Imagine streaming a live sports event on your smartphone with every roaring cheer from the crowd coming through in vivid sound. Behind the scenes, tiny electronic parts of your phone act as translators: quick as lightning, they convert electric signals into physical vibrations within the phone’s speakers, replicating the stadium’s exciting soundscape in the comfort of your room.
Known as microelectromechanical systems (MEMS), these devices underlie advanced communications systems like 5G as they act as electromechanical couplers, turning electricity into movement and vice versa. Huajun Liu, Group Leader at the A*STAR Institute of Materials Research and Engineering (A*STAR IMRE), described the limits of MEMS as a key part of the 5G puzzle.
“MEMS are vital in radio frequency (RF) front-end chips, where they act as acoustic filters that muffle or remove unwanted signals,” Liu explained. “Their bandwidth determines the speed of data transfer. In turn, that bandwidth largely depends on the electromechanical coupling coefficient of thin film materials used within MEMS; in other words, how efficiently those thin films convert one form of energy into the other.”
Emerging data-heavy applications like self-driving vehicles and augmented or virtual reality (AR/VR) demand faster wireless speeds. To meet that demand, Liu and a global team including co-corresponding author, Yeng Ming Lam, from Nanyang Technological University, Singapore; SINGA scholar Baichen Lim; and colleagues at the A*STAR Institute of High Performance Computing (A*STAR IHPC); explored ways to increase the electromechanical coupling coefficient in thin films for MEMS.
Liu’s team took a novel approach by developing sodium niobate (NaNbO₃) thin films with competing antiferroelectric (AFE) and ferroelectric (FE) phases. AFE and FE are contrasting states: materials in an AFE phase are polarised in two opposing directions, causing them to cancel each other and have no net electrical polarisation overall. On the other hand, those in an FE phase are fully polarised in one direction, generating a net electrical polarisation.
Atomic images of the antiferroelectric (AFE) and ferroelectric (FE) phases of sodium niobate crystal thin films, captured using transmission electron microscopy.
© A*STAR Research
“When you apply an electric field to AFE materials, their polarisations fully switch into one direction. Essentially, they transition into an FE phase, which drastically changes their volume and causes significant mechanical movements,” said Liu.
To tap into this phenomenon, the team chose NaNbO₃ as at ultralow temperatures (-100 °C) it naturally exhibits both AFE and FE phases with very similar energy levels. Through theoretical calculations, they identified ideal single-crystal substrates to grow their thin films on, which helped stabilise them at room temperature and still enable rapid phase changes.
Liu’s team confirmed that their thin films showed an exceptionally strong electromechanical response. “Electric testing revealed that our films had effective piezoelectric coefficients over 5000 pm/V, setting a new record in the literature,” Liu added.
This novel technology could pave the way for next-generation MEMS that support the more robust wireless networks of the future. “We’re currently working on optimising and integrating our thin films on silicon wafers so that we can make use of mature semiconductor fabrication technologies to translate our materials into commercial products,” said Liu.
The A*STAR-affiliated researchers contributing to this research are from the A*STAR Institute of Materials Research and Engineering (A*STAR IMRE) and the A*STAR Institute of High Performance Computing (A*STAR IHPC).
