Protons to power next-generation memory devices and neuromorphic processing chips

Researchers led by KAUST discovered a proton-mediated method that induces multiple phase transitions in ferroelectric materials, potentially facilitating the development of high-performance, low-power memory devices and neuromorphic computing chips.

A proton-mediated approach that stimulates multiple phase transitions in ferroelectric materials could pave the way for the creation of high-performance memory devices, including brain-inspired neuromorphic computing chips, according to an international team of researchers led by KAUST.

Ferroelectric materials such as indium selenide are inherently polarized and can change polarity when subjected to an electric field. This feature makes them an attractive option for the development of memory technology. The resulting memory devices exhibit superior read/write endurance and write speeds when operating at low voltages. However, they are constrained by their limited storage capacity.

The limitation of the capacitance stems from the fact that current techniques can only induce a few ferroelectric phases, and recording these phases poses significant experimental challenges, explains Xin He, co-lead of the study. Lui conducted this research under the guidance of Fei Xue and Xixiang Zhang.

A new method for ferroelectric materials

The team’s new approach depends on the protonation of indium selenide to generate a multitude of ferroelectric phases. Researchers incorporated the ferroelectric material into a silicon-supported stacked heterostructure transistor for evaluation.

They layered an indium selenide film over the heterostructure, which consisted of an insulating sheet of aluminum oxide nestled between a layer of platinum at the bottom and porous silica at the top. The platinum layer served as electrodes for the applied voltage, while the porous silica served as the electrolyte, supplying protons to the ferroelectric film.

Protonation and its effects

The researchers gradually injected or removed protons from the ferroelectric film by changing the applied voltage. This reversibly produced several ferroelectric phases with varying degrees of protonation, which is critical for implementing multilevel memory devices with large storage capacity.

Higher positive voltages increased protonation, while higher negative voltages significantly reduced protonation levels.

Protonation levels also varied depending on how close the film layer was to the silica. They reached maximum values ​​in the lower layer, which was in contact with the silica, and gradually decreased to reach minimum amounts in the upper layer.

In an unexpected turn of events, the proton-induced ferroelectric phases returned to their initial state when the voltage was cut off. We observed this unusual phenomenon because the protons diffused out of the material and into the silica, Xue explains.

Advances in low-power memory devices

By creating a film with a uniform and continuous interface with silica, the team achieved a highly efficient proton injection device that operates below 0.4 volts. This is an essential factor in the development of low power memory devices.

Xue acknowledges that reducing the operating voltage was a significant challenge, but explains that the efficiency of proton injection at the interface controls the operating voltages and can be tuned accordingly.

Our biggest challenge was to reduce the operating voltage, but we realized that the efficiency of proton injection at the interface governed the operating voltages and could be adjusted accordingly, says Xue.

We are committed to developing ferroelectric neuromorphic computing chips that consume less power and work faster, says Xue.

Reference: Proton-Mediated Reversible Switching of Metastable Ferroelectric Phases with Low Operating Voltages by Xin He, Yinchang Ma, Chenhui Zhang, Aiping Fu, Weijin Hu, Yang Xu, Bin Yu, Kai Liu, Hua Wang, Xixiang Zhang, and Fei Xue, May 24, 2023, The progress of science.
DOI: 10.1126/sciadv.adg4561