Layered memory survives more than 100 billion state changes

A memory must clearly distinguish its electrical states, retain them without continuous power and survive repeated rewriting. Yue Wang and colleagues built an experimental junction that endured more than 100 billion switching cycles. The device reported in Science changed state with 13-nanosecond pulses at an estimated energy of 6.5 femtojoules per pulse—6.5 quadrillionths of a joule.

The assembly stacks atomically thin materials: rhombohedral molybdenum disulfide, hexagonal boron nitride, monolayer graphene and chromium. These sheets form a van der Waals heterostructure, layers held together by relatively weak interatomic attractions. Instead of moving ions inside a thick crystal, an applied voltage makes neighboring layers slide slightly. The new position reverses polarization—the collective orientation of charge—and remains recorded after the pulse ends.

Reading the state requires turning that small rearrangement into a current difference. Electrons cross the thin barrier through quantum tunneling, a process in which a particle has a probability of appearing beyond a barrier it could not overcome in classical physics. The architecture combines two changes: polarization alters both the barrier height and the concentration of charge carriers. Together they produced a tunneling-electroresistance ratio above 10 million, according to the article abstract.

In the high-conductance state, current density reached 222 amperes per square centimeter at 0.5 volts. That wide readout window addresses a known weakness of sliding ferroelectrics: the sheets tolerate repetition because they move with little friction, but their polarization is far smaller than in conventional ferroelectrics and usually yields a modest signal. The team converted the weak signal into a measurable contrast without adding a third terminal to the component.

A separate study published on September 1 in Chinese Physics B by Xinyu Lv and colleagues helps place the mechanism in context. In calculations for twisted hexagonal boron nitride on a molybdenum diselenide electrode, polarization shifted the energy band edges by about 0.2 electronvolts and the model predicted an electroresistance ratio near 100. In that distinct system, the electrode's density of states, rather than only the tunnel barrier, dominated amplification. It does not replicate the Science device, but independently shows how small polarization can control a larger readout.

The figures place the new junction among promising low-power, nonvolatile-memory prototypes. They do not yet amount to a manufacturable memory: the primary abstract does not report yield in large arrays, retention over years or integration with industrial circuitry. The demonstrated contribution is at the physics-and-device level—fast switching, low estimated energy, readable current and exceptional cycling endurance in the tested sample. The decisive next test is to preserve all four properties when millions of cells are fabricated and connected.