To bring the inner workings of the human body into focus, ultrasound probes used in diagnostic imaging must be incredibly sensitive. These technologies rely on piezoelectric materials—substances that act like a bridge between mechanical and electrical worlds by converting electrical energy into mechanical motion, and vice versa.
Senior Principal Scientist and Senior Group Leader for Piezo Tech at A*STAR’s Institute of Materials Research and Engineering (IMRE), Kui Yao, stated that identifying the right 'recipe' for optimal piezoelectric materials is a significant challenge for the field.
“Chemical compositional stoichiometry or obtaining the precise control of ingredients according to the atomic ratio in the molecular formula, is often desired for achieving optimal material properties,” explained Yao.
Collaborating with researchers from the National University of Singapore; Xi’an Jiaotong University, China; University of Missouri, USA; and colleagues from A*STAR’s Institute of High Performance Computing (IHPC) and Institute of Sustainability for Chemicals, Energy and Environment (ISCE2), Yao and team investigated the mechanism and potential of using thin films made of potassium sodium niobate (KNN) to surmount the stoichiometry hurdle.
Due to their distinct structure and internal electric charge organisation, KNN films were suggested as a path forward for high-performance, eco-friendly piezoelectric devices.
Yao and team experimented with various compositions of KNN films and systematically examined their structure and composition, as well as how they respond to electrical signals using state-of-the-art imaging and analytical techniques.
Furthermore, they used theoretical models rooted in quantum mechanics to predict and explain the piezoelectric behaviour of these films at an atomic level, connecting their intricate structure to their overall electromechanical features.
Through subtle tweaks of the KNN thin film nanostructure, the team achieved a giant effective piezoelectric coefficient (~1900 pm/V at 1 kHz), with their films being nearly twice as responsive to electrical signals as previously possible.
Speaking on how introducing tiny structural changes greatly improved the thin films’ sensitivity, Yao said, “Planar faults involve adding or removing a plane of atoms in the crystal structure, causing an imbalance in electric polarisation and electrostatic forces around them.
“This imbalance leads to the local accumulation of charge and stress, causing significant structural distortions and internal electric field.”
Yao remarked on the transformative potential of their discovery for microelectromechanical systems (MEMS), which can result in smaller, more efficient and less power-intensive actuators. Such advancements can revolutionise automation and self-operating devices by making them more compact and more responsive to electrical signals.
With a patent pending for their innovative approach, the team is now focused on adapting KNN films to silicon substrates to accelerate their integration into mainstream technology.
The A*STAR-affiliated researchers contributing to this research are from the Institute of Materials Research and Engineering (IMRE), the Institute of High Performance Computing (IHPC) and the Institute of Sustainability for Chemicals, Energy and Environment (ISCE2).
