An innovative ferroelectric material could allow

Article Highlight | June 22, 2022

First report of room-temperature ferroelectricity in bulk hafnia may extend Moore’s Law for data storage.

DOE/US Department of Energy

Science

Ferroelectric materials are substances with spontaneous electrical polarization. Polarization refers to the separation of negative and positive charges in a material. For ferroelectric materials, this means that the “memory” of the material’s previous state (called hysteresis) can store information in a manner similar to magnetic storage devices such as hard drives. Ferroelectric materials based on the hafnium element are promising because they are more compatible with today’s silicon computer circuits than other potential materials. In the past, researchers obtained ferroelectricity on ultrathin films. These films can be delicate and difficult to use. Scientists have now reported the first experimental evidence of room temperature ferroelectricity in crystals made of a hafnium-based compound, bulk yttrium-doped hafnium dioxide.

The impact

Hafnia-based ferroelectric materials have many advantages for computer memory. They offer high speed, durability, low operating power, and the ability to retain data when power is lost. However, researchers do not fully understand these materials. This research has developed an innovative ferroelectric material based on bulk hafnia. The results provide information about the behavior of these materials and how to control them. The results also remove the upper size limit of materials, making these materials easier to use in real-world applications. The large sample size will facilitate further experiments to better understand the ferroelectric properties of the material. This in turn will help researchers create next-generation non-volatile memory devices.

Summary

Intel co-founder Gordon Moore postulated in 1965 that the number of transistors on a computer chip would double every two years, a prediction known as Moore’s Law. Since then, chipmakers have been able to maintain this rate of miniaturization, but face increasing challenges due to the laws of physics. Hafnia-based ferroelectric materials can help further miniaturize nonvolatile memory devices, but researchers have not developed a bulk form of the material. The new yttrium-doped ferroelectric hafnium dioxide developed in this research could enable such development, leading to increased use of hafnia on computer chips and the extension of Moore’s Law.

A team of researchers 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 a high-resolution powder neutron diffractometer that allows the characterization of the crystalline, magnetic and local structures of new polycrystalline materials. The team synthesized single crystals of yttrium-doped hafnium dioxide at varying levels of yttrium doping and ground them into powder for characterization. The POWGEN data showed that at certain doping levels, the raw phases were stable and the oxygen atoms shifted to allow reversible polarization, thus confirming the ferroelectricity of hafnia at room temperature. Other measurements, including the polarization-electric field hysteresis loop and computer simulations, supported the structural analyses, representing an important step towards future hafnia-based technologies.

Funding

The research was supported by the Gordon and Betty Moore Foundation’s EPiQS-funded Center for Quantum Materials Synthesis, 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.

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