From structure to function: Tailoring wurtzite MgSiN₂ for next-generation electronics

Wurtzite-structured crystals, characterized by their hexagonal symmetry, are widely valued for their unique electronic and piezoelectric properties—their ability to generate an electric charge when subjected to mechanical stress. Among these, gallium nitride (GaN), a key material in blue light-emitting diodes, and aluminum nitride (AlN), used in high-frequency radio frequency (RF) filters in smartphones, are prominent examples. These materials play a crucial role in advanced semiconductors, sensors, and actuators.

Scientists at Institute of Science Tokyo (Science Tokyo), Japan, have made a significant breakthrough in expanding the wurtzite structure to include heterovalent ternary nitrides, specifically for potential piezoelectric and ferroelectric applications. Their paper, which was made available online on February 6, 2025, in Advanced Electronic Materials, describes the fabrication of the first-ever magnesium silicon nitride (MgSiN₂) heterovalent nitride in a wurtzite structure with piezoelectric properties. This pioneering study was led by Professor Hiroshi Funakubo from MDX Research Center for Element Strategy, Science Tokyo, in collaboration with Mr. Sotaro Kageyama, a second-year Master's student, Assistant Professor Kazuki Okamoto, and Professor Hiroko Yokota from the School of Materials Science and Engineering, Science Tokyo. The research team also included Professor Venkatraman Gopalan from Pennsylvania State University, Associate Professor Yoshiomi Hiranaga from Tohoku University, Professor Hiroshi Uchida from Sophia University, and others.

Wurtzite structures, such as AlN and GaN, are usually made of trivalent cations. However, these materials face challenges due to high coercive electric fields—the energy required to switch polarization for piezoelectric charge generation and ferroelectric properties. Incorporating heterovalent cations with valencies of II/IV alters the structural rigidity due to differences in cation radii. This alteration has been shown to facilitate polarization and lower the coercive field. To explore this effect, the researchers selected the heterovalent ternary nitride MgSiN₂, composed of Mg²⁺ and Si⁴⁺.

MgSiN₂ typically crystallizes in the orthorhombic β-NaFeO₂ structure. However, the research team successfully stabilized it in a wurtzite phase using reactive RF magnetron sputtering of Mg and Si ions at 600 °C in a nitrogen-rich atmosphere. This structural transformation introduced a random cationic ordering.

“The ability to synthesize MgSiN₂ in a new wurtzite phase is a major advancement in the field of piezoelectric materials,” explains Funakubo. “Our findings could open new avenues for developing high-performance materials with tailored electronic properties.”

The results confirmed the piezoelectric nature of wurtzite-MgSiN₂ using advanced characterization techniques, including X-ray diffraction, transmission electron microscopy, and piezoresponse force microscopy. The fabricated material exhibited a converse piezoelectric coefficient (d₃₃_,f = 2.3 pm/V) comparable to those of conventional simple nitrides, indicating its ability to effectively convert mechanical stress into electric charge. This breakthrough creates potential applications in ultrasonic transducers, nanoelectromechanical systems, and energy harvesters.

The piezoelectric MgSiN₂ exhibited a wide bandgap of approximately 5.9 eV (direct) and 5.1 eV (indirect), comparable to traditional piezoelectric wurtzite AlN. This suggests that the material provides excellent insulation by restricting electron movement between the valence band (where electrons are bound to atoms) and the conduction band (where electrons are free to move and conduct electricity). A wider bandgap indicates strong resistance to electrical conduction under normal conditions, confirming the material’s durability and stability. These properties make MgSiN₂ a promising candidate for next-generation electronics.

“Our research lays the foundation for further exploration of heterovalent ternary nitrides with piezoelectric properties. Fine-tuning the deposition parameters could lead to greater improvements in polarization switching and further validate the material’s ferroelectric properties,” concludes Funakubo.

As the researchers continue to investigate new material phases for piezoelectric applications, the wurtzite-structured MgSiN₂ emerges as a promising candidate for next-generation piezoelectric and ferroelectric technologies, paving the way for advancements in electronic materials.

About Institute of Science Tokyo (Science Tokyo)

Institute of Science Tokyo (Science Tokyo) was established on October 1, 2024, following the merger between Tokyo Medical and Dental University (TMDU) and Tokyo Institute of Technology (Tokyo Tech), with the mission of “Advancing science and human well-being to create value for and with society.”