WARF TECHNOLOGIES

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.

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

• 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

For More Information About the Inventors

• Chang-Beom Eom

Tech Fields

• Semiconductors & Integrated Circuits : Design & fabrication