as a weakly screening electrode whose available carriers are sensitive to that polarization change. Together, the altered tunneling barrier and graphene carrier population turn a small polarization reversal into a much larger difference between readout states. The same design approach was applied to 1T′-ReS₂. 89

This separates the material responsible for switching from the layer that supplies the tunneling barrier. It lets the researchers pursue a strong electrical readout while retaining the reported cycling advantage of sliding polarization over conventional oxide ferroelectrics. 89

What the devices demonstrated

At a 0.5 V read bias, the reported tunneling electroresistance ratio was 1.9 × 10⁷—more than four orders of magnitude above previously reported sliding-ferroelectric tunnel junctions, according to the research coverage. The on-state current density reached 222 A/cm². The device also switched reliably with pulses as short as 13 ns, with a reported switching energy of 6.5 fJ per bit, and endured more than 10¹¹ switching cycles. 10

The team fabricated an 8 × 8 array in which all 64 cells showed consistent bistable, nonvolatile switching. That result supports further work on dense nonvolatile memory and crossbar compute-in-memory devices. It does not, by itself, establish how a much larger array and its supporting circuitry would perform. 1011