Ferroelectrics, like indium selenide, are intrinsically polarized substances that change polarity when exposed to an electric field, making them desirable for use in-memory technologies. The resulting memory devices have limited storage capacities but outstanding maximum read/write endurance and speed. However, they also require low operating voltages. This is because only a few ferroelectric phases may be triggered by current techniques, and it is difficult to capture these phases experimentally.
A KAUST-led international team has now developed a proton-mediated approach that produces multiple phase transitions in ferroelectric materials. Moreover, it could help establish high-performance memory devices, such as brain-inspired or neuromorphic computing chips. This new approach is based on the protonation of indium selenide to generate a multitude of ferroelectric phases. Scientists used a transistor made of a silicon-supported layered heterostructure and ferroelectric material for testing.
They deposited a multilayered indium selenide film on the heterostructure, made up of an aluminum oxide insulating sheet sandwiched between a platinum layer at the bottom and porous silica at the top. The porous silica functioned as an electrolyte and provided protons to the ferroelectric film, while the platinum layer served as electrodes for the applied voltage. By adjusting the applied voltage, the researchers gradually added or subtracted scientists from the ferroelectric layer. This reversibly produced several ferroelectric phases with varying degrees of protonation to construct multilayer memory devices with significant store capacity.
Higher applied positive voltages increased protonation, but negative voltages with larger amplitudes significantly reduced protonation levels. The proximity of the film layer to silica affected the protonation levels as well. In the bottom layer, which was in touch with silica, they reached the highest values, then gradually reduced to reach minimal importance in the top layer.
Unexpectedly, when the applied voltage was removed, the proton-induced ferroelectric phases returned to their original state.
Fei Xue said, “We observed this unusual phenomenon because protons diffused out of the material and into the silica.”
“By manufacturing a film that displayed a smooth and continuous interface with silica, we obtained a high proton-injection efficiency device that operates below 0.4 volts, which is key for developing low-power memory devices.”
“Our biggest challenge was to reduce the operating voltage, but we realized that the proton-injection efficiency over the interface governed operating voltages and could be tuned accordingly.”
“We are committed to developing ferroelectric neuromorphic computing chips that consume less energy and operate faster.”
