Piezoelectric materials generate electrical voltages when they are deformed and, conversely, change shape when an electrical voltage is applied to them. These materials can therefore be used to convert motion into electrical signals and electrical signals into motion. They are used in micro-actuators, for example to drive chip speakers or to set tiny laser scanner mirrors in motion. Developers utilise the reverse effect when it comes to generating electrical signals from movement, as is the case, for example, in microphones or magnetically operated sensors.

At the Institute of Materials Science at Kiel University (CAU), research is being carried out into, amongst other things, aluminium scandium nitride (AlScN) – a III-V compound semiconductor – as a promising piezoelectric material. During this research, materials scientist Simon Fichtner discovered that this material also possesses ferroelectric properties. This means that AlScN crystals can have a permanent, spatial electrical orientation that can be switched by applying an electrical voltage. “This property can be used, for example, to store information or to generate particularly high forces for highly efficient actuators. This discovery could therefore have far-reaching implications in the world of technology. This is particularly true given that, in terms of key ferroelectric parameters, AlScN is breaking new ground that was previously unattainable with established materials,” explains Dr Fabian Lofink, Head of the MEMS Applications Business Unit at Fraunhofer ISIT.

The project ‘Ferroelectricity in AlScN: From the discovery of the effect to disruptive components’, which has received €2.3 million in funding from the Federal Ministry of Education and Research, will now explore the innovative potential of this discovery over the next four years. Together with colleagues from Fraunhofer ISIT and Fraunhofer IAF, scientists at Kiel University (CAU) are focusing on two types of components in this project: a chip loudspeaker and a special power transistor. Four companies are also involved in the project to accelerate the transfer of the scientific findings into future applications.

By utilising the ferroelectric effect, different layers of AlScN can be stacked on top of one another without the need for additional control circuits or intermediate insulation. This results in micro-actuators that are significantly more powerful than conventional piezoelectric devices. One of the aims of the project is to develop an efficient loudspeaker driven by AlScN structures.

But this discovery could also provide a boost to innovation in the world of electrical microchips. As part of the project, the Fraunhofer IAF is working to develop non-volatile transistors based on ferroelectric properties; unlike conventional transistors, these retain their circuit state even when the electrical control voltage is switched off. “This could, for example, make it possible to integrate switching functions in the field of power electronics,” explains Dr Michael Mikulla, Head of the Power Electronics Business Unit at Fraunhofer IAF. As part of the project, ferroelectric AlScN layers are to be combined with gallium nitride-based components for modern microelectronics.

“With this project, we aim both to maintain our scientific lead and to transfer the results promptly into applied projects that have the potential for breakthrough innovations,” explains Prof. Bernhard Wagner, head of the research group at CAU and deputy director of Fraunhofer ISIT, outlining the objectives of the joint project. However, the materials science research is also far from complete. Discoverer Simon Fichtner: “Alongside this project, we will of course also consider other piezoelectric materials and investigate whether these substances might also be modified in such a way that they possess ferroelectric properties.”