There is widespread use of ferroelectric materials due to their ability to be switched between two different states. It has been a challenge to overcome the limit of ferroelectrics in order to achieve any arbitrary value.
Information is stored and processed in the form of zeros and ones in modern electronics. Many electronic components rely on materials that are inherently binary. Information is stored in the remanent magnetization of a ferromagnet that is defined by the magnetic hysteresis and can take on two different values. Memory bits can be found in the hard disk's magnetic domains.
While many achievements have been achieved, they are reaching their fundamental size related limits. It is impractical to mimic analog biological systems, such as the synaptic transmission in the brain, that hold great promise in the future.
Researchers from the Laboratory for Multifunctional ferroic Materials and the Electron Microscopy Center at EMPA have been able to set any arbitrary value of the polarization at remanence. They achieved this in thin films of lead zirconate titanate (PbZr x Ti 1-x O 3, in short PZT), the most relevant ferroelectric material that has found widespread use.
The team combined two aspects of their approach in order to achieve continuous switchability. They focused on a chemical composition of PZT that is close to a phase instability, where electric fields can induce large materials responses. Second, they chose to prepare epitaxial films with a thickness of just a few nanometers, where the strain that is caused by the underlying single Crystallization Substrate acts as a handle to control the ferroelectric domain architecture.
The PZT films were prepared using an atomically precise pulsed laser deposition system that was equipped with state of the art in-situ monitoring tools. They found that the application of an electric field can reverse the polarization in each domain. It was possible to switch only a fraction of the domains with one applied voltage value because of the wide distribution of switch barriers. By averaging over a few domains, they were able to maintain the value of the polarization at remanence between the two states.
Two proof-of-concept experiments were performed to show the technological relevance of a continuous nanoscale polarization control. For their first application, they showed that it is possible to control the net polarization in order to tune the efficiency for second harmonic generation. They showed a quasi-continuous tunability of the tunnel current that flows through the PZT film. The manipulation of current flow opens exciting possibilities for the fabrication of artificial sphinxes.
Nature Communications publishes their study.
More information: Martin F. Sarott et al, Multilevel polarization switching in ferroelectric thin films, Nature Communications (2022). DOI: 10.1038/s41467-022-30823-5In situ monitoring of epitaxial ferroelectric thin-film growth is reported in the journal. There is a book titled "1088 1361-648X/abf979."
Journal information: Nature Communications
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