As piezoelectric materials continue to grow increasingly advanced, Tokyo’s MDX Research Center for Element Strategy has taken significant strides towards sweeping innovation. Yet they managed to stabilize their heterovalent ternary nitride MgSiN₂ in a wurtzite phase. This advance is a breakthrough not only in the field of materials science. This was accomplished by reactive RF magnetron sputtering at 600 °C in a nitrogen-rich environment, shedding new light on the electronic structure of MgSiN₂.
Traditionally, MgSiN₂ crystallizes in the orthorhombic β-NaFeO₂ structure, prohibiting its application in electronic devices. Such an unprecedented wurtzite-structured thin film demonstrates promising piezoelectric properties. These features might go a long way towards increasing its user-friendliness for various tech applications. The research team is headed by Professor Hiroshi Funakubo, with Mr. Sotaro Kageyama, Assistant Professor Kazuki Okamoto, and Professor Hiroko Yokota. They published their discoveries in the journal Advanced Electronic Materials on Feb. 6, 2025. The DOI for the paper is 10.1002/aelm.202400880.
Promising Electronic Properties
The caveat of the wurtzite-structured MgSiN₂ thin film is its remarkable wide bandgap. Its band gap is 5.9 eV for direct transitions and ~5.1 eV for indirect transitions. This bandgap is significantly wider than conventional piezoelectric materials such as wurtzite AlN. This indicates that MgSiN₂ can be a potentially attractive alternative for applications requiring materials with superior electrical insulation.
The thin film’s ability to prohibit electron hopping between the VB and CB increases its insulating quality. These features are key to maintaining high performance in electronic and optoelectronic applications, especially where controlling the flow of electrical charge is critical.
Besides its large thermal insulating properties, MgSiN₂ is a piezoelectric material where its converse piezoelectric coefficient (d₃₃,f) equals 2.3 pm/V. This lattice coefficient corresponds to the values of the corresponding conventional simple nitrides. Its discovery underscores the material’s outstanding ability to efficiently convert mechanical stress into electric charge.
Implications for Future Research
In consideration of future studies, Professor Funakubo noted the important applications of this research.
“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.” – Hiroshi Funakubo
Further, this statement serves as an important call-out for new, exciting opportunities for continued investigation. By further optimizing the properties of MgSiN₂ and related materials, we can increase their performance in next-generation technologies. The discovery of the new wurtzite phase of MgSiN₂ can be considered a considerable breakthrough in material science. Aside from the vastly improved parameterization, this development has potentially revolutionary implications for piezoelectric applications.
Collaborative Efforts and Broader Impact
As part of this study, the research team worked with Professor Venkatraman Gopalan from Pennsylvania State University. Their combined skills allowed a multidisciplinary approach to understand and later to optimize the ideal electronic properties of MgSiN₂.
The dual successful stabilization of MgSiN₂ in the wurtzite phase is an encouraging step toward further exploring the exciting realm of heterovalent ternary nitrides. We hope that these findings will inspire similar interest around the world by researchers. They might investigate different materials with comparable features, spurring breakthroughs in electronics, sensors, and energy harvesting tools.