Physics

Band-pass filter

Nanotechnology

Bandwidth (computing)

Wideband

Insertion loss

Resonator

Engineering

Acoustics

Materials science

Nitride

Electronic engineering

Layer (electronics)

Computer science

Optoelectronics

Center frequency

Telecommunications

Microsystems & Nanoengineering

Bulk acoustic wave (BAW) filters have been extensively used in consumer products for mobile communication systems due to their high performance and standard complementary metal-oxide-semiconductor (CMOS) compatible integration process. However, it is challenging for a traditional aluminum nitride (AlN)-based BAW filter to meet several allocated 5G bands with more than a 5% fractional bandwidth via an acoustic-only approach. In this work, we propose an Al0.8Sc0.2N-based film bulk acoustic wave resonator (FBAR) for the design of radio frequency (RF) filters. By taking advantage of a high-quality Al0.8Sc0.2N thin film, the fabricated resonators demonstrate a large Keff2 of 14.5% and an excellent figure of merit (FOM) up to 62. The temperature coefficient of frequency (TCF) of the proposed resonator is measured to be -19.2 ppm/°C, indicating excellent temperature stability. The fabricated filter has a center frequency of 4.24 GHz, a -3 dB bandwidth of 215 MHz, a small insertion loss (IL) of 1.881 dB, and a rejection >32 dB. This work paves the way for the realization of wideband acoustic filters operating in the 5G band.

Aluminum scandium nitride thin-film bulk acoustic resonators for 5G wideband applications