Wisconsin Alumni Research Foundation

Semiconductors & Integrated Circuits
Semiconductors Integrated Circuits
Ferroelectric Thin Films for Improving Memory Technology
WARF: P08062US

Inventors: Chang-Beom Eom, Ho Won Jang

The Wisconsin Alumni Research Foundation (WARF) is seeking commercial partners interested in developing BiFeO3 thin films with enhanced ferroelectric properties that can be exploited in memory devices.
The semiconductor industry constantly is seeking new methods to improve memory speed and efficiency that are compatible with large-scale fabrication processes and environmentally-friendly.

Currently, Flash memory is the most commonly used type of memory in personal electronic devices. It has a higher storage density and is less expensive to manufacture than previous technologies because more components are packaged into the same space on a single chip. However, reducing component size can eliminate the ferroelectric properties of some materials so they are no longer usable. In addition, Flash memory only can be used for a limited number of write-erase cycles.

Ferroelectric memory (FeRAM) is one of a growing number of alternative non-volatile memory technologies offering similar functionality as Flash memory. FeRAM’s advantages over Flash include lower power usage, faster write speeds and a much greater maximum number of write-erase cycles.

To make them more competitive with Flash memory, FeRAM devices have been improved to exploit the properties of BiFeO3 in a thin film process. In comparison to other FeRAM materials, such as Pb(Zr,Ti)O3 and SrBi2Ta2O9, BiFeO3 is lead free and poses no environmental risks or health concerns.

However, strain control is important in the production of non-volatile FeRAM. Current fabrication methods yield heterogeneous BiFeO3 layers that experience varying degrees of strain, especially when undergoing thermal changes. This undesirable strain hinders the ferroelectric properties of the BiFeO3 films and results in other unwanted effects. Methods of controlling strain are needed before BiFeO3 films can be used effectively in FeRAM memory storage devices and other applications.
The Invention
UW-Madison researchers have developed a method for fabricating and transferring BiFeO3 thin films onto a variety of substrates, thereby allowing limitless strain control. The BiFeO3 layer can be epitaxially grown over a variety of materials, called perovskite, with the same type of crystal structure as calcium titanium oxide.

The perovskite layer functions as a buffer to protect the thin film during the chemical release process. Additionally, it improves the epitaxial growth of strain-free BiFeO3 layers on different sacrificial substrates. Once released from their original sacrificial substrates, the free-standing BiFeO3-perovskite heterostructures may be transferred onto a variety of host substrates to exhibit improved ferroelectric characteristics that include increased remnant polarization, reduced coercive field, reduced leakage current, and/or reduced fatigue.

This new fabrication method expands the prospect of fine tuning BiFeO3 thin film characteristics to advance memory technology.
  • Memory modules, such as hard drives and FeRAM
  • Solar cells
  • Radio frequency (RF) tags
  • Displays
  • Electro-optic modulators
Key Benefits
  • Can be transferred to a variety of substrates (i.e., plastic, metal, glass, etc.)
  • Offers advantages of strain-controlled films, which exhibit increased remnant polarization, reduced coercive field, reduced leakage current, and/or reduced fatigue
  • Offers advantages of BiFeO3 thin films, which produce the highest remnant polarization and lowest coercive field when compared to other ferroelectrics
  • Provides lead-free and environmentally friendly ferroelectric films that are compatible with large-scale fabrication processes
  • Provides improved features compared to Flash-based memory, including lower power usage, faster write speeds and a much greater maximum number of write-erase cycles
Additional Information
For More Information About the Inventors
For current licensing status, please contact Michael Carey at [javascript protected email address] or 608-960-9867