Enhancing next-generation ferroelectric memory technology

A research team led by Professor Jang-Sik Lee from Pohang University of Science and Technology (POSTECH) has enhanced the data storage capacity of ferroelectric memory devices by utilising hafnia-based ferroelectric materials and an innovative device structure.

With the exponential growth in data production and processing due to advancements in electronics and artificial intelligence (AI), the importance of data storage technologies has surged. NAND flash memory — a type of non-volatile storage that uses charge-trap transistors to trap electrical charges — is one of the most prevalent technologies for mass data storage. It can store more data in the same area by stacking cells in a three-dimensional structure rather than a planar one. However, this approach relies on charge traps to store data, which results in higher operating voltages and slower speeds.

Hafnia-based ferroelectric memory is a promising next-generation memory technology, as hafnia (hafnium oxide) enables ferroelectric memories to operate at low voltages and high speeds. However, a significant challenge has been the limited memory window for multilevel data storage.

Now, the researchers from POSTECH have addressed this issue and enhanced the performance of hafnia-based memory devices by doping the ferroelectric materials with aluminium, creating high-performance ferroelectric thin films. They also replace the conventional metal-ferroelectric semiconductor (MFS) structure, where the metal and ferroelectric materials that make up the device are simply arranged, with a metal-ferroelectric-metal-ferroelectric-semiconductor (MFMFS) structure.

The researchers controlled the voltage across each layer by adjusting the capacitance of the ferroelectric layers, which involved fine-tuning factors such as the thickness and area ratio of the metal-to-metal and metal-to-channel ferroelectric layers. This efficient use of applied voltage to switch ferroelectric material improved the device’s performance and reduced energy consumption.

While conventional hafnia-based ferroelectric devices typically have a memory window of 2 V, the new device achieved a memory window exceeding 10 V. It also demonstrated high stability after more than one million cycles and operated at voltages of 10 V or less, significantly lower than the 18 V required for NAND flash memory. The device also exhibited stable characteristics in terms of data retention.

The research findings have been published in the journal Science Advances.

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