Innovative ternary alloy film paves the way for ultra-low power memory devices

Recent research has reported by researchers in Science and Science (Science Tokyo), where record-breaking scandium levels have record-breaking scandium levels, which can be exciting for ultra-low power memory devices. Using reactive magnetron sputtering, they fine-tuned the composition of the ternary alloy to overcome previous stability limitations.

Besides enabling efficient data storage, these films show promise for noise filters in 6G communication and optical computing thanks to their attractive piezoelectric and photoelectric properties.

Electronic devices are smaller than ever and more capable than ever, creating a demand for memory technology that can store more data while consuming less power. A promising solution to this problem is nonvolatile ferroelectric memory. By maintaining inherent electrical polarization, these devices can retain stored information without the need for constant power. This increases battery life and allows for more refined mobile computing.

Materials already used in LEDs, gallium nitride (GAN) and aluminum nitride (ALN) have unique crystal structures in which positive and negative charge centers naturally replace. This displacement creates switchable polarization that can be controlled by applied external voltages, forming the basis for nonvolatile memory functionality.

Scientists know that incorporating scandium (SC) into these crystal structures can significantly reduce operating voltages and allow for ultra-low power operation. However, increasing the concentration of SCs has proven to be extremely difficult due to the fundamental limitations of the stability of both Gan and Aln.

Against this backdrop, a research team led by Professor Philosijima of the Tokyo Institute of Science (Science Tokyo) in Japan achieved a major breakthrough by successfully synthesizing (AL, GA, SC) N thin films with unprecedented SC concentrations. Their research, published online at APL Materials, shows that by alloying GAN and ALN at an appropriate rate, the amount of SC that can be incorporated into the final crystal structure can be significantly increased.

First, the researchers adopted reactive magnetron sputtering, a physical vapor deposition technique, to deposit carefully controlled compositions of (al, ga, sc)n thin films on platinum and titanium coated silicon substrates. By meticulously adjusting the sputtering parameters and target power, various ternary alloys with different proportions of each element were synthesized.

These films were rigorously characterized by assessing their ferroelectricity and dielectric properties using advanced techniques such as X-ray diffraction and using electrical measurements to examine crystal structures, microstructures for conducting electron microscopy. Their systematic approach allowed us to map the so-called “phase diagrams” of the Aln-Gan-SCN system, revealing new regions of ferroelectrically active Wurtzite crystal structures with higher SC content when a small number of gallium is present.

An important result of this study was that a significant reduction in the material’s forced field (EC) (the electric field required to switch polarization) was accompanied by an increase in the SC content of the ternary alloy. The team observed that EC decreased significantly from 5.8 mV/cm to 1.8 mV/cm as the SC ratio increased.

“This EC value is much lower than most of the values ​​reported in previous works for the various dopants in ALN ​​and GAN-based Wurtzite films. This is extremely promising for the development of memory devices,” says Funakubo. Further analysis of the results revealed that the entropic effect is responsible for this effect.

In particular, the voltage reduction achieved can be directly converted to reducing the power consumption of memory devices, and can address one of the most pressing challenges in modern electronics. Beyond memory applications, these new ferroelectric films also exhibited excellent piezoelectric and photoelectric properties.

“These properties open up potential applications for high-frequency noise filters and ultra-low-power optical computing systems needed for next-generation 6G smartphones and optical computing devices that operate at ultra-low power,” says Funakubo.

Overall, with reduced operating voltage, enhanced functional properties, and compatibility with existing semiconductor processing technologies, (AL, GA, SC)N films are promising materials for next-generation electronics.