Researchers have discovered that incipient ferroelectricity can revolutionize computer memory, enabling ultra-low power devices.

These unique transistors shift behavior based on temperature, making them suitable for both traditional memory and neuromorphic computing, which mimics the brain’s energy efficiency. The use of strontium titanate thin films reveals unexpected ferroelectric-like properties, hinting at new possibilities in advanced electronics.

Harnessing Incipient Ferroelectricity for Next-Gen Memory

Scientists at Penn State have discovered a way to create a new type of computer memory using a unique material property called incipient ferroelectricity. This breakthrough could lead to electronic devices that use far less energy and function reliably in extreme environments, including outer space.

Their research, published in Nature Communications, focuses on two-dimensional field-effect transistors (FETs) — tiny electronic components that use ultra-thin layers of material to control electrical signals. These FETs are ferroelectric-like, meaning they can switch the direction of their electrical conduction when exposed to an external electric field. This ability makes them highly valuable for computing, where signal control is essential.

Tackling AI’s Energy Problem with Low-Power Computing

One of the biggest challenges in modern computing, especially in AI-driven tasks like image recognition, is the high energy consumption of traditional systems. The new ferroelectric transistors require much less power, offering a more sustainable and efficient alternative for the future of computing.

“AI accelerators are notoriously energy-hungry,” said Harikrishnan Ravichandran, a doctoral student in engineering science and mechanics and co-author of the study. “Our devices switch rapidly and consume far less energy, paving the way for faster, greener computing technologies.”

What Is Incipient Ferroelectricity?

Incipient ferroelectricity, a previously overlooked property of FETs, may be to thank for the quicker, more sustainable devices. Incipient ferroelectricity refers to materials that show signs of temporary, scattered polarization, meaning parts of it can switch charges like tiny dipoles — opposing magnetic poles a small distance apart — but it does not settle into a stable state under normal conditions.

Think of it like a material that has the potential to become ferroelectric, but it needs a little push. Incipient ferroelectricity is means the material is on the verge of becoming ferroelectric — it can hold an electrical charge, but needs certain conditions to achieve an electrical charge.

“Incipient ferroelectricity means there’s no stable ferroelectric order at room temperature,” said Dipanjan Sen, doctoral candidate in engineering science and mechanics and lead author in the study. “Instead, there are small, scattered clusters of polar domains. It’s a more flexible structure compared to traditional ferroelectric materials.”

Unlocking Ferroelectric Potential in Extreme Conditions

While this trait is often considered a limitation, the team found that the incipient ferroelectricity became less incipient and more traditional at colder temperatures. According to Ravichandran, the devices displayed unique behaviors across temperature ranges, suggesting a flexibility that could enable possible new applications.

“The main goal of the project was to explore whether incipient ferroelectricity, usually seen as a disadvantage because it leads to short memory retention, could actually be useful,” said corresponding author Saptarshi Das, Ackley Professor of Engineering and professor of engineering science and mechanics at Penn State. “In cryogenic conditions, this material exhibited traditional ferroelectric-like behavior suitable for memory applications. But at room temperature, this property behaved differently. It had this relaxor nature.”

Relaxor Behavior and Neuromorphic Computing

Relaxor behavior refers to a more disordered, short-range polarization response. This type of behavior is less predictable and more fluid, which contrasts with the stable, long-range order seen in traditional ferroelectrics. This means the material’s ferroelectric properties are weaker or less stable at room temperature. Instead of being a drawback, the researchers said it showed potential for use in neuromorphic computing, which aims to imitate how the human brain processes information using neurons and uses much less energy than traditional computers. Like our brain, it saves energy by only using power when needed, like flipping a light switch on and off, instead of staying on all the time like traditional computers.

Mimicking the Brain: Energy-Efficient Neural Computing

“These devices acted like neurons, mimicking biological neural behavior,” said Mayukh Das, doctoral candidate in engineering science and mechanics and study co-author. “To test this, we performed a classification task using a grid of three-by-three pixel images fed into three artificial neurons. The devices were able to classify each image into different categories. This learning method could eventually be used for image identification and classification or pattern recognition. Importantly, it works at room temperature, reducing energy costs. These devices function similarly to the nervous system, acting like neurons and creating a low-cost, efficient computing system that uses a lot less energy.”

Fabricating the Future: Strontium Titanate and Thin Films

Collaborators at the University of Minnesota developed the FETs by depositing a layer of atoms on a substrate to form a thin film. These films, made of strontium titanate, were then combined with molybdenum disulfide, a two-dimensional material.

Strontium titanate is typically non-ferroelectric, meaning it does not have a permanent electric field. However, freestanding nanomembranes of strontium titanate exhibit polar order, the researchers said, which can enable the material to exhibit ferroelectric-like behavior, especially at very low temperatures.

Strontium titanate thin films, along with their incipient ferroelectricity, are also a perovskite material. Perovskites, materials with a specific type of crystal structure, are valued for their exceptional electronic properties.

“We were surprised to see that these well-known perovskite materials could exhibit exotic ferroelectric properties at the device level,” Sen said. “It wasn’t something we anticipated, but once we started fabricating the devices, we saw behaviors that could really redefine advanced electronics.”

Looking Ahead: Challenges and Future Research

The researchers noted that future research will include addressing current challenges such as scalability and commercial viability while exploring other potential materials.

“Right now, this is at the research and development stage,” Sen said. “Perfecting these materials and integrating them into everyday devices like smartphones or laptops will take time, so there’s so much more to explore. In addition, we’re examining other materials, like barium titanate, to uncover their potential. The opportunities for growth are immense, both in materials and device applications.”

Reference: “Multifunctional 2D FETs exploiting incipient ferroelectricity in freestanding SrTiO3 nanomembranes at sub-ambient temperatures” by Dipanjan Sen, Harikrishnan Ravichandran, Mayukh Das, Pranavram Venkatram, Sooho Choo, Shivasheesh Varshney, Zhiyu Zhang, Yongwen Sun, Jay Shah, Shiva Subbulakshmi Radhakrishnan, Akash Saha, Sankalpa Hazra, Chen Chen, Joan M. Redwing, K. Andre Mkhoyan, Venkatraman Gopalan, Yang Yang, Bharat Jalan and Saptarshi Das, 30 December 2024, Nature Communications.
DOI: 10.1038/s41467-024-54231-z

Along with Sen, Das and Ravichandran, other authors of the study from Penn State include Pranavram Venkatram, graduate student in engineering science and mechanics; Zhiyu Zhang, graduate student in engineering science and mechanics; Yongwen Sun, graduate student in engineering science and mechanics; Shiva Subbulakshmi Radhakrishnan, graduate student in engineering science and mechanics; Akash Saha, graduate student in materials science and engineering; Sankalpa Hazra, graduate student in materials science and engineering; Chen Chen, assistant research professor, thin films in the Two-Dimensional Crystal Consortium (2DCC-MIP); Joan Redwing, director of the 2DCC-MIP and distinguished professor of materials science and engineering and of electrical engineering; Venkat Gopalan, professor of materials science and engineering and of physics; and Yang Yang, assistant professor of engineering science and mechanics and of nuclear engineering. From the University of Minnesota, co-authors of the study include Sooho Choo, Shivasheesh Varshney, Jay Shah, K. Andre Mkhoyan and Bharat Jalan.

The U.S. National Science Foundation and the Army Research Office supported this work.