Global internet traffic has surged past three trillion gigabytes annually, largely due to high-definition video streaming. As our insatiable appetite for data grows, so does the need for faster, more efficient communication systems. However, the invisible highways of electromagnetic (EM) waves—known as frequency bands—that connect Wi-Fi and mobile networks are becoming increasingly congested.
“Due to the development of 5G and 6G communications, frequency bands below 6 GHz are almost fully occupied,” said Xinghua Wang, a Scientist at A*STAR’s Institute of Microelectronics (IME). “It will be increasingly critical to tap into lesser-used higher frequencies with potential for further exploitation, such as the Ku band (12-18 GHz) and the millimetre-wave (mmWave) spectrum.”
However, signals at higher frequencies have shorter wavelengths, making them more prone to interference and signal loss over long distances. One engineering hurdle is that current designs for bulk acoustic wave (BAW) resonators—essential electronic parts in mobile devices which help filter out specific frequencies—can only operate on frequencies up to 8 GHz.
“Developing high-frequency BAW resonators paves the way for acoustic filters that go above 10 GHz, providing a solution with a much smaller footprint and lower power loss versus current EM filters,” Wang said.
Wang and IME colleagues hypothesised that a BAW resonator based on a thin film of scandium-doped aluminum nitride (ScAIN) could overcome existing limitations in creating more efficient, compact filters able to handle greater bandwidths. Scandium enhances the material’s piezoelectric properties—its ability to convert electrical signals into mechanical vibrations—thereby boosting the filter's performance across higher frequencies.
The team successfully fabricated 15 GHz acoustic resonators and filters using a 90 nm thin ScAIN film of specific proportions (Sc0.2Al0.8N) deposited on a 200 mm wafer. They then conducted extensive testing to ensure their prototypes could precisely filter out unwanted signals with an ample bandwidth and a low pass-through loss.
The team reported that their resonators performed exceptionally well, with a quality factor exceeding 200, enabling them to handle signals with a low energy loss. Their filters also demonstrated an insertion loss of just 3.5 dB and a 10 percent fractional bandwidth, making them among the top performing designs reported at the 15 GHz range.
“Our biggest achievement was scaling the film’s thickness down to 100 nm while keeping its crystallinity and stress at levels comparable to existing technologies,” Wang noted.
Wang added that mmWave technologies like their ScAlN-based filters are promising in areas like virtual reality, smart factories and faster mobile networks as they can help shrink systems, boost efficiency and cut costs through seamless integration with existing electronics.
The team is now aiming to break new ground by developing filters that operate at over 20 GHz, while also capturing industry interest to deploy their ScAIN technology in existing mmWave applications like satellite communications.
The A*STAR-affiliated researchers contributing to this research are from the Institute of Microelectronics (IME).
