Achieve ultra-high-density information storage with self-winding ferroic oxide films


May 15, 2023

(Nanowerk Highlights) Ferroelectric memory, a type of nonvolatile memory, offers significant advantages in terms of speed, power efficiency and durability, making it a promising candidate for the next generation of memory technology. To meet the growing demand for higher data storage densities in ferroelectric memory, researchers have developed a new approach inspired by coil-like storage methods.

Traditional methods of increasing storage density involve reducing the size of memory cells or creating 3D cell stacks. However, reducing memory cell size faces physical limitations, and integrating single-crystalline ferroelectric oxide films in 3D stacks remains challenging. To overcome this limitation, researchers have introduced a method that allows a single crystalline ferroelectric oxide to self-coil into a coil-like 3D memory structure.

They report their findings in a recent paper at Advanced Functional Materials (“Self-Rolling-Up Enabled Ultrahigh-Density Information Storage in a Seperate Single Crystal Ferroic Oxide Film”). Self-rolling-up enables high-density information storage in ferroic oxide membranes Self-rolling-up enables high-density information storage in ferroic oxide membranes. a) Flat and pre-patterned thin film optical images with QR codes. b) Optical image of the self-winding process (black arrows indicate the winding direction). c) The optical image of the scroll is compared to a human hair. d) Front (left) and back (right) sides of the roll. (Reprinted with permission by Wiley-VCH Verlag)

In this study, the researchers chose a prototype film made of PbZr0.3From0.7HI3 (PZT), a type of ferroelectric oxide. The material is grown on a stressor layer made of another oxide, which has little lattice mismatch, meaning the atoms in the crystal structure of the two materials don’t line up perfectly. The PZT/stressor structure is then separated from the substrate in which it is grown.

This unwinding process is where the magic happens: internal stresses caused by the lattice mismatch between the two materials make the PZT/stressor film unwind on its own, like a reel. This phenomenon, called “self-rolling”, turns flat membranes into 3D structures.

Next, the researchers applied piezoelectric force microscopy, a method that uses mechanical stress to switch polarization in ferroelectric materials. They used this method to write high-density information onto flat PZT/stressor membranes before self-rolling-up occurred. When rolled up, the membrane exhibits an impressive increase in information density — up to 45 times greater than before.

This self-rolling-up behavior isn’t just an experimental curiosity; it has significant theoretical underpinnings as well. Freestanding PZT/stressor membranes have a strong intrinsic tendency to coil, driven by mismatches in their atomic structure. This trend could result in an area ratio increase of 100-450 times, which translates to a very high density information storage capacity of 100 Tbit/In.2. Scheme of self-rolling-up freestanding membrane with crossbar structure Scheme of self-rolling-up freestanding membrane with crossbar structure. These include epitaxial thin film deposition, bottom pattern single crystal oxide electrode, ferroelectric oxide film epitaxial growth, top pattern metal electrode, dissolving the sacrificial layer to obtain coils, and writing and reading information. (Reprinted with permission by Wiley-VCH Verlag)

In conclusion, the researchers developed a new method for information storage that exploits the self-rolling-up property of ferroic oxide films. This method involves writing information to the nanofilm and then allowing the film to roll and store the data in the 3D roll form.

This approach has been shown to increase the storage density by about 45.7 times, compared to the traditional planar structure. Theoretically, the self-rolling-up method can achieve ultra-high-density information storage of 100 Tbit/In2.

In addition to its impressive storage density, this method also has several other advantages. It uses a simple preparation process, enables robust heterogeneous integration, and is compatible with mass production techniques.

The authors conclude that “the method is applicable to any bilayer ferroic oxide film structure with internal stresses, providing a new pathway for the development of high-density information storage.”

Michael Berger

– Michael is the author of three books by the Royal Society of Chemistry:
Nano-Society: Pushing the Boundaries of Technology,
Nanotechnology: A Small Future And
Nanoengineering: Skills and Tools for Making Technology Invisible
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