Hafnia-based ferroelectric materials benefit computer memory

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Ferroelectric materials are known as substances that exhibit spontaneous electrical polarization. Polarization involves the isolation of negative and positive charges present inside a material.

The structure of yttrium-doped hafnia dioxide crystals (partially shaded orange) exhibit ferroelectric polarization (blue arrows) that changes direction when the external electric field is reversed. Image Credit: Oak Ridge National Laboratory.

This means that for ferroelectric materials, the “memory” of the material’s previous state, known as hysteresis, can store data in a manner similar to magnetic storage devices such as hard drives.

Ferroelectric materials based on the hafnium element hold great promise as they appear to be highly compatible with currently available silicon computer circuits compared to other potential materials.

Previously, it was possible for scientists to obtain ferroelectricity on ultrathin films. Such films could be fragile and difficult to use. Scientists have now reported the first experimental evidence of room temperature ferroelectricity in crystals made of a hafnium-based compound and bulk yttrium-doped hafnium dioxide.

The impact

Hafnia-based ferroelectric materials appear to possess many advantages for computer memory. They offer high durability, reduced operating power and speed, and the ability to retain data when power is lost. But scientists don’t fully understand these materials.

This study developed a creative ferroelectric material based on hafnia. The results offer insight into how these materials tend to behave and how to regulate them. Additionally, the findings eliminate the upper size limit of the materials, thereby making these materials easier to use in real-world applications.

The huge sample size will help further experiments to better understand the ferroelectric properties of the material. In turn, this will help scientists create next-generation non-volatile memory devices.

Summary

In 1965, Intel co-founder Gordon Moore deduced that the number of transistors on a computer chip would double every two years, a prediction called Moore’s Law. Since then, chipmakers have been able to maintain this pace of miniaturization but tend to face increasing difficulties due to the laws of physics.

Hafnia-based ferroelectric materials could help further miniaturize non-volatile memory devices. However, scientists have not found a bulk form of the material.

In this study, the novel yttrium-doped ferroelectric hafnium dioxide developed could enable such development, leading to increased use of hafnia on computer chips and extension of Moore’s Law.

A research group led by Rutgers University performed neutron powder diffraction measurements on yttrium-doped hafnium dioxide using the POWGEN, a general-purpose powder diffractometer instrument at Spallation Neutron Source, a Department of Energy (DOE) user facility at Oak Ridge National Laboratory (ORNL).

POWGEN is known as a high-resolution neutron powder diffractometer for defining the magnetic, crystalline and local structures of new polycrystalline materials. The research group synthesized single crystals of yttrium-doped hafnium dioxide at multiple levels of yttrium doping and then ground them into powder for characterization.

The POWGEN data showed that at a few levels of doping, the raw phases were firm and the oxygen atoms shifted to allow reversible polarization. Hence, this verifies the ferroelectricity of hafnia at room temperature.

Other measurements, such as the bias electric field hysteresis loop and computer simulations, have aided structural analyzes and are a significant step towards hafnia-based technologies in the future.

The study was financially supported by the Center for Quantum Materials Synthesis funded by the Gordon and Betty Moore Foundation’s EPiQS Initiative, Rutgers University, the Office of Naval Research, and the Department of Defense. Neutron characterization was performed with the Spallation Neutron Source, a DOE Office of Science user facility at ORNL.

Journal reference:

Xianghan, X. et al. (2022) Kinetically stabilized ferroelectricity in bulk monocrystalline HfO2:Y. Natural materials. doi.org/10.1038/s41563-020-00897-x

Source: https://www.energy.gov/

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