Exploring the ‘dark side’ of a single-crystal complex oxide thin film


Argonne researchers have actually taken a look at the regional ferroelectric residential or commercial properties of the bottom atomic layers of freestanding complex oxide PZT separated from the epitaxial substrate. Credit: Argonne National Laboratory

Analysis from a group led by Argonne scientists exposes never-before-seen information about a type of thin film being checked out for innovative microelectronics.


Research from a group led by researchers at the U.S. Department of Energy’s (DOE) Argonne National Laboratory provides a brand-new, nanoscopic view of complex oxides, which are  guaranteeing for innovative microelectronics.

Complex oxides are multifunctional products that might ultimately cause energy-efficient, innovative electronic memory parts and quantum computing gadgets. Usually, these products are produced layer-by-layer on an atomically matched substrate, a procedure referred to as epitaxial development.

To utilize complex oxides in electronic devices, they require to be produced on silicon—a difficult job for existing epitaxial development methods, because the atomic structures of these 2 products do not match. One possible workaround is to grow the complex oxides in other places and after that transfer the film to another substrate. Nevertheless, a crucial concern emerges: Will the regional residential or commercial properties of a complex oxide thin film stay undamaged if you raise it from one substrate and deposit it on another?

The brand-new research study exposes insights about freestanding complex oxides that might ultimately produce a completely brand-new research study field: complex oxide microelectronics. The work is detailed in a paper, “Ferroelectric Domain Wall Motion in Freestanding Single Crystal Complex Oxide Thin Film,” just recently released in the journal Advanced Materials.

Using scanning probe microscopy, the group studied lead zirconium titanate (PZT), a type of single-crystal complex oxide ferroelectric thin film. Such single-crystal movies have residential or commercial properties perfect for microelectronics—they are extremely polarized, endurable and fast-switchable, making them appropriate for future ferroelectric random-access memory chips, for instance.

Growing these thin movies needs temperature levels of about 700 °C (1292 °F), which weakens the interfacial layer’s residential or commercial properties if straight grown on silicon. So the scientists grew the PZT on a more open substrate—a base of strontium titanate (STO) with a “sacrificial layer” of lanthanum strontium manganite (LSMO) sandwiched in between. To move the PZT thin film to another substrate, the scientists broke the bonds that joined it with the LSMO.

“PZT grows beautifully on LSMO,” stated Saidur Rahman Bakaul, an assistant products researcher at Argonne who led the research study. “We wanted to see what happens if we cut that interface.”

After changing the PZT into a freestanding film, the research study group turned the film over and carefully redeposited it onto a similar STO-LSMO substrate. This permitted a first-ever view of PZT’s separated underside.

“It’s like looking at the other side of the moon, which you normally don’t see,” Bakaul stated.

The group utilized electrostatic force microscopy with 20-nanometer-radius probes to determine the product’s regional ferroelectric residential or commercial properties. Their analysis revealed the regional fixed residential or commercial properties of the bottom surface area of freestanding PZT were rather comparable compared to those of the leading surface area. This finding, Bakaul stated, is really motivating for future complex oxide microelectronics, due to the fact that it validates that the interfacial surface area of the moved PZT film is a premium ferroelectric layer. That indicates the transfer strategy must have the ability to integrate the finest products from various worlds, such as PZT (ferroelectric) and silicon (semiconductors). Up until now, no direct development strategy has actually attained this without damaging the interfacial surface area.

Using piezoresponse force microscopy images , researchers discovered that the separated layer’s ferroelectric domain wall speed—a procedure of the electrostatic energy landscape of complex oxides—was nearly 1,000 times slower than highly bonded as-grown PZT movies.

To learn why, the group initially taken a look at the atomic layers at the bottom surface area of the PZT film with atomic force microscopy, which exposed abnormalities on the surface area. For an even more detailed look, they relied on Argonne’s Center for Nanoscale Materials, a DOE Office of Science User Facility, where they utilized an X-ray nanoprobe to see the tilts in atomic aircrafts, exposing never-before-seen ripples.

The ripples, Bakaul stated, increase to the height of just a millionth of a pinhead’s size, however still can produce a strong electrical field that keeps the domain wall from moving, the theoretical analysis exposed. This claim was additional supported with measurements from a scanning capacitance microscopic lense.

The existence of such structural ripples in complex oxides, which utilized to be referred to as nonbendable ceramics, is an amazing brand-new clinical discovery and a future play area to check out strong pressure gradient-induced physical phenomena such as flexoelectric impacts. Nevertheless, in microelectronic gadgets, these small ripples can cause device-to-device irregularity.

The work, which was supported by DOE’s Office of Basic Energy Sciences, deals a special and essential level of information about the residential or commercial properties of freestanding complex oxide thin movies.

“Our study shows that this material is ready to go for future microelectronic applications,” Bakaul stated, “but it will require further research on ways to avoid these ripples.”


‘Sandwich’ structure secret to thin LSMO movies maintaining magnetic residential or commercial properties


More details:
Saidur R. Bakaul et al, Ferroelectric Domain Wall Motion in Freestanding Single‐Crystal Complex Oxide Thin Film, Advanced Materials (2019). DOI: 10.1002/adma.201907036

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Exploring the ‘dark side’ of a single-crystal complex oxide thin film (2020, January 6)
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